hbsc 3203

Table of Content Reading List …………………………………………………………………… i TOPIC 1 : THE AIR AND RESOURCES AROUND US ………………… 1 TOPIC 2 : METALS …............................................................................ 41 TOPIC 3 : ELECTROLYSIS…………………………..………….………… 66 TOPIC 4 : OXIDATION AND REDUCTION ……………………………… 85 Appendix 1 Appendix 2

TOPIC 5 : SPEED OF CHEMICAL REACTIONS ………….…………… 137 TOPIC 6 : HYDROCARBON COMPOUNDS I …………………………. 172 TOPIC 7 : HYDROCARBON COMPOUNDS II ………………………… 238 Appendix 3 Appendix 4 TOPIC 8 : NATURAL MATERIALS AND MANUFACTURED OR MAN–MADE MATERIALS …………………………………… 275

TTooppiicc 11 The Air andResourcesAround Us

LEARNING OUTCOMES

By the end of this topic, you should be able to:

1. Describe the composition of air;

2. Explain the percentage of nitrogen, oxygen and carbon dioxide in the air;

3. Examine the properties of oxygen and carbon dioxide using water and

sodium hydroxide;

4. Discuss the importance of oxygen in respiration and combustion;

5. Describe air pollution, its sources, effects, and steps to control and prevent

air pollution;

6. Examine the different resources on earth and their importance; and

7. Describe the agencies involved in environmental protection and their

approach.

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TOPIC 1 THE AIR AND RESOURCES AROUND US

2

INTRODUCTION

Do you know this song? If you are not familiar with it, this lovely song was sung by Jordin

Sparks, the 2007 American Idol winner. The lyrics describe how important it is to have

someone that you care around you, as important as it is to have air around you.

Air is all around us, wherever we are. We know that even though we cannot see it. In fact,

there is a huge layer of air surrounding the earth. We call this the atmosphere. We use the air

in the atmosphere for a lot of things. Breathing is one of them. Can you name other uses?

Have you ever flown a kite or seen anyone doing so? How does the kite manage to sway in

the sky? The reason is there is air which maintains the kite’s position. The moving air makes

it possible to fly a kite. We will discuss the air further as we study the composition of air and

the properties of oxygen and carbon dioxide.

ACTIVITY 1.1

Tilt the mouth of an empty bottle in a basin of water.

Answer the following:

(a) Do you see bubbles coming out of the bottle?

(b) Do you hear any bubble sound?

(c) Can you guess what is in the bottle?

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TOPIC 1 THE AIR AND RESOURCES AROUND US 3

COMPOSITION OF AIR

Before we learn about the composition of air, let us do this activity. Put out your hand in front

of your face and breathe in deeply. Then, gently blow outward towards your fingers. What do

you feel? Do your fingers feel cool and tingly? I am sure you felt something blowing past

your fingertips. This is commonly referred to as the air.

Our earth is surrounded by a thick layer of air which we call atmosphere. The air is held

around the earth by the force of gravity. This gravity pulls the gas particles towards the earth.

Do you know the composition of the air that we breathe in? In ancient times, people thought

that air was only one substance. Now, we know that the air is actually a mixture of gases.

These gases are nitrogen, oxygen, carbon dioxide and inert gases. The inert gases in the air

include argon, neon, helium, krypton, xenon and methane. Let us look at Table 1.1, which

illustrates the composition of air.

Table 1.1: Composition of Air

Name Symbol Per Cent by Volume

Nitrogen N2 78.084%

Oxygen O2 20.9476%

Argon Ar 0.934%

Carbon Dioxide CO2 0.0351%

Neon Ne 0.001818%

Helium He 0.000524%

Methane CH4 0.0002%

Krypton Kr 0.000114%

Hydrogen H2 0.00005%

Xenon Xe 0.0000087%

Source: CRC Handbook of Chemistry and Physics

1.1

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4

PERCENTAGE OF GASES IN THE AIR

What are the characteristics of air? Air is colourless, tasteless and odourless. Air supplies the

oxygen necessary for life. Air is also a mixture of gases – nitrogen, oxygen and carbon

dioxide. Do you know that the most abundant gases found in our atmosphere are nitrogen and

oxygen? This is true as nitrogen makes up around 78% of the total atmosphere, oxygen 21%

and carbon dioxide 0.035%. This means when you inhale, you breathe in 78% nitrogen, 21%

oxygen, and 1% argon, with trace amounts of other gases, such as methane, hydrogen,

helium, neon, krypton and carbon dioxide. These percentages of gases are shown in Figure

1.1.

Figure 1.1: Composition of our atmosphere

ACTIVITY 1.2

Try these activities to show your students that there is

air around us.

(a) Ask two students to run along the corridor.

(b) Next, ask them to run again along the same

Corridor, holding a large sheet of card in front of them.

So, which was easier – running with the card or without it? Ask your students to

explain.

1.2

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However, this does not mean nitrogen will keep on increasing in the atmosphere. It is

constantly being removed or cleansed from the atmosphere. A small amount of nitrogen is

removed by living organisms. Rain and snow also wash nitrogen out of the atmosphere.

As we learnt before, plants consume carbon dioxide. Plants use carbon dioxide in the air for

photosynthesis and release oxygen during the process. This oxygen is later removed from the

air by animals and other life forms. Oxygen is the most important gas in our atmosphere due

to its strong relation with human and animal life. Without it, each of us, and most of the

animals on earth would perish in a matter of minutes. Now, let us conduct an experiment to

find out how much oxygen is in the air. The following is an experiment to find the

percentage of oxygen in the air.

Experiment 1.1

Objective:

To find out how much oxygen is in the air.

Procedure: Start by pushing in completely one gas syringe.

Heat up the copper turnings strongly.

As they are heated, air is passed over them by pushing in one syringe first

and then the other.

As the reaction happens, you will notice the copper turnings becoming black.

This is because they have reacted with the oxygen from the air.

What do you think is the name of this black compound?

Continue heating until no more copper turnings turns black and the amount of air

in the syringes stays the same.

Result:

You will find that the amount of air left in the syringes at the end is 79cm3. How

much air has been used up? You will find that this is the amount of oxygen in

100cm3 of air. As you can see, nearly one-fifth of the air is filled with oxygen.

Next, let us do an activity to calculate the exact percentage of oxygen in the air.

Let us start!

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ACTIVITY 1.3

SELF-CHECK 1.1

1. Air is a mixture of gases. State two reasons to support this statement.

2. State the percentage of nitrogen, oxygen and carbon dioxide in the air.

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PROPERTIES OF OXYGEN AND CARBON DIOXIDE

We know that oxygen and carbon dioxide are two of the most important gases in the air. The

amount of carbon dioxide is very small, about three parts in ten thousand. However, oxygen

comprises 20.94% of the air. We are now going to look into the properties of oxygen and

carbon dioxide. We will look into three matters:

(a) Their solubility in water;

(b) Their reactions with sodium hydroxide; and

(c) The tests for oxygen and carbon dioxide.

Before we discuss further, let us look at the general properties of oxygen and carbon dioxide

first (Table 1.2).

Table 1.2: Seven General Properties of Oxygen and Carbon Dioxide

Properties Carbon Dioxide Oxygen

Features Colourless and odourless Colourless and odourless

Solubility in water More soluble than oxygen Slightly soluble

Solubility in sodium

hydroxide solution

Very soluble Not soluble

Solubility in alkaline

pyrogallol solution

Not soluble Soluble

Lime water reaction

Turns cloudy No effect

Combustion Does not support and does not

burn Supports but does not burn

pH Acidic Neutral

1.3

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1.3.1 Solublity in Water

We have just learnt the properties of oxygen and carbon dioxide in Table 1.2. Now, let us

look at the difference of solubility of these gases by doing Experiment 1.2.

Experiment 1.2

Objective:

To show the solubility of oxygen and carbon dioxide in water.

Procedure:

Invert two test tubes containing oxygen and carbon dioxide in a beaker of water.

Watch the rise in the water level. What can you conclude about this experiment?

Result:

You will notice that in the test tube containing oxygen, a little water enters the test

tube (Figure a). This shows that oxygen dissolves slightly in water.

However, in the test tube containing carbon dioxide, more water enters the test

tube (Figure b). This shows that carbon dioxide is more soluble in water than

oxygen.

(a) (b)

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1.3.2 Reaction with Sodium Hydroxide

What are the reactions of oxygen and carbon dioxide with sodium hydroxide?

Let us find out by doing Experiment 1.3.

Experiment 1.3

Objective:

To show the reactions of oxygen and carbon dioxide to sodium hydroxide. Procedure:

Invert a test tube of oxygen into a beaker of sodium hydroxide solution(Figure a).

Remove the stopper and shake the test tube gently.

Observe the flow of sodium hydroxide solution into the test tube.

Repeat the experiment using a test tube containing carbon dioxide (Figure b).

(a) (b)

Result:

Sodium hydroxide solution does not rise in the test tube containing oxygen. This

shows that oxygen is not soluble in sodium hydroxide solution.

Sodium hydroxide solution rises rapidly in the test tube containing carbon dioxide.

This indicates that carbon dioxide is very soluble in sodium hydroxide solution.

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1.3.3 Tests for Oxygen and Carbon Dioxide

We can test the presence of oxygen by testing it with a burning splinter. As for carbon

dioxide, we will test it with lime water. Look at Experiments 1.4 and 1.5 on how to conduct

these tests.

Experiment 1.4

Objective:

To test the presence of oxygen.

Procedure:

Light up a burning splinter.

Insert the burning splinter into a test tube containing oxygen (Figure a).

What can you see?

Result

You will see that the burning splinter will light up (Figure b). The

splinter glows because oxygen supports combustion.

(a) (b)

Burning splinter

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Experiment 1.5

Objective:

To test the presence of carbon dioxide.

Procedure:

Put lime water into a test tube that has been filled with carbon dioxide gas.

Close the test tube with a cork. Shake the test tube for a while. What can you see

after that?

Result:

The lime water will turn cloudy in the presence of carbon dioxide. Carbon

dioxide reacts with lime water to form calcium carbonate, which is insoluble in

water.

ACTIVITY 1.1

Look at the diagram.

1. Which candle in the diagram takes a longer time to extinguish?

2. What conclusion can you arrive at from this observation?

SELF- CHECK 1.2

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IMPORTANCE OF OXYGEN

As mentioned earlier, oxygen is a basic element in life. How about its features? It is

colourless, highly reactive and is said to come from water vapour. It turns into a bluish liquid

at a temperature of -183°C.

We are aware that oxygen plays an important role in our lives. Can you name some of its

uses? It is used for breathing, decomposition of organic wastes, the support of aquatic life in

the form of oxygen dissolved by water and creation of energy in living cells.

1.4.1 Respiration

Why do you think oxygen is needed in respiration? Let us find out!

All organisms require energy to carry out all living processes such as growth, reproduction,

response, movement, breathing, digestion and excretion. Energy is stored in the form of

chemical energy in organic substances such as carbohydrates, lipids and proteins. It needs to

be converted into a form of energy which can be readily used by cells. This calls for

respiration as respiration is the chemical breakdown of food to release the energy which is

essential for all living things.

Do you know that respiration is divided into two stages? Let us look at what these two stages

are as shown in Figure 1.2.

Figure 1.2: Two stages of respiration

1.4

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Now, let us look at the definition of external respiration.

Can you imagine how this process works? Look at Figure 1.3. During breathing or external

respiration, oxygen is inhaled and carbon dioxide is released

Figure 1.3: Breathing or external respiration

How about internal respiration? Internal respiration occurs inside the cells and tissues of the

body. Thus, it is often called cell respiration, or tissue respiration. To respire, we need a

constant supply of oxygen. When this oxygen reaches the cells, it combines with glucose (a

sugar which comes from food that has been converted). Energy is then released, together with

waste products of carbon dioxide and water. Respiration, which uses oxygen, is called

aerobic respiration. However, under certain circumstances, energy can be released from food

without oxygen. This process is called anaerobic respiration.

External respiration is a mechanical process of

inhalation and exhalation of air through the

respiratory system.

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As a conclusion, we have learnt that the products of respiration are energy, carbon dioxide

and water vapour (Figure 1.4).

Figure 1.4: The products of cellular respiration

This chemical reaction can be written as:

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

Glucose Oxygen Carbon dioxide Water

SELF-CHECK 6.1

The following statements are false. Rewrite them to make them true.

1. Respiration and breathing are the same process.

2. Only animals carry out respiration.

3. Acrobatic respiration is the process where energy is made from sugar in the

presence of oxygen.

4. The reactants used in respiration are water and carbon dioxide.

5. The only gas we breathe in is oxygen.

SELF-CHECK 1.3

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1.4.2 Combustion

What is combustion? Let us look at what combustion stands for.

Here is a simple principle behind combustion. For combustion to occur, fuel, oxygen (air) and

heat must be present together. In other words, combustion takes place when chemicals mix

together and give off heat and light in the form of fire. For example, the charcoal in a

barbecue grill burns because it mixes with oxygen in the air. In Figure 1.5, the fire goes out if

the grill is closed because air cannot reach the coals. Figure 1.6 shows us materials containing

chemicals that burn easily when heated

Figure 1.5: Charcoal burning in a barbecue grill

Source: World Book Illustration

Combustion is the process of burning.

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Figure 1.6: Materials containing chemicals that burn easily

Source: World Book Illustration

Now that you have understood what combustion is, let us carry out an experiment. What gas

do you think is needed for combustion to occur? Yes, oxygen is needed for combustion. So,

how do we conduct an experiment to show that oxygen is needed for combustion? Let us do

Experiment 1.6.

Experiment 1.6

Objective:

To show that oxygen is needed for combustion.

Procedure:

You need to do this experiment in pairs.

Get two glass jars of different sizes.

Light two candles and put each in a jar.

Mount the candle on a thick cardboard.

Then seal the jar to ensure that the supply of oxygen is cut off. Observe the flame.

Result:

As the flames consume the oxygen in the jars, the flames will go out. The

candle flame in the bigger jar (A) will burn out last.

Can you explain what made the flame burn out? The flame uses up oxygen as it burns and

when enough has been used up, the flame goes out.

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1. Define combustion.

2. List three conditions necessary for combustion to occur.

AIR POLLUTION

Let us look at Figures 1.7 and 1.8. What do both pictures have in common?

Figure 1.7: Burning forest Figure 1.8: Burning building

The trees and buildings are on fire. We call this process combustion. Can you name the

products of combustion? In the pictures, you can see smoke, dirt and damage to trees and

buildings. In fact, smoke and dust cause pollution to the environment.

When we talk about air pollution, the images conjured in our minds would be those of smog,

acid rain, chlorofluorocarbons (CFCs) and other forms of outdoor air pollution. However,

pollution also happens inside our homes and other buildings. Every year, the health of many

people is affected by chemical substances found in the air within buildings.

Let us learn more about air pollution. In this subtopic, we will discuss the definition of air

pollution, its sources and effects. We will then discuss the importance of clean air and how to

keep the air clean in order to control and prevent further air pollution. Let us start the topic

with Activity 1.4.

1.5

SELF-CHECK 1.4

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Let us find out how dirty or clean the air in your classroom is. You will need three sheets

of white paper or cardboard and petroleum jelly. This is how you do it:

Smear one side of two sheets of paper with petroleum jelly.

Put the sheets next to each other, with the smeared side up, on a windowsill and

clamp the sheets in place with the closed window.

Take in one of the sheets at the end of one week and see how dirty it looks (compare

it to a clean sheet of paper).

What can you conclude about this?

What is air pollution? Do you know that our earth is the only planet we know that has air and

water? That is why (as far as we know) only earth can cater to living creatures. Without air

and water, the earth would be unable to sustain life. We have a diverse community of plants

and animals and they have thrived on this planet for millions of years, sustained by the sun

and supported by the soil, water and air.

We breathe in air which supplies us with oxygen. Oxygen is essential for our body systems to

function. Air consists of 99.9% nitrogen, oxygen, water vapour and inert gases. Our activities

can release substances into the air. Some of these substances can cause problems for humans,

plants and animals. One of the problems is air pollution. How does it occur?

1.5.1 Sources of Air Pollution

Now, let us find out what the sources of air pollution are. As we learnt before, air pollution

occurs when the air contains pollutants. Air pollutants are substances that are released into the

environment. These substances are harmful to us and other living things. There are seven

sources of air pollution as described in Table 1.3.

ACTIVITY 1.4

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Table 1.3: Seven Sources of Air Pollution

Source Description

1. Natural Sources There are many natural sources of air pollution such as eruption of

volcanoes, biological decay and forest fires caused by lightning strikes.

2. Industrial Activities Our economy is mainly based on manufacturing (especially electronics),

chemical and rubber industries. In order to increase output, industries

increase their normal production. This leads to higher emissions of

organic and inorganic gases, chemicals and dust. Different industries

emit different pollutants. For example, the chemical industry releases

emissions that contain many nitrogen and sulphur compounds while

refineries discharge sulphur dioxide and hydrocarbons. The metal

working industry is partially responsible for the emissions of sulphur

dioxide and large amounts of toxic dust.

3. Development

Activities

Unplanned and uncontrolled development of industrial premises or

zones leads to noise pollution and vibration disturbance. The use of

conventional piling methods and the sound of exhaust fans in factories

are some of the common activities that generate a high sound level.

4. Motor Vehicles Modern societies rely heavily on motorised transportation such as cars,

trucks and railways. Automobiles rely mostly on the burning of fossil

fuels. They not only cause emissions of smoke and dust but are also

responsible for the increase in noise. In 2004, nearly 14 million vehicles

were registered in Malaysia, almost double the number from a decade

earlier. The number will increase in the next few years due to higher

disposable incomes, rural-urban migration and the lack of an efficient

public transport system.

5. Power Generation Most of the energy produced in conventional power plants is by burning

fossil fuels like natural gas, oil and coal. The burning of fossil fuels will

result in the emission of smoke and dust.

6. Everyday Routines Households contribute to air pollution mainly through the use of energy

that is required to run machines and electrical appliances such as

refrigerators. Refrigerators and air conditioners not only consume

energy but also pollute the environment when their coolant fluids

release CFCs into the atmosphere. Chemicals used in houses and

gardens are also sources of pollution as well as toxic waste.

7. Open Burning Some countries practise open burning of older plantations as a method

for re-planting. This results in large amounts of soot particles. These

soot particles can be blown over long distances and are mainly

responsible for the haze that often covers the sky above Malaysia. These

fires can also destroy the rich habitat of flora and fauna.

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Do you realise that even our homes contribute to air pollutants? Find out the causes of air

pollution from our homes (Figure 1.9) and the outdoors (Figure 1.10).

Figure 1.9: Air pollutants inside and outside a house

Figure 1.10: Outdoor air pollutants

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1.5.2 Effects of Air Pollution

There are thousands of air pollutants. However, we are going to focus only on a few

pollutants, including their sources and effects on our health. Let us refer to Table 1.4.

Table 1.4: Pollutants, Their Sources and Effects on Human Health

Pollutant Source Human Health Effect Particles - Air Particle

Index (API)

Internal combustion

engines (e.g. cars and

trucks)

Industry (e.g. factories)

Burning wood

Cigarette smoke

Bush fires

Long-term exposure is

linked to health problems

such as

Lung cancer

Heart disease

Lung disease

Asthma attacks

Nitrogen Dioxide (NO2) Motor vehicles are the

biggest contributors

Other combustion

processes

Exposure to high levels of

NO2 may lead to:

Lung damage

Respiratory disease

Asthma and respiratory

problems

Increased mortality

Sulphur Dioxide Burning of coal and

petroleum in factories and

power-generating stations

Breathing

difficulties

Bronchitis

Acid rain occurs when

sulphur dioxide

dissolves in rainwater

Carbon Monoxide (CO) Burning of hydrocarbon

Exhaust gases from

motor vehicles

Cigarette smoke

Dizziness and headache

Can cause death if a

large amount is inhaled

Lead (Pb) Vehicle exhaust fumes

Other atmospheric

sources of lead include

waste incineration and

renovation of old

houses (from leaded

paint)

Affects children’s learning and

development of their

nervous system

Affects almost every

organ in the body,

whether it is inhaled or

ingested. Young

children are particularly

susceptible Smoke Soot Dust Burning of waste and

fuels by factories

Forest fires

Cigarette smoke

Smoke from vehicles’

exhaust

Pollutes the environment

Slows down

photosynthesis

Damages respiratory

system

Can cause cancer

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Carbon Dioxide Burning of rubbish and

fuels

Causes greenhouse

effect (increase in

temperature on earth) Chlorofluorocarbon (CFC) Aerosol cans,

refrigerators, air

conditioners

Depletion of the ozone layer

Diseases related to

ozone layer depletion

(e.g. cataract, skin cancer)

Ask your students to explain the effects of the following pollutants on our health:

Transportation

Factories

Agricultural activities

Present the findings in class.

Air pollution has consequences to the environment. There are three main consequences of air

pollution to the environment as presented in Table 1.5.

Table 1.5: Three Main Consequences of Air Pollution to the Environment

Consequence Description

Acid rain Acid rain happens when sulphur and nitrogen pollution

from industrial smokestacks combine with moisture in the

atmosphere (see Figure 1.11). The resulting rain is acidic

which destroys natural ecosystems and buildings.

Greenhouse effect The planet’s temperature increases as heat energy from

sunlight is trapped by the gaseous atmosphere. Excess

carbon dioxide and water vapour increase this global

warming effect.

Thinning of the ozone layer The ozone in the ozone layer is destroyed due to the

presence of chlorine from manmade CFCs and other forces.

The layer is thinning because the ozone is destroyed faster

than it is regenerated by natural forces.

ACTIVITY 1.5

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Now, let us look at Figure 1.11, which shows the cycle of acid rain.

Figure 1.11: Acid rain cycle

Source: www.newint.org

How about the greenhouse effect and depletion of ozone layer? Let us refer to

Figures 1.12 and 1.13.

Figure 1.12: Greenhouse effect

Source: www.coolmob.org

Figure 1.13: Depletion of ozone layer

Source: www.scienceclarified.com

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What causes the thinning of the ozone layer? What effects does it have on us?

List five things we use in our everyday life which contribute to the thinning of the

ozone layer.

1.5.3 Step to Prevent Air Pollution

In order to prevent or control air pollution, we have to keep the air clean. Let us look at the

steps to keep the air clean.

After discussing how important the air is to us and learning the effects of air pollution, let us

think of the ways to keep the air clean. Remember, everybody has the power to make a

difference to the quality of the air and environment. All of us, whether we realise it or not,

contribute to air pollution in one way or another. In order to improve the quality of the air we

breathe in, we must be aware of the activities that can contribute to pollution and take action

against it. We can take action personally, at home or at school, or by doing something with

others in the community.

Now, what actions can we take to keep the air clean? Let us refer to Table 1.6.

Table 1.6: Ways to Keep the Air Clean

Way SuggestionMake a difference on the road Walk or ride your bike instead of getting a lift in a car.

Where possible, use public transport instead of riding in

your parents’ car.

When running errands, combine trips so that you do not use

your car for single purpose trips.

Drive wisely and do not idle. Save petrol by switching off

the engine even when you are stationary for a while.

Use non-ozone depleting refrigerant for your car’s air

conditioning system.

Use unleaded petrol to reduce the amount of lead particles in

the air.

Make a difference at home Use household and garden chemicals wisely. Avoid using

CFC-based products.

Be sure to read labels for proper use and disposal of

products.

If you purchase a new air conditioning system or heat pump,

purchase one that uses a non-ozone depleting refrigerant.

Practise wise waste management. Recycle aluminium cans,

glass bottles, plastics, cardboards and newspapers. This will

SELF-CHECK 1.5

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reduce waste and conserve natural resources.

Buy products made of recycled content.

Stop practising open burning.

Take part in tree-planting activities.

Industrial sectors can make a

difference

Practise cleaner production technology.

Use energy-saving products.

Carry proper servicing and maintenance on equipment and

machinery used.

Stop open burning.

Practice Zero Burning Technique (agricultural sector).

Reduce the use of pesticides that are non-environmental

friendly (agricultural sector).

Lastly, let us look at the steps needed to control and prevent air pollution. Preventing and

controlling air pollution require the efforts of people from all walks of life. Previously, we

mentioned what we and also industrial sectors can do to keep the air clean. Now, we will

discuss the steps required by the relevant authorities to control and prevent air pollution.

The steps are:

(a) Implementation of law: Malaysia has implemented the Environmental Quality Act

(EQA) 1974. This Act was enacted to prevent, abate, control pollution and enhance

the quality of the environment.

(b) Inspection and enforcement visits. These are carried out to industrial premises to

ensure that industrial sectors comply with the Environmental Quality Act 1974.

(c) Conducting roadside inspections on motor vehicles.

(d) Conducting aerial and ground surveillance on pollution sources.

(e) Daily monitoring of air quality.

(f) Conducting awareness programmes to educate public on the need to protect the

environment.

Do you know that there is a simple way to measure the air pollution level? The simple way is

the Air Pollution Index (API). This index describes the air pollution levels to provide timely

information about air pollution to the public. Table 1.7 shows the API status indicator used in

Malaysia.

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1. What is air pollution? Name five air pollutants.

2. List the pollutants which affect the environment. Describe one pollutant

and what it does to the environment.

3. Name three pollutants from a factor which affects a person’s health.

4. Why must we keep our air clean? How do we know the air is clean?

5. Name two substances which can cause acid rain. State the effects of acid

rain to our health.

Table 1.7: Malaysian API Status Indicator

API Status0 50 Good51 100 Moderate101 200 Unhealthy201 300 Very unhealthy301 500 Hazardous

Above 500 Emergency

You can get more on the daily readings of the API by visiting

http://www.doe.gov.my/index.php?option=com_content&task=view&id=188&

Itemid=370&lang=en

Let us conduct an activity to reduce air pollution in your school.

Hold a class discussion on air pollution. Discuss the main sources of air

pollution in the school area. Suggest possible ways and activities to

reduce air pollution in your school. Carry out the activities suggested.

ACTIVITY 1.6

SELF-CHECK 1.6

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VARIETY OF RESOURCES ON EARTH

The Carson Fall in Mount Kinabalu, Malaysia is an

example of undisturbed natural earth’s resource.

Waterfalls provide spring water for humans, animals

and plants for survival and also a habitat for hydro

organisms. The water current can be used to turn

turbines for hydroelectric generation.

Figure 1.14: The Carson Fall in Mount Kinabalu

Source: http:/ www. Google.wikipedia.com

1.6.1 Different Resources on Earth

Who need resources? Why do we need resouces? What types of resources do we have?

Human beings, animals and plants need food, water, air and shelter in order to survive. The

earth has the resources needed to sustain life. The resources are air, water, soil, minerals,

fossil fuels and living things.

1.6.2 Important of Earth’s Resources

The earth is rich in natural resources that we use daily. These resources are any valuable

material of geologic origin that can be extracted from the earth. It is nearly impossible to

cease consuming natural or geologic resources altogether. Here are just a few examples of

things you commonly use, but probably do not think about:

A pencil uses zinc and copper (to make the brass), petroleum for the eraser, iron (in

the machinery to make the pencil), pigments, clay and graphite. The only renewable

resource in your pencil is the wood!

Your jeans, although they may be almost all cotton, are usually blended with

petroleum-based synthetic fibres to cut down on shrinking.

Eye glasses and windows are made of quartz sand and petroleum.

Dental fillings are made of mercury and silver.

Videotapes are made of vinyl, iron and chromium.

1.6

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Please refer to Table 1.8 to learn more about the impotance of earth’s resources.

Table 1.8: The Importance of Earth’s Resources

Types of

Earth

Resources

The Importance of Earth’s Resources

Air Air is needed by all living things to survive.

The atmosphere is a layer of air that envelops the earth.

Air is a mixture of gases. Air contains gases such as oxygen, nitrogen and

carbon dioxide.

Oxygen and carbon dioxide are two very important gases that support life

on earth.

a. Oxygen

i. Used for respiration by living things

ii. Used in combustion of materials

iii. Used in industries

iv. Released during photosynthesis.

b. Carbon dioxide

i. Used by green plants to carry out photosynthesis

ii. Used in fire extinguishers

iii. Released during respiration and combustion

Water Water covers a total of about three quarters of the earth.

The sources of water are oceans, seas, rivers, lakes, rainfall and ground

water.

Importance of water

a. To animals/humans

i. It provides a medium for chemical process and body

metabolism;

ii. It is the main component of the blood;

iii. It transports nutrients to all cells in the body;

iv. It carries excretory products to the kidneys for excretion; and

v. It helps to control the body temperature.

b. To plants

i. It helps to maintain the turgidity of plant cells;

ii. It is used in photosynthesis;

iii. Need for the germination of seeds;

iv. Dissolves minerals slats in the ground for absorption by the roots of

plants;

v. Helps to support aquatic plants; and

vi. Cools down the plants (transpiration).

28


Soil Soil refers to the outer layer of the earth.

Soil contains mineral matter, organic matter, air and water.

The soil organic matter includes:

· Organic litter such as fallen leaves, twigs, fruit, animal dropping, etc.

· Humus formed from the composition of organic litter.

· Microorganisms living in the soil.

Air and water are found in pore spaces between the soil particles.

The presence of air and water in the soil makes it a natural habitat for

various types of plants and animals.

Importance of soil:

· Source of minerals and fossil fuels;

· Source of clay for making pottery;

· Source of sand for making glass and cement;

· Base for agricultural activities; and

· Foundation for construction of houses, buildings, roads and other

structures.

Living

Things

i. Flora and fauna (plants and animals) are also natural resources that

sustain life.

ii. Plants and animals are resources needed by human beings.

iii. We can obtain food, fuel, materials for making clothes and building

materials from plants and animals.

iv. Green plants can make their own food by carrying out photosynthesis.

v. Animals are not able to make their own food.

vi. Some animals such as giraffes and elephants feed on plants.

vii. Some animals such as tigers and snakes feed on other animals.

viii. Aquatic plants and animals are also important resources for sustaining

life.

Mineral i. Minerals are inorganic substances found naturally on land and in seas

or oceans.

ii. Examples of minerals are feldspar, quartz, iron, zinc, aluminium, tin,

silver and gold.

iii. Some minerals such as aluminium and iron are mined because they

can be used as raw materials in various industries.

There are two types of earth’s resources – renewable and non-renewable resources.

Earth’s resources that can be replaced and reused by nature are termed renewable. Natural

resources that cannot be replaced are termed non-renewable. Renewable resources are

replaced through natural processes at a rate that is equal to or greater than the rate at which

they are used, and depletion is usually not a worry.

Some common examples include:

Air (wind);

Fresh water;

Soil;

29


30

Living organisms (trees); and

Sunlight.

Non-renewable resources are exhaustible and are extracted faster than the rate at which they

formed. Some common examples are:

Fossil fuels (coal, oil, natural gas);

Diamonds and other precious gems and minerals; and

Types of metals and ores.

1.6.3 Preservation and Conservation of Earth’s Resources

With the increased use of virtually all natural earth’s resources, there is concern that

resources will be exhausted and that others will not be able to use them in the future. Can you

imagine a world without clean water, clean air, sustainable land or living oceans?

Our natural resources exist in a delicate balance and are vulnerable to environmental changes.

That is why it is important that we all do our part to conserve, preserve and care for the

earth’s resources and protect the environment that sustains us with food, fuel, shelter and

medicine.

Because of the severe impact that we impose on the land, air, and water, preservation and

conservation has become increasingly important. Let us check the meaning of preservation

and conservation.

Conservation is to spend or use sparingly

Preservation is to keep and maintain what you have

30


1.6.4 Recycling of Materials

“Reduce, Reuse, Recycle”

Figure 1.15: Reduce, Reuse and Recycle

The symbol and the phrase above are very common. Do you know its meaning?

Reduce : Do not use a resource if there is an alternative (walking versus driving).

Reuse : Use a resource again without changing it or reprocessing it; use glassware

as opposed to paper plates and Styrofoam.

Recycle : Reprocess a resource so that the materials can be used in another item.

People can recycle just about anything from cardboard to old shoes!

Discuss in a group of four to find out the meaning of preservation and

conservation in terms of natural earth’s resources. Please visit the following

websites to get more information.

http://www.ecoca.ro/meteo/tutorial/Sustainability/Older/Conservation_and_Pre

servation.html

http://feelfriendly.com/information-preservation-conservation.html

ACTIVITY 1.7

31


32

Waste

Products

Solid Waste Medical

Waste

Hazardous

Waste

WASTE PRODUCTS

“Wastes are substances or objects which are disposed of or are intended to be

disposed of or are required to be disposed of by the provisions of national law”

Source: http://wikipedia.google.com

1.7.1 Sources and Types of Waste Products

Figure 1.16: Three types of waste

Source: Von ( 2004)

There are various sources of waste such as domestic sources, commercial sources, industrial

sources, clinic or biomedical sources, mineral sources, agricultural sources and nuclear

sources. Table 1.9 shows a breakdown of common waste types and its sources.

Please observe the picture given.

Identify the materials that can be

recycled.

1.7

SELF-CHECK 1.7

32


Table 1.9: Common Sources and Types of Waste Products

Source Typical Waste Generators Types of Solid Wastes

Residential Single and multi-family

dwellings

Food wastes, paper, cardboard, plastics,

textiles, leather, yard wastes, wood,

glass, metals, ashes, special wastes (e.g.

bulky items, consumer electronics, white

goods, batteries, oil, tyres), and

household hazardous wastes

Industrial Light and heavy

manufacturing fabrication,

construction sites, power and

chemical plants

Housekeeping wastes, packaging, food

wastes, construction and demolition

materials, hazardous wastes, ashes,

special wastes

Commercial Stores, hotels, restaurants,

markets, office buildings, etc

Paper, cardboard, plastics, wood, food

wastes, glass, metals, special wastes,

hazardous wastes

Institutional Schools, hospitals, prisons,

government centres

Paper, cardboard, plastics, wood, food

wastes, glass, metals, special wastes,

hazardous wastes

Construction

and

Demolition

New construction sites, road

repair, renovation sites,

demolition of buildings

Wood, steel, concrete, dirt, etc

Municipal

Services

Street cleaning, landscaping,

parks, beaches , other

recreational areas, water

and wastewater treatment

plants

Street sweepings, landscape and tree

trimmings, general wastes from parks,

beaches, and other recreational areas,

sludge

Process Heavy and light

manufacturing, refineries,

chemical plants, power

plants, mineral extraction

and processing

Industrial process wastes, scrap

materials, off specification products,

slag, tailings

Agriculture Crops, orchards, vineyards,

dairies, feedlots, farms

Spoiled food wastes, agricultural wastes,

hazardous wastes (e.g. pesticides)

33


34

1.7.2 Pollution Caused by Waste Products

Figure 1.17: Dead fish caused by water pollution Source: Image Google.com

Many things can cause water pollution but most water pollution is caused by waste products

from humans. Types of waste products that can pollute our water are sewage drainage into

our water cycle, oil from vehicles, oil spills, fertilisers from crops. Rubbish dumps also can

run into our water system when it rains.

Figure 1.18: Water Pollution

Source: http://google.image.com

Do you think why all the

fish in Figure 1.17 were

dead?

34


Do You Know?

Waste products (Figure 1.19) also can cause land pollution and air pollution. Land

pollution is caused by an excessive amount of trash going into our landfills. When too

much trash is in our landfills, it can cause water pollution over time by getting in our

water cycle. Another form of land pollution is littering.

Figure 1.19: Solid waste products

Source: http://google.image.com

1.7.3 Environmental Protection

Environmental protection is a practice of protecting the natural environment on individual,

organisational or governmental levels, for the benefit of both the natural environment and

humans. Discussion concerning environmental protection often focuses on the role of

government, legislation and law enforcement. Protecting the environment is a responsibility

of all people.

SELF-CHECK 1.8

Observe Figure 1.18.

Identify the types of waste products that cause water pollution.

35


36

(a) Government Organisations’ Involvement

i. Environmental Quality Act, 1974 (Act 127)

An Act relating to the prevention, abatement, control of pollution and enhancement

of the environment:

Part IV – Prohibition and control of pollution

Section 22: Restrictions on pollution of the atmosphere

Section 23: Restrictions on noise pollution

Section 24: Restrictions on pollution of the soil

Section 25: Restrictions on pollution of inland waters

Section 27: Prohibition of discharge of oil into Malaysian waters

Section 29: Prohibition of discharge of wastes into Malaysian waters

Section 34: Report on impact on environment resulting from prescribed

activities

ii. Incorporate Department of Environment (DOE) within the Ministry of Science,

Technology and Environment (MOSTE)

In charge with environmental administration

iii. Incorporate an environmental policy aimed at integrating environmental concerns

into development planning. For example:

The Seventh Malaysian Plan (1996-2000) states that the objectives of

Malaysia’s national environmental policies are to achieve a clean, safe and

healthy living environment for current and future generation and to promote

lifestyles and modes of production and consumption consistent with the

principles of sustainable development.

(b) Non-governmental Organisation’s Involvement

Dissemination of environmental information through the Environmental

Management and Research Association of Malaysia (ENSEARCH)

(c) Environmental Education in the School Syllabus

Environmental education will make our citizens aware of the environmental

problems and equip us with knowledge to overcome the problems.

SELF-CHECK 1.9

Find out the involvement of international agencies in

Malaysia’s environmental protection.

36


The air is actually a mixture of gases. These gases are nitrogen, oxygen, carbon

dioxide and inert gases. The inert gases in the air include argon, neon, helium,

krypton, xenon, methane and xenon.

Under properties of oxygen and carbon dioxide, we look into three matters, namely,

the solubility in water, reactions with sodium hydroxide and the tests for oxygen and

carbon dioxide.

Oxygen plays an important role in our lives. We use oxygen for breathing,

decomposition of organic wastes, supporting aquatic life in the form of oxygen

dissolved by water and creation of energy in living cells.

Air pollution affects our health and the environment. Air pollution occurs

when the air contains gases, dust, fumes or odour in harmful amounts.

Our natural resources include air, water, soil, minerals, fossil fuels, plants and

animals. Each of these resources is important to us in their own ways.

Conservation is the sustainable use of our natural resources. Preservation is keeping

natural resources in their current state, untouched by humans.

Recycle is the process of reprocess a resource so that the materials can be

used in another item.

Waste are substances or objects, which are disposed of or are intended to be

disposed of or are required to be disposed of by the provisions of national

law. It can be divided into three, solid waste, medical waste and hazardous

waste.

Environmental protection can be done by the government, non governmental

organisations, international agencies and national citizens through

introducing environmental education in the school syllabus.

37


38

Air

Air Pollution Index (API)

Carbon dioxide

Chlorofluorocarbon (CFC)

Combustion

Conservation

Environment

External respiration

Global warming

Greenhouse effect

Internal respiration

Land pollution

Natural resources

Oxygen

Preservation

Products

Recycle

Respiration

Waste product Water pollution

Conoley, C., & Hills, P. (2002). Collins advance science chemistry (2nd ed.). UK: Collins

Educational.

Environmental Quality Act 127. (1974). Retrieved from

https://www.elaw.org/system/files/MalaysiaEQA1974_0.pdf

Gallagher, R. M. (1997). Complete chemistry. UK: Oxford University Press.

Milner, B., Martin, J., & Mills, J. (2002). Core chemistry. UK: Cambridge University Press.

Nivaldo, J. T. (2000). Chemistry in focus (2nd ed.). USA: Thomson.

South Carolina Geological Survey. (2005). Earth’s natural resources and human impacts.

Retrieved from ftp://ftpdata.dnr.sc.gov/geology/Education

Von, L. L. (2004). Case study on the management of waste materials in Malaysia. Forum

Geoökol, 15(2), 7.

Zumdahl, S. S. (2004). Introductory chemistry: A foundation (5th ed.). New York: Houghton

Mifflin.

38

INTRODUCTION

Figure 2.1: Gold and copper coins

Source: editmentor.wordpress.com

TTooppiicc 22 Metals

LEARNING OUTCOMES

By the end of this topic, you should be able to:1. Describe the physical properties of metals;2. Differentiate the structures of metals and alloys;3. Describe the chemical reactions of metals;4. Identify the order of reactivity of metals;5. Describe the method of extraction of iron and aluminium; and6. Discuss the uses of metals.

41

TOPIC 2 METALS

2

2.1

Have you ever seen coins such as the ones in Figure 2.1? Gold and copper were the

first metals discovered in the earth, since 6,000BC. Gold and copper coins have been

used since ancient civilisation. Gold articles were found extensively in antiquity

mainly as jewellery such as bracelets and rings. The symbol for gold is Au from the

latin aurum meaning “shining dawn”. The use of copper in antiquity was of more

significance than gold as the first tools, implements and weapons were made from

copper. The symbol for copper is Cu and comes from the latin cuprum meaning “from

the island of Cyprus”.

Currently, there are 86 known metals. Scientists have categorised metals into three

groups – alkali metals, alkali earth metals and transition elements. You can explore the

names and symbols of all known metals in the Periodic Table of the Elements.

PHYSICAL PROPERTIES OF METALS

Metals consist of positive ions embedded in moving clouds of electrons (Figure 2.2).

The negatively charged electrons attract all the positive metal ions and bond them

together with strong electrostatic forces of attraction as a single unit called metallic

bond.

Figure 2.2: Metals consist of positive ions surrounded by a cloud of electrons

SELF-CHECK 2.1

1. Name three metals in a group of alkali metals.

2. Name two metals in a group of alkali earth metals.

3. Name two common metals in transition elements.

42

TOPIC 2 METALS 3

2.1.1 Structures of Metals and Alloys

Pure metals have the following properties;

They usually have high melting and boiling points. This is due to the strong

attraction between the positive metal ions and the mobile clouds of electrons.

They conduct electricity due to the mobile electrons (electrons cloud) within

the metal structure. When a metal is connected in a circuit, the electrons move

towards the positive terminal.

They are malleable and ductile. If a force is applied to a metal, rows of ions

can slide over one another. They reposition themselves and the strong bonds

re-form as shown in Figure 2.3.

Figure 2.3: The positions of the positive ions in a metal before and after a

force has been applied

[Source: http://www.chem istry.org/materi_kimia/struktur_atom_dan_ikatan/jenis_struktur_atom/s

truktur_logam/]

They have high densities, as the atoms are arranged in order and closely

packed together as can be seen in Figure 2.4.

Figure 2.4: Arrangement of ions in a metal

[Source: http://martinmm.wiki.manheimcentral.org/84]

43

TOPIC 2 METALS

4

Different metals show different types of packing and in doing so they produce the

arrangement of atoms shown in Figure 2.5.

Figure 2.5: Relating different structures to the density of metal

[Source:

http://www.substech.com/dokuwiki/doku.php?id=metals_crystal_structure]

Alloys are a mixture of;

Two or more metals (for example, brass is an alloy of zinc and copper); or

A metal and non-metal (for example, steel is an alloy of iron and carbon).

Figure 2.6 shows the alloy structure. The blue circles represent atoms of metal A and

the white circles are atoms of metal B which is added to make the alloy. These

different atoms give the alloy different physical properties from that of the pure metal.

Figure 2.6: Structure of an alloy[Source: http://www.chem.qmul.ac.uk/surfaces/scc/scat6_4.htm]

Atom of metal A

Atom of metal B

44

TOPIC 2 METALS 5

2.2

Alloys are formed by mixing the molten substances thoroughly. But why make alloys?

The reasons why alloys are made are:

(a) To increase the strength and hardness of a pure metal. The presence of the

atoms of other elements disrupts the orderly arrangement of the pure metal.

The layers of metal atoms are prevented from sliding over one another easily.

This makes alloys stronger and harder than pure metals.

(b) To increase the resistance to corrosion of a pure metal. Alloying can prevent

metals from corrosion. This is because alloying helps to prevent the formation

of oxide layer on the surface of the metal (We will discuss the reaction of

metals in subtopic 2.2).

(c) To improve the appearance of a pure metal. Alloying helps to keep the metal

maintain the glossy nature of the surface as it prevents the formation of the

metal oxide.

Table 2.1 shows some of the more common alloys with their composition.

Table 2.1: Composition of common alloys

[Source: Ryan (2001)]

Alloy Composition

Brass 65% copper, 35% zinc

Bronze 90% copper, 10% tin

Cupro-nickel 30% copper, 70% nickel

Duralumin 95% aluminium, 4% copper,1% magnesium, manganese and

iron

Magnalium 70% aluminium, 30% magnesium

Pewter 30% lead, 70% tin, a small amount of antimony

Solder 70% lead, 30% tin

CHEMICAL PROPERTIES OF METALS

The metals in ores are chemically bonded to other elements. So how can we extract

the metals? To answer this, we must understand the Reactivity Series of metals. In

the Reactivity Series, the most reactive metals are at the top. The less reactive ones are

at the bottom. We can start putting the metals in order by looking at their actions with

heat, water and dilute hydrochloric acid.

45

TOPIC 2 METALS

6

2.2.1 Chemical Reaction of Metals with Heat

Conduct Experiments 2.1 and 2.2 to judge the reactivity by putting the metals into

competition with each other. In these two experiments, the metals will “fight” each

other to “win their prize” which is oxygen. The more reactive metal will win the

fight.

Copper starts off with the oxygen in copper oxide. However, iron is more reactive, so

it takes the oxygen away from copper. We say that iron has displaced (“kicked out”)

the copper.

Copper oxide + iron iron oxide + copper

CuO(s) + Fe(s) CuO(s) + Cu(s)

This is a displacement reaction. It shows us that iron is more reactive than copper.

There actually will not be a reaction between iron oxide and copper because copper is

less reactive than iron.

Experiment 2.1

1. Mix a spatula of iron fillings and copper oxide

in a test tube. Heat the mixture strongly

Is there a reaction? Look for a red glow

spreading through the mixture.

2. When the tube has cooled, empty it into a dish.

Can you see any brown copper metal left?

SELF CHECK 2.2

In Experiment 2.1, what do you expect will happen if we change:

copper oxide with iron; and

iron with copper?

Will there be any reaction? Why?


46

TOPIC 2 METALS 7

You can now try some other displacement reactions as in Experiment 2.2.

2.2.2 Chemical Reaction of Metals with Water

You have already seen how the action of heat with metals in the displacement

reaction. Now, you can arrange the order of the reactivity of metals iron, zinc, copper

and magnesium:

i. Magnesium

ii. Zinc

iii. Iron

iv. Copper

We can also judge reactivity by observing the metal’s reaction with water. Let us look

at the reaction of lithium, sodium and potassium with water.

From Experiment 2.3, you can observe that lithium moves slowly on the surface of the

water, while sodium melts to become a small sphere, move rapidly and randomly on

Experiment 2.2

Try heating the mixtures of metals and oxide

shown in the table:

Look for any signs of reaction. Tick ( ) in the

“Reaction Table” if there is a reaction.

(Be careful when looking for signs of reaction.

Zinc oxide turns yellow when you heat it by

itself. It turns white again when it cools down).

Write word equations for the reactions you

have ticked)

Metal/

Metal

oxide

Zinc

oxide

Iron

oxide

Copper

oxide

Zinc

Iron

Copper

Magnesium

Reaction Table

Experiment 2.3

1. Put water in three different glass basins.

2. Drop small pieces of

Lithium in basin 1

Sodium in basin 2

Potassium in basin 3

3. Collect the gas given off as shown;

Test the gas with a lighted splint

4. Test the solution formed with red litmus

paper.

Is the solution left acidic or alkaline?


47

TOPIC 2 METALS

8

the water surface with a hissing sound as it reacts. Potassium gets so hot that it lights

the hydrogen gas that water gives off. It burns with a lilac flame, move very rapidly

and randomly on the water surface with a hissing and popping sound. The colourless

solution formed turns red litmus paper to blue.

The chemical equation for the reaction of lithium with water is as follows:

Lithium + Water Lithium hydroxide + Hydrogen

2Li(s) + 2H2O (l) 2LiOH (aq) + H2 (g)

In the case of magnesium, this metal normally reacts slowly with water. But we

can speed up the reaction by heating up the water to make steam as in Experiment

2.4.

The magnesium reacts strongly with the steam. It leaves white magnesium oxide in

the test tube. Hydrogen gas is given off.

Experiment 2.4

1. Heat the magnesium strongly.

Every now and again, switch the

flame briefly to the ceramic wool

to make a steam.

2. As the reaction starts, the gas

given off can be lit at the end of

the tube.

Can you name the gas?


When red litmus paper turns to blue,

the solution formed is an alkaline!

SELF-CHECK 2.3

Write the word and symbol equations for sodium and potassium

reacting to water.

48

TOPIC 2 METALS 9

Magnesium + Steam Magnesium oxide + Hydrogen

Mg (s) + H2O (g) MgO(s) + H2 (g)

The oxygen atom in H2O has “swapped partner”! It start off with hydrogen, but ends

up with magnesium.

Table 2.2 gives the different observations when metals react with water and steam.

Table 2.2: Reaction of metals with water and steam

T

a

b

l

e

2

.

2

2.2.3 Chemical Reaction of Metals with Diluted

Hydrochloric Acid

Another simple way to judge the reactivity of metals is to compare the reaction with

diluted acid. Metals will react quicker with diluted acid compared to water especially

the metals below calcium in Table 2.2.

Conduct Experiment 2.5 to compare the reactivity of metals when react with dilute

hydrochloric acid.

Notice that copper does not react with hydrochloric acid. However, the other metals

tested do react. For example, magnesium:

Metals Reaction with Water Reaction with Steam

Potassium

Sodium

Lithium

Calcium

Fizz, giving off hydrogen gas and

leaving an alkaline (hydroxide)

solution.

Explode

Magnesium

Aluminium

Zinc

Iron

Very slow reaction.

(Aluminium is protected by a layer

of aluminium oxide on its surface).

React, giving off hydrogen gas and

forming the metal oxide.

Experiment 2.5

1. Clean the metals with sand-paper.

2. Set up the boiling tube as shown:

Can you see bubbles?

(If you see no bubbles, you can warm the

tube gently in a beaker of hot water)

3. Record your results in a table.

(Do your results agree with the order in

Table 2.3 ?)


49

TOPIC 2 METALS

10

Magnesium + Hydrochloric acid Magnesium chloride + Hydrogen

Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g)

Table 2.3: Reaction of metals with dilute hydrochloric acid

Metals Reaction with Dilute Hydrochloric Acid

Calcium

Magnesium

Aluminium

Zinc

Iron

Fizz, giving off hydrogen gas.

(Aluminium is protected by a tough layer of oxide on

its surface)

Tin

Lead

Gives off hydrogen very slowly .

(The acid needs to be warmed up)

Copper

No reaction.

2.2.1 Order of Reactivity of Metals

Now, we can form the Reactivity Series of metals according to the reactivity of metals

based on the metals’ reaction to heat, reaction to water and reaction to diluted

hydrochloric acid (Figure 2.7).

SELF CHECK 2.4

Write word equations for the reactions of calcium, aluminium, zinc,

iron, tin and lead with dilute hydrochloric acid.

ACTIVITY 2.1

Discuss why we never add potassium, sodium or lithium to acid.

50

TOPIC 2 METALS 11

Figure 2.7: Reactivity series of metals

K Potassium

Na Sodium

Li Lithium

Ca Calcium

Mg Magnesium

Al Aluminium

Zn Zinc

Fe Iron

Sn Tin

Pb Lead

Cu Copper

Ag Silver

Au Gold

Pt Platinum

Most reactive

Least reactive

Figure shown is a message from

the Lonely Hearts section of the

‘Zoo of the World’. Can you come

up with your own mnemonic

sentence to help you remember

the Reactivity Series?

ACTIVITY 2.2

51

TOPIC 2 METALS

12

2.3

EXTRACTION OF IRON AND ALUMINIUM

In the earlier sub-topic, we learned about the Reactivity Series. We will now look at

how to get metals from their ores. This includes iron, which is the most widely used of

all metals. Figures 2.8 and 2.9 show iron ore and the mining of iron ore.

2.3.1 Extraction of Iron

Figure 2.8: Iron ore, haematite

[Source: http://www.e-rocks.com/Products.aspx?action=showproduct&id=107003]

Figure 2.9: Mining of iron ore in Karnataka

[Source: http://khanija.kar.ncode.in/SitePages/EAuctionData.aspx]

52

TOPIC 2 METALS 13

Carbon is important in the extraction of iron. Carbon is a non-metal, but we can put it

into our Reactivity Series of metals. It is placed in between aluminium and zinc. This

means that carbon can displace any metal below aluminium in the Reactivity Series

(Figure 2.10).

Figure 2.10: The position of carbon in the Reactivity Series

We get carbon from coal. Coal is cheap and there is plenty of it at present. We use

coke (a cheap form of carbon which is made from coal) as one of the raw materials

besides iron ore (mainly haematite- iron(III) oxide) and limestone (to get rid of sandy

waste) in the process of extracting iron. We use blast furnace to get the iron from its

ore. Figure 2.11 shows the diagram of blast furnace used to extract iron.

Reactions in the blast furnace

The coke (carbon) reacts with oxygen in the hot air to make carbon oxide.

C(s) + O2(g) CO2 (g)

This carbon dioxide reacts with more hot coke to produce carbon monoxide

gas.

CO2 (g) + C(s) 2CO(g)

K Potassium

Na Sodium

Li Lithium

Ca Calcium

Mg Magnesium

Al Aluminium

Zn Zinc

Fe Iron

Sn Tin

Pb Lead

Cu Copper

Ag Silver

Au Gold

Pt Platinum

CARBON

Carbon cannot be used to

extract the more reactive

metals

These metals can be

extracted using carbon

53

TOPIC 2 METALS

14

The carbon monoxide then reacts with iron oxide to get iron.

Fe2O3(s) + 3CO(g) 2 Fe(l) (s) + 3CO2 (g)

At the high temperature (up to 1900°C) in the furnace, the iron is in molten form

(liquid). So, it sinks to the bottom of the furnace. The iron then will run off into

mould. The molten slag floats to the top of the iron. The slag is tapped off, cooled and

used for making roads.

Figure 2.11: The blast furnace

[Source: http://images.yourdictionary.com/blast furnace]

2.3.2 Extraction of Aluminium

Figure 2.12: Aluminium ore, bauxite

[Source: http://www.greener

industry.org.uk/pages/aluminium/aluminium_4PMsummary.htm]

54

TOPIC 2 METALS 15

As shown in the Reactivity Series (refer Figure 2.10), the position of aluminium is

before carbon. This means aluminium is more reactive than carbon, so carbon cannot

be used to extract aluminium. So, how do we extract aluminium from its ore, bauxite,

which contains aluminium oxide, Al2O3?

2.3.3 Extraction of Aluminium – Electrolysis of Aluminium

Oxide

Figure 2.13 shows the electrolytic cell used for the extraction of aluminium.

Figure 2.13: Extraction of aluminium

[Source: http://www.meritnation.com/ask answer/question/explain the

process of extraction of aluminiun/metals and non metals/2230314]

Aluminium oxide is mixed with cryolite, Na3AlF6, to lower the melting

point of aluminium oxide (2045°C) to about 900°C.

Blocks of carbon act as the anode while the carbon lining of the cell acts as

the cathode.

At the cathode, the aluminium ions are discharged to form aluminium

metal.

Al3+(l) + 3e Al(l)

Liquid aluminium is denser than the electrolyte and will be collected at

the bottom of the cell.

At the anode, the oxide ions are discharged to form oxygen gas.

2O2 (l) O2(g) + 4e

Reactive metals can only be extracted from

their ores by electrolysis!

55

TOPIC 2 METALS

16

2.4

The overall chemical reaction is:

2Al2O3(l) 4Al(l) + 3O2(g)

The oxygen liberated at the anode will react with the carbon electrode

to produce carbon dioxide gas.

C(s) + O2(g) CO2(g)

Consequently, the anode is corroded slowly and must be replaced

from time to time.

THE USES OF METALS

Steel is used more than any other metal. It is important in the building industry. It is

used for girders and for the rods inside reinforced concrete. Steel tubes, called scaffold,

are used when buildings are made or repaired.

Steel is made mainly from iron. It has a small amount of carbon in it. The amount of

carbon affects its properties as can be seen in Table 2.4

Table 2.4: Types of Steel

Type of Steel Amount of Carbon Hardness Uses

Mild steel 0.2% Can be easily shaped Car bodies, wires,

pipe, bicycles

Medium steel 0.3% to 0.6% Hard Girders, springs

High-carbon

steel

0.6% to 1.5 % Very hard Drills, hammers,

other tools

Unfortunately, iron and steel rust. Is there a way to prevent this? You have learned about

alloy. How to make steel alloy?

However, stainless steel is expensive. It has mainly been used for making smallitems, such as knives and spoons.

ACTIVITY 2.3

Name 20 items that are made of stainless steel.

If chromium and nickel are added to steel, you will

get stainless steel, a steel which does not rust!

56

TOPIC 2 METALS 17

Another metal that has many useful properties is aluminium. It conducts heat and

electricity well. It has low density for a metal. It does not corrode.

Platinum is used in catalytic converters, fitted to car exhausts. It cuts down the

amount of pollution from cars.

A radioactive isotope of cobalt is used to treat patients with cancer.

Figure 2.14 shows some uses of common metals around the home.

Figure 2.14: Some uses of metals at home


ACTIVITY 2.4

Look at the compund of your school. Name the metals and

the uses of metals at your school.

57

TOPIC 2 METALS

18

• Metal consists of atoms which are arranged very closely packed in an

orderly manner.

• The atoms in metal bond with strong electrostatic force called metallic

bond.

• Metals are good conductors of heat and electricity. They are shiny,

malleable (can be hammered into shapes) and ductile (can be drawn out

into wires). Most metals are hard, dense and have high melting points.

• The properties of metals can be improved with alloying.

Alloy is a mixture of two or more metals or a metal and a non metal.

Generally, alloying produces a metallic substance which has more useful

properties than the original pure metal it was made from.

The Reactivity Series lists metals in order of reactivity.

We can use the Reactivity Series to make predictions about reactions.

A more reactive metal can displace a less reactive metal from its

compound.

Carbon is placed between aluminium and zinc in the Reactivity Series.

Extraction of metal from its ore depends on its place in the Reactivity

Series. The more reactive a metal, the harder it is to extract.

The metals placed above carbon in the Reactivity Series can be extracted

by electrolysis (potassium, sodium, lithium, calcium, magnesium and

aluminium).

The metals placed below carbon in the Reactivity Series can be extracted

by using carbon as an oxidising agent (zinc, iron, tin and lead).

Metals have a wide range of uses. Metals are used in building industries,

household products, medicine, agriculture, etc.

Blast furnaceCarbonDiluted hydrochloric acidDisplacement reactionElectrolysisHeat

MetalMetallic bondReactivity seriesStainless steelSteelWater

58

TOPIC 2 METALS 19

Earl, B., & Wilford, D. (2009). IGCSE chemistry. United Kingdom: HodderEducation.

Eng, N. H., & Lim, Y. C. (2007). Focus Super Chemistry. Bangi: PenerbitanPelangi.

Farndon, J. (2003). The elements: Aluminium. Malaysia: Federal Publications.

Ryan, L. (2001). Chemistry for you. United Kingdom: Stanley Thornes.

Sparrow, G. (2003). The elements: Iron. Malaysia: Federal Publications.

59

TOPIC3 : MATERIAL WORLD TOPIC 4: OXIDATION AND REDUCTION Readings Rose Marie Gallgher (1997). Complete Chemistry, Oxford Universiti Press, UK.

Ralph A. Burns (2003). Fundamentals of Chemistry, Prentice Hall, Ney Jersey

Bryan Milner, Jean Martin, John Mills (2002). Core Chemistry, Cambridge Universiti Press

J. G. R. Briggs (2003). Chemistry Insight, Pearson Education Asia Pte. Ltd. Singapore

J.G. R. Briggs (2003). Science in Focus Chemistryfor GCE ‘O’ Level, Pearson Education Asia

Pte.Ltd. Singapore.

Bahagian Pendidikan Guru, KementerianPendidikan Malaysia. (1995) BukuSumber Pengajaran

Pembelajaran Sains Sekolah Rendah, Jilid 3:Strategi Pengajaran dan Pembelajaran Sains.

Projek PIER Bahagian Pendidikan Guru serta dan Bahagian Perancangan dan

Penyelidikan Dasar Pendidikan, Kuala Lumpur.

Whitten, K.W., Davis, R.E.,Peck,M.L and Stanley, GG. (2008). Chemistry (Ninth Edition).2010

Brooks/Cole.

Keywords - oxidation - reduction - oxygen - ozone - nonmetal oxides - metal oxides Learning Outcomes At the end of this Topic, the learner will be able to;

1. Define oxidation and reduction.

2. Explain the meaning of redox and giving examples.

63

3. Demonstrate the ability to write balanced formula and the ability to identify oxidizing

agents and reducing from given oxidation-reduction reactions.

4. Ability to differentiate oxygen and ozone.

5. Demonstrate the ability to compare and contrite the properties of oxygen and

hydrogen.

6. Describing with examples the reactions Group 1A and Group 2A with oxygen.

7. Describing what happens to the oxides of Group 1A and Group 2A when it dissolve in

water.

8. Ability to summarize the reactions of O2 with nonmetals ,reactions of nonmetal oxides

with water and the reactions of metal oxides with nonmetal oxides.

Study Questions Task 1 : Read the definition of oxidation and reduction on Page 225 (highlighted in yellow). In

your own words, describe oxidation and reduction. Task 2 : It is said that oxidation and reduction occur simultaneously and are referred to as

oxidation-reduction reactions or redox. Read 6-5 Oxidation-Reduction Reactions : Introduction (pg 225). In your own words explain what redox mean and give examples in your explanation.

Task 3 : Read Example 6-4 Redox Reactions. After going through and understanding the

section, do the following

(a) write balanced formula unit equations for the following redox reactions:

(i) nitrogen reacts with hydrogen to form ammonia (ii) aluminum reacts with sulfuric acid to produce aluminum sulfate and hydrogen (iii) zinc sulfide reacts with oxygen to form zinc oxide and sulfur dioxide (iv) carbon reacts with nitric acid to produce nitrogen dioxide, carbon dioxide and water

64

(b) identify the oxidizing agents and reducing agents in the above oxidation-reduction reactions. Task 4 : Read 5-9 Oxygen and the oxides (pg 198).Can you differentiate between oxygen and

ozone?

Task 5 : Read 5-8 Hydrogen and hydrides (pg 194) and 5-9 Oxygen and oxides (pg 198). In

your own words, compare and contrast the properties of oxygen with those of

hydrogen.

Task 6 : Read Reactions of O2 with metals on page 198-199. Describe in your own words and

with examples, what happens when Group 1A and Group 2A react with oxygen.

Task 7 : Refer to Page 200, Reactions of Metal Oxides with water. Describe what happens to

the oxides of Group 1A and Group 2A when it dissolve in water.

Task 8 : With reference to page 201-203, write a summary of the following reactions:

(v) Reactions of O2 with nonmetals (vi) Reactions of nonmetal oxides with water (vii) Reactions of metal oxides with nonmetal oxides.

65

INTRODUCTION

This topic is to teach students about food. As an introduction, you should explain the

importance of food to us. Food is very important to all living beings: humans, animals

and plants. They need food for energy. The energy will be used for growth, development,

repair damaged cells and tissues, reproduction, and maintain general health. In humans

and animals, energy is also used for movement and activity for their everyday life. For

instance, the body cells that are destroyed need to be repaired.

The process of which living organisms obtains food for growing and repairing body cells

is called nutrition. Nutrition is obtained from food. Food provide nutrients. Nutrients

are chemical substances needed in order for us to live and stay healthy. Hence, the energy

is obtained from nutrition in foods utilised to carry out our everyday activities.

TTooppiicc

33

Material

World III


1. Explain to students the classes of food and its importance;

2. Conduct a suitable experiment to identify the area of the tongue for different

tastes;

3. Debate about rusty objects; and

4. Conduct suitable experiment to determine the conditions for iron to become

rusty.

LEARNING

66

TOPIC 3 MATERIAL WORLD III 34

CHEMICAL PROPERTIES OF MATERIALS

3.1.1 Classes of Food

To teach the classes of food, you can use the explanation strategy. Firstly, the teacher

should explain the seven classes of food. The basic nutrients we get from foods are

categorised into seven major classes or categories based on their properties. They are:

Carbohydrates

Proteins

Fats

Vitamins

Minerals

Fibres

Water

Then the teacher can continue the explanation with the functions for every classes of

food. Human and animal bodies need all types of foods to carry out different functions.

The correct proportions of food we consume contain all sources of food. This is called

diet. Diet is the kinds of food we consume and drink regularly.

As mentioned earlier, good diet means we eat food and water at the correct proportions. A

balanced diet should contain about 60% carbohydrates, 20% proteins and 20% fats

coming from food groups. The food will supply nutrients, energy necessary to sustain the

body, for growth and repair and maintain health. The functions of these food are:

(a) Carbohydrates are to supply energy.

(b) Proteins are to provide materials for body growth and repair.

(c) Fats are to supply energy and store excess food.

ACTIVITY 3.1

Testing for the presence of carbohydrate.

The presence of carbohydrate in our food can be tested in the lab. Using tapioca

flour, potato, rice, bread and other samples of food requested by the science

teacher, students may conduct the experiment using iodine solution. Divide your

classroom into several groups for this experiment. Discuss your results.

3.1

67


(d) Vitamins are to provide maintenance and healthy body.

(e) Mineral salts are for healthy teeth, bones, muscles and other parts of the body.

(f) Fibres are to help intestines to function properly.

(g) Water is to process all chemicals in the body and transport substances in the blood.

Lastly, you should explain the importance of the right proportion of the food consumed

everyday. We should eat the right types and amount of food daily to get all the energy

needed. This is called a balanced diet. In order to do this, the relative amounts of different

kinds of food eaten by a person has to be considered. The type of foods consumed can be

illustrated in the form of a Food Pyramid as shown in Figure 3.1.

Figure 3.1: Food Pyramid

Source: www.lifeclinic.com/foods/nutrition/foodpyramid.asp

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3.1.2 Taste of Foods

To teach this lesson, you can use the experiment strategy. Before we do the experiment,

the teacher should explain about the taste of foods. We eat all kinds of food. Food have

different tastes. Food can be categorised into different tastes: sweet, sour, bitter and salty.

Other kinds of tastes are the combinations of these four major tastes. The taste of food

can be detected only by a sensory organ in our mouth called the tongue. The tongue is the

sensory organ that has sensitive cells on the surface. These cells are called taste buds

which contain many taste receptors. These receptors detect the different type of tastes of

our foods. However, the taste of foods can only be detected at different areas on the

tongue (Figure 3.2)

Figure 3.2: Area of the tongue responding to different tastes

Source: http://library.thinkquest.org/3750/taste/taste.html

After explaining the different areas on the tongue that can detect different tastes, you can

use the following experiment to give your students the experience of different types of

taste.

ACTIVITY 3.2

Balanced diet

Balanced diets provide all essential nutrients in the correct amount and

proportion of food. It should contain all the seven classes of food. Adults,

adolescents and children need diet with different proportion. Divide your

classroom into seven groups to represent each class of food. In your assigned

group, discuss the factors that determine a person’s balanced diet. List all

factors and present the findings to the class.

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3.1.3 Acids and Alkalis

Food are grouped based on their tastes. They are sweet, sour, bitter and salty. Foods that

are sour belong to the acid group. The word “acid” is from the Latin word “acidus” which

means sour. Many sour fruits, especially those which are not ripe, contain acid. All acids

are not of the same strength; some are strong and some are weak. Other food or fruits that

are bitter fall in the alkali group. There are also strong and weak alkalis (see Figure 3.3).

ACTIVITY 3.3

Taste areas of the tongue

This is a lab activity. Work in pairs of two. Blindfold your partner. Pour little

amount of solutions of different tastes: salty (salt solution); sweet (sugar

solution); sour (lime juice); and bitter (coffee). Ask your partner to rinse his

tongue with distilled water. Using a straw, place a drop of salt solution onto the

tip of his tongue. Ask him to identify the taste without pulling his/her tongue.

Record your results using a table whether your partner is right (/) or wrong (x).

Repeat the steps on four other areas (tastes) of his tongue but make sure that he

rinses the tongue using the distilled water before each solution is repeated.

70


Figure 3.3: Acidic and alkaline foods and fruits

Source: http://buywaterfilter.my

Using a specific procedure in the lab, you can use a litmus or pH paper to test the

presence of acid or alkali in the substances you select. Most of the time, materials

containing acid will turn the blue litmus or pH paper to red colour. On the other hand,

alkali will turn the red litmus or pH paper to blue. (Figure 3.4). Can you list at least two

substances in your everyday life in both groups of acid and alkali?

Figure 3.4: pH scale ranges from 1 to 14 to indicate the strength of an acid or alkali

Source: dtc.prima.edu/~biology/.../lesson2d.htm

71


3.1.4 Household Products

You can also explain further the use of acid and alkali for cleaning purposes. Different

objects in the house will require different types of cleaning products; hence, we need to

use the products that have specific functions. The household products can be categorised

into two groups: acidic or alkaline. Most of the household products like alkaline are

sodium hydroxide (for making soap and detergent); ammonia (household cleaner,

drainage opener, sink opener), lime (to raise the pH value of acidic soil for healthy

growth of plants); magnesium hydroxide (used in antacid to ease stomachache due to

excessive acid); toothpaste; baking soda solution; bleach; and many more.

The other group of household products like nitric acid (to make fertiliser and dye); citric

acid and tartaric acid (to make fruit salt); acetic acid (to make synthetic fibre); boric acid

(an eyewash); benzoic acid (to preserve food); carbonic acid (in carbonated drinks);

lemon juice (for drinks); vinegar; and sulfuric acid (liquid from car battery); are some

example of uses of acids. I believe, you can find and name more of the household

products surrounding you from the departmental store during your shopping, as compared

to browsing through the Internet! Then you can use this example to explain or discuss

with your students.

ACTIVITY 3.4

Identification of substances: acidic or alkaline

You can ask your students to bring anything from home like fruit (lemon, lime,

mango, guava, papaya, banana, etc.) carbonated drink, toothpaste, detergent,

soap, shampoo, hair conditioner, milk, vinegar, distilled water or others by your

science teacher. In the laboratory, you will be conducting an experiment to

identify those substances whether they are acid or alkali. Use the litmus or pH

paper to indicate the presence of acid and alkali.

Source: dtc.prima.edu/~biology/.../lesson2d.htm

72


RUSTING

3.2.1 Investigate Material that can Rust Up

Start this lesson by asking student these questions; when you walk at the children

playground, can you trace which objects can become rusty and which ones cannot? Can

you differentiate the properties of the objects that can rust and which one cannot? (Figure

3.5)

Figure 3.5: Playground

Source: http://boston.about.com/od/walkingtours/ss/bcWalkingTour_6.htm

Objects that are made from iron and steel can become rusty. These objects have a

reddish-brown stuff formed on their surface when rusty. The mass of the objects will

increase when the rust formed on the surface. This process of rust formation is known as

rusting. However, not all objects can become rusty. Objects made from clay, wood, fibre,

3.2

ACTIVITY 3.5

Browse through the Internet. Find out on how to make:

1. Soap (using alkali)

2. Salt (using alkali and acid)

Write your report and present them to the class according to groups.

73


plastic and glass are the few examples of non-rusty objects. Find and list more examples

about rusty and non-rusty objects. To make the teaching process more interesting, you

can ask students to do the activity below:

3.2.2 Why do Objects Rust?

Before this, we have learned that objects made of iron and steel can become rusty. For

example, a nail, can become rusty. When you compare a nail in your house and the nail

outside the house, why is the nail outside the house often rusty? Can you explain this

phenomenon? Is it possible for us to infer why that one nail has become rusty, but others

still look gray and shiny? Why do objects like nails rust? To understand this behaviour,

we need to learn some chemical reactions which underlies the process of rusting. Perhaps

you have never heard of oxidation reactions. Yet, this type of reaction has many

important applications in our everyday life. When you see a rusty nail, you are actually

observing a process of oxidation.

Historically, the term oxidation was used for reactions of the elements with oxygen to

form oxides. All metals exhibit a tendency to be oxidised, some more easily than others.

Metals used in building materials, such as iron, eventually oxidise, which causes

deterioration of the metal. Known as corrosion, this process results in rust and other

corrosion on cars, bridges, ships and underground pipes.

ACTIVITY 3.6

Should we replace all rusty objects with non-rusty objects? Form your own

group and make your stand whether you are for or against this motion.

74


Figure 3.6: An abandoned rusty car

Source: http://www.nsls.bnl.gov/about/everyday/corrosion.html

3.2.3 Factors Needed for Iron to Rust

Now we know that iron can become rusty through the process of oxidation. What is the

meaning of oxidation? To understand this, we should identify the determining factors

needed for iron to rust. Then ask your students to do the experiment below:

75


ACTIVITY 3.7

Experiment 1: Rusting

Students will conduct experiment to determine what conditions are necessary

for iron to change into the iron oxide compound.

Materials:

Test tubes (4)

Stopper

Test tube rack

100ml graduated cylinder

250ml cylinder

Few pieces of nails

Salt

Pencil

Procedure:

1. Students work in groups of four.

2. Students hypothesise which nail will rust.

3. Students will be given data table.

4. Label the test tubes W, X, Y, and Z.

5. Measure 50ml of vegetable oil and pour into a 100ml beaker.

6. Measure 50ml of water and pour into a second 100ml beaker.

7. Measure 50ml of water and pour into third 100ml beaker. Add salt until

no more salt will dissolve.

8. Place one piece of nail into each of the three 100ml beakers. Drop the

fourth nail into the test tube W. Put a stopper on the test tube and place

in the test tube rack.

9. Use forceps to remove the nail from the oil and place into the bottom of

test tube X. Place in the rack.

10. Repeat the process for the nail from both water and salt solutions and

place into test tubes Y and Z.

11. Students work in groups of four.

76


12. Students hypothesise which nail will rust.

13. Students will be given data table.

14. Label the test tubes W, X, Y, and Z.

15. Measure 50ml of vegetable oil and pour into a 100ml beaker.

16. Measure 50ml of water and pour into a second 100 ml beaker.

17. Measure 50ml of water and pour into third 100ml beaker. Add salt until

no more salt will dissolve.

18. Place one piece of nail into each of the three 100ml beakers. Drop the

fourth nail into the test tube W. Put a stopper on the test tube and place

in the test tube rack.

19. Use forceps to remove the nail from the oil and place into the bottom

of test tube X. Place in the rack.

20. Repeat the process for the nail from both water and salt solutions and

place into test tubes Y and Z.

21. Measure 100ml of water into the 250ml beaker. Tape the four test tubes

together and invert them into the beaker and support them.

22. Record your observations in the data table everyday for three days.

Data and observation

Test tube Day one Day two Day three

W The nail still looks

gray and shiny

The nail still looks

gray and shiny


gray and shiny

X The nail still looks

gray and shiny


gray and shiny


gray and shiny

Y A reddish-brown stuff

appears on the surface

of the nail

A reddish-brown

stuff appears on the

surface of the nail

A reddish-brown


surface of the nail

Z More reddish-brown


surface of the nail

compared to Y

More reddish-brown


surface of the nail

compared to Y

More reddish-brown


surface of the nail

compared to Y

77


Here are some tips that you can give to your students when they are doing a science

project or experiment.

Tips

To do science project systematically, you may follow the following steps. First, you

must realise the purpose of doing this science project (Are you testing different

substance that are able to prevent rust from forming? Or, to determine which rust

remover was more efficient in removing rust from iron?).

Secondly, you should determine the hypothesis of this experiment. You can create your

hypothesis creatively, but I suggest you to consider substance that you believe to be the

most effective in preventing the act of rust.

Questions:

1. In which test tubes did the nail change into the compound iron oxide?

2. Why didn't the nails rust in the other test tubes?

3. What factor increased the rate of the reaction? Why?

4. What was the purpose of test tube W?

5. What is necessary for the formation of the compound iron oxide?

Answers:

1. In test tubes Y and Z

2. Either oxygen or water was not in contact with the nail. In test tube W,

the lack of water prevented the iron from oxidising. In test tube X, the

vegetable oil protected the nail from rusting

3. Salt increased the rate of chemical change. The salt solution cleaned the

surface of the nail

4. Control

5. Iron, oxygen and water

78


Thirdly, you should design your experiment in order to test your hypothesis. You

should recognise which variable is constant, how you can manipulate certain variable

and observe or measure the effect of this manipulated variable on certain independent

variable. You may discuss with your friends about the variable which is to be held

constant for this experiment However, it is suggested that different kind of rust

inhibitor as the manipulated variable. Rust inhibitor is defined as a substance to prevent

the act of rust from occurring. Paints are used on cars, bridges and many other items

that are usually exposed to damp air. In car radiators, anti-freeze is used since is has a

high boiling point, allowing the car to run at a high temperature without boiling away

the coolant and contains chemicals that can inhibit water’s tendency to rust. Tinplate is

used for manufacturing cans and protects the steel from rusting and corrosion. Waxes

are used in manufacturing as rust preventatives. Well, now we have already determined

which element act as manipulated variable. How about the dependent or responding

variable? Can you find any material around your house to be used as the responding

variable? Maybe you can use a nail, since it is cheap and easy to obtain.

After you have collected all the relevant materials, the fourth step you should do is to

conduct the experiment. The rust inhibitors which act as manipulated variable in this

experiment are the paint, the paraffin wax and the car polish. Therefore, we can decide

that there are three experimental groups in this study and one control group. Following

are the detail of each group.

Group Characteristic

Experiment 1 A nail coated with paraffin wax

Experiment 2 A nail coated with paint

Experiment 3 A nail coated with car polish

Control Does not have any rust inhibitor applied on it

Let all the nails dry overnight. After you have let the nails dry, sprinkle them with tap

water on the morning, afternoon and evening. Do this for a week. After a week, can

you discover which nail has a lot of rust and which nail doesn’t? After you have the

result, what can you conclude?

At the end of this lesson, you can ask students to make conclusion. What can they

conclude from this experiment? Let us read more to relate with the findings. Three things

are required for iron to turn into iron oxide. These things are water, oxygen and iron

itself. When a drop of water strikes an iron object, two things begin to occur almost

instantaneously. First, the water, a good electrolyte, combines with carbon dioxide in the

air to form a weak carbonic acid, an even better electrolyte. As the acid is formed and the

iron dissolved, some of the water will begin to break down into its component, that is

hydrogen and oxygen. The free oxygen and dissolved iron bond into iron oxide, in the

79


process of freeing the electrons. The electrons liberated from the anode portion of the iron

flow to the cathode, which may be a piece of a metal less electrically reactive than iron,

or another point on the piece of iron itself.

The chemical compounds found in liquids like acid rain and seawater, make them better

electrolytes than pure water. This allows their presence to speed up the process of rusting

on iron and other forms of corrosion on other metals. The type of metal also plays a big

role in the rate at which corrosion occurs. For example, chromium corrodes much slower

than iron. Other valuable metals like sterling silver, platinum and gold are hardly

corroded at all. The environment also plays a role in corrosion. Metals corrode faster in

hot humid climates and slower in cold dry ones.

Another way to understand how the process of rusting happens is through several

chemical equations. The process of rusting requires an anode and cathode in different

places on the surface of a piece of iron. In one area of the iron (Fe) surface, called the

anode region, the oxidation half reaction takes places.

Anode (oxidation): Fe(s) Fe2+(aq) + 2e-

or 2Fe(s) 2Fe2+(aq) + 4e-

The electrons move through the iron metal from anode to an area called the cathode

region where oxygen (O2) dissolved in water is reduced to water (H2O).

Cathode (reduction): O2(g) + 4H+(aq) + 4e- 2H2O(l)

By combining the half reactions that occur in the anode and cathode regions, we can write

the overall oxidation-reduction process.

2Fe(s) + O2(g) + 4H+(aq) 2Fe2+(aq) + 2H2O(l)

The formation of rust occurs as Fe2+ ions move out of the anode region and come in

contract with dissolved oxygen (O2). The Fe2+ oxidises to give Fe3+, which reacts with

oxygen to form of rust.

4Fe2+(aq) + O2(g) + 4H2O(l) 2Fe2O3 + 8H+(aq)

We can write the formation of rust starting with solid Fe reacting with O2 as follows.

There is no H+ in the overall equation because H+ is produced in equal quantities.

Corrosion of iron

4Fe(s) + 3O2(g) 2Fe2O3

Rust

80


3.2.4 Protection Against Rust

Rusty objects look unattractive and old. They become brittle and corrode slowly.

Basically, we can prevent rusting by preventing the iron objects from coming into contact

with air and water. This can be done by coating the objects with non-rusting material like

paint, oil, grease or any non-rusting materials. Iron objects also can be galvanised to

prevent the iron from rusting.

Other than that, we can also remove rust by using electrolysis (see Figure 3.7). In doing

this, you need a plastic bucket, battery charger, baking soda and electrode. It can be done

by providing a flow of electrical current and the rust will move with the electrical current.

To get the current flow, fill your plastic bucket with water. Add about a tablespoon of

baking soda per gallon to the water. Once the current is started, adding more soda will not

make the process go faster. Put the object into the water with the NEGATIVE lead on it.

Now, put in your electrode which could be a nail, screw, or any piece of metal. Stainless

steel works the best. Then, attach the POSITIVE lead to the “electrode”. Now switch

ON the battery charger and observe the rust going away.

Figure 3.7: The process of electrolysis

Source: http://www.thepontiactransampage.com/rust.html

3.2.5 The Benefits of Protection against Rust

The problem associated with rusting can be associated with utilities, transportation and

infrastructure. Therefore, it is important to prevent metals around us, especially iron, from

rusting. An old iron object need not be replaced if we can prevent it from rusting.

Therefore, it will save cost. Iron objects which are not rusty look shiny and new

compared to iron objects which have become rusty. Look at Figure 3.8. It shows a

photograph of a badly corroded truck after many years of marine atmospheric exposure.

81


Figure 3.8: A badly corroded truck after many years of marine atmospheric exposure

Source: http://www.electrochem.org/dl/interface/spr/spr06/spr06_p24-26.pdf

The teacher also can give students a group work assignment and science project as

activity below so that they can understand better.

ACTIVITY 3.8

There are so many mega structures in Malaysia. Yet, our country has a climate

that is humid and hot. Based on this circumstance, it is possible that rusting is

one of the problems which are faced by us in Malaysia when maintaining those

mega structures. Can you find information to show an example about how to

maintain one of the mega structures in Malaysia which is associated with

rusting? Do some presentation in front of the class to report about your work.

ACTIVITY 3.9

Conduct a science project to investigate the most effective way to protect iron

object against rust. Do some demonstrations to compare several methods which

are used to prevent materials from rusting.

82


Food can be categorised into seven classes: carbohydrates, proteins, vitamins, fats,

minerals, fibres and water.

Food have different tastes. They are sour, sweet, bitter and salty.

Food are also classified into two groups. They are acid and alkali.

Acid changes the blue litmus paper to red. While, alkali turns the red litmus paper to

blue.

Household products are also divided by the characteristics of being acidic and

alkaline.

Materials can be divided into rusty and non-rusty objects.

Rusting process is due to the presence of water, oxygen and iron. This process is

called oxidation.

Rust can be prevented by certain methods like painting, galvanising and electrolysis

of the metals.

There are benefits through the prevention against rust. Some metals can stay longer

and have a good looking appearence because of the prevention from rusting.

Acid

Alkali

Bitter

Corrosion

Iron

Oxidation

Oxygen

Rust

Salty

Sour

Sweet

Water

83


Burns, R. A. (1992). Fundamentals of chemistry (2nd ed.). Englewood Cliffs, NJ:

Prentice Hall.

Hazen, R. M. , & Trefil, J. (1997). The physical sciences: an integrated approach. New

York, NY: John Wiley & Son, Inc.

Kotz, J. C., Treichel, P. M. & Weaver, G.C. (2006) Chemistry and chemical reactivity

(6th ed.). Belmont, CA: Thomson Brooks/Cole.

Milner, B., Martin, J., & Mills, J. (2002). Core chemistry. Cambridge: Cambridge

University Press.

Timberlake, K. C. (2005). Basic chemistry. San Francisco, CA: Pearson

Education Co.

Abandoned rusty car (n.d). http://www.nsls.bnl.gov/about/everyday/ corrosion.html

Retrieved July 6, 2007.

Area of tongue (n.d). http://greenfield.fortunecity.com/rattler/46/upali2.htm Retrieved

July 7, 2007.

Badly corroded truck. (n.d). http://www.electrochem.org/dl/interface/spr/

spr06/spr06_p24-26.pdf Retrieved July 6, 2007.

Food Pyramid. (n.d). www.lifeclinic.com/foods/nutrition/foodpyramid.asp Retrieved July

7, 2007.

Household products. (n.d). http://images.search.yahoo.com/search/images/

householdproducts Retrieved July 7, 2007.

pH scale. (n.d). dtc.prima.edu/~biology/.../lesson2d.htm Retrieved July 7, 2007

The process of electrolysis (n.d). http://www.thepontiactransampage. com/rust.html

Retrieved July 6, 2007.

84

Rao, C. N. R.. Understanding Chemistry.: World Scientific Publishing Co., . p 238http://site.ebrary.com/id/10422534?ppg=238Copyright © World Scientific Publishing Co.. . All rights reserved.May not be reproduced in any form without permission from the publisher,except fair uses permitted under U.S. or applicable copyright law.

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134

INTRODUCTION

If there is a running competition between a rabbit and a tortoise, which

animal will win? Surely the answer will be the rabbit (if the rabbit does not

fall asleep during the competition, that is). Rabbits run faster than tortoises.

The tortoise will get to thefinish line eventually, but will probably reach

there muchlater.This means that the rabbit runs ata greater speed than the

tortoise.

In everyday life, if you put granulated sugar and fine sugar in different

glasses of water with the same volume and temperature, which sugar will

dissolve first?

TTooppiicc 55 Speed OfChemicalReactions

Yes! fine sugar will dissolvefirst. It is because fine sugar

has a larger surface area that comes in contact with water.

LEARNING OUTCOMES


1. Define the speed of chemical reaction;

2. Calculate the speed of a chemical reaction;

3. Distinguish the effects of particle size, concentration, pressure,

temperature and catalysts on the speed of chemical reaction; and

4. Evaluate the effect of activation energy on the speed of a reaction.

137

T

2

When coo

ordinary

refrigerato

everyday

The speed

change in

products

rate at wh

5.1.1 C

What are

physical c

matter. Fo

or becom

substance

substance

What hap

powder?

5.1

A

Wh

Put

exp

An

TOPIC5 SPEE

oking meat, it

pot. Ever wo

or take longe

occurrences

DEFINI

d of reaction

n concentratio

per unit time

hich the reacta

Chemical R

e chemical re

changes. Phy

or example, w

mes gasses if

e is formed.

es formed.

ppens when

ACTIVITY 5.1

hich metal disso

t magnesium p

periment by repl

nswer the follow

Which form o

Did you see a

Can you state

ED OF CHEMIC

t is better to u

ondered why?

er to go rott

are actually th

ITION O

n for a given

on of the react

e (Odufalu, C

ants of a chem

Reaction

eactions? In

ysical changes

water turns in

f the tempe

However, in

you put ma

1

olves faster in an

powder in a te

lacing the magn

wing questions:

of magnesium (t

any bubble relea

e what type of g

CAL REACTIO

use a pressure

? Why do ve

ten? Do you

he result of ch

OF SPEED

chemical rea

tants or the ch

Chacha, Mud

mical reaction

previous top

s are related t

nto ice when

rature is hig

n chemical c

agnet to a m

n acid? Find out

st tube contain

esium powder w

the powder or th

ased?

as was released?

NS

e cooker rathe

getables that

realise that

hemical react

D OF RE

action is the

hange in conc

dda, Iskandar

n form the pro

pics, we hav

to the change

the temperatu

gher than 1

changes, ther

mixture of sul

through this acti

ning hydrochlor

with a magnesium

he strip) will dis

?

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are kept in t

these commo

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EACTION

measure of t

centration of t

r, n.d.). It is t

oducts.

ve learnt abo

e of the state

ure reaches 0

00°C. No ne

re will be ne

lphur and ir

ivity!

ric acid. Repea

m strip.

solve faster?

an

the

on,

N

the

the

the

out

of

0°C

ew

ew

ron

at the

138

[Source

Iron pow

powder

you heat

The chem

Iron (s)

A

Figur

e: http://halya

wder will be

from the sulp

t the mixture?

mical equation

+ Sulphur (s)

ACTIVITY 5

The mixture is

a chemical reac

have now becom

Mix sulphur a

mixture. Put th

the mixture is

TOPIC

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angyuhao.blo

field

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CHEMICAL R

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REACTIONS

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139

TOPIC5 SPEED OF CHEMICAL REACTIONS

4

5.1.2 Nature of Chemical Reactants

In order for a reaction to occur, there must be a collision between the

reactants at the reactive site of the molecule with correct orientation and it

has to achieve activation energy. This will lead to effective collision and

chemical reaction will occur.

Figure 5.3: Particles showing the effective and ineffective collision[Source: http://2012books.lardbucket.org/books/principles of general

chemistry v1.0m/s18 07 the collision model of chemica.html]

Particles might be atoms, molecules or ions. Before we can get a chemical

reaction, particles must crash together. They must collide. This is called the

collision theory.

Figure 5.4:Collisionbetween particles

[Source: http://minhaji.net/classes/ 3107]

140

TOPIC 5 SPEED OF CHEMICAL REACTIONS 5

5.1.3 Speed of Chemical Reaction

The area of chemistry concerned with the speed or rates at which a chemical

reaction occurs is called chemical kinetics. The word “kinetic” suggests

motion. Here, kinetics refers to the speed of a reaction, or the reaction speed,

which is the change of the concentration of reactant or product with time.

Let us look at the general equation:

Reactants Products

This equation tells us that, during the course of a reaction, reactant

molecules are consumed while product molecules are formed. Two obvious

changes will occur, namely:

i. The decrease in the quantity of a reactant with time; and

ii. The increase in the quantity of a product with time.

As a result, we can follow the progress of a reaction by monitoring:

i. Either the decrease in concentration of the reactants or the

increase in concentration of the products;

ii. Decrease in the mass of reactant or increase in the mass of

product;

iii. Increase in the volume of gas released;

iv. Formation of precipitate as a product; or

v. Change in pH, temperature or electrical conductivity.

For reactions that occur rapidly, the speed of reaction is high. Conversely,for

a reaction that occurs slowly,the speed of reaction is low. The time taken for

a fast reaction is short, whereas the time taken for a slow reaction is long.

How do wemeasure the speed of chemical reaction?

Speed of chemical reaction is the speed at which reactants

are converted into the products in a chemical reaction.

141

T

6

To see ho

a look at t

5.2

S

Des

liber

Experime

1. Fill the

the me

2. Weigh

flask.

3. Measu

and po

4. Immed

Start th

5. Record

second

6. Plot th

same a

7. Calcul

the rat

TOPIC5 SPEE

MEASCHEM

w the speed o

the following

SELF-CHECK

cribe one oth

rated from Ex

ent 5.1 (The Re

e basin and bu

eniscus at 50cm

ht 6g of medium

ure 50cm³ of 0.1

our it into the c

diately, cover t

he stopwatch a

d the volume

ds.

he graph of th

axis as in Exper

late the averag

te of reaction in

Figure 5.5: W

ED OF CHEMIC

SURINGMICAL R

of a chemical

example:

CTIK 5.1

her method

xperiment 5.1

eaction betwee

rette with wat

m³ (Figure 5.4).

m marble chips

1 mol dm ³ hy

conical flask.

the conical flas

at the same tim

of gas collect

he volume of c

riment 5.1

ge rate of react

n the second m

Water displaceme

CAL REACTIO

G THE SPREACTIO

l reaction is ac

IVITY5.3

that can be

1

en Marble Chip

er. Invert the b

s (in excess) an

drochloric acid

sk with a rubb

me.

ted in the bur

carbon dioxide

tion, the rate o

minutes for this

ent method to co

NS

PEED OFON

ctually measu

used to colle

ps and Hydroc

burette into the

nd put the chip

d using the me

er stopper and

rette every 30

e released aga

of reaction at 5

experiment.

ollect carbon dio

F

ured, let us ta

ect the gas

chloric Acid)

e basin and ma

ps into the conic

easuring cylind

d shake the flas

seconds for 3

ainst time on t

50 secondsand

oxide gas

ake

ark

cal

der

sk.

360

the

in

142


The chemical equation for the reaction between marble chip (calcium

carbonate, CaCO3) and hydrochloric acid is:

CaCO3(s) + HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)

Figure 5.6 shows the volume of carbon dioxide gas released measured at

certain intervals plotted against time.

Figure 5.6:The volume of carbon dioxide gas liberated against time

How fast areaction progresses over an interval of time is the average speed

of reaction. It is calculated as follows:

Average speed= The change in the amount of reactant or product

The time taken for the change to happen

From the graph in Figure 5.6, we can calculate the average speed of chemical

reaction between marble chip and hydrochloric acid.

Volume of CO2 gas/ cm3

Time/min

143


8

Average speed of reaction = The total volume of carbon dioxide gas released

Time taken for the total carbon dioxide gas release

= 94.00cm3

4.5 min

= 20.90cm3min 1

Can you calculate the speed of reaction at any given time?

Let us take a look at the next example:

Based on the graph of volume of carbon dioxide gas liberated against time

(Figure 5.6), you can also:

a. Calculate the average rate of reaction in the first one minute;

Figure 5.7: The average rate of reaction in the first one minute

The exact speed of reaction at any given time is

called the instantaneous speed of reaction.


Time/min

144


The average rate of reaction in the first one minute

= Total volume of CO2 collected in the first 1 minute

Time taken

= 54.00cm3

1 min

= 54.00cm3min 1

b. Calculate the average rate of reaction from 1 minute to 2 minutes; and

Figure 5.8:The average rate of reaction from 1 minute to 2 minute

The average rate of reaction from 1 minute to 2 minutes

= Total volume of CO2 collected from 1 minute to 2 minutes

Time taken

= (77.00– 54.00)cm3

(2 1) min

= 23.00cm3

1 min

= 23.00cm3min 1


Time/min

145


10

c. Calculate the average speed of reaction atthe 2 minutespoint by

drawinga tangent at the curve point.

Figure 5.9:The average speed of reaction calculatedby drawing a tangent line

at the curve point

The speed of reaction at the 2nd minute = The gradient of the tangent of the

graph at the second minute

The speed of reaction at the 2nd minute = 100.00 – 50.00cm3

3.3 – 0.4 min

= 50.00cm3

2.9 min

= 17.24cm 3min 1


Time/min

ACTIVITY 5.3

From the graph in Figure 5.8, calculate:

The average speed of reaction in 3 minutes.

The average speed of reaction from 3 minutes to 4 minutes.

The average speed of reaction from 2 minutes to 4.5 minutes.

Tangentline

146

Another

reaction

formic ac

After we

we will n

In aque

(HCOOH

Molecula

progress

monitore

with a sp

the react

The aver

concentr

Wh

incr

Mg

rate

S

A

Fro

At

example we

is actually m

cid.

e have seen ho

now learn to w

ous solution

H) as follows:

Br (aq) + H

ar bromine

ses, the conce

ed easily by

pectrometer.

tants.

rage rate of th

ration over a c

hen magnesiu

rease of volum

.Which obser

e of reaction?

SELF-CHECK

ACTIVITY 5.

om the graph The instan The instan The instan

which time is

TOPIC

can look at to

measured is

ow thespeed

write speed e

ns, molecular

:

HCOOH (aq)

has a distin

entration of B

measuring t

Note that tim

he reaction ca

certain time in

um (Mg) react

me inhydrog

rvable change

Explain why

K 5.2

4

in Figure 5.9,ntaneous speentaneous speentaneous spees the reactian

5 SPEED OF

o understand

the reaction

of reactionis

expressions us

r bromine (B

2Br (aq)

nctivered bro

Br steadily d

the molecular

me zero is the

an be defined

nterval. That

ts with dilute

en gas (H2) a

e would you

y.

, calculate;d of reactiond of reactiond of reactionthe fastest? A

CHEMICAL R

d how the spe

n of molecula

measured via

sing the expe

Br2) reacts w

+ 2H+ (aq) + C

own colour.

decreases. Thi

r fading of b

e time just aft

d as the chang

is,

ed acid, we c

and the decre

u measure to

at 1 minute,at 3 minutes,at 4 minutes.At 1, 2, 3 or 4 m

REACTIONS

eed of a chem

ar bromine w

a Experiment

rimental data

with formic a

CO (g)

As the react

is change can

bromine’s col

ter the mixing

ge in the reac

can observe a

ease in mass

determine th

minutes?

11

mical

with

5.1,

a.

acid

tion

n be

lour

g of

tant

an

of

he

147

T

12

Where

concentra

quantity.

is needed

Some che

to speed u

There are

(a) Part

(b) Con

(c) Pres

(d) Tem

(e) Cata

The v

as fo

Time

Volu

i. D

ii. C

m

SEL

5.3

TOPIC5 SPEE

A

[Br ] = [Br

ation of Br de

But the speed

in the speed

FACTOA REA

emical reactio

up the slow o

several facto

ticle size of th

ncentration of

ssure of gaseo

mperature; an

alysts.

volume of O2 g

llows:

e (min) 0

ume (cm3) 0

Draw a graph o

Calculate the a

minute.

LF-CHECK 5.

ED OF CHEMIC

Average rate =

=

]final – [Br ]in

ecreases duri

d of thereacti

expression to

ORS AFFACTION

ns are fast; o

ones and slow

ors that affect

he reactants;

f the reactants

ous reactants;

d

gas produced d

0 2

0 60

of the volume o

average rate of

.3

CAL REACTIO

= [Br ] final – [B

tfinal – t in

[Br ]

t

nitial and t

ing the time i

ion is a positi

o make the ra

FECTING

thers are slow

w down the fas

the speed of a

s;

;

due to the deco

4

78

of the O2 gas a

reaction and t

NS

Br ] initial

nitial

= tfinal – tiniti

interval, [Br

ive quantity, s

te positive.

G THE S

w. Sometimes

st ones.

a reaction:

omposition of H

6 8

82 84

gainst time.

the rate of reac

ial. Because t

r ] is a negati

so a minus si

SPEED O

s chemists wa

H2O2is recorded

10

4 84

ction at the thir

the

ive

ign

OF

ant

d

rd

148


If you want to produce as much of a product as possible with the shortest

amount of timeviaa chemical reaction, you must consider the kinetics of the

reaction.

5.3.1 Effect of Particle Size of Chemical Reactants

Reaction depends on collisions. The more surface area on which collisions

can occur, the faster the reaction.

You can hold a burning match to a large chunk of coal and nothing will

happen. But if you take that same piece of coal, grind it up very, very fine,

throw it up into the air, and strike a match, you’ll get an explosion because

of the increased surface area of the coal.

We find that small pieces of solids, especially powders, react faster than

larger pieces. It is like frying two pans of chips! One has the potato cut into

small, thin chips. The other pan has bigger, thicker chips (Figure 5.10).Which

chips do you think will be cooked first?Which chips have the larger surface

area?

Surface area is a measure of how much surface is exposed. So for the same

massof potato, small chips have a larger surface area than big chips.

Figure 5.10: Small chips with larger surface area

149


14

Let us carry out Experiment 5.2 to see how particle size can affect the speedof chemical reaction.

Now, can you explain how the particle size of chemical reactants can affect

the speed of reaction?Observe Figure 5.11 to help you with your

explanation.

From the figure given,

Which size of marble

chips has the largest

surface area?

What would the graph

look like if we use the

same mass of powdered

calcium carbonate?

Explain why.

Experiment 5.2

1. Repeat Experiment 5.1 but replace medium marble chips with

small marble chips.

2. The mass of small marble chips, the volume and concentration of

hydrochloric acid used are the same.

3. Plot the graph of the volume of carbon dioxide released against

time on the graph paper as in Experiment 5.1.

4. Calculate the average speed of reaction and in the rate of reaction

in the second minute for this experiment.

5. Repeat Experiment 5.1 once again but at this time replace

medium marble chips with large marble chips.

SELF-CHECK 5.4

150


Figure 5.11: (a) Bigger sized reactant; (b) Smaller sizedreactant

The smaller the size of reactant, the larger is the surface area exposed. This

translates to an increase to the speed of chemical reaction.

5.3.2 Effect of Concentration of Chemical Reactants

Increasing the number of collisions will speed up the reaction rate. The more

reactant molecules there are colliding, the faster the reaction will be. As the

concentration becomes higher, the numberof molecules perunit volume also

increases (Figure 5.12). For example, a wood splint burns moderately in the

air (20 percent oxygen), but it burns much faster in pure oxygen.

(a) (b)

Pour 800ml of water in two different pots.Put 1kg of whole chicken

without cutting it into the first pot and in another pot put another

1kg of chiken that had been cut in eight.Which pot of chicken will

be done first? Explain why.

ACTIVITY 5.4

151


16

Figure 5.12:(a) Low concentration; (b) High concentration of reactant

In most simple cases, increasing the concentration of the reactants increases

the speed of reaction. However, if the reaction is complex and has a complex

mechanism (series of steps in the reaction), this may not be the case.

Determining the concentration effect on the speed of reaction can give you

clues as to which reactant is involved in the rate, thus determining the step

of the mechanism.

You can do this by testingthe reaction withseveral different concentrations

and observing the effect on the speed of reaction as in Experiment 5.3.

(a) (b)

152


Experiment 5.3

1. Using a pencil, mark an “X” on a piece of white paper, as follows:

2. Using the 50cm³ measuring cylinder, measure 50cm³ of 0.2 mol dm ³

sodium thiosulphate solution and pour it into a conical flask. Place

the flask on the “X” mark on the white paper.

3. Measure 5cm³ of 1 mol dm ³ sulphuric acid with a 10cm³ measuring

cylinder.

4. Immediately, pour the sulphuric acid into the conical flask

containing 50cm³ of sodium thiosulphate solution and shake the

flask. At the same time, start the stopwatch.

5. Observe the yellow precipitate of sulphur at the top part of the

conical flask. Record the time when the “X” mark on the white

paper is no longer visible.

6. Repeat the experiment using 50cm³ of the 0.4 mol dm ³, 0.6mol

dm ³, 0.8 mol dm ³ and 1.0 mol dm ³sodium thiosulphate

solution.The volume and concentration of the sulphuric acid used

are the same.

7. Plot two graphs:

a) Graph of concentration of sodium thiosulphate solution against

time.

b) Graph of the concentration of sodium thiosulphate solution

against 1 Time

8. Calculate the average speed of reaction for all the experiment. What

can be represented by 1 Time?

153

T

18

Sodium th

speed to f

equation f

Na2S2

http://ww

The graph

a) Gr

Figure 5.1

time

TOPIC5 SPEE

hiosulphate s

form a yellow

for the reactio

2O3(aq) + H2

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14: Graph of c

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nt 5.3 should

odium thiosul

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ow

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154


b) Graph of concentration of sodium thiosulphate solution against time

Figure 5.15: Graph of concentration of sodium thiosulphate solution against

time

From Experiment 5.3, the time taken for the formation of a fixed quantity of

sulphur to cover the mark “X” until it disappears from sight can be used to

measure the speed of reaction.

Speed of reaction is directly proportional to:

1

time taken for the mark “X” to disappear from sight

Concentration

of sodium

thiosulphate

solution

(mol/dm3)

1

Time (s-1)

155


20

5.3.3 Effect of Pressure of Gaseous Reactants

The pressure of gaseous reactants has basically the same effect as

concentration. The higher the reactant pressure, the higher the reaction

speed. This is due to the increased number of collisions (Figure 5.16).

Figure 5.16: (a) Low pressure ; (b) High pressure

5.3.4 Effect of Temperature

Increasing the temperature causes molecules to move faster, so there is an

increased chance of them colliding with each other and reacting. But

increasing the temperature also increases the average kinetic energy of the

molecules.

Figure 5.17shows an example of how increasing the temperature affects the

kinetic energy of the reactants and increases the reaction speed.

156


Figure 5.17:The effect of temperature on the kinetic energy of reactants

At any given temperature, not all of the molecules are moving with the same

kinetic energy. A small number of molecules are moving very slow (low

kinetic energy), while a few are moving very fast (high kinetic energy). A

vast majority of the molecules are somewhere in between these two

extremes.

In fact, temperature is a measure of the average kinetic energy of the

molecules. As you can see in Figure 5.17, increasing the temperature

increases the average kinetic energy of the reactants, essentially shifting the

curve to the right towards higher kinetic energies.

But also notice the minimum amount of kinetic energy needed by the

reactants to provide the activation energy (the energy required to get a

reaction going) during collision. The reactants have to collide at the reactive

site, but they also have to transfer enough energy to break the bonds so that

new bonds can be formed. If the reactants do not have enough energy, a

reaction will not occur even if the reactants do collide at the reactive site.

Notice that at the lower temperature, very few of the reactant molecules

have the minimum amount of kinetic energy needed to provide the

activation energy. At the higher temperature, many more molecules possess

157


22

the minimum amount of kinetic energy needed, which means a lot more

collisions will be energetic enough to lead to reaction.

Increasing the temperature not only increases the number of collisions but

also increases the number of collisions that are effective — that transfer

enough energy to cause a reaction to take place (Figure 5.18).

Figure 5.18: Effect of temperature on the reaction between particle A and particle B

Design and carry out an experiment to study the effect of

temperature on the rate of reaction. The various temperatures that

are suggested for this experiment are 30°C, 35°C, 40°C, 45°C and

50°C. The materials and apparatus supplied are as shown in the

following:

Materials: 1 mol dm ³ sulphuric acid, H2SO4, 0.2 mol dm ³ sodium

thiosulphate solution, Na2S2O4, white paper.

Apparatus: 100cm³ conical flask, 50cm³ measuring cylinders,

stopwatch, Bunsen burner, wire gauze, tripod stand, thermometer.

Calculate the rate of reaction at the third minute.

ACTIVITY 5.5

158

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The catalyst may react to form an intermediate, but it is regenerated in a

subsequent step of the reaction. In the laboratory preparation of molecular

oxygen, a sample of potassium chlorate is heated, as shown in Figure 5.19,

andthe reaction is noted as follows:

2KCIO (s) 2KCI (s) + 3O (g)

However, this thermal decomposition will occurvery slowly in the absence

of a catalyst. The rate of decomposition can be increased dramatically by

adding a small amount of the catalyst manganese (MnO ), a powdery black

substance.All of the MnO can be recovered at the end of the reaction, just as

all of the iodine ions,I ,remain following H O decomposition.

Regardless of its nature, a catalyst speeds up a reaction by providing a set of

elementary steps with a more favourable kinetics than those that exist in its

absence. The smaller the activation energy, E , the greater the rate. In many

cases, a catalyst increases the rate by lowering the activation energy for the

reaction.

Let us carry out Experiment 5.4 to study the effect of catalyst on the speed of

reaction.

160


Experiment 5.4

1. Fill the basin and small measuring cylinder with water. Invert the

measuring cylinder into the basin that is filled with water (Figure

5.20).

2. Measure 50cm³ of 20 volume of hydrogen peroxide solution using

a measuring cylinder and pour it into the conical flask.

3. Put a weighing bottle containing a half spatulamanganese (IV)

oxide powder into the hydrogen peroxide solution.

4. Immediately cover the conical flask with the rubber stopper and

shake the flask slowly. Start the stopwatch at the same time.

5. Record the volume of oxygen released every 30 seconds for 300

seconds (5 minutes).

6. Repeat the experiment by adding a spatula of manganese (IV)

oxide powder.

7. The volume and concentration of the hydrogen peroxide solution

used are the same.

8. Then, plot two graphs of the volume of gas against time with

different amount of catalyst, on the same graph paper.

9. Calculate the average rate of reaction for each experiment. Does

the amount of catalyst increase the rate of reaction?

Figure 5.20: Set up of the apparatus for Experiment 5.4

161


26

The graph obtained from Experiment 5.4 should be as shown in the

following:

Figure 5.21: The effect of catalyst on the speed of reaction of hydrogen peroxide

solution

SELF-CHECK 5.5

European regulations state that all new

cars have to be fitted with catalytic

converters as part of their exhaust system.

Using the Internet and/or other resources,

explain how catalytic converters work.In

your explanation, state the name of

catalyst used.

The following two sets of experiments are carried out:

Set I – 1g of granulated zinc is added to 30cm3 of 0.5 mol/dm3

hydrochloric acid

Set II 1g of granulated zinc is added to 30cm3 of 0.5 mol/dm3

hydrochloric acid and 2cm3 of 1 mol/dm3 copper(II) sulphate

solution.

Explain why the initial rate of set II is higher than that of set I using

the collision theory.

ACTIVITY 5.6

162


THE EFFECT OF ACTIVATION

ENERGY ON THE SPEED OF A

REACTION

All molecules possess a certain minimum amount of energy. The energy can

be in the form of kinetic energy and/or potential energy. When molecules

collide, the kinetic energy of the molecules can be used to stretch, bend and

ultimately break the bonds, leading to chemical reactions.

If molecules are moving too slowly with little kinetic energy, or collided

with an improper orientation, they will not react and simply bounce off each

other. However, if the molecules are moving at a fast enough velocity with a

proper collision orientation, such as the kinetic energy upon collision is

greater than the minimum energy barrier, then a reaction will occur. The

minimum energy barrier that must be met for a chemical reaction to happen

is called the activation energy, Ea. It can be represented by trying to push a

stone to the other side as shown in Figure 5.22.

Figure 5.23: The man is trying to push the stone from point A to point B

[Source: http://sites.tenafly.k12.nj.us/~shilfstein/demo_notes.htm]

The reaction pathway can be observed in Figure 5.23. In order to get the

product to react, the reactant has to overcome the activation energy, or a

new product cannot be achieved if it does not have the same amount of

energy.

5.4

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166

TOPIC 6: HYDROCARBON COMPOUNDS I TOPIC 7: HYDROCARBON COMPOUNDS II

Readings

Rose Marie Gallgher (1997). Complete Chemistry, Oxford Universiti Press, UK.

Ralph A. Burns (2003). Fundamentals of Chemistry, Prentice Hall, Ney Jersey

Bryan Milner, Jean Martin, John Mills (2002). Core Chemistry, Cambridge Universiti Press

J. G. R. Briggs (2003). Chemistry Insight, Pearson Education Asia Pte. Ltd. Singapore

J.G. R. Briggs (2003). Science in Focus Chemistryfor GCE ‘O’ Level, Pearson Education Asia Pte.Ltd. Singapore.

Bahagian Pendidikan Guru, Kementerian Pendidikan Malaysia. (1995) BukuSumber Pengajaran Pembelajaran Sains Sekolah Rendah, Jilid 3: StrategiPengajarandan Pembelajaran Sains. Projek PIER Bahagian Pendidikan Guru sertadan Bahagian Perancangan dan Penyelidikan Dasar Pendidikan, Kuala Lumpur

Whitten, K.W., Davis, R.E.,Peck,M.L and Stanley, GG. (2008). Chemistry (Ninth Edition).2010 Brooks/Cole.

Keywords

. alcohols and phenols

. primary, secondary and tertiary

. polymerization

. polymers

. condensation reaction

. condensation polymerizations

. nylon

. carboxylic acids

169

Learning Outcomes

At the end of this Topic, the learner will be able to;

1. Ability to differentiate between alcohols and phenols.

2. Ability to differentiate between primary, secondary and tertiary alcohols. Illustrate by writing names and formulas for three alcohols of each type.

3. Explain the trends in boiling points and solubilities of alcohols in water.

4. Describe the physical properties of alcohol.

5. Describe some uses of alcohol.

6. Describe polymerization, write equations for three polymerization reactions, explain two classes of polymers and naming three polymers commonly found in the classroom and give their uses or functions.

7. Give an example of a condensation reaction. Name the essential feature of monomers used in the condensation polymerizations.

8. Define nylon? Describe in your own words how nylon is prepared.

9. Define carboxylic acids. Write structural formals for five carboxylic acids.

10. Define esters. Write structural formulas for four esters.

Study Questions

Task 1 : Read section 27-9 Alcohols and phenols and answer questions 1 – 3

(a) What do you understand about alcohols and phenols?

(b) How do they differ?

(c ) Why are alcohols and phenols be viewed as derivatives ofhydrocarbons?

Task 2 : Can you differentiate between primary, secondary and tertiary alcohols? Illustrate by writing names and formulas for three alcohols of each type.

Task 3 : Refer to Table 27-8. Explain the trends in boiling points and solubilities of alcohols in water.

170

Task 4 : Describe the physical properties of alcohol. Refer to Page 998-999.

Task 5 : Describe some uses of alcohol. Refer to Page 999 for the information.

Task 6 : Refer to page 1020-1024 for questions 6 - 8. In your own words,

(i) describe polymerization.

(ii) write equations for three polymerization reactions.

(iii) explain two classes of polymers.

(iv) Name three polymers commonly found in the classroom and give their uses or functions.

Task 7 : Give an example of a condensation reaction. Name the essential feature of monomers used in the condensation polymerizations.

Task 8 : What is nylon? Describe in your own words how nylon is prepared.

Task 9 : Refer to section 27-13 Carboxylic acids for questions 9 - 10. Define carboxylic acids. Write structural formals for five carboxylic acids.

Task 10 : Define esters. Write structural formulas for four esters.

171

TTooppiicc

88

Natural

Materials and

Manufactured

or Man-made

Materials


1. Define material;

2. Describe each type of materials;

3. Explain the properties of materials;

4. State the importance of materials;

5. Compare natural materials and manufactured materials;

6. Describe how to preserve our natural materials;

7. Describe composite materials; and

8. Discuss the materials in industry in the context of soap, natural and

synthetic rubber, natural and synthetic fibre and plastics.

LEARNING OUTCOMES

275

TOPIC 8 NATURAL MATERIALS & MANUFACTURED OR MAN-MADE MATERIALS

71

INTRODUCTION

Materials are the things that you can observe all around you. From falling rain

to plants and human beings, from window curtains to floor mats and from

computers to printing materials, these are all materials. The air that you

breathe in and out is also a material.

Materials are very useful to human beings for their survival. They not only use

natural materials but also create new materials in order to fulfil their needs.

DEFINITION, PROPERTIES AND IMPORTANCE OF MATERIALS

A cloud is seen as a bulk of moving object in the air. When it is very heavy, it

starts to drop tiny droplets of water. When the sun shines on the water

droplets, it turns to vapour. Have you ever thought of the processes that occur

in this event?

This event is just one in a thousand of events that involve materials. Materials

are the things all around you. Materials have mass and occupy space. Gases,

woods, plastics, foods, animals and water are all examples of materials.

According to the ancient Greek, there should be four things to make up a

substance. These four things are earth, fire, air and water. The Greeks believed

that these four things mix together in different amounts to make different

materials.

8.1.1 Definition of Materials

What is material? Material is defined as follows.

8.1

Material is made up of thousands of small particles, not visible to thenaked eye, called atoms. The composition of atoms in the material makes itdifferent from one another.

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72

Based on these compositions of atom, material can be divided into three

categories: element, compound andmixture.

(i) Element

An element is the simplest substance of a material. It cannot be broken

down or separated by chemical or physical methods into any simpler

components. An element is made up of only one type of atom. Some

elements have atoms of the same types, which are combined to form

molecules. There are 112 types of elements, in which 92 of these elements

occur naturally in the earth and 20 are created by scientists.

Elements can be grouped into metals and non metals. Gold, zinc, iron,

aluminium, oxygen, carbon, hydrogen and nitrogen are examples of

elements.

Figure 8.1 shows the atom of an element with its nucleus at the centre

and electrons moving around the nucleus.

Figure 8.1: The atom of an element

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73

(b) Combined Elements

There are two types of combined elements – compounds and mixtures.

(i) Compound

Two or more elements can be combined together chemically to form

a new material called a compound. A molecule is the smallest

particle in a compound. Water is an example of a compound. A

water molecule is made up of one oxygen atom and two hydrogen

atoms, which are combined chemically (see Figure 8.2).

Figure 8.2:Water molecule

Table 8.1 shows several types of compounds and its elements.

Oxygen atom

Hydrogen

atoms

ACTIVITY 8.1

Look outside your laboratory. Identify the objects and list down the

objects. They are made of different types of materials. Most of the

materials are made from a combination of elements. Some are made

of only one type of element. Can you guess which objects are made

of only one element? Can you name the element in each case? Write

down your findings.

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74

ACTIVITY 8.2

Table 8.1: Several Types of Compounds

Compound Elements

Carbon dioxide One carbon atom, two oxygen atoms

Sodium chloride One sodium atom, one chloride atom

Benzene Six carbon atoms, six hydrogen atoms

Ammonia One nitrogen atom, three hydrogen atom

Water One oxygen atom, two hydrogen atoms

The components of a compound cannot be separated by physical methods

such as crushing or by magnetic force. Components of a compound can be

separated by chemical methods. For example, pure water can be broken

down into its elements that are oxygen and hydrogen by using electrolysis.

Compounds can be prepared by a chemical reaction. Heat energy is released

or absorbed when a compound is formed. This will form a new substance

that is different from its early substances. The characteristics of a

combination of elements which are combined by specific ratios are different

from each of the origin element.

(ii) Mixtures

Material that is made up of a combination of two or more substances

that are combined physically is called a mixture. This means that the

mixture can be separated by physical methods such as filtration,

evaporation, distillation, chromatography, extraction, precipitation,

magnetic forces, sieving and heating or evaporation processes. By

these separation methods, the chemical structure of the component is

not changed because the substance in a mixture does not unite.

ACTIVITY 8.2

Have you ever burnt a magnesium ribbon? Magnesium and

oxygen can be combined to make a compound. Hold a small piece

of magnesium ribbon by using a tong and move it slowly into a

flame. Observe the appearance of magnesium and oxygen before

and after it was burnt. Identify the end product of the experiment.

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75

There are two types of mixture – homogenous and heterogeneous. A

homogenous mixture is formed when its substances are mixed

evenly and the identity of each substance cannot be identified easily.

A heterogeneous mixture is formed when its substance can be

identified easily. When sugar is put in a glass of hot drink, it

becomes a homogenous mixture. A mixture of sulphur with iron

fillings and air are examples of a heterogeneous mixture (see Table

8.2).

Table 8.2: Several Types of Mixtures

Mixture Components

Air Oxygen, nitrogen, hydrogen, carbon dioxide, inert

gases, microorganisms and water vapour

Soil Water, clay, loam, sand, humus, gravel

Sea water Sodium chloride, water, magnesium, plumbum,

oxygen

Chocolate

cake

Flour, water, oil, egg, chocolate powder

Blood Blood cells, hormones, minerals, water, plasma,

oxygen

During the formation of a mixture, heat energy is not absorbed or

released. There is also no combination of elements in a specific ratio

and each component retains its original property. The components of

a mixture can be easily identified.

SELF-CHECK 8.1

1. What is a material?

2. Name a few examples of materials.

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76

(c) Making New Materials

Some materials around us are natural while others are man-made. Wool from

sheep and wood from trees are natural materials. All these materials are made

from elements.

Scientists sometimes combine elements in new ways. This is a way to make

useful man-made materials. Synthetic materials are an example of man-made

materials.

8.1.2 Properties of Materials

What are the physical properties of materials? Matter is the general word for

all materials. Therefore, specific matter such as wood, stone and paper are

called material. We know that materials can be divided into two types –

natural materials and synthetic materials. Natural materials are made from

organic material like paper or inorganic material like sand and lava. Humans

cannot create natural materials. However, scientists have managed to make

synthetic materials. Plastics and ceramics are two types of synthetic materials.

Each material has its unique physical properties, which means different

materials have different properties. Some of the important physical properties

of materials are elasticity, shine, buoyancy, water absorbency, electrical

conductivity, heat conductivity and magnetism. Other physical properties of

materials are hardness, toughness and brittleness, strength, flexibility,

solubility and waterproof.

SELF-CHECK 8.2

State the types of combining elements.

ACTIVITY 8.3

Do you know how to separate gases in the air? What are the

procedures that should be taken to turn it into liquid? Discuss with

your coursemates.

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77

Scientists distinguish material properties according to their interesting

contextual factors. Among these properties are:

(a) Mechanical properties like elasticity;

(b) Thermodynamic properties like specific heat capacity and melting point;

(c) Electromagnetic properties like specific magnetic susceptibility and

specific electric conductivity;

(d) Chemical properties like the capacity for oxidation or the solubility in a

certain liquid;

(e) Biological or biochemical properties like LD50, antibiotic or anaesthetic

effect;

(f) Ecological properties like ozone depletion potential, greenhouse effect

factor; and

(g) Mixed material properties (two or more interesting factors are

combined) like photo chemical, thermo electrical, thermo electro

chemical.

Let us now take a look at the types of material properties.

(a) Elasticity

What is elasticity?

Materials that are able to return to their old shape when force is no

longer applied are called elastic materials. However, materials which

retain their new shapes when force is no longer applied are called plastic

materials or non elastic materials. Some materials such as rubber bands,

balloons and gloves are elastic materials but some materials such as

plastic, wood and belt are non elastic materials. To determine whether

materials are elastic or non elastic, you may need to carry out some

activity.

Elasticity is the ability of a material to return to its original shape and

size after being bent, twisted, stretched and squeezed.

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78

Scientists spend a lot of their time investigating the properties of

materials mainly to find out how they behave in a variety of situations.

The most important property is how a particular material responds to

forces. When an elastic material is pulled, it stretches and increases in

length. However, the increase in length will stop when it reaches a point

where the material no longer returns to its original shape. This pull is

also known as the elastic limit of the material. If the pull still increases,

the material may break down (please refer to Figure 8.3).

Figure 8.3: Effect of force on materials

(i) Elastic Change

When enough force is applied to an object, it deforms. However,

when the force is removed, the material will often return to its

original shape.

(ii) Plastic Change

When a larger force is applied, a material may continue to deform.

However, when the force is removed, it will stay in this new shape.

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79

(iii) Break

If enough force is applied to a material, it will become brittle and

eventually break or fracture.

Some materials that exhibit elastic behaviour are:

(i) Rubber: Large deformation if warm, then fracture or small

deformation and fracture if cold;

(ii) Metals: Small deformation, then permanently deform;

(iii) Ceramics: Small deformation, then fracture;

(iv) Electronic materials: Small deformation, then fracture or deform;

(v) Glass: Small deformation, then fracture.

(vi) Human skin: Large deformations.

(vii) Polymers: Temperature dependent.

(viii) Liquids under uniform hydrostatic pressure.

(b) Shiny

When it comes to material properties, what does shiny mean?

Shine is important in making jewellery and accessories. In relation to this

shiny property of materials, some materials allow light to pass through

them but some do not. Materials such as glass and plastic allow light to

pass through them. On the other hand, materials such as wood and

metal do not allow light to pass through them. According to the ability

of materials to allow light to pass through them, materials can also be

SELF-CHECK 8.3

1. State the importance of physical properties of materials.

2. Give an example of a material for each physical property.

Some materials are shiny and some are not. Shiny materials can

reflect the light such as some types of metals and glasses.

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80

divided into three types. There are transparent materials, translucent

materials and opaque materials. Figure 8.4 shows objects made of

transparent, translucent and opaque materials.

Figure 8.4: Objects made of transparent, translucent and opaque

materials

• Transparent materials

If the materials allow most of the light to pass through them, it is

known as transparent materials. Examples of this type are glass,

plain plastic, air, water, aquariums, some doors and walls of

buildings made from clear glass. We can clearly see objects behind

these materials.

• Translucent materials

If the materials allow some of the light to pass through them, it is

known as translucent materials. Objects behind a translucent

material cannot be seen clearly. It will appear blurred. Examples of

these materials are tissue paper, wrapping plastic, some window

panes, bulbs, food containers and sunglasses.

• Opaque materials

Opaque materials are materials which cannot allow any light to pass

through them. We cannot see anything behind opaque materials.

Metals, woods, rubber, bricks, roofs, walls, bags, hats and paper

boxes are examples of these materials.

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81

(c) Buoyancy

How do we define buoyancy? Let us take a look at the following

definition.

Why do some things float? Dense objects sink and light objects float.

Therefore, buoyancy is also related to density. Density is mass per unit of

volume.

Floating is related to the volume of liquid displaced by an object. The liquid is

pushed aside when an object is placed in it. Therefore, our body displaces the

water. When an object floats in water, only a part of it displaces the water.

The other part of the object remains above the water. The objects float after a

definite amount of water is displaced. According to Archimedes, the ancient

Greek physicist, when the mass of the displaced liquid is equal to the mass of

the objects, the objects will float. Plastic, wood and rubber are examples of

floating materials. Figure 8.5 shows floating materials and liquids of different

densities.

Figure 8.5: Floating materials and liquids of different densities

Buoyancy is the ability of materials to float in liquid.

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82

(d) Water Absorbency

Materials which can absorb water are known as absorbent materials and

materials which cannot absorb water are known as non absorbent

materials. The materials that are able to absorb water become completely

wet. Examples of absorbent materials are wood, paper and cotton cloth.

Raincoats, umbrellas, plastic and hats are examples of non absorbent

materials.

(e) Electrical Conductivity

A material that allows electricity to pass through it is a material that

conducts electricity. Almost all types of metal such as zinc, copper, brass

and gold are materials that conduct electricity. Non metals such as glass,

wood, plastic, cotton wool and leather are materials that do not conduct

electricity. Electrical conductivity is a measure of the ease with which an

electrical current can move in a material. It may be inferred by looking at

their resistivity, which refers to its ability to resist the passage of an

electrical current. Figure 8.6 shows the test of electrical conduction.

ACTIVITY 8.4

ACTIVITY 8.4

Your friend’s child is asking you about absorbent materials. How do

you explain to your friend’s child to test absorbent and non-absorbent

materials? Discuss in pairs.

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Figure 8.6: Test of electrical conduction

Table 8.3 summarises the electrical resistivity of some common materials.

Table 8.3: Electrical Resistivity of Some Common Materials

Materials Electrical Resistivity (10 8 ohms/m)

Copper 1.67

Aluminium 2.65

Iron 9.71

Steel 12.0

Pyrex glass 105

Concrete 0.1

Nylon 1016

Rubber —

Softwood —

ACTIVITY 8.5

How do you test for electrical conduction? Arrange equipment to find

out which materials are electrical conductors and which are electrical

insulators. Figure 8.6 will help you do the test. Place the material

between the battery and the bulb to be tested. See what happens to the

lightbulb. Test several types of samples such as pencil, flower, soil,

water and spoon.

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(f) Heat Conductivity

What is heat conductivity?

Metals can conduct heat while non metals cannot conduct heat. Each

material conducts heat in its own special way. A good conductor would

be used in radiators whereas a poor conductor would be used to insulate

extreme heat.

Scientists have a way of measuring the value of how well heat is

conducted. If the value of a material is larger, it is a better heat conductor

compared to materials with small values. Table 8.4 shows the values of

heat conduction of some materials. A piece of copper with a heat

conduction value of about 8000 is a better heat conductor than foamed

plastic with a heat conduction value of about 1 because copper ranks

higher than plastic.

Table 8.4: Values of Heat Conduction of Some Materials

Materials Values of Heat Conduction (Relative)

Copper 8000

Aluminium 4000

Brass 2500

Steel 1100

Pyrex glass 24

Concrete 2

Solid plastic 6

Rubber 2

Foamed Plastic 1

A material that allows heat to pass through it easily is a material that

conducts heat.

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(g) Magnetism

Magnetism is the property of materials to attract iron, for example, iron

oxide, cobalt, nickel and certain types of alloy. Actually, it is quite

difficult to explain the definition of magnetism; however, it is much

easier to explain what magnets do. Some of the characteristics of

magnetism are as follows.

(i) Magnetic materials can be attracted by magnets;

(ii) Attraction may happen from a distance;

(iii) Every magnet has two poles: north and south poles;

(iv) Different poles will be attracted but similar poles will be repelled;

(v) The region around a magnet is known as a magnetic field;

(vi) Bringing iron into close contact with a magnet will produce a

temporary magnet;

(vii) Bringing steel into close contact with a magnet will produce a

permanent magnet; and

(viii) Magnetism is reduced by heating or hammering a magnet.

(h) Other Properties of Materials

Other properties of materials are hardness, toughness and brittleness,

strength, flexibility, solubility and waterproof. Table 8.5 summarises

these properties.

Table 8.5: Other Properties of Materials

Properties Explanation

Hardness The shape of a hard material is difficult to change. It will

dent or scratch a softer material. It can also withstand

impact without changing.

Toughness

and

brittleness

Resistance to breaking by cracking. It is the opposite of

brittle. It may be dented by the impact but it is difficult to

break.

Strength The material is difficult to break by applying force.

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Materials may have tensile strength and compressive

strength. Tensile strength means resistance to stretching

such as squeezing and pulling on the rope. It depends on

its cross sectional area. Compressive strength means

resistance to pressure, meaning it is hard to break by

crushing.

Flexibility The material, which is easy to bend without breaking, has

both tensile strength and compressive strength.

Solubility The solubility is the concentration of solute in a saturated

solution. It is stated as the mass in grams of the solute that

will saturate 100 grams of solvent at a certain temperature.

Waterproof Resistance to liquids. Repels water.

8.1.3 Importance of Materials

Materials play a pivotal role in our life, particularly in the areas of living

environment, health, communication, consumer goods and transport. Pressing

environmental concerns force us to use materials more efficiently. It will help

in the long run if we develop new energy generation technologies, more

energy efficient devices, and easily recyclable, less toxic materials. As far as

consumer goods are concerned, we need to emphasise not only on the

material products but also on the way they are handled such as packaging,

faster production and higher quality goods.

In health, materials are important to help us overcome disease and provide

worldwide medical care. In transport, we need durable, high performance

materials that make travelling faster, safer and more comfortable. In

ACTIVITY 8.6

Go on the Internet and find out more on materials and their uses

based on their properties. Discuss your findings with you

coursemates.

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communication, the development of new electronic inventions is very

important and requires optical and magnetic materials. Without development

of materials in all areas, we may face many difficulties.

(a) Importance of Physical Properties of Materials

Knowledge about the properties of materials is very important, especially

in choosing suitable materials to make various objects. Sometimes these

objects need more than one type of physical property. For thousands of

years, people only used natural properties of natural materials. However,

scientists have now developed many new materials, influencing its

properties in the process.

(b) Use of Properties of Materials in Everyday Life

Humans have exploited physical properties of materials for their own use

in everyday life. We use materials that conduct electricity to produce

conductors and insulators. We use materials that allow light to pass

through them to produce transparent, translucent and opaque objects.

Table 8.6 shows other uses of properties of materials in producing some

everyday objects.

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Table 8.6: Other Uses of Properties of Materials in Producing Some EverydayObjects

Property Materials Uses

Strength

Metals

Structural components

E.g., rolled steel joints

Malleability Water pipes

Thermal

conductivity

Radiators, saucepans, ovens

Electrical

conductivity

Electrical cables

Hardness Drill bits, hammerheads

Strength

Ceramics

Brick, concrete

Heat resistance Ovenware

Abrasion

resistance

Crockery

Thermal

insulation

Glass Loft, cavity wall insulation

Transparency Windows

Flexibility

Plastics

Moulded items

Electrical

insulation

Sheathing of electrical cables

Thermal

insulation

Saucepan handles

Lightness and

strength

Construction, window frames

Lightness and

strength Wood

Construction, doors, window

frames,

furniture

Flexibility,

insulationFabrics

Curtains, clothing, furnishing

Adapted from: Farrow, S. (1996). The really useful science book: A

framework of knowledge for primary teachers. London: Falmer Press.

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NATURAL MATERIALS

All living things and non living things are sources of materials. Materials that

are originated from nature such as living organisms, plants and animals are

classified as biotic or biological derived natural material. Materials originated

from soil, petroleum or metals are classified as abiotic or non biological

natural materials. We need these materials to support our daily needs.

Natural materials are made naturally after a long period of time. For example,

a rubber tree may take many years to become mature and ready for cutting

down to make furniture, papers and insulators. Chemistry has enabled us to

synthesise new materials, which have desired properties, thus making them

even better than natural materials in a shorter period of time.

(a) Identifying Natural Materials

Materials that are classified as natural materials originated from soil,

rocks, water, plants, animals or minerals. Air is a mixture of gases, which

make up the earth’s atmosphere and has an abundance of components.

Parts of their uses can be seen in Table 8.7.

Table 8.7: Gases and Their Uses

Gas % Present

in Air

Uses

Nitrogen 78.0 Nitrates in soil, use in ammonia production.

Oxygen 21.0 Respiration, oxidation, medical application

Carbon dioxide 0.04 Photosynthesis, dry ice

Neon Trace Lighting

Argon Trace Domestic light bulb

Helium Trace Airships

Krypton Trace High temperature light bulb

Xenon Trace High temperature light bulb

8.2

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Water is a colourless, odourless liquid, which is originally derived fromthe earth’s atmosphere. It is recycled from the atmosphere to the crust ofthe earth. It is important because it supports life on the planet, as almostall the significant reactions at cellular level depend on the aqueoussolutions.

Wood, metal, leather, cotton, rubber and silk are materials that are made

of natural materials. These materials are considered valuable in their

relatively unmodified (natural) form.

(b) Objects from Natural Materials

Materials from natural materials vary in their use. Table 8.8 shows

natural materials and their uses.

Table 8.8: Natural Materials and Their Uses

Natural Material Uses

Rubber Latex

Wood Timber

Paraffin wax and stearic acid Candles

Carbon black and water or oil Ink

Vegetable fibre Wood pulp

Vegetable waxes, oil and sap Carnauba wax, linseed oil

Animal fibre Wool, alpaca

Animal product Leather , tallow, lard

(c) Source of RawMaterials

Raw materials are materials that are extracted from the earth. Processed

raw materials are called ”semi finished materials”. When it is transferred

into a new cycle of production, the end product is ready for use.

The earth is the main source of raw materials. Biotic materials and non

biotic materials are the types of sources of raw materials. Wood, straw,

humus, spider silk, and bone are examples of biotic materials. Biotic

materials are usually biodegradable, renewable and processing has

minimal impact on the environment. Somehow, in certain cases,

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processing produces carbon emission. Polylactic acid, cornstarch and

bioplastic are examples of non biodegradable biotic materials. Non

biotic materials are materials that do not originate from plants and

animals. Water, soil, coal, crude oil, natural gas, rocks and air are

examples of non biotic raw materials.

Another example is cotton. Cotton is produced from a matured flower of

a cotton tree. It is harvested by plucking from a matured cotton tree

flower. The fluffy white material is then brought to the factory and

processed to produce cotton thread.

MANUFACTURED MATERIALS

Manufactured materials are made from a mixture of natural materials

through chemical processes. These materials are also called man made

materials. These materials are processed in factories with a combination of a

few different types of materials or from one type of natural material.

(a) Identifying Manufactured Materials

Basic manufacturing processes frequently used in the production of

manufactured materials are relatively simple, often involving

irreversible chemical reactions. These reactions are important in order to

provide further raw materials for more complicated secondary

processes.

The physical process of raw materials would include the refining of

metals from ores, the firing of ceramic from clays and the making of

glass from sand and minerals.

SELF-CHECK 8.3

1. What is a natural material?

2. State some objects that are made from natural materials.

3. Give as many examples as you can of raw materials that can be found

in your surroundings.

8.3

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The sawing of timber, the production of paper from wood pulp and the

production of latex from rubber are examples of basic manufacturing

processes that involve biological raw materials. Secondary industries

involve the production of plastics (including synthetic fibres such as

nylon and terylene) from crude oil derivatives, detergents, paint and

perfume from coal, and others.

Manufactured materials usually have better properties compared to the

natural materials from which they come from. They are usually designed

for specific needs, like tyres are made of latex and sulphur. Metals, glass,

ceramics, plastics (including rubber), paper and fabrics are examples of

manufactured materials.

(b) Objects from Manufactured Materials

Table 8.9 lists a few examples of objects from manufactured materials

and their uses. You can list your own examples that are used in our daily

life.

Table 8.9: Objects from Manufactured Materials

Manufactured

Material

Synthetic

PolymerUses

Synthetic

rubber

Styrene butadiene

rubber (SBR)Tyres, shoe soles

Neoprene rubber Water pipes, hand gloves

Butyl rubber Tyres, shoe soles, hoses

Metals

Stainless steel Cooking utensil,

Bronze Medals,

Duralumin Cooking utensil

ACTIVITY 8.7

Search the Internet for manufactured materials. Find out the

properties of manufactured materials.

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GlassPyrex

Laboratory apparatus, cooking

utensil

Crystal Cooking utensil

Ceramic

Brick Building

Tiles Building

Pottery Decoration

Fabric Nylon Cloth

Plastic

Polyvinyl chlorideElectrical insulators, music records,

pipes, bottles

Nylon Synthetic textile, string, parachutes

Polythene Plastic bags, food containers, pails

PolystyrenePackaging materials, heat insulators,

toys

Melamine Plates, cups

Epoxy glue Glue, electrical insulators

SELF-CHECK 8.4

1. Explain what manufactured materials are.

2. State the processes that are applied to produce manufactured

materials .

3. Give examples of objects from manufactured materials.

ACTIVITY 8.8

You are given a sample of two materials. One is a natural

material and the other one is a manufactured material. In your

group, plan an investigation to compare the materials by

choosing a suitable characteristic. Make a prediction. Then plan a

fair test.

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PRESERVATION OF NATURAL

MATERIALS

About a century ago, almost the entire country was covered with forests. Wild

cutting of forests during the early settlement caused vast areas of bared land.

This phenomenon of cutting down plants for timber and development

continues today.

Preservation refers to the effort to maintain natural resources in their original

state or in good condition. Generally, preservation is related to conservation.

Conservation refers to the sustainable use and management of natural

materials to prevent loss, wastage or damage.

The importance of preservation is to ensure a continuous supply of natural

resources, reduce environmental pollution, maintain balance in nature,

prevent extinction of living organisms, prevent loss of habitats and keep the

environment clean and conducive for healthy living.

Preservation should be practised. Some of the actions that should be taken to

preserve natural materials are:

(a) Preventing Forest Fires

Forest fires are wildly destructive. Plants and wildlife are killed. Forest

fires are caused by lightning (natural cause) and people’s carelessness

(accidental cause).

(b) Improvement Cutting

Unwanted trees in a forest are removed from the stand. Crooked, aged

and diseased trees as well as trees of less desirable species are cut. In this

way, space is provided for the growth of healthy, more valuable trees.

This practice increases lumber yield and improves its quality.

(c) Enforcement of Laws and Regulation

This action is taken to protect endangered species and to prevent them

from becoming extinct. Examples of protected endangered species are

the Malayan tiger, Sumatran rhinoceros, leatherback turtle, orang utan

(see Figure 8.7) and deer.

8.4

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Figure 8.7: The government today has enforced laws and regulation to protect

the orang utan and their habitat

COMPOSITE MATERIALS

Composite materials are those that combine the properties of two or more

constituents in order to get the exact properties needed for a particular job.

The examples of material usually used are metals, alloys, glass, ceramics,

plastics and polymers. A composite material has properties that are superior

to those of the original components.

There are many examples of composites in nature. A tree can grow to great

heights and support heavy branches because it is a composite of flexible

8.5

SELF-CHECK 8.5

What actions should we take to preserve our natural materials?

ACTIVITY 8.9

1. What natural resources are destroyed by forest fire?

2. In a group, discuss what action should be taken to prevent forest

fire.

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cellulose fibres in a lignin matrix (see Figure 8.8). Seashells and limestone are

both made of calcium carbonate, but seashells are much harder because they

are composites of crystalline calcium carbonate with embedded polypeptide

fibres.

Figure 8.8: The combination of cellulose fibres and lignin make the cell wall

strong

The composite industry was launched in the early 1960s with the development

of fibreglass or glass reinforced plastic. It is made by embedding short fibres

of glass in a matrix of plastic. The glass fibres give the plastic extra strength so

that it does not break when it is bent or moulded into shape. The finished

product has the lightness of plastic as well as the strength and flexibility of the

glass fibres. They have found in many marine, housing, construction, sports

and industrial applications. Figure 8.9 shows the use of glass reinforced

plastic in making the body of the boat.

Figure 8.9: The glass reinforced plastic used to make boats

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Another composite material which is usually used for the construction of large

structures like high rise buildings, bridges and oil platforms are reinforced

concrete (see Figure 8.10). Concrete is a composite material that consists of a

mixture of stones, chips and sand bound together by cement. It is strong but

brittle and weak in tensile strength. To overcome this weakness, the concrete

can be reinforced with steel wire netting or steel rod, which results to a very

tough material with high tensile strength. Reinforced concrete is relatively

cheap and can be moulded into any shape.

Figure 8.10: The reinforced concrete with steel wire netting and steel rods

The strongest new composite are the advanced composites, in which fibres are

aligned or interwoven before being set within the resin. Advanced composites

have extraordinary strength in the direction of the aligned fibres and are

relatively weak in the perpendicular direction. Weakness in one direction can

be overcome by laminating layers together at different angles, as in plywood,

a familiar composite. Strength in all directions can be achieved by weaving the

fibres into a three dimensional network. Besides strength, advanced

composites are also known for their lightness, which make them ideal for car

parts, sporting goods and artificial limbs. Advanced composites tend to be

expensive, however because much of their production is still done by hand.

Aeroplane parts, and even whole aeroplane, are now being fabricated out of

lightweight advanced composites in order to save fuel. In 1986, the first plane

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built with all advanced composites material is ”Voyager”, which can fly

around the world without refuelling (see Figure 8.11).

Figure 8.11: The all advanced composite ”Voyager” aeroplane

MATERIALS IN INDUSTRY

Let us now learn on the materials in industry.

8.6.1 Soap

Millions of tonnes of soaps are manufactured worldwide every year (see

Figure 8.12). Soap is manufactured by heating natural fats and oils of either

plants or animals with a strong alkali. These fats and oils, called triglycerides,

are complicated ester molecules. Pioneers prepared their soap by boiling

animal fat with an alkaline solution obtained from the ashes of hardwood. The

resulting “lye” soap could be “salted” out by adding sodium choride, because

soap is less soluble in a salt solution than in water.

8.6

ACTIVITY 8.10

1. What is a composite and what are some examples found in nature other

than given in the text?

2. Where are you most likely to find composites in the marketplace today?

3. Why are composites an ideal material for aircraft?

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Figure 8.12: Soap is manufactured by heating natural fats and oil with a strong

alkali

Nowadays, fat is boiled with aqueous sodium hydroxide to form soap. The

esters are broken down in the presence of water hydrolysed. This type of

reaction is called saponification. The equation given below is that for the

saponification of glyceryl stearate (a fat) (see Figure 8.13).

Figure 8.13: Saponification reaction

glyceryl stearate + sodium hydroxide sodium stearate + glycerol

(soap)

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The cleaning properties of the soap depend on its structure and bonding.

Sodium stearate consists of a long hydrocarbon chain which is hydrophobic

(water hating) attached to an ionic ”head” which is hydrophilic (water loving)

(see Figure 8.14).

Figure 8.14: Simplified diagram of a soap molecule

Covalent compounds are generally insoluble in water but they are more

soluble in organic solvents. Ionic compounds are generally water soluble but

tend to be insoluble in organic solvents. When soap is put into water which

has a greasy dish (or a greasy cloth) in it, the hydrophobic hydrocarbon chain

on each soap molecule become attracted to the grease and become embedded

in it (Figure 8.15).

Figure 8.15:How soaps work

with

agitation

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On the other hand, the hydrophilic ionic head group is not attracted to the

grease/dirt/oil but is strongly attracted to the water molecules. When the water

is stirred, the grease/dirt/oil is slowly released and is completely surrounded

by the soap molecules. The soap is able to remove the grease/dirt/oil because

of the combination of the covalent and ionic bonds present.

8.6.2 Natural and Synthetic Rubber

In the 1930s, more than 90 per cent of the natural rubber used in the United

States came from Malaysia. In the days after Pearl Harbour was attacked in

December 1941 and the United States entered World War II, Japan had

captured Malaysia. As a result, the United Stated faced its first natural

resource crisis. The military implications were devastating because without

rubber for tyres, military aeroplanes and jeeps were useless. Petroleum based

synthetic rubber had been developed in 1930 by DuPont chemist Wallace

Carothers but was not widely used because it was much more expensive than

natural rubber. With the ongoing war, however, cost was no longer an issue.

Synthetic rubber factories were constructed across the nation, and within a

few years, the annual production of synthetic rubber rose from 2,000 tonnes to

about 800,000 tonnes.

Natural rubber is a polymer with its monomer unit, isoprene (see Figure 8.16).

During polymerisation, thousands of isoprene units will join together to form

poly(isoprene) or natural rubber (see Figure 8.17).

Figure 8.16: Isoprene unit

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Figure 8.17: Polyisoprene (natural rubber)

Natural rubber commonly has highly elasticity but is unstable to heat and oxidation.

When it is warmed above 50°C, it softens and becomes sticky and will decompose if

we heat it to a temperature above 200°C. The presence of double bonds in the polymer

chain makes it susceptible to oxidation and breaks up the polymer chains.

Vulcanisation is a manufacturing process discovered by Charles Goodyear in 1939 to

convert natural rubber into a tough useful product. In this process, about 1% to 3% by

weight of sulphur is added to raw rubber and the mixture is carefully heated. Sulphur

atoms form cross links between adjacent chains of rubber polymer at the carbon

carbon double bonds (see Figure 8.18).

Figure 8.18: Vulcanised rubber showing disulfide cross links

Synthetic rubber is any type of artificial elastomer mainly synthesised from

petroleum by products. An elastomer is a material with the mechanical (or

material) property that it can undergo much more elastic deformation under

stress than most materials and still return to its previous size without

permanent deformation. Synthetic rubber, like natural rubber, has uses in the

automotive industry for door and window profiles, hoses (see Figure 8.19),

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belts, matting, flooring and dampeners (antivibration mounts). Table 8.10

shows the differences between synthetic rubber and natural rubber.

Table 8.10: Comparison of Properties between Manufactured Materials

(Synthetic Rubber) and Natural Materials (Natural Rubber)

Synthetic Rubber Properties Natural Rubber

Synthetic Type of polymer Natural

Able to withstand

high temperatureHigh temperature effect

Decomposes and

become liquid

Very permeable to

gas and water

Permeability to gas and

water

Not permeable to gas

and water

Does not react to

acid and alkali

Ability to withstand

actions of acid and

alkali

React to acid and

alkali

Low ability

Ability to absorb

pressure, vibration and

sound

High ability

Can be vulcanised Vulcanisation Easily vulcanised

Figure 8.19: Product from synthetic rubber

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8.6.3 Natural and Synthetic Fibres

Natural fibres can be defined as substances produced by plants and animals

that can be spun into filament, thread or rope and in a next step be woven,

knitted, matted or bound. The oldest fibres used by mankind are cotton

(5,000BC) and silk (2,700BC), but even jute and coir have been cultivated since

antiquity. The main reasons for the popularity of biocomposites or natural

fibre composites are the availability and consistent quality of a wide range of

fibres, and their environmental friendliness. Moreover, new production

processes, such as injected moulded components, make it possible to use these

materials for industrial products.

Additional key advantages of natural fibres are their high strength and

stiffness per weight along with benefits such as acoustic isolation, safety

management, rapid production and potentially low cost. The most viable

structural fibres typically derive from specifically grown textile plants and

fruit trees. There are two categories of natural fibres, vegetable fibres and

animal fibres. Vegetable fibres are subdivided into bast fibres (flax, hemp, jute

and kenaf) leaf fibres (sisal, pineapples and henequen), grass fibres (bamboo

and miscanthus), straw fibres (corn and wheat), seed fibres (cotton and

capok), wood fibres (pinewood) and fruit fibres (coconut), whereas animal

fibres are silk, avian, hair and wool (see Figure 8.20). Figure 8.21 shows kenaf

plants which is from the bast fibres category.

Figure 8.20: Two categories of natural fibres

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Figure 8.21: Kenaf plants is a source of natural fibre

Synthetic fibres are made from synthesised polymers or small molecules. The

compounds that are used to make these fibres come from raw materials such

as petroleum based chemicals or petrochemicals. These materials are

polymerise into a long, linear chemical that bond two adjacent carbon atoms.

Different chemical compounds will be used to produce different types of

fibres. Although there are several different synthetic fibres, they generally

have the same common properties. Synthetic fibres are commonly very heat

sensitive, resistant to most chemicals, insect, fungi and rot. It has low moisture

absorbency, flame resistant, low melting temperature. Synthetic fibres are also

very easy to wash and maintain and the main thing is that it is often less

expensive than natural fibres.

The first synthetic fibre known as nylon was discovered in 1931. Its novel use

as a material for women’s stocking overshadowed more practical uses, such as

a replacement for the silk in parachutes and other military uses. Other

common synthetic fibres are modacrylic, olefin, acrylic, polyester and carbon

fibre. Specialty synthetic fibres include vinyon, saran, spandex, vinolon,

aramids, modal, sulfar, orlon, zylon, vecran, derclon and rayon. Figure 8.22

shows two examples of synthetic fibres.

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\

Figure 8.22:Nylon and polyester

8.6.4 Plastics

With a record of wartime successes, plastics were readily embraced in the

post war years. In the 1950s, Dacron polyester was introduced as a substitute

for wool. The 1950s was also the decade during which the entrepreneur Earl

Tupper created a line of polyethylene food containers known as Tupperware

(see Figure 8.23).

ACTIVITY 8.11

1. Compare and contrast natural fibres and synthetic fibres.

2. Find out the uses of all common natural and synthetic fibre

given in the text

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Figure 8.23: Tupperware, polyethylene food container

A plastic material is any material of a wide range of synthetic or semi

synthetic organic solids that are mouldable. Plastics are typically organic

polymers of high molecular mass, but they often contain other substances

known as additives. They are usually synthetic, most commonly derived from

petrochemicals, but many are partially natural. The amount of additives range

from zero percentage for polymers used to wrap foods to more than 50% for

certain electronic applications. Example of additive is fillers which function to

improve performance and/or reduce production costs. Stabilising additives

include fire retardants to lower the flammability of the material.

Plastics are usually classified by their chemical structure of the polymer’s

backbone and side chains. Some important groups of these classifications are

the acrylics, polyesters, silicones, polyurethanes and halogenated plastics.

Other type of classification is based on the chemical reaction toward heat.

Examples are thermoplastics and thermosetting polymers. Thermoplastics are

the plastics that do not undergo chemical change in their composition when

heated and can be moulded again and again. This type of plastics includes

polyethylene, polypropylene, polystyrene and polyvinylchloride.

Thermosetting polymers can melt and take shape once. After they have

solidified, they stay solid because in the thermosetting process, a chemical

reaction occurs that is irreversible. An example is the vulcanised rubber.

Other classifications are based on qualities that are relevant for manufacturing

and also on the physical properties.

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By the 1960s, a decade of environmental awakening, many people began to

recognise the negative attribution of plastics. Being cheap, disposable, and

non biodegradable, plastic readily accumulated as litter and as landfill. With

petroleum so readily available and inexpensive, however, and with a growing

population of plastic dependent baby boomers, little stood in the way of an

ever expanding array of plastic consumer products. By 1977, environmental

concerns started to grow, and in 1980s plastics recycling programmes began to

appear. Researches to produce biodegradable plastics have been done

progressively. An example is the use of starch powder mixed with plastics as a

filler to allow it to degrade more easily, but it still does not lead to complete

breakdown of the plastic. Some researchers have actually genetically

engineered bacteria that synthesise a completely biodegradable plastic.

Physical properties of materials include elasticity, shininess, buoyancy,water absorbency, electrical conductivity and heat conductivity.

Other physical properties of materials include hardness, toughness andbrittleness, strength, flexibility and solubility.

Elasticity is the ability of a material to return to its original shape and sizeafter being bent, twisted, stretched and squeezed. Materials that are able toreturn to their old shape when force is no longer applied are called elasticmaterials.

Some materials are shiny and some are not.

Materials can also be divided into three types according to its ability toallow light to pass through it. These are transparent materials, translucentmaterials and opaque materials.

Buoyancy is the ability of materials to float in liquid.

SELF CHECK 8.6

Search from the Internet or other resource on research/products of

biodegradable plastics that has been done in Malaysia.

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Materials which can absorb water are known as absorbent materials andmaterials which cannot absorb water are known as non absorbentmaterials.

A material that allows electricity to pass through it is a material thatconducts electricity.

A material that allows heat to pass through it easily is a material thatconducts heat.

Magnetism is the property of materials to attract iron, for example, ironoxide, cobalt, nickel and certain types of alloy.

Knowledge about the properties of materials is very important, especiallyin choosing suitable materials to make various objects.

The properties of materials have many useful applications in our daily life.

Materials are made of thousands of small particles called atoms.

Materials can be divided into three categories according to their

components of atom: element, compound and mixture.

Materials can be classified into two types according to their use: natural

materials and man made materials or manufactured materials.

Natural materials originate from soil, rocks, water, plant, animal or

minerals.

Manufactured materials are made from a mixture of natural materials

through chemical processes.

Manufactured materials are designed according to the needs of the market.

Preservation refers to the effort to maintain natural resources in their

original state or in good condition.

Conservation refers to the sustainable use and management of natural

materials to prevent loss, wastage or damage.

Composite materials are the materials which combine the properties of

two substances in order to get the exact properties required for a particular

job.

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Saponification is the process of making soap by heating natural fats and oil

with a strong alkali.

Polymerisation is the process of isoprene units join together to form

poly(isoprene) or natural rubber.

Synthetic rubber is any type of artificial elastomer mainly synthesised

from petroleum by products with better quality than natural rubber.

Natural fibres is substances produced by plants and animals that can be

spun into filament, thread or rope and in a next step be woven, knitted,

matted or bound, while synthetic fibre are made from synthesised

polymers or small molecules.

A plastic material is any of a wide range of synthetic or semi synthetic

organic solids that are mouldable. All plastics are polymers but not all

polymers are plastics.

Abiotic

Biotic

Component

Composite materials

Conservation

Element

Fibre

Manufactured material

Material

Mixture

Natural material

Plastics

Preservation

Raw material

Rubber

Soap

Synthetic

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