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Using Resources

AQA Chemistry topic 10

10.1 Using the Earth’s Resources and obtaining Potable Water

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Natural Resources 21/11/2017

Some examples of natural resources. What are they used for?

Wood

Farming

Wool

Fuels

Can we replace any of these with artificial or synthetic products?

Finite Resources 21/11/2017

Q. Are the following resources examples of finite or renewable ones?

Quarrying Farming

Dumping waste Building new homes

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Sustainable Development Sustainable development is all about preserving the world for

tomorrow.

Examples of sustainable development in fishing include:

1) Limiting the number of fish allowed in a catch (a “quota”)

2) Controlling the size of the net

The main point is – “don’t use resources at a rate quicker than they are made”. For

example, don’t fish too much!

Population growth and Water 21/11/2017

The number of people on the Earth has risen dramatically in the last 100 years:

What will this mean for the supply of drinking (potable) water?

Water that is safe to drink is called “potable water”. Potable water is not pure as it contains dissolved substances but its still safe to drink as the quantities of substances are low.

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Water Amazing facts about water:

1) 95% of your body mass is water (94% in women due to a higher body fat content)

2) Dinosaurs would have drunk the same water you do

3) Water dissolves more substances than any other liquid – most ionic substances are soluble and most covalent substances are insoluble

4) Around 75% of the world’s surface is made of water

5) To feel thirsty you need to lose around 1% of your body water

6) 5,000 children die every day due to not having clean drinking water

7) An average person in the West uses 200-300 litres of water every day

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Water resources There are many different water resources in the UK and the method used to make water potable depends on the source:

Rivers

Lakes Reservoirs

Aquifiers

Potable water is produced by: 1) Choose an appropriate source 2) Pass the water through a filter bed 3) Sterilise it with chlorine, ozone or UV light

Other ways to treat water 21/11/2017

1) Distilling seawater to boil off clean water – “desalination”

2) Using a membrane filter to filter out bacteria through reverse osmosis

Unfortunately, both of these processes take lots of energy and are therefore expensive

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Pollutants in water Many different pollutants can find their way into our water:

Industrial waste water may require removal of organic matter and harmful chemicals

Nitrates used in farming which are washed into lakes by rainwater – organic matter and harmful microbes must be

removed

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Waste Water Treatment Our water supplies obviously contain various microbes and dissolved substances. To be used as drinking water it has to be treated:

1) Sedimentation 2) Filtration/screening 3) Chlorination

We can also use anaerobic digestion or aerobic biological treatment of sludge/effluent.

Extracting and purifying copper 21/11/2017

Copper can be extracted from copper-rich ores by heating the ores in a furnace (displacing it with scrap iron) and then purifying it by electrolysis.

Extracting copper uses large amounts of

heat and energy

Bingham Canyon copper mine in Utah, one of the

largest in the world

Unfortunately, the supply of copper ore is limited. What are the possible solutions?

New ways of extracting metals 21/11/2017

“Phytomining” – growing _____ that absorb metals and then ______ them to extract the metal from __.

“Bioleaching” – using ______ to produce leachate solutions that contain metal _________.

Words – compounds, plants, bacteria, burning, ash

Q. What are the advantages and disadvantages of each method?

10.2 Life Cycle Assessment and Recycling

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Life Cycle Assessments (LCAs)

Step 1: Raw materials and Manufacture

What resources are needed? What effect will this have on the environment?

Step 2: Use

How much energy will be needed? What is the effect on the environment?

Step 3: Disposal

How is the product disposed of? What is the effect on the environment?

LCAs are carried out to assess the environmental impact of products at each of these stages:

An example LCA – Carrier Bags 21/11/2017

1) Drill for crude oil 2) Put the oil through fractional

distillation 3) Crack alkanes to make ethene 4) Use heat to polymerise ethene 5) Transport plastic bags to shops 6) Transport bags to landfill sites

Steps in the bag’s life cycle

1) Use recycled materials 2) Reduce consumption of the

bags 3) Manufacture them closer to

shops 4) Recycle the bags after use

Ways to reduce the pollution or environmental cost

Q. Consider the humble plastic bag. What steps are involved in its life cycle and how can the carbon footprint of each step be reduced?

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Recycling Why recycle metals?

1) Less space will be needed for landfill sites

2) Recycled metals only need about 1/10th of the energy to produce compared to producing new metals

3) Recycling saves on raw materials – plastics, glass and ceramics come from limited raw materials

4) Less excavation and mining costs

Reduce, reuse, recycle!

Two Examples of Recycling 21/11/2017

Metal Metals can be recycled by melting and recasting into different products. Sometimes a substitute can be used, e.g. some scrap steel can be added to iron to reduce the amount of iron needed.

Glass Glass bottles can be crushed and melted to make other glass products.

10.3 Using Materials (Chemistry only)

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Rusting

Rust is a hydrated form of iron oxide. It is formed when iron and/or steel combines with oxygen and water:

Iron + oxygen + water hydrated iron (III) oxide

Aluminium has an oxide coating that protects the metal from further corrosion.

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Rusting Task: To investigate what causes rusting

Tube 1 – drying agent

Tube 2 – boiled water

Tube 3 – water + air

Tube 4 – water + air

+ salt

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Rusting Task: To investigate what causes rusting

No rust No rust Rust Lots of rust

Iron + oxygen + water hydrated iron oxide

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Ways to prevent rust

There are several ways to prevent rust:

1) Electroplating

2) Sacrificial protection (using a more reactive metal to coat the iron)

3) Using oil or grease

4) Painting

21/11/2017 Galvanising and Sacrificial Protection

“Galvanising” is when iron is coated with a layer of zinc which stops oxygen getting to the iron and also acts as a sacrificial metal.

Tin plating works by coating the iron in tin, e.g. in food cans. However, this only works if the tin remains intact – if it is scratched the iron rusts more quickly than if it wasn’t coated.

Sacrificial protection works by using a metal that’s more reactive than iron. The more reactive metal loses electrons instead of iron.

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Alloys Steel is an “alloy” – i.e. a mixture of metals. Here are other alloys:

Gold mixed with copper, silver or zinc

Aluminium mixed with magnesium and copper – strong but low density

Bronze is an alloy of copper and tin. Brass is an alloy of copper and zinc.

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Gold alloys Gold can be mixed with zinc, silver or copper to make alloys with different properties. For example:

24-Carat gold

“Pure gold” – 99.99% of the atoms in this bar are gold atoms (fineness off 999.9). Pure and malleable but soft.

9-Carat gold

“9 carat gold” – around 9/24ths of the atoms in these earrings are gold atoms. Harder than pure gold but less malleable.

21/11/2017 21/11/2017 Using impurities to strengthen Iron

In pure iron all impurities are removed. This makes the iron soft:

Adding 1% impurities makes the iron much stronger:

21/11/2017 21/11/2017 Making steel

Amount of carbon added (%) 0.5% 1%

Strong

Weak

1.5%

Strength

Hardness

Steel with a low carbon content is easily shaped

Steel with a high carbon content is strong but brittle

Steel with chromium and nickel is called stainless steel

Ceramics 21/11/2017

Most of the glass we use is soda-lime glass, made from _____, sodium carbonate and _______. We also use borosilicate glass (using boron trioxide), which has a higher ______ point.

Clay ceramics (including pottery and bricks) are made by shaping wet _____ and then heating in a _____.

Words – furnace, clay, melting, limestone, sand

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Polymers recap

C C H H

H H

Ethene

Here’s ethene again. Ethene is called a MONOMER because it is just one small molecule. We can use ethene to make plastics…

Step 1: Break the double bond

Step 2: Add the molecules together:

This molecule is called POLYETHENE, and the process that made it is called POLYMERISATION

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Properties of Polymers

C C n

H H

H H

C C n

H H

H Cl

C C n

F F

F F

Polythene. Used to make bags and crates. Can be either low density (LD) or high density (HD).

Polyvinylchloride (PVC). Used to make water pipes and coating for window frames.

PTFE tape. Used for non-stick coating in frying pans.

LD vs HD Polythene 21/11/2017

LD Polythene HD Polythene

Properties: Soft, flexible

Uses: bags, cling film

Monomer: Ethene

Reaction conditions: 200OC, 2000 atm pressure and oxygen catalyst

Properties: Hard, strong

Uses: buckets, pipes

Monomer: Ethene

Reaction conditions: 60OC, 2 atm pressure and a Ziegla-Natta catalyst

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More about Polymers 1) Some plastics have ____ intermolecular forces between each molecule – these have __ melting points. These are “thermosoftening polymers”.

2) Some plastics have _____ forces between each molecule. These have ____ melting points and are ____. These are called “thermosetting polymers”.

Words – high, low, strong, weak, rigid

Composites 21/11/2017

A “composite material” is a material made from two other materials. Fibres or fragments of one material (the “reinforcement”) are surrounded by a material called a “binder” or “matrix”. Some examples:

Composite material

Matrix/ binder

Reinforcement fibre/fragment

Uses

Concrete Cement and water

Sand and crushed rock

Buildings

Composite wood (e.g. plywood)

Adhesives Wood fibres Buildings, furniture

Natural wood

Lignin Cellulose fibres Buildings, furniture

Carbon fibre composites

Polymer Carbon fibres or nanotubes

Sports equipment

10.4 The Haber Process and use of NPK Fertilisers (Chem only)

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Reversible Reactions recap Some chemical reactions are reversible. In other words, they can go in either direction – the reactants will make the products and the products will then make the reactants again:

A + B C + D

NH4Cl NH3 + HCl

e.g. Ammonium chloride Ammonia + hydrogen chloride

The direction of the reaction can be affected by changing the conditions

heat

cool

21/11/2017 Reversible Reactions and energy changes

A + B C + D

If a reaction is EXOTHERMIC in one direction what must it be in the opposite direction?

For example, consider copper sulphate:

CuSO4 + H2O CuSO4.5H2O

endothermic

exothermic

Q. Which direction would you push the reaction in if you heated it up?

If a reaction is endothermic, it wants to take in energy. Therefore, by heating it, you help it.

Hydrated copper sulphate (blue)

Anhydrous copper sulphate (white)

+ Heat + Water endothermic

exothermic

21/11/2017 21/11/2017 Reversible Reactions and Equilibrium When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants are added or taken away) an EQUILIBRIUM is achieved – in other words, the reaction goes at the same rate in both directions (a “dynamic equilibrium”):

A + B C + D

Higher Tier only - What happens if we change the conditions of an equilibrium? What does it do to a reaction?

Henry Le Chatelier, 1850-1936

We can use Le Chatelier’s Principle to work out how changes in concentration, temperature and pressure will affect an equilibrium. My principle is: “If the system is at equilibrium and a change is made, the system responds to counteract the change.” Here’s the idea:

21/11/2017 21/11/2017 Le Chatelier’s Principle 1 – Concentration (HT only)

A + B C + D

Consider a reaction where reactants A and B make products C and D:

If the concentration of reactant A was increased, the system is no longer at equilibrium. More products will be formed to restore the equilibrium (and vice versa).

21/11/2017 21/11/2017 Le Chatelier’s Principle 2 – Temperature (HT only)

Endothermic reactions

Increased temperature:

Decreased temperature:

A + B C + D

A + B C + D

More products

Less products

Exothermic reactions

Increased temperature:

Decreased temperature:

A + B C + D

Less products

More products

A + B C + D

Increasing the temperature of a system basically means giving the system energy, i.e. you will help an endothermic reaction:

21/11/2017 21/11/2017 Le Chatelier’s Principle 3 – Pressure (HT only)

Nitrogen + hydrogen Ammonia

N2 + 3H2 2NH3

Consider a reaction where nitrogen and hydrogen are used to make ammonia:

An increase in pressure will push the reaction towards the side with the lower number of molecules (i.e. you’ll make more ammonia). A decrease in pressure will make more hydrogen and nitrogen.

Q. How many molecules are on this side of the equation?

How many are on this side?

A. 4 A. 2

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Making Ammonia

Nitrogen + hydrogen Ammonia

N2 + 3H2 2NH3

•High pressure

•450O C

•Iron catalyst

Recycled H2 and N2

Nitrogen

Hydrogen

Mixture of NH3, H2 and N2. This is cooled causing NH3 to liquefy.

Fritz Haber, 1868-1934

Guten Tag. My name is Fritz Haber and I won the Nobel Prize for chemistry. I am going to tell you how to use a dynamic

equilibrium in a reversible reaction to produce ammonia, a very important chemical. This is called the Haber Process.

You get the raw materials from the air (nitrogen) and natural gas (hydrogen). To produce ammonia from nitrogen

and hydrogen you have to use three conditions:

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Haber Process: Economics A while ago we looked at reversible reactions:

A + B C + D

Endothermic, increased temperature

A + B C + D

Exothermic, increase temperature

Exothermic Endothermic

1) If temperature was DECREASED the amount of ammonia formed would __________...

2) However, if temperature was INCREASED the rate of reaction in both directions would ________ causing the ammonia to form faster

3) If pressure was INCREASED the amount of ammonia formed would INCREASE because there are less molecules on the right hand side of the equation

Nitrogen + hydrogen Ammonia

N2 + 3H2 2NH3

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The Haber Process Economics

The cost of electricity/gas

The cost of wages

How quickly ammonia is made

Cost of reactants

Cost of equipment

Temperature Pressure

Catalyst

Factors affecting the cost of making ammonia

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Haber Process Summary

•200 atm pressure

•450O C

•Iron catalyst

Recycled H2 and N2

Nitrogen

Hydrogen

Mixture of NH3, H2 and N2. This is cooled causing NH3 to liquefy.

To compromise all of these factors, these conditions are used:

A low temperature increases the yield of ammonia but is too slow

A high temperature improves the rate of reaction but decreases the yield too much A high pressure increases the yield of ammonia but costs a lot of money

Production and Use of NPK Fertilisers 21/11/2017

Here’s a bag of NPK fertiliser. What’s so special about it?

1) NPK contains nitrogen, phosphorus and ______ compounds

2) Use of fertiliser improves ______ productivity

3) They are formulations of different ____

4) Ammonia is used to make ammonium salts and _____ acid

5) Potassium chloride, potassium sulfate and phosphate rock are obtained by ______.

6) Phosphate rock cannot be used directly as a _______ but can be treated with nitric acid or sulfuric acid to produce soluble salts that can.

Some facts:

Words – fertiliser, potassium, salts, farming, nitric, mining

Naming Fertiliser Salts 21/11/2017

Name the salts made by…

1) Treating phosphate rock with nitric acid

2) Treating phosphate rock with sulfuric acid

3) Treating phosphate rock with phosphoric acid

Calcium nitrate

Calcium phosphate + calcium sulfate

Calcium phosphate