chemistry revision
DESCRIPTION
OCR 21st Century ScienceTRANSCRIPT
Chemistry
1
Pictures.
You are about to see some pictures all about C1.
Make a note of why they are there.
The Atmosphere
• The Atmosphere contains various chemicals.
• Human activity is changing the atmosphere.
The concentration of nitrogen, oxygen and argon in the atmosphere should be pretty constant. However little by little humans are adding pollutants to the air.
Nitrogen = 78%
Oxygen = 21%
Argon = 1%
•Pollutants come from burning fuels in power stations and vehicles.
•Some pollutant gases are directly harmful to humans, such as vehicle exhausts. These can cause disease or death.
•Pollutants can also be indirectly harmful to humans. For example leading to acid rain and climate change.
Questions.
1. What three gases is the atmosphere mainly made from and in what amounts?
2. What Is changing the amounts of these gases in the atmosphere?
3. Where do pollutants come from?
4. Name one direct and one indirect result of pollution that would be harmful to humans.
Fossil Fuels • Hydrocarbons are massively
important chemicals. • You can use diagrams to
represent hydrocarbon molecules.
• Fossil fuels are formed from the remains of dead plants and animals.
• Crude oil is drilled out of the Earth and then refined to make petrol or diesel.
• The differences between petrol, diesel and fuel oil is the size of the hydrocarbons.
Coal is not a hydrocarbon!
It is mainly just carbon.
Questions.
1. What are hydrocarbons made from?
2. Where is crude oil from and what is it turned into?
3. Is coal a hydrocarbon?
4. What is the difference between petrol and diesel?
Chemical Reactions. • When you burn fuel a chemical
reaction occurs. • In a chemical reaction the fuel
reacts with atoms from the air. • The atoms then rearrange
themselves to form another substance.
• When coal burns you usually get carbon dioxide.
Burning a hydrocarbon.
Methane + Oxygen Carbon dioxide + Water
NO atoms disappear during a chemical reaction.
Reactants and products are usually have very different properties.
Finnish this reaction.
hydrogen Carbonoxygen
+
Methane Oxygen.
Carbon dioxide water
Air Pollution – Carbon
• If carbon burns where there is lots of oxygen, nearly all the carbon ends up as carbon dioxide.
• If carbon burns where there is very little oxygen the carbon ends up as carbon monoxide.
• Carbon dioxide, carbon monoxide and carbon particles are all pollutants.
• If carbon dioxide is not removed from the atmosphere it causes problems.
• Carbon dioxide can be removed from the atmosphere naturally. It can be used in photosynthesis and can b e dissolved in rainwater, seas lakes and rivers.
• Carbon monoxide is poisonous.
• Particulate carbon is just particles of carbon. They leave buildings looking dirty.
Match.
Carbon Dioxide
Carbon Monoxide
Carbon Particulate
Is poisonous
Makes buildings look dirty
Is removed from the atmosphere in photosynthesis.
Air Pollution – Sulfur • Sulfur comes from impurities in fuels. • Sulfur causes acid rain. • When a fuel burns Sulfur does too. • When sulfur atoms burn they combine
with oxygen to produce the pollutant sulfur dioxide.
• Sulfur dioxide usually ends up in the atmosphere.
• Sulfur dioxide will stay in the atmosphere until something gets rid of it.
• Sulfur dioxide usually leaves the atmosphere through acid rain.
• When sulfur dioxide mixes with the moisture in the clouds, a dilute sulphuric acid is formed.
Acid rain causes lakes to become acidic, killing plants and animals such as fish.
It also kills trees, and damages buildings and statues made from limestone or chalk.
Questions.
1. What is made when sulfur dioxide mixes with moisture in clouds?
2. What Is the symbol for sulfur dioxide?
3. How is sulfur dioxide removed from the atmosphere?
Air Pollution – Nitrogen. • Nitrogen pollution involves nitrogen
from the air. • Nitrogen oxides are nitrogen monoxide
and dioxide.• Nitrogen pollution doesn’t come from
the fuel itself, it is formed in the air when the fuel burns.
• Fossil fuel burns at such high temperatures that the nearby atoms in the air react with each other.
• Nitrogen oxides are formed in car engines.
• Nitrogen oxides are pollutants.
• Nitrogen monoxide Is formed when nitrogen and oxygen in the air are exposed to very high temperatures. (car engines)
• Nitrogen dioxide is formed when nitrogen monoxide goes on to react with more oxygen.
NITROGEN OXIDES ALSO FORM ACID RAIN. ( NITRIC ACID)
Questions.
1. How is nitrogen monoxide and nitrogen dioxide formed?
2. What is the symbol for nitrogen oxides?
3. How are nitrogen oxides removed from the atmosphere?
Reducing Pollution. They are plenty of things we can do to reduce pollution.
From Power Stations. Use less electricity.
Reduce the amount of fossil fuels we use.
Find an alternate energy source.
From Cars.
Use more efficient engines that produce less waste.
Use low-sulfur fuel.
Catalytic converters.
Public Transport.
How do these pictures relate to reducing pollution.
Chemistry
2
Natural and synthetic materials.
• Everything is made from chemicals. • Chemicals are made up of atoms or groups of atoms that are bonded together. • Iron is a chemical element, it is made of iron atoms. • Water is a chemical. This molecule is a group of atoms joined together.
Synthetic Materials.
• Man made materials are called synthetic materials.
• Rubber can be made in a factory, the advantage of this, is that the properties can be controlled.
• Clothes are made from fabrics like nylon or polyester. Clothes can be made to be stretchy or water-proof.
• Most paints are mixtures of man-made chemicals.
Natural Materials.
•Some materials we have are made from living things like plants or animals.
•Wood and Paper are both made by trees.
•Cotton comes from cotton plants.
•Wool Is made from sheep.
•Silk is made by a silkworm.
•Leather comes from cows.
Questions.
1. What are ALL materials made of?2. Name two things that are made from plants. 3. Name two things that are made from animals. 4. What are synthetic materials?5. Name some synthetic materials. 6. What is the advantage of synthetic materials?
Materials and Properties.• Most materials that are pure have a
unique melting point. • A melting point is the point a solid
turns into a liquid. • Strength is how good a material is at
resisting force. • Tensile Strength is how much a
material can resist a pulling force. • Compressive strength is how much a
material can resist a pushing force. • A stiff material is not good at bending
when a force is applied to it.• Steel is very stiff. • Rubber Is not stiff.
• The hardness of material is how difficult it is to cut into.
• The diamond is the hardest material found to date.
• Many industrial drills have diamond tips.
• Density is the material’s mass per unit.
Questions.
1. What is a melting point?
2. What is strength?
3. What is stiffness?
4. What is harness?
5. What is density?
6. What is the hardest material ever to be found?
Materials, properties and uses.
• Material all have different properties as they all have different jobs.
• Plastics can be hard and stiff, and have a low density. Some are mouldable.
• Rubber is strong and flexible, also mouldable.
• Nylon Fibres are soft and flexible and have good tensile strength.
• Some products are made from a variety of materials.
• How long a material will last depends on the properties of the materials it is made from.
Cooking utensils must be made from something with a high melting point and be non toxic.
A toy car must be non-toxic and should be strong, stiff and have a low density.
Questions.
• Describe Plastics, rubber and nylon fibres.
• What properties must these things have:1. Cooking Utensils
2. Toy cars3. Clothing Fabrics.
Crude oil and chemical synthesis.
– Crude oil Is formed from the buried remains of plants and animals, it a fossil fuel.
– Crude oil is drilled from the ground.
– Crude oil is a mixture of hydrocarbons.
– Hydrocarbons are molecules which are made from chains of
carbon and hydrogen.
• Crude oil is useless straight out of the ground. But If you separate the mixtures you get loads of useful things.
• The hydrocarbons are sorted into groups with chains of similar lengths.
This process is called refining.
Crude Oil: petrol,naptha, diesel, lubricating oil.
Questions.
• What is crude oil?
• How is crude oil formed?
• What is refining?What useful products come out of crude oil?
Polymerisation.• Polymers are one of the most
important man-made materials. • Polymerisation means loads of small
molecules linking together. • These small molecules are called
monomers. • Different polymer have different
physical properties.
• Polymers have replaced natural materials for some uses.
• Synthetics materials such as nylon and polyester are often used to replace cotton wool or silk.
• Synthetic materials tend to be lighter, more durable, water resistant and often cheaper.
Questions.
• What is one of the most important manmade materials?
• What are small molecules called?• What have polymers replaced?• Why are synthetic materials seen to be better
than natural ones?
Structures and properties of Polymer.
1. A polymer’s properties decide it’s uses.
2. It’s properties depend on how the molecules are arranged.
3. The forces between the different chains of the polymer hold it together as a solid mass.
4. Crosslink's hold chains firmly together. They are chemical bonds between the polymer chains.
5. The stronger bonds between the polymers the higher the melting point.
1. You can chemically modify polymers to change their properties.
2. A crystalline polymer has straight chains with no branches so that the chains can fit close together.
3. Crystalline polymers have higher densities, are stronger and have a higher melting points.
Questions.
• How is a polymers use decided?
• What does the property of a polymer depend on?
• What are crosslink's?
• What is meant by the term crystalline?
Chemistry 3
Recycling Elements.• Elements are constantly being
recycled. • As plants grow they take in elements
like oxygen, nitrogen and carbon. When they die and decompose, most of these elements are returned into the soil.
• Dead animals and plant matter are broken down by microbes.
• At this point the cycle begins again. • The nitrogen cycle is a good example
of recycling an element.
The Nitrogen Cycle.
• The nitrogen cycle is a constant cycle of nitrogen through the atmosphere, soil and organisms in it.
Into soil Out of soil
Lightening
Nitrogen fixing bacteria in the soil.
Plants
Denitrifying bacteria.
Questions.
• Why do things need to be recycled?
• What do plants take in during their life?
• How are things returned to the soil?
• How are things removed from the soil?
• Define the nitrogen cycle.
Organic and Intensive Farming.
Organic
Organic farmers do no use artificial fertilizers, they use natural substances instead. These include animal-manure, compost or human sewage. They also use plants like Clover as they have nitrogen-fixing bacteria in them.
Organic farmers also do crop cycles, this means they plant different crops each year.
Intensive
Intensive farming relies on artificial fertilisers. They use pure chemicals so it is easy know how much the plant will need. These fertilisers come in the form of pellets or spray.
Harvesting crops removes elements from the soil. When plants are taken to be sold, nothing is returned to the soil, this causes problems. Nitrogen, Phosphorous and Potassium are lost. This means over a period of time no plants will be able t grow there. The way farmers replace the soil depends on whether their farms are organic or intensive.
Questions.
• What removes nutrients from the soil?• What three things are lost in the soil and where
do they go?• How can they be returned?• What does organic farming rely on?• What does intensive farming rely on?• What do organic farms use to fertilise their
crops?• What do intensive farms use to fertilise their
crops?
Pest Control• They are different ways to deal with
pests and diseases. • Some pests like Aphids, are insects
that eat crop plants. • Disease like potato blight can kill or
damage plants.
Intensive farming uses chemicals. They spray their crops with man-made chemicals that destroy pests and diseases. Chemical pesticides are usually more effective than organic methods. However this method will kill everything, even organisms that may have been useful.
Organic farming uses natural biological processes. They are not allowed to use man made chemicals.
1. Natural predators/.
2. Crop rotation
3. Field edges left grassy.
4. Natural pesticides.
Questions.
• What causes problems in farming?
• What pest and diseases can be found?
• How does organic farming deal with pests and diseases?
• How does intensive farming deal with pests and diseases?
Natural Polymers. • It’s not just things like plastic and other
man-made products that contain polymers. Natural things do to.
• Carbohydrates and proteins are natural polymers.
• Carbohydrates are polymers built by linking together simple sugars and glucose.
• Proteins are built by linking small molecules called amino acids.
Proteins contain, hydrogen, carbon, oxygen AND
NITROGEN.
Carbohydrates.
They consist of carbon, hydrogen and oxygen.
Questions.
• Name two natural polymers?
• What are carbohydrates made from?
• What are proteins made from?
• What elements are in Carbohydrates?
• What elements are in Proteins?
Digestion. • Digestion involves breaking down big
molecules. • Starch, proteins and fats are still too
bug after entering the mouth and are still insoluble.
• So they are broken down in the small intestine and enters the bloodstream there.
• Amino acids are built up into new proteins.
• Skin, hair, muscles and tendons are all made up of proteins.
• Haemoglobin is the red “stuff” In your blood. It is also a protein called globin.
• Excess amino acids are disposed of in urine.
• They are taken into the blood and broken down by the liver.
• They are then converted into soluble substances called urea, which is then released into the blood.
• This urea is then excreted.
Questions.
1. What is digestion?
2. Which molecules are not soluble after entering the mouth?
3. Where are these insoluble's broken down?
4. What are amino acids built up into?
5. What in your body is made from protein?
6. What Is haemoglobin?
7. How does the body get rid of excess amino acids?
8. Which major organ in the body does the blood pass through in this process?
Insulin and Diabetes. • Diabetes is when the body can not control blood sugar levels in the body. Normally the
body produces a hormone called insulin in the pancreas. Insulin helps the body move glucose from the blood into the body cells. Insulin also controls the storage of glucose. The amount of insulin the body produces is down to how much sugar is in the blood.
They are two types of diabetes. Type one and type two. Poor diet and obesity increase your risk of developing type 2 diabetes.
Type 1 Type 2
The pancreas STOPS making insulin. This means sugar can not be removed from the bloodstream. A high blood sugar level could result in a coma or death. However it can be controlled by insulin injections and controlling diet.
The symptoms develop gradually and they include weight loss, needing to wee more often and tiredness. Types 2 stops the body from making enough insulin or the body stops responding to insulin. Both of these things are linked to poor diet and obesity. Type 2 an be controlled by diet, loosing weight and exercising. Sometimes insulin is taken.
Questions.
• What is diabetes?• What does the pancreas produce?• What does insulin do?• Poor diet and obesity is linked to what?• Does type one develop in young or older
people?• How can type one diabetes be controlled?• Who is effected most by type 2 diabetes?• How can type 2 diabetes be controlled?
Harmful Chemicals in food.
• Some foods are dangerous naturally.• Some plants contain poisonous
chemicals and some only if they are not cooked properly. Others cause allergic reactions in some people.
• Examples of these foods would :
Peanuts
Mushrooms
Cassava
Gluten
• Others develop chemicals during storage.
• Nuts and cereals along with dried fruit can become contaminated by a poisonous substance called aflatoxin. It Is produced by a mould. Aflatoxin can cause liver cancer.
Cooking can form dangerous chemicals. For example burning foods. This tends to happen when food is cooked aver 150 degrees.
Some foods contain chemicals left over from farming.
Pesticides and herbicides used in farming can be present in small amounts on fruit and veg. Washing and peeling them would get rid of these.
Questions.
• Which plants are dangerous naturally and how can the danger be prevented?
• What is used in farming that is dangerous, and how can they be prevented?
• Which foods can become contaminated during storage?
• What is aflatoxin and what can it cause?
• Burning foods can cause what?
Food Additives. • Food Colourings: make food look more
appetising.
• Flavourings: added to give foods a new taste.
• Flavour enhancers: bring out a taste or smell of a food without adding another taste.
• Artificial sweeteners: used in diet foods and drinks instead of sugar.
• Preservatives: added to prevent the growth of harmful microbes.
• Emulsifiers and stabilisers: prevent water and oil from mixing. E.g.. Mayonnaise or tomato sauce.
• The use of food additives are regulated. They have to pass a safety test before they can be used. (E numbers).
Questions.
Describe what the following additives do:– Food colours – Flavourings– Flavour enhancers – Artificial sweeteners– Antioxidants – Preservatives– Emulsifiers and Stabilisers.
– What has to pass safety tests?– What does an E number mean?