IGCSE Chemistry

Unit 2: Water And Air Part 1: Air

Composition of clean air.

Name of gas in the air Percentage of the gas in the air

Oxygen nitrogenCarbon dioxideNoble gases (mainly argon)Water vapour Variable (e.g 100%o in tropics, 0% in deserts)

Two Famous experiments that show that 20% of the air is oxygen

Explanation.

As the candle wax _____, it uses up the _______ in the air inside the bell jar. This is a _________ reaction:

Write an equation for this reaction:

The water rises up and takes the place of the oxygen that has gone.

Or if phosphorus is used instead of a candle the equation would be:

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Calculation.

Volume of air before the candle is lit. V1= _______cm3

Volume of air after the candle has been lit (and gone out), V2 =____ cm3

So volume of air that has been used up, V1-V2 =

So the percentage of oxygen in the air is____ x 100 =____%

2. Passing air over clean copper metal.

The apparatus used in this experiment is shown below.

Explain in your own words what is happening within this experiment, the equations shown below may help you.

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Fractional distillation of air.

Air is a mixture. The main gases in air are shown in the table below:

Air can be liquefied and then separated by fractional distillation. This is done in industrv to produce oxygen, nitrogen and some noble gases.

The process of fractional distillation is shown simply in the figure below:

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The steps involved in fractionally distilling air are:

l. Water vapour and carbon dioxide are removed.These components are removed by cooling the air which freezes the water vapour and carbon dioxide gas. The solid H2O and co2 are then removed.

2. The air is then liquefied. Air is a gas. To liquefy a gas means to turn it into a liquid. This is done by compressing the air with huge pumps and then allowing the air to expand suddenly.

3. The liquid air is then distilled in a fractionating column.An electric heater is used to boil the liquid air. The gases are separated according to their boiling points. Nitrogen has the lowest boiling point. It boils first and comes out at the top of the column. Then argon boils and comes out lower down the column. This process carries on until all the components of the air have been separated out. Krypton and xenon must be fuither distilled to separate them.

Uses of oxygen.

a)___________________________________________________

b)___________________________________________________

c)___________________________________________________

d)___________________________________________________

e)___________________________________________________

f)____________________________________________________

Uses of Nitrogen

a)___________________________________________________

b)___________________________________________________

c)___________________________________________________

d)___________________________________________________

e)___________________________________________________

f)____________________________________________________

Uses of the Halogens

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a)___________________________________________________

b)___________________________________________________

c)___________________________________________________

d)___________________________________________________

e)___________________________________________________

References

IGCSE Chemistry pages 149-152

Learning Objectives

Candidates should be able to:

Describe the composition of clean air

Describe the separation of oxygen and nitrogen from liquid air by fractional distillation.

Name the uses of oxygen in oxygen tents in hospitals and with acetylene (a hydrocarbon) in welding.

Unit 2: Water And Air Part 2: Common Pollutants of the air.

Task 1: Fill in the missing words.

1. Carbon Monoxide. COCarbon monoxide gas is produced by the __________combustion (burning) of carbon containing substances like coal, gas, oil and petrol. Carbon monoxide gas is a deadly poison because it stops ______ being transported by the haemoglobin in red _____ cells.

Note: incomplete combustion takes place when there is not enough ______ present to convert all the carbon into carbon dioxide.

2. Sulphur dioxide, SO2

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Sulphur dioxide gas is made when ______ fuels (that contain sulphur) are _____.

Sulphur + oxygen → sulphur dioxide(from fuels) (from air)

SOz is also produced by volcanoes. Sulphur dioxide combines with water in the atmosphere to make acid rain.

Sulphur dioxide in the air reacts with oxygen and water vapour to form sulphuric acid:

2SO2 + O2 + 2H2O→ 2H2SO4

Write a word equation for this reaction:___________________________________________

The sulphuric acid dissolves in rain water, making it acidic.

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Nitrogen dioxide also undergoes a similar reaction in the atmosphere, forming nitric acid:

4NO2 + 02 + 2H2O → 4HNO3

The nitric acid also dissolves in rain water, making it acidicThe acidity of rain water, caused by man-made sulphur dioxide and nitrogen dioxide from air pollution, is called acid rain.

Acid rain is very corrosive. In addition to the harmful effects shown in the diagram above, acid rain also damages our lungs by destroying the moist walls of the alveoli.

List the effects of acid rain:____________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. Oxides of nitrogen.Oxides of nitrogen are NO, nitrogen oxide and NO2, nitrogen dioxide. These two oxides of nitrogen are often described simply as NOx. They are produced by internal combustion engines (the engines of cars and trucks) when they are running; N2 (g) and O2 (g) react and combine together to form NOx.

Fumes from the engine containing these oxides of nitrogen come out of the exhaust pipe. Oxides of nitrogen cause acid rain and smog in cities. (look at the diagram above).

Oxides of nitrogen are also produced by lightning activity.

4. Methane.Methane gas is produced by bacterial decay of vegetable matter. Methane is a greenhouse gas and so contributes towards global warming.

5. Unburnt hydrocarbons.

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Unbumt hydrocarbons are released into the air from the exhaust pipes of internal combustion engines.

6. Ozone, 03.

Ozone is a pollutant that is produced by photochemical reactions (reactions that are catalysed by light). These photochemical reactions are also responsible for smog in city air.

Some chemical reactions that can be used to remove pollutant gases.

(a) The redox reactions in catalytic converters to remove combustion pollutants. The hydrocarbons petrol and diesel are burnt by air in motorcar engines. The fumes from petrol engines are a major cause of air pollution. The main pollutants in exhaust gases are listed below:

Carbon monoxide (from incomplete combustion of the hydrocarbon petrol)

Nitrogen oxides Hydrocarbons (from unburnt petrol) Lead compounds (from lead compounds added to the petrol).

In recent years, motorcars have been modified to reduce this pollution. Some changes are shown in the diagram below:

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The use of lead-free ('unleaded') petrol prevents any lead pollution and the amount of lead in the air is being reduced as cars switch from leaded to unleaded petrol.Pollution is also being reduced by making engines more efficient. However, most of the pollution can be greatly reduced by fitting a catalytic converter to the motorcar exhaust. The catalytic converter consists of a thin layer of platinum metal spread over a honeycomb shaped piece of ceramic. The honeycomb shape ensures a large surface area for the exhaust gases to react.

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In the catalytic converter, the unburnt petrol, nitrogen oxides and carbon monoxide react on the platinum catalyst to produce harmless water, carbon dioxide and nitrogen.

(b) Sulphur dioxide pollution from power stations and other industries is prevented by spraying the chimney exhaust gases with wet calcium hydroxide or calcium carbonate (limestone) before the gases are released into the atmosphere. For example, calcium hydroxide reacts with the sulphur dioxide to produce solid calcium sulphite:

Ca(OH)2 (aq) + SO2 (g) → CaSO3(s) + H2O(l)

(c) Calcium carbonate (limestone) is added to the soil to neutralise soil aciditv as a result of acid rain.

References

IGCSE Chemistry pages 157-158

Learning Objectives

Candidates should be able to:

Name the common pollutants in the air as being carbon monoxide, sulphur dioxide, oxides of nitrogen and lead compounds

State the source of each of these pollutants sulphur dioxide from the combustion of fossil fuels which contain sulphur compounds (leading to ‘acid rain’)

Describe and explain the presence of oxides of nitrogen in car exhausts and their catalytic removal.

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Unit 2: Water And Air Part 3: Carbon dioxide.

The Carbon cycle

The amount of carbon in plants and animals, in the crust of the earth and in the air does not change. The carbon is in:- the bodies of animals (as carbohydrates, fats and proteins) - plants (as carbohydrates, fats and proteins) - the atmosphere as carbon dioxide ( CO2)The total amount of carbon does not change. However the form that the carbon is in can change. The carbon cycle shows this:

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Green plants remove carbon dioxide from the atmosphere (air) during the process called photosynthesis. The green plants combine the carbon dioxide with water to make glucose (C6H12O6). The glucose is then used to make the roots, leaves and stem of the plant.When the plants are eaten by animals the carbon inside the plant is changed into animal tissue. In this way the carbon atoms of the plant become part of the animal.

Carbon dioxide is released into the atmosphere by the process called respiration. Remember that respiration is the breakdown of food in-our bodies in the presence of oxygen' The waste products of respiration are CO2 and H2O. Both plants and animals 'breathe' out CO2 and H2O.

Carbon dioxide is also released into the air by the process of combustion.Remember that combustion (burning) is the burning of carbon-containing fuels such as wood, coal, petrol and natural gas. The waste products of combustion, like respiration, are CO2 and H2O. So when a fire is burning the gases CO2 and H2O are produced which thenrise up into the atmosphere.

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Use your previous knowledge and text book to write equations for the processes occurring in the carbon cycle. (Shown in the diagram above)

Metal Carbonate + Acid

Carbon dioxide is also one of the products produced when a metal carbonate reacts with an acid:

Metal Carbonate + acid Salt + Water + Carbon Dioxide

1. Describe how you would test for carbon dioxide and what you would see.…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………............................................................................................

2. How could you tell a chemical reaction had taken place?……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

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3. What salt would you make when you add copper carbonate to sulphuric acid?…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

4. Write a word equation to summarise the reaction that would take place……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

5. Complete the word equations below:Sulphuric acid + Zinc Carbonate

Hydrochloric acid + Magnesium Carbonate

Nitric Acid + Calcium Carbonate

6. Using the following information construct symbol equations for the word equations written in questions 5 + 6:

(Zinc Carbonate = ZnCO3 Hydrochloric acid = HCl, Sulphuric acid =H2SO4, Nitric acid =HNO3)

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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……………………………………………………………………………………………………………………………………………...

References

IGCSE Chemistry pages 121-124

Learning Objectives

Candidates should be able to:

Describe the formation of carbon dioxide. as a product of complete combustion of carbon-containing substances, as a product of respiration and as a product of the reaction between an acid and a carbonate.

Unit 2: Water And Air Part 4:The Green House Effect /CFC’S

The Greenhouse Effect.

Air contains a very small amount of (only about 0.03%) of carbon dioxide. This atmospheric carbon dioxide is very important, as it is used by green plants in photosynthesis.

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The amount of carbon dioxide in the air has increased by 25% over the past 200 years and, is still steadily increasing (see graph). Scientists believe that the increase is due to extra carbon dioxide being added to the air from burning fuels such as oils, gas and coal. The consumption of these fuels has increased: greatly this century to provide energy for more industries and motor vehicles.

The Earth's surface is heated by radiation from the Sun. Carbon dioxide and methane in the air trap this heat radiation and prevent much of it escaping into space. This is called the Greenhouse Effect.The greater the amount of carbon dioxide and methane, the larger is the amount of heat that is trapped and the hotter the Earth becomes.

Possible consequences of global warming.

The atmospheric warming may cause the ice caps to melt, increasing the sea levels and flooding low-lying coastal areas. Higher temperatures can also harm production of food crops such as rice and wheat by reducing the yield.

Chlorofluorocarbons. CFC’s

These compounds, simply called CFCs, are made of the elements chlorine, fluorine and carbon. Two important examples have molecular formulas CFCl3 and CF2Cl2. CFCs are used in aerosol propellants and coolant fluids for refrigerators and air conditioners. Expanded polystyrene cups and packaging are blown into foam with CFCs. When an aerosol can is used or polystyrene packaging is burnt, CFC molecules escape into the air. In addition to this, when old refrigerators and air conditioners are discarded, CFC molecules

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escape into the air. CFCs are harmless to plants and animals. But CFC molecules rise high into the atmosphere where they are decomposed by sunlight to produce chlorine atoms. These chlorine atoms destroy ozone molecules in the ozone layer. It is the ozonelayer which protects the Earth from intense radiation from the sun.Since 1978, the amount of ozone in the ozone layer over Antarctica has decreased. By 1987 up to half the ozone over Antarctica has been destroyed. This is now called the Ozone Hole.

Dangerous ultra-violet radiation from the Sun streams through this hole. Scientists are concerned that the Ozone Hole could spread to other continents. If this happens there maybe a big increase in the occurence of skin cancer due to the increased ultra-violet radiation from the Sun, and food crops could also be damaged.

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Research task

You are going to work in groups of three. Using the internet and reference books you have to research the effects of a different pollutant gas in terms of how it is produced, its adverse effects and methods for solving the problem. The posters target audience is 12-13 year olds so the appropriate language should be used. You should present your research the form of a poster, you should ensure that you poster:

Contains accurate English (10 Marks) Has a clear, neat layout, with appropriate titles and

subtitles (5 Marks) Contains accurate scientific information (10 Marks) Is not copy and pasted directly from the internet!!! ( 5

Marks) Each group member can explain the concepts with the

poster (10 Marks)

It is important that you are able to explain concepts included in your graph as you will be asked questions. THIS IS AN ASSESSED PIECE OF WORK

References

IGCSE Chemistry pages 178-179

Learning Objectives

Candidates should be able to:

State the adverse effect of common pollutants on buildings, health and the environment.

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Unit 2: Water And Air Part 5:Water

WaterBecause water is such a good solvent, it will dissolve a great variety of substances. These dissolved substances can be:

(a) Naturully occurring.

For example minerals salts dissolved from rocks as river water flows along, oxygen from the air and organic matter from living things.

Mineral salts and oxygen are beneficial for living things. Mineral salts are a necessary part of the diet of aquatic life and oxygen is needed for respiration.

(b) Pollutants.

From the land, the main impurities are dissolved fertilisers. Rain water washes or leaches fertilisers out of the soil and into the river water. This dissolving or leaching can have severe biological effects. One is called eutrophication, which means unintentional enrichment of water with fertilisers. Eutrophication causes:

Rapid growth of plants called algae. Algae feed on phosphates from the fertilisers in the water. These algae restrict the normal growth of other plants, and fish, as they reduce the oxygen content of the water (see also other effects below).

Many fertilisers contain ammonia which bacteria in the water oxidise to nitrates, thereby removing oxygen from the water.

Industrial pollution is a severe problem. Factory discharge or effluent includes heavy metals such as mercury, lead and cadmium. These are a hazard to health because their concentrations can build up as they pass through the food chain.

At Minimata, a coastal town of Japan, over 40 people were killed were killed at one time by eating locally caught fish and shell fish which were highly contaminated with mercury. Also many babies were being born with mental and physical defects. A local plastics factory had discharged waste water,

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containing mercury, into the bay. The diagram illustrates how food chains concentrate a pollutant at each step in the chain.

Detergents- Many countries encourage the use of biodegradable detergents. This means that the detergent molecule is broken down by bacteria in the water, preventing the detergent from foaming up in a river. However, many detergents also contain phosphates which are excellent fertilisers for algae. Large amounts of algae cause the river to become de-oxygenated. Under these conditions anaerobic bacteria attack decaying vegetation to produce toxic wastes products like ammonia, methaneand hydrogen sulphide. These products are all a hazard, to health.

Human pollution of water- Waste water from washing, using the toilet etc. is called sewage. Sewage contains many pollutants including harmful microbes (bacteria) e.g. cholera.

Purification of the water supply.

The main steps to purify water include:

(i) filtration to remove solids

(ii) chlorination to disinfect the water.

(iii) use of carbon to remove tastes and odours (water filters containing carbon are attached to taps in the home.The diagram below illustrates water treatment.

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In your own words describe what is happening at each stage of the purification process. Give as much detail as possible (Use your text books to help you:

Stage 1

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Stage 2

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Stage 3

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Stage 4

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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……………………………………………………………………………………………………………………………..

Stage 5

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

List 5 uses of Water

……………………………………..

……………………………………..

……………………………………..

………………………………………..

………………………………………..

Testing for water in the laboratory

When testing for water within a laboratory you have a number of problems.

1)  Water has no colour or smell.

2)  It has no effect on moist litmus paper,or moist universal indicator paper - it is neutral.

3)  It will put out a lit splint

There are a number of Specific test for Water or Water Vapour, you have to remember them!

Water or its vapour will turn blue cobalt chloride paper pink.

It will also turn white anhydrous copper(II) sulfate crystals blue

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Rusting

What do you think will happen to the iron nails in each test tube after about two weeks?

A______________________________________________________B______________________________________________________

C______________________________________________________

Rust is formed when iron reacts with water AND oxygen. It’s an example of an oxidation reaction which can be sped up using salt. There are several ways of dealing with rust:

1) Regular painting or oiling

2) Galvanising – this is when iron objects are coated with zinc

3) Making objects out of a non-rusting metal, such as stainless steel

4) Attaching zinc bars to ships – the water will react with the zinc before it reacts with the iron, because zinc is more reactive

References

IGCSE Chemistry

IGCSE Chemistry pages 178-179

Learning Objectives

Candidates should be able to:

. Describe, in outline, the purification of the water supply in

terms of filtration and chlorination. Name some of the uses of water in industry and in the home.

Unit 2: Water And Air Part 6: Sample exam questions

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Q1 Below is a simple diagram illustrating how the gases which make up air are separated.

(a) Why is the air filtered in Step 1?

(1)[1]

(b) Which two chemicals are removed from the air in Step 2?

(2)

…………………………………………………………………………………………………………………………………………

..................................................................................................................................... [2]

(c) What happens to the air when it is cooled to -200°C in Step 4?

(1)..................................................................................................................................... [1]

(d) What is the name of the process used to separate the gases in Step 5? (one line)

(1)

..................................................................................................................................... [1]

(e) Nitrogen boils at –196oC, oxygen at –183oC and argon at –186oC.Which of these gases separates at the top of the column in Step 5 [1]

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

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Q2 It is thought that over 4000 million years ago the Earth’s atmosphere may have contained carbon dioxide, ammonia and water vapour but very little oxygen. The temperature of the atmosphere was very much higher than it is today.

(a)The early atmosphere contained a large percentage of water vapour.Why is there only a small percentage of water vapour in the atmosphere today?……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… [3]

(b) As simple plant life developed the amount of oxygen in the atmosphere began to increase.

(i) Name the process by which these plants added oxygen to the atmosphere.

(one line)

(1)………………………………………………………………………………………………………………………………[1]

(ii) Name the gas which was removed from the atmosphere by this process.

(1)………………………………………………………………………………………………………………………………… [1]

(c) Some of the oxygen produced turned into ozone and formed the ozone layer.

(i) Write down the chemical formula for ozone.

(1)

………………………………………………………………………………………………………………………………[1]

(ii) Explain the importance of the formation of the ozone layer.

(2)

………………………………………………………………………………………………………………………………[2]

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Q3 Large amounts of carbon dioxide in the atmosphere can cause problems.

(a)What name is given to the problem caused by excess carbon dioxide in the atmosphere?

(1)

………………………………………………………………………………………………………………………………[1] (b) Explain why scientists are concerned about the problem.

(3)

…………………………………………………………………………………………………………………………………

…………………………………………………………………………………………………………………………………

………………………………………………………………………………………………………………………………… [3]

(c) State one way in which the amount of carbon dioxide in the atmosphere is being increased.

(2)

………………………………………………………………………………………………………………………………[1]

(d) Give two ways in which the increase in carbon dioxide can be slowed down.

…………………………………………………………………………………………………………………………………

………………………………………………………………………………………………………………………………… [2]

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Q4The apparatus below was used to determine the amount of oxygen in a sample of clean dry air.

(a) The copper is heated and at the same time the air is pushed over it from one syringe to the other. The experiment is continued until there is no further change in the volume of air in the syringe. The apparatus is left to cool down, then the final volume of air measured.

(i) Why does the volume of air decrease?...................................................................................................................................................................................................................................................................................[1]

(ii) Write a word equation for the reaction which occurs during the experiment....................................................................................................................................................................................................................................................................................[1]

(iii) Why is it important to let the apparatus cool down before measuring the final volume?...............................................................................................................................................................................................................................................................................................................................................................................................................................[2]

(iv) Why is it better to use copper turnings in the experiment rather than larger lumps of copper?...............................................................................................................................................................................................................................................................................................................................................................................................................................[2]

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(v) Name two gases which will be present in the air inside the syringe at the end of the experiment.................................................................................................................................................................................................................................................................................. [2]