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 airOxygen
nitrogen
Carbon dioxide
Noble 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:
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.
______
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:
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
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. CO
Carbon 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
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.
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 acidic
The 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.
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:
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.
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.
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:
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 then
rise up into the atmosphere.
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?
……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..
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)
…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………...
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.
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 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 ozone
layer 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.
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.