Air Quality & Climate (Cambridge (CIE) IGCSE Chemistry)

Separate: Chemistry and Extended Only

Ozone is a form of oxygen. Ozone is present in the upper atmosphere and it prevents dangerous solar radiation from reaching the Earth’s surface. Some of the chemicals that diffuse into the upper atmosphere decompose ozone. Chemicals that have this effect are methane (CH₄), chloromethane (CH₃Cl) and an oxide of nitrogen (NO₂).

i) Which of these three chemicals diffuses the most slowly? Give a reason for your choice.

[2]

ii) Chloromethane is formed when seaweed decomposes. Name the compounds in the environment from which seaweed might have obtained the following elements:

carbon; ..........................................................................................................hydrogen; ..........................................................................................................chlorine. ..........................................................................................................

[3]

iii) How can chloromethane be made from methane?

reagent ........................................................................................... condition ........................................................................................

[2]

iv) The oxides of nitrogen are atmospheric pollutants. Describe how they are formed.

[2]

The major gases in unpolluted air are 79% nitrogen and 20% oxygen.  

i) Name another gaseous element in unpolluted air.

[1]

ii) Name two compounds in unpolluted air.

[2]

Extended Only

Two common pollutants in air are carbon monoxide and the oxides of nitrogen.  

i) Name another pollutant in air.

[1]

ii) Describe how carbon monoxide is formed.

[2]

iii) How are the oxides of nitrogen formed?

[2]

iv) Explain how a catalytic converter reduces the emission of these two gases.

[2]

This question is concerned with the following oxides.

sulfur dioxide
carbon monoxide
lithium oxide
aluminium oxide
nitrogen dioxide
strontium oxide

Two of the oxides are responsible for acid rain.

Identify the two oxides and explain their presence in the atmosphere.

Lithium oxide is an ionic compound.

i) Identify another ionic oxide in the list in part a).

[1]

ii) Draw a diagram which shows the formula of lithium oxide, the charges on the ions and the arrangement of the valency electrons around the negative ion.

Use x to represent an electron from an atom of oxygen. Use o to represent an electron from an atom of lithium.

[2]

Extended Only

When nitrogen dioxide is cooled, it forms a yellow liquid and then pale yellow crystals. These crystals are heated and the temperature is measured every minute. The following graph can be drawn.

i) Describe the arrangement and movement of the molecules in the region A–B.

 ii) Name the change that occurs in the region B–C

Extended Only

Nitrogen dioxide and other oxides of nitrogen are formed in car engines.

i) Explain how these oxides are formed.

 ii) How are they removed from the exhaust gases?

Nitrogen dioxide, oxygen and water react to form dilute nitric acid.

Describe how lead(II) nitrate crystals could be prepared from dilute nitric acid and lead(II) oxide.

Separate: Chemistry and Extended Only

The reactions in this question are all examples of photochemical reactions.

Explain the phrase photochemical reaction.

Separate: Chemistry Only

Many millions of years ago, the Earth’s atmosphere was rich in carbon dioxide and contained negligible amounts of oxygen. After the appearance of green plant-like bacteria, the proportions of these two gases in the atmosphere changed.

i) What are the approximate percentages of these two gases in the atmosphere now?

 carbon dioxide = .....................................

 oxygen = .................................................. 

[2]

ii) Explain how the green plant-like bacteria changed the composition of the atmosphere.

[4]

Minimising air pollution is essential for health and for the environment.

Natural gas is methane.

i) Write the equation for complete combustion of methane.

[2]

ii) Explain why it is dangerous to use a gas fire in a poorly ventilated room.

[2]

Low sulfur fuels are being introduced. Ordinary diesel contains 500 ppm of sulfur but low sulfur diesel contains less than 50 ppm. Why is this an advantage to the environment?

Extended Only

Catalytic converters reduce pollution from motor vehicles, as shown in the following diagram.

i) What type of elements are the metals rhodium, platinum and palladium?

[1]

ii) Rhodium catalyses the decomposition of the oxides of nitrogen.

2NO → N₂ + O₂

Two other pollutants are carbon monoxide and unburnt hydrocarbons. How are they made into less harmful substances?

[2]

Coal is a solid fossil fuel.

Name two other fossil fuels.

Two of the elements present in a sample of coal are carbon and sulfur. 

A sample of coal was heated in the absence of air and the products included water, ammonia and hydrocarbons.

Name three other elements present in this sample of coal.

Sulfur, present in coal, is one major cause of acid rain. Sulfur burns to form sulfur dioxide which reacts with rain water to form sulfuric acid.

i) Describe how the high temperatures in vehicle engines are another cause of acid rain.

[3]

ii) Give two harmful effects of acid rain.

[2]

In 2010, a large coal-burning power station in the UK was converted to burn both coal and wood.

Explain why the combustion of wood rather than coal can reduce the effect of the emissions from this power station on the level of carbon dioxide in the atmosphere.

The properties of five alkenes at room temperature are shown in the table.

When propene undergoes incomplete combustion, carbon monoxide is formed.

What condition is needed for incomplete combustion?

Give one adverse effect of carbon monoxide on health.

Clean dry air contains mainly nitrogen and oxygen.

Name two other gases that are in clean dry air.

Air often contains pollutants. Identify three common gaseous pollutants in air and state how each of these pollutants are produced.

pollutant gas 1 ..................................................

how it is produced ..................................................

pollutant gas 2 ..................................................

how it is produced ..................................................

pollutant gas 3 ..................................................

how it is produced ..................................................

Air is a mixture of gases.

The main constituents are the elements oxygen and nitrogen.

i) Name another element in air.

[1]

 ii) Give the formula of a compound in unpolluted air.

[1]

Common pollutants present in air are the oxides of nitrogen and sulfur dioxide.

i) How are the oxides of nitrogen formed?

[2]

ii) How is sulfur dioxide formed?

[2]

iii) These oxides are largely responsible for acid rain.

State two harmful effects of acid rain.

[2]

The percentage of oxygen in air can be determined by the following experiment.

The gas syringe contains 50 cm³ of air. The large pile of copper is heated and the air is passed from one gas syringe to the other over the hot copper. The large pile of copper turns black. The gas is allowed to cool and its volume measured. The small pile of copper is heated and the remaining gas passed over the hot copper. The copper does not turn black. The final volume of gas left in the apparatus is less than 50 cm³.

i) Explain why the copper in the large pile turns black.

[2]

ii) hy must the gas be allowed to cool before its volume is measured?

[1]

iii) Explain why the copper in the small pile did not turn black.

[1]

iv) What is the approximate volume of the gas left in the apparatus?

[1]

.

Plant growth is improved by the availability of essential elements, such as nitrogen, and by the soil having a suitable pH.

Nitrogen-based fertilisers are made from ammonia. Ammonia is manufactured by the Haber process.

i) Describe the Haber process giving reaction conditions and a balanced equation. (Do not discuss reaction rate and yield.)

[5]

ii) Fertilisers contain nitrogen. Name the other two elements essential for plant growth commonly found in fertilisers.

[2]

Crops do not grow well if the soil is too acidic.

i) One cause of acidity in soil is acid rain. Explain how acid rain is formed.

[3]

ii) Name two bases which are used to increase the pH of acidic soils.

[2]

Polluted air contains two oxides of carbon and two oxides of nitrogen. A major source of these pollutants is motor vehicles.

i) Describe how carbon dioxide and carbon monoxide are formed in motor vehicle engines.

[3]

 ii) State one adverse effect of each of these gases.

[2]

iii) Nitrogen monoxide, NO, is released by motor vehicle exhausts. Explain how nitrogen monoxide is formed in motor vehicle engines.

[2]

iv) When nitrogen monoxide is released into the atmosphere, nitrogen dioxide, NO₂, is formed. Suggest an explanation why this happens.

[1]

Predict the possible adverse effect on the environment when this non-metal oxide, NO_2, reacts with water and oxygen.

How are the amounts of carbon monoxide and nitrogen monoxide emitted by modern motor vehicles reduced?

Include an equation in your answer.

Three common pollutants in the air are carbon monoxide, the oxides of nitrogen, NO and NO₂ and unburnt hydrocarbons. They are all emitted by motor vehicles.

Describe how the oxides of nitrogen are formed.

Describe how a catalytic converter reduces the emission of these three pollutants.

i) Coal is a solid fossil fuel. Name another fossil fuel.

[1]

ii) Explain what is meant by the term fossil fuel.

[2]

The burning of fossil fuels is largely responsible for the formation of acid rain. Two of the acids in acid rain are sulfuric acid and nitric acid.

i) Explain how the combustion of coal can form sulfuric acid.

[3]

ii) High temperatures generated by the combustion of fossil fuels can lead to the formation of nitric acid. Explain.

[3]

iii) Nitric acid contains nitrate ions.

Describe a test for nitrate ions.

[2]

iv) Explain how you could determine which one of two samples of acid rain had the higher concentration of hydrogen ions.

[2]