Air Worked ExamplesIGCSE Chemistry 0620

The pie chart shows the composition by volume of clean, dry air.

(a) Name gas X and gas Y. [2]

(b) Z is a mixture of gases. Name the two types of gas in Z. [2]

Choose from this list to answer the questions. Any substance may be chosen once, several times or never.

carbon dioxide · carbon monoxide · methane · nitrogen · oxides of nitrogen · particulates · sulfur dioxide

Which substance:

(a) causes acid rain and comes from burning fossil fuels that contain sulfur compounds [1]

(b) is a toxic gas formed by the incomplete combustion of carbon-containing fuels [1]

(c) causes photochemical smog [1]

(d) increases the risk of respiratory problems and cancer and is formed by incomplete combustion [1]

(e) comes from the decomposition of vegetation? [1]

A student uses the apparatus shown to find the percentage of oxygen in a sample of air. The air is pushed from syringe A to syringe B and back several times over the heated copper. The apparatus is then left to cool and the volume of gas is measured. The final volume is $79.2 \text{ cm}^3$.

(a) State the colour change of the copper. [1]

(b) Write the symbol equation, with state symbols, for the reaction of copper with oxygen. [2]

(c) Calculate the percentage of oxygen in the air sample. [2]

(d) Explain why the gas is passed over the copper several times. [1]

(e) Explain why the apparatus is cooled before the final volume is read. [1]

Car exhaust gases contain oxides of nitrogen. Which statement explains how they form?

A The petrol contains nitrogen compounds, which burn.

B At the high temperature inside the engine, oxygen reacts with nitrogen from the air.

C The catalytic converter oxidises nitrogen gas in the exhaust.

D Carbon monoxide reacts with nitrogen in the exhaust pipe.

The diagram shows a catalytic converter fitted to a car.

(a) Name the two pollutant gases in the list of gases in that the converter removes. [1]

(b) Write the balanced equation, with state symbols, for the reaction between these two gases in the converter. [2]

(c) Use oxidation numbers to show which gas is oxidised and which is reduced. [3]

(d) Suggest why the catalyst is spread over a honeycomb structure. [1]

Which statement about the gases leaving a petrol car is not correct?

A Carbon monoxide forms when the fuel burns in too little oxygen.

B Oxides of nitrogen form because air is heated to a high temperature in the engine.

C Carbon dioxide from the engine is removed by the catalytic converter.

D Sulfur dioxide forms if the fuel contains sulfur compounds.

Petrol contains octane, $\text{C}_8\text{H}_{18}$.

(a) Write a balanced equation for the complete combustion of octane. [2]

(b) In a poorly tuned engine, some octane burns to form carbon monoxide and water only. Write a balanced equation for this reaction. [1]

(c) Some octane burns to form carbon (soot) and water only. Write a balanced equation for this reaction. [1]

(d) State the adverse effect of carbon monoxide and of particulates. [2]

A power station burns coal that contains $2.0\%$ sulfur by mass. The sulfur burns to form sulfur dioxide, which is removed from the waste gases by calcium oxide:

$\text{S}\text{(s)} + \text{O}_2\text{(g)} \rightarrow \text{SO}_2\text{(g)}$

$\text{CaO}\text{(s)} + \text{SO}_2\text{(g)} \rightarrow \text{CaSO}_3\text{(s)}$

(a) Calculate the mass of sulfur in $1.00$ tonne of coal. ($1 \text{ tonne} = 1.00 \times 10^{6} \text{ g}$) [1]

(b) Calculate the mass, in kg, of sulfur dioxide formed from $1.00$ tonne of coal. [2]

(c) Calculate the mass, in kg, of calcium oxide needed to remove all of this sulfur dioxide. [2]

(d) State the environmental problem that this process reduces, and give one other way of reducing sulfur dioxide emissions. [2]

$A_r$: O = 16; S = 32; Ca = 40

The graph shows how the concentration of nitrogen monoxide, NO, in the exhaust gas of an engine changes with the temperature inside the engine.

(a) Use the graph to find the concentration of NO when the temperature is $2000\,^{\circ}\text{C}$. [1]

(b) Describe how the concentration of NO changes as the temperature increases from $1000\,^{\circ}\text{C}$ to $2500\,^{\circ}\text{C}$. [1]

(c) Explain how NO forms in the engine. Include an equation. [2]

(d) Apart from acid rain, state two adverse effects of oxides of nitrogen. [2]

A student bubbles the exhaust gas from a diesel generator through two reagents in turn.

(a) The first reagent tests for sulfur dioxide. Name the reagent and state the colour change for a positive result. [2]

(b) The second reagent tests for carbon dioxide. Name the reagent and state the observation for a positive result. [2]

(c) The sulfur dioxide test is positive. Suggest what this shows about the diesel fuel. [1]

The bar chart shows the mean concentrations of three pollutants in a city in 2016 and in 2026. During this time the city required low-sulfur fuels and catalytic converters on all new cars.

(a) Calculate the percentage decrease in sulfur dioxide from 2016 to 2026. [2]

(b) Calculate the percentage decrease in nitrogen dioxide over the same period. [1]

(c) Explain which strategy caused each of these decreases. [2]

(d) Suggest why the decrease in nitrogen dioxide was smaller than the decrease in sulfur dioxide. [1]

(e) Suggest why these strategies do not reduce carbon dioxide emissions. [1]

A sample of exhaust gas contains $150 \text{ cm}^3$ of carbon monoxide and $90 \text{ cm}^3$ of nitrogen monoxide. In the converter: $2\text{CO}\text{(g)} + 2\text{NO}\text{(g)} \rightarrow 2\text{CO}_2\text{(g)} + \text{N}_2\text{(g)}$

All volumes are measured at the same temperature and pressure.

(a) Identify the limiting reactant and calculate the volume of the other reactant left over. [2]

(b) Calculate the volumes of carbon dioxide and nitrogen formed. [2]

(c) The converter also lets the excess carbon monoxide react with oxygen: $2\text{CO}\text{(g)} + \text{O}_2\text{(g)} \rightarrow 2\text{CO}_2\text{(g)}$. Calculate the volume of oxygen needed, and the total volume of carbon dioxide leaving the converter. [2]