Sec 4 Combined Science (Chemistry) Maintaining Air Quality topical questions

State the approximate composition of clean, dry air by volume.

Name the toxic gas formed when a fuel burns in too little oxygen, and explain why it is dangerous.

Name the pollutant gas formed inside hot car engines from the reaction of two gases of the air, and identify those gases.

State two harmful effects of acid rain.

Name the pollutant gas in each case and state its source: (a) formed from the two main gases of the air inside a hot car engine; (b) formed when the impurity in coal burns; (c) a greenhouse gas from cattle and rotting waste.

A 250 cm³ sample of clean, dry air is analysed. Calculate the approximate volume of nitrogen and of oxygen it contains.

A table of air-quality readings shows: CO near a congested road; SO₂ near a coal-fired plant; NOₓ near an airport; CH₄ near a landfill; O₃ on a hot sunny afternoon. Explain each reading by naming the source of that pollutant.

(a) Write the word equation for complete combustion of a hydrocarbon fuel, and state what changes when the oxygen supply is limited. (b) Explain, step by step, why people are warned never to run a car engine in a closed garage.

A city's limestone cathedral stands downwind of a power station burning coal with sulfur impurities. (a) Explain how the cathedral's stone is eroded, naming the pollutant and the chemistry of the erosion. (b) State one effect of the same pollution on the city's residents.

A coal-burning power station stands upwind of a forest lake. (a) Name the impurity in coal and the pollutant gas its burning forms. (b) Explain how that gas reaches and acidifies the lake. (c) State two effects the acidified water can have on the lake's life.

After mowing, a gardener has a bag of grass clippings. Compare the effect on atmospheric carbon dioxide of: (a) composting the clippings; (b) burning them on a bonfire; (c) leaving the lawn uncut to keep growing. Which option keeps atmospheric CO₂ lowest over a year? Give reasons for each.

Explain how the carbon cycle regulates the amount of carbon dioxide in the atmosphere, naming three processes with their directions, and explain why deforestation upsets the balance.

(a) Name two greenhouse gases and give one source of each. (b) Explain what greenhouse gases do and state two consequences of their rising levels. (c) Methane levels also rise when wetland soils warm. Suggest why, using decay.

A monitoring station records atmospheric CO₂ climbing steadily, with small dips every northern summer. (a) Explain the overall climb using two named human activities and the carbon-cycle processes they affect. (b) Explain the summer dips. (c) State one global consequence if the climb continues.

A country plans to replace coal power stations with natural-gas stations. (a) State two pollutants whose emissions should fall, each with its reason. (b) Explain why CO₂ emissions will not fall to zero. (c) One engineer suggests the savings still matter. Comment with reference to greenhouse gases.

The same fuel — petrol — can leave an engine as CO₂ and water, as CO and soot, or accompanied by NOₓ. Explain, using conditions, how each set of products can arise.

Two monitoring stations record average pollutant levels. Site 1 (city centre): CO 12 ppm, NO₂ 40 ppm, SO₂ 8 ppm. Site 2 (rural coast): CO 1 ppm, NO₂ 6 ppm, SO₂ 3 ppm. (a) State which sources the city-centre readings point to, quoting the data. (b) Suggest why SO₂ is low at BOTH sites. (c) Explain why NO₂ is so much higher at the city site.

A country must expand its electricity supply and weighs three options: (i) build another coal-fired power station; (ii) install solar panels across unused rooftops; (iii) plant large areas of new forest. Evaluate each option's effect on atmospheric CO₂, give one limitation of each, and recommend which to prioritise, with a reason.