Chemistry of the Environment: Chemistry 0620 (Cambridge O Level / IGCSE)

An outdoor education centre on the shore of Silverlynn Lake collects rainwater in a butt behind the boathouse to top up the freshwater aquarium tanks used in its marine biology classes. Before the water is used, a technician runs some simple checks on a sample.

(a) The technician places a few drops of the rainwater onto white anhydrous copper(II) sulfate powder. State the colour change she would see if the powder confirms that the liquid contains water. [1]

(b) The technician then heats a sample of the rainwater and finds that it boils at exactly $100\,^\circ\text{C}$ at standard atmospheric pressure. State what this result shows about the purity of the rainwater, and explain why a boiling point test, rather than the colour-change test in (a), is used to check the purity of water. [2]

(c) Before reaching the header tank, the rainwater passes through the centre's own small treatment unit. State the purpose of each of the following stages in this unit: (i) sedimentation and filtration (ii) passing through a carbon filter (iii) chlorination [3]

A hydroponics technician preparing a nutrient feed for a strawberry polytunnel dissolves three compounds together to make a single combined feed:

• ammonium nitrate
• calcium phosphate
• ammonium chloride

Which element, needed to make this an NPK fertiliser, is missing from the combined feed?

Rowanhaven City Council installs an air-quality monitor beside a busy ring road to gather evidence for a proposed low-emission zone. On a still winter morning, the monitor first analyses a 500 dm³ sample of background air away from the traffic to confirm it is essentially clean, dry air.

(a) Calculate the volume, in dm³, of nitrogen gas contained in this 500 dm³ background air sample. [1]

(b) The monitor then analyses fumes collected directly above the traffic queue and identifies raised levels of carbon monoxide and sulfur dioxide. For carbon monoxide, and then for sulfur dioxide, state one source and one adverse effect of the pollutant. [4]

(c) The council wants to reduce the harmful effect of the sulfur dioxide detected. State one strategy, other than the use of catalytic converters, that could reduce sulfur dioxide emissions from vehicles and fuel-burning appliances, and briefly explain how it works. [2]

Researchers monitoring the peat bog at Fenwick Moor use an instrumented weather balloon to sample the gases released as the bog dries out and stored organic matter decomposes. Their data logger recorded the average atmospheric methane concentration above the moor as $1850$ parts per billion (ppb) in 2010 and $2035$ ppb in 2025.

(a) Calculate the percentage increase in the methane concentration between 2010 and 2025. [2]

(b) Explain, in terms of the absorption, reflection and emission of thermal energy, how increased concentrations of methane and carbon dioxide in the atmosphere cause global warming. [4]

(c) State one strategy, other than reducing livestock farming, that could help reduce the levels of greenhouse gases such as methane and carbon dioxide in the atmosphere. [1]

At the Ardmoor Motor Testing Facility, engineers investigate the exhaust of a delivery van both before and after it passes through the vehicle's catalytic converter.

(a) Explain, in terms of the gases present and the conditions inside the engine, how oxides of nitrogen form in a car engine. [2]

(b) Inside the catalytic converter, carbon monoxide reacts with nitrogen monoxide according to the equation: $2\text{CO} + 2\text{NO} \rightarrow 2\text{CO}_2 + \text{N}_2$ A sample of the van's exhaust gas passing over the catalyst contains $0.60\ \text{mol}$ of carbon monoxide and $0.60\ \text{mol}$ of nitrogen monoxide.

(i) Calculate the maximum amount, in mol, of nitrogen gas that could be produced. [2]

(ii) State why converting the carbon monoxide and nitrogen monoxide into carbon dioxide and nitrogen, as in this reaction, reduces the harm caused by the van's exhaust. Even though carbon dioxide is still released. [2]

Clean, dry air is a mixture of gases, but two elements make up the vast majority of it by volume.

Which option correctly gives the approximate percentages by volume of these two gases, with the remainder made up of a mixture of noble gases and carbon dioxide?

A pharmaceutical company buys in bulk deliveries of water from an external supplier for use in a laboratory. Before each delivery is accepted, a quality-control technician runs simple checks on a sample of the water.

(a) The technician touches a strip of blue anhydrous cobalt(II) chloride paper into a drop of the water sample. State the colour change that would show her that water is present in the sample. [1]

(b) The technician then slowly cools a portion of the same water sample in a freezer and records the exact temperature at which it starts to freeze. Pure water freezes at exactly $0\,^\circ\text{C}$ at standard atmospheric pressure. State what it would mean about the sample if its freezing point were recorded as below $0\,^\circ\text{C}$, and explain why. [2]

(c) Explain why the cobalt(II) chloride test in part (a), on its own, would NOT be a reliable way to decide whether this delivery of water is pure enough to accept. [2]

A haulage company runs a fleet of older diesel delivery vans. Mechanics notice that one poorly maintained van produces thick black smoke containing particulates (soot) from its exhaust, while a newer, well-maintained van in the same fleet, burning the same diesel fuel, produces almost no visible smoke.

(a) State the source, in terms of the type of combustion taking place, of the particulates in the poorly maintained van's exhaust smoke. [1]

(b) State two adverse effects on human health of breathing in particulates such as those in this exhaust smoke. [2]

(c) The newer van's engine is tuned so that its diesel fuel undergoes complete combustion instead of incomplete combustion. Identify the main carbon-containing gas produced by complete combustion, and explain why switching to complete combustion greatly reduces the particulates (and carbon monoxide) released, even though a different environmental concern remains. [3]

An environmental scientist compares air-quality readings from two monitoring stations: one beside a busy urban ring road, where oxides of nitrogen are the main pollutant of concern, and one near a coal-burning power station several kilometres outside the city, where sulfur dioxide from the combustion of sulfur-containing fuel is the main pollutant of concern.

(a) State the source of the oxides of nitrogen detected at the ring-road station. [1]

(b) Both oxides of nitrogen and sulfur dioxide contribute to the same adverse environmental effect. Name this shared effect. [1]

(c) State one further adverse effect of oxides of nitrogen, on people or the environment, that is not caused by sulfur dioxide. [1]

(d) Suggest one reason why fitting a catalytic converter to a car, which reduces the oxides of nitrogen (and carbon monoxide) in its exhaust, would NOT reduce the sulfur dioxide produced by the power station. [1]

A research team fits an experimental catalytic converter to a test engine. Instead of removing nitrogen monoxide, this converter is designed to remove nitrogen dioxide from the exhaust gas, converting it together with carbon monoxide into carbon dioxide and nitrogen gas according to the equation: $4\text{CO} + 2\text{NO}_2 \rightarrow 4\text{CO}_2 + \text{N}_2$

A sample of exhaust gas passing over the catalyst contains $8.4\ \text{g}$ of carbon monoxide and $13.8\ \text{g}$ of nitrogen dioxide. ($M_r$: $\text{CO} = 28$, $\text{NO}_2 = 46$, $\text{N}_2 = 28$.)

(a) Calculate the number of moles of carbon monoxide and the number of moles of nitrogen dioxide in the sample. [2]

(b) Show that carbon monoxide is the limiting reactant, and calculate the maximum mass, in g, of nitrogen gas that could be produced from this sample. [3]

(c) State one adverse effect of nitrogen dioxide that is removed by this reaction, and explain why the carbon dioxide produced is still a cause for environmental concern, even though it is less immediately harmful than the original exhaust gases. [2]