Chemistry 9701 · AS & A Level · Equilibria

Equilibria — practice question

As the world’s population rises at a rapid pace, access to clean drinking water is essential. In many countries, groundwater supplies, rather than stored rainwater or river water, are crucial. Groundwater is water located in the pore spaces and fractures of rock and sediment below the Earth’s surface. The World Health Organisation (WHO) gives maximum recommended concentrations for different ions in drinking water.
(a(i))

Nitrate, $\text{NO}_3^-$, ions are hard to remove from groundwater. Why is this?

(a(ii))[4]

State which ions in the table above are likely to be removed from the water by treatment with powdered limestone, $\text{CaCO}_3$, and give a reason for each answer.

(b(i))

Nitrates and phosphates may enter water courses such as rivers or streams because of human activity. Both ions are nutrients for algae. What is the source of these nitrates?

(a)

The geological character of the soil controls the chemical make-up of the groundwater. The table shows some ions that may contaminate groundwater.

(b)

Nitrates and phosphates may enter water courses such as rivers or streams because of human activity. Both ions are nutrients for algae.

(b(ii))

Suggest a source for the phosphates found in water courses.

(b(iii))[3]

How do nitrates and phosphates affect water courses?

(c)

Acid rain can seriously affect natural waters, especially lakes. In recent years, there has been a worldwide effort to cut the amount of acid rain produced.

(c(i))

Write equations to show how acid rain is produced from sulfur dioxide, $\text{SO}_2$.

(c(ii))[2]

The use of fossil fuels is one major source of sulfur dioxide. Name one other major industrial source.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: Nitrates are readily soluble

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