Junior Secondary · Science

Water purification: Practice Questions

5 multiple-choice questions marked as you go, and 5 written questions with worked solutions. All on Water purification.

10 questions24 marksFree, no account

Question 1

1 mark

What is the primary purpose of the filtration stage in a conventional water treatment plant?

Question 2

1 mark

In a municipal Water purification plant, why is the sedimentation process conducted in a large tank with a very low water flow rate?

Question 3

1 mark

A major challenge in modern drinking water purification is controlling the formation of disinfection byproducts (DBPs), such as trihalomethanes (THMs). THMs form when chlorine, the common disinfectant, reacts with residual dissolved organic matter (DOM) present in the water.
If a water treatment facility must continue using chlorine for final disinfection but aims to significantly reduce the concentration of THMs produced, which supplementary step is the most effective strategy to implement immediately before the final chlorination stage?

Question 4

1 mark

In a large-scale water treatment facility, which of the following processes is specifically used to remove large solid particles by allowing them to settle at the bottom of a tank over time?

Question 5

1 mark

A student is building a simple filtration column using sand, gravel, and charcoal. What is the primary function of the sand and gravel layers in Water purification?

Question 6

2 marks

What is the main objective of filtering water during the water purification process?

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Question 7

3 marks

Explain why distillation is considered a physical process rather than a chemical process in water purification.

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Question 8

5 marks

Large-scale reverse osmosis (RO) is an effective method for removing dissolved salts, such as from seawater, producing highly purified water. Explain the specific chemical property issue inherent to this extremely pure RO water that necessitates a mandatory post-treatment step like remineralization or stabilization, and state the two critical problems this remedial step prevents in municipal systems.

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Question 9

4 marks

Distillation is a common method used in laboratories to obtain pure water from a mixture.

(a) Explain why distillation can be used to separate dissolved salts from water, whereas simple filtration cannot. (2 points)
(b) In a laboratory distillation setup, why is the thermometer bulb placed exactly at the level of the side arm of the flask rather than being dipped into the boiling liquid? (2 points)

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Question 10

5 marks

A laboratory setup for distillation is used to obtain pure water from a mixture of salt, sand, and water. A diagram of the apparatus shows a flask connected to a Liebig condenser.

(a) Explain the specific roles of the 'boiling' and 'condensation' processes in separating the water from the salt. (2 points)
(b) Why is distillation a more effective Water purification method than filtration if the goal is to remove dissolved minerals? (1 point)
(c) If the mixture contains sand, where will the sand be located at the end of the distillation process? Explain why it does not move to the collection beaker. (2 points)

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