Water for a town is treated in four stages, A, B, C and D, before it is supplied to homes. At stage A large floating objects such as leaves and twigs are tr...
Question 1 Report
Water for a town is treated in four stages, A, B, C and D, before it is supplied to homes. At stage A large floating objects such as leaves and twigs are trapped by a metal grid.
(a) Name stages B, C and D. [3]
(b) Suggest a name for stage A. [1]
(c) Complete the table to describe what happens to the water at stages B and C. [2]
| Stage | What happens to the water |
|---|---|
| B | |
| C |
(e) Describe a chemical test, with its result, to show that the treated liquid contains water. [2]
(f) The purity of the water is checked by measuring its boiling point. State the boiling point of pure water and explain how a dissolved impurity would change it. [2]
(g) Give one use of large amounts of water in industry. [1]
Answer Details
This question extends water treatment to four stages: an initial screening to catch large debris, then the familiar sedimentation, filtration and chlorination. Each stage targets a progressively finer or different type of impurity.
(a) Naming the stages: B is sedimentation (settling) [1], C is filtration [1], and D is chlorination (sterilisation). [1]
(b) Stage A, where large floating objects are trapped by a metal grid, is screening. [1]
(c) Completing the table:
| Stage | What happens to the water |
|---|---|
| B | heavy insoluble particles settle to the bottom and are removed [1] |
| C | the water passes through sand and smaller insoluble particles are trapped [1] |
(d)(i) The substance added at stage D is chlorine. [1] (ii) Stage D is necessary because chlorine kills bacteria / microorganisms [1], making the water safe to drink and preventing waterborne disease. [1]
(e) To show the treated liquid contains water, add anhydrous copper(II) sulfate; [1] it changes from white to blue. [1]
(f) Pure water boils at 100°C [1] (at normal atmospheric pressure); a dissolved impurity raises the boiling point above 100°C. [1]
(g) One industrial use of large amounts of water: cooling (as a coolant), or as a solvent, for cleaning, or for raising steam. [1]
Exam tip: match each stage to its purpose: screening removes big debris, sedimentation removes heavy solids, filtration removes fine solids, chlorination kills microbes. Only chlorination affects living organisms.
Download The App On Google Playstore
Everything you need to excel in your exams
