O LevelChemistryCambridge (CIE)Exam Questions10. Chemistry of the Environment10.1 Water & Water Pollution

Water & Water Pollution (Cambridge (CIE) O Level Chemistry): Exam Questions

Exam code: 5070

50 mins9 questions

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10.1 Water & Water Pollution

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1a
4 marks

This question is about chemical tests for water.

Complete these sentences about the test for water using the words from the list.

hydrated 

green 

anhydrous

white

blue

sulfur

yellow

sulfate

Cobalt chloride paper will turn from .......................... to pink in the presence of water.

.............................. copper ........................ will turn from ........................... to blue in the presence of water. 

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1b
4 marks

Describe how a student could test to see if a sample of water is pure.

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1c
2 marks

Explain why tap water is not used for chemical reactions.

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2a
1 mark

This question is about the testing and purification of water.

Which of these statements describes the correct test for water? Tick one box.

Hydrated copper(II) sulfate stays white

Hydrated copper(II) sulfate turns pink

Cobalt chloride paper turns pink

Cobalt chloride paper turns white

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2b
1 mark

When water is added to anhydrous copper(II) sulfate heat is produced. What type of reaction is this?

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2c
2 marks

Untreated water contains soluble and insoluble impurities. 

Name the two processes that remove insoluble impurities during the treatment of water.

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2d
1 mark

Complete the following sentence using the words from the list

chlorine carbon sand 

In order to remove odours and tastes water is passed through ........................

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1a
3 marks

This question is about water.

Describe a chemical test which shows the presence of water.

Give the test and the colour change seen if water is present.

How did you do?

1b
1 mark

How could you show that a sample of water is pure?

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1c
2 marks

Describe how water is treated before it is supplied to homes and industry.

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2a
3 marks

The diagram below shows part of the Water Cycle.

A water cycle diagram. At the lower right a shaded horizontal band labelled sea carries the label H~2~O (l), with the Sun drawn above it and arrows from the Sun pointing down onto the sea. An upward arrow labelled H~2~O (g) rises from the sea, and a horizontal arrow then points left into a cloud labelled cloud H~2~O (l). Dashed lines labelled rain fall from the cloud onto a hill labelled land.

i) State the name of each of the following changes of state.

H2O (l) → H2O (g)

H2O (g) → H2O (l)

[2]

ii) Which one of the above changes of state is exothermic? Explain your choice.

[1]

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2b
2 marks

The rain drains into rivers and then into reservoirs. Describe how water is treated before it enters the water supply.

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2c
6 marks

i) Explain how acid rain is formed. 

[4]

 

ii) Fish live in water which is neutral (neither acidic nor alkaline). Acid rain decreases the pH of water in lakes and rivers. Both of the bases, calcium oxide and calcium carbonate, can neutralise this acid and increase the pH.

Explain why calcium carbonate is a better choice. 

[2]

How did you do?

1a
6 marks

A scientist finds an unlabelled bottle on a shelf.

She thinks the bottle contains a solution of ammonium sulfate, (NH4)2SO4.

Describe tests the scientist could do to show that the solution is ammonium sulfate.

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1b
2 marks

Ammonium sulfate is often used as a fertiliser.

It is prepared by reacting ammonia (NH3) with sulfuric acid (H2SO4). 

i) Name the type of reaction that occurs between ammonia and sulfuric acid. 

[1]

 ii) Write a chemical equation for the reaction of ammonia with sulfuric acid. 

[1]

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1c
3 marks

A common test for water is to use anhydrous copper(II) sulfate. If water is present an exothermic reaction takes place and the solid turns from white to blue and becomes hydrated copper(II) sulfate. This reaction is reversible.

6.25 g of blue hydrated copper(II) sulfate, CuSO4∙xH2O, was gently heated in a crucible until the mass remaining was 4.00 g. This is the white anhydrous copper(II) sulfate.

Use this information to calculate a value for x in CuSO4∙xH2O.

Ar: Cu = 64, S = 32, O = 16, H = 1

How did you do?

1d
3 marks

Cobalt(II) chloride paper is used to test for water as well. Hydrated cobalt chloride has the formula CoCl2∙6H2O. 

i) State the colour change when cobalt chloride paper is added to water. 

[1]

 ii) When hydrated cobalt chloride is heated, water is given off. Write the balanced symbol equation for this reaction.  

[2]

How did you do?