Water & Water Pollution (Cambridge (CIE) IGCSE Chemistry)

Exam Questions

2 hours30 questions
1a4 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. 

1b4 marks

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

1c2 marks

Explain why tap water is not used for chemical reactions.

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2a2 marks

This question is about water:

State two industrial uses of water.

2b2 marks

State two uses of water in the home.

2c2 marks

Before water is used in industrial processes and in the home it must be purified. Give two substances which are found in natural water before purification.

2d1 mark

State the term that describes a rock that store water.

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3a1 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

 

 

 

Hydrate copper(II) sulfate turns pink

 

 

 

Cobalt chloride paper turns pink 

 

 

 

Cobalt chloride paper turns white 

 

3b1 mark

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

3c2 marks

Untreated water contains soluble and insoluble impurities. 

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

3d1 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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4a1 mark

Fertilisers are concentrated forms of plant nutrients

Which of the following ions do plants need for growth?

Tick one box.

Cu2+

 

 

 

PO43–

 

 

 

SO42-

 

 

 

OH– 

 

4b1 mark

Potassium nitrate is used as a fertiliser. The potassium ion has the formula K+ and the nitrate ion has the formula NO3

Give the formula for potassium nitrate.

4c1 mark

What property must fertilisers have in order for plants to take up the ions through their roots.

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5a1 mark

The flow chart shows stages in producing drinking water.

bold reservoir bold rightwards arrow bold sedimentation bold space bold tank bold rightwards arrow bold filtration bold space bold tank bold space bold rightwards arrow bold space bold antibacterial bold space bold treatment bold space bold tank bold rightwards arrow bold storage bold space bold tank bold rightwards arrow bold mains

At which stage is chlorine added to the water.

5b1 mark

Chlorine is a toxic substance. Suggest why it is safe to be added to drinking water.

5c1 mark

Suggest another use for which chlorinated water is required.

5d1 mark

Describe what happens in the sedimentation tank.

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1a3 marks

This question is about water.

Describe a chemical test which shows the presence of water.

test ..................................................

colour change if water is present  ..................................................

1b1 mark

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

1c2 marks

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

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2a4 marks

Water is needed for industry and in the home.

i) Rain water is collected in reservoirs. How is it treated before entering the water supply?

 [2]

 ii) State two uses of water in the home.

[2]

2b2 marks

In many regions, drinking water is obtained by the distillation of sea-water. Explain how distillation separates the water from sea-water.

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3a3 marks

The diagram below shows part of the Water Cycle.

screen-shot-2023-02-22-at-11-18-34

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

 H2O (l) → H2O (g)

 name ..................................................

 H2O (g) → H2O (l)

 name ..................................................

 [2]

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

 [1]

3b2 marks

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

3c6 marks

Separate: Chemistry Only

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]

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4a3 marks

Separate: Chemistry Only

Plants require three main elements for healthy growth which be provided by fertilisers.

Give the formulae of three ions used to make fertilisers which provide the three required elements.

4b1 mark

Calcium nitrate is used as a fertiliser to help prevent blossom end rot in tomatoes which causes browning of the bottom of the fruit. It provides both calcium and nitrogen.

Write the formula for calcium nitrate.

4c
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2 marks

Separate: Chemistry and Extended Only

Using your answer to part (b) calculate the percentage by mass of nitrogen in calcium nitrate.

(Ar: Ca = 40, N = 14, O = 16) 

4d2 marks

Separate: Chemistry Only 

Explain why salts from fertilisers end up in bodies in groundwater.

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5a2 marks

Waste water like this needs to be treated before being released into the environment. Waste water may require removal of organic matter and harmful chemicals. The three main steps are sedimentation, filtration and chlorination.

Explain what happens in sedimntation.

5b3 marks

Explain why chlorination is required.

5c
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3 marks

Table 5.1 shows some information about how the treated solid sludge was disposed of from one sewage treatment plant in 2000 and 2020.

Table 5.1

Mass of treated solid sludge in tonnes

Year

Used as fertiliser

Sent to landfill

Other

Total

2000

56

22

55

132

2020

152

2

39

193

Calculate the percentage of treated solid sludge that was sent to landfill in 2000.

Give your answer to 3 significant figures.

5d3 marks

The total mass of treated solid sludge increased from 2000 to 2020 and the proportions of how the sludge was disposed of changed.

Suggest one reason for the increase in the total mass of treated solid sludge and two reasons for the changes in the proportions of the disposal methods.

Use Table 5.1 to help you answer.

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1a3 marks

Fertilisers are used to promote plant growth.

Two fertilisers are ammonium phosphate, (NH4)3PO4, and calcium dihydrogenphosphate,Ca(H2PO4)2.

Describe a test to distinguish between these two fertilisers.

test ..................................................

result ..................................................

1b4 marks

Separate: Chemistry and Extended Only

Many fertilisers are manufactured from ammonia.

Describe how ammonia is made in the Haber process. Give the essential conditions and an equation for the process.

1c1 mark

Separate: Chemistry Only

State the essential plant nutrient not supplied by ammonium phosphate.

1d3 marks

Separate: Chemistry and Extended Only

The soluble compound, calcium dihydrogenphosphate is made by heating the insoluble mineral rock phosphate, Ca3(PO4)2, with sulfuric acid.  

i) Why would rock phosphate not be effective as a fertiliser?

 [1]

 ii) The phosphate ion, PO43–, from the rock phosphate is changed into the dihydrogenphosphate ion, H2PO4.

 PO43– + 2H2SO4→ H2PO4+ 2HSO4 

 What type of reagent is the phosphate ion? Give a reason for your choice.

 [2]

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2a4 marks

Separate: Chemistry Only

The Atacama desert in Chile has deposits of the salt sodium nitrate.

Very large amounts of this salt were exported to Europe for use as a fertiliser. After the introduction of the Haber process in 1913, this trade rapidly diminished.

 i) Explain why the introduction of the Haber process reduced the demand for sodium nitrate.

 [2]

 ii) Suggest why surface deposits of sodium nitrate only occur in areas with very low rainfall such as desert areas.

 [1]

 iii) The desert has smaller surface deposits of potassium nitrate. Suggest why potassium nitrate is a better fertiliser than the sodium salt.

 [1]

2b
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5 marks

Extended Only

The equation for the decomposition of copper(II) nitrate is given below.

2Cu(NO3)2 → 2CuO + 4NO2 + O2

Copper(II) nitrate forms a series of hydrates with the formula Cu(NO3)2.xH2O.

All these hydrates decompose to form copper(II) oxide.

1 mole of Cu(NO3)2.xH2O forms 1 mole of CuO.  

i) What is meant by 1 mole of a substance?

 [1]

ii) 7.26 g of a hydrate, Cu(NO3)2.xH2O, formed 2.4 g copper(II) oxide.

number of moles of CuO formed = ...................... number of moles of Cu(NO3)2.xH2O in 7.26 g = ...................... mass of 1 mole of Cu(NO3)2.xH2O = ...................... g mass of 1 mole of Cu(NO3)2 is 188 g the value of x in this hydrate = ......................

 [4]

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3a4 marks

Groundwater can contain fertilisers washed from fields. An example of a fertiliser that can be found is ammonium nitrate. 

i) Write a balanced equation, including state symbols, to show how ammonium nitrate can be made by a student via a neutralisation reaction. 

 [2]

 ii) Describe how the student could perform a chemical test for the presence of nitrate ions.

 [2]

3b
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3 marks

Separate: Chemistry and Extended Only

Drinking water extracted from rivers in agricultural areas often contain nitrates. The first legal standard for nitrate in drinking water was set in 1980. The current UK drinking water standard is 50 mg / dm3 to safeguard against cases of methaemoglobinaemia or blue baby syndrome. 

Calculate the maximum mass in grams of nitrate that would be safe in a 240 cm3 glass of water. Give your answer to two significant figures.

3c2 marks

Separate: Chemistry Only

An alternative fertiliser is ammonium phosphate.   

i) Give the formula for ammonium phosphate.

 [1]

 ii) Which ion that plants need is missing from this fertiliser?

 [1]

3d
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3 marks

Separate: Chemistry and Extended Only

Phosphates can be found in reservoirs from which drinking water is obtained. A maximum of 0.025 mg / dmof phosphate ions is allowed by water companies. 

A sample of reservoir water has a concentration of 0.00014 mol / dm3.

Calculate the percentage of the maximum mass allowed of phosphate ions in the sample of reservoir water.

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4a3 marks

Water from reservoirs is treated to make it suitable for drinking. Even though the water has been treated it is not pure. One method to purify water is de-ionisation.

Describe another method which will produce pure water.

4b2 marks

Separate: Chemistry Only

Explain why it is beneficial to drink water that is not deionized.

4c1 mark

Chlorine is added to drinking water in order to make it safe to drink. The chlorine kills miro-organisms that can cause illnesses such as cholera and typhoid.

Suggest a concern with adding chlorine to drinking water.

4d3 marks

Separate: Chemistry and Extended Only

When chlorine is added to water it undergoes a reaction which forms hydrogen chloride and chloric(I) acid. The chloric(I) acid is the compound that kills the bacteria. 

Cl2 + H2O → HCl + HClO

In this reaction chlorine is both oxidised and reduced. Explain why.

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5a6 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.

5b2 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]

5c
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3 marks

Separate: Chemistry and Extended Only

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) sulphate, CuSO4.xH2O was gently heated in a crucible until the mass remaining was 4.00 g. This is the white anhydrous copper(II) sulphate. 

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

Ar's Cu = 64, S = 32, O = 16, H = 1 

x = ..............

5d3 marks

Separate: Chemistry Only

Cobalt(II) chloride paper is used to test for water as well. Hydrated cobalt chloride has the formula CoCl26H2O.

 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]

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