C3.2 WATER PAST GCSE QUESTIONS – TRY AND SELF ASSESS
Q1.
This information has been taken from two bottles of Australian spring water.
(a)
The labels show the names of the ions present in Ridgway and Homeland spring
waters.
Describe how these ions got into the water.
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(2)
(b)
Both Ridgway and Homeland spring waters are hard.
(i)
There are two ions shown on the labels which make these spring waters hard.
Name one of these ions.
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(1)
(ii)
Ridgway spring water is about twice as hard as Homeland spring water.
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Use the information on the labels to explain why.
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(2)
(iii)
Describe how you could use soap solution to show that Ridgway spring water
is about twice as hard as Homeland spring water. You should state how the
experiment is made fair.
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(3)
(Total 8 marks)
Q2.
The label shows the ions present in the bottle of spring water. This water is
temporarily hard.
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(a)
Name the compound that would be present in the greatest amount if this water
were evaporated to dryness.
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(2)
(b)
(i)
What is hard water?
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(2)
(ii)
State one advantage of hard water.
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(1)
(c)
Describe an experiment that would show that this water is temporarily hard.
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(4)
(d)
This hard water may be softened as shown.
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What name is given to this process?
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(1)
(Total 10 marks)
Q3.
Water is a natural resource. Drinking water in some parts of the UK is soft, but in
other parts drinking water is hard. Calcium ions in water cause water to be hard.
There are two types of hard water, permanent hard water and temporary hard water.
•
Permanent hard water can be caused by calcium sulfate (CaSO4) dissolved in the
water
•
Temporary hard water can be caused by calcium hydrogencarbonate (Ca(HCO3)2)
dissolved in the water
(a)
Temporary hard water causes the formation of scale on heating elements.
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Photograph © Steve Gorton / Getty Images
(i)
Explain how scale forms on heating elements.
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(2)
(ii)
Suggest why scale on heating elements causes problems.
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(1)
(b)
Permanent hard water can be softened.
(i)
Explain how adding sodium carbonate (Na2CO3) softens permanent hard
water.
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(2)
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(ii)
Explain how a water filter containing carbon, silver and ion exchange resin
softens permanent hard water.
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(2)
(Total 7 marks)
Q4.
Good quality water is needed for a healthy life.
In the United Kingdom, obtaining safe water for drinking is as simple as turning on a tap.
The water is made safe to drink by water companies.
However, in many parts of Africa and Asia, water used for drinking is contaminated and
untreated. It is estimated that 2.2 million people die each year as a result of drinking
contaminated water.
DADA DANESHANANDA, Man with filtered water from the
Mafi-Zongo water project. www.amurt.net/africa/ghana/2005
(a)
Sea water is not used as drinking water.
Suggest why.
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(1)
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(b)
Explain why water for drinking is filtered and then treated with chlorine.
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(2)
(Total 3 marks)
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M1.
(a)
water came into contact with rocks / ground / soil
ignore mountains
erode gets first mark
1
ions or compounds or chemicals or they dissolved / soluble / leached / reacts /
forms a solution
do not accept gets picked up
accept water dissolves them from the rocks for 2 marks
1
(b)
(i)
calcium or magnesium
accept Ca2+ or Mg2+ or Ca or Mg
do not accept Ca+ alone
1
(ii)
answers must involve both calcium and magnesium
totals required for 2 marks
Ridgway: Ca + Mg = 53
1
Homeland: Ca + Mg = 27
accept there is (almost) twice as much
Magnesium and Calcium in Ridgway water for 1 mark
1
(iii)
equal volumes / quantities / amounts of water
1
add soap with / shaking / mixing / agitation
same amounts of soap = max 2
do not accept just add
do not accept solid soap
1
the harder sample (Ridgway) needs 2 × more soap to give lather
or the less hard sample (Homeland) needs half as much
soap to give lather can get twice as much scum with harder
(Ridgway) sample
1
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[8]
M2.
(a)
calcium
allow formulae
1
carbonate
1
(b)
(i)
soap
allow 2 marks for
“contains CaSO4 / Ca(HCO3)2 / Ca2+ / Mg2+”
1
forms scum / no bubbles / no lather
allow 1 mark for “contains Ca / Mg”
do not allow “contains CaCO3”
1
(ii)
taste / strengthen bones, teeth etc / health reason e.g. less heart
disease / makes better beer
1
(c)
(shake with) soap; makes scum / no lather
1
boil (a fresh sample)
1
retest with soap
1
result/comparison
alternative answers:
boil (not to dryness)
cloudiness in water/some deposit formed
if a comparison is made with a sample of a soft water, a
further 2 marks would be possible
1
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(d)
ion-exchange
1
[10]
M3.
(a)
(i)
on heating, the calcium hydrogencarbonate decomposes
1
forming a scale of insoluble calcium carbonate
1
(ii)
the scale reduces the efficiency of the heating element
or the scale increases energy costs / uses more energy
1
(b)
(i)
the sodium carbonate / carbonate ions react with calcium /
magnesium ions, forming a precipitate of calcium
carbonate / magnesium carbonate
1
therefore the water is softened because this removes the
calcium / magnesium ions, which cause hardness, from
the water
1
(ii)
sodium / hydrogen ions are present in the ion exchange resin
1
therefore the water is softened because these ions take
the place of calcium / magnesium ions that cause
hardness in the water
1
[7]
M4.
(a)
contains (large amounts of) dissolved solids / difficult to remove dissolved
solids
allow salty / too much salt
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allow sea water makes you thirsty / vomit
allow polluted / untreated / contaminated
1
(b)
filtered: removes solids / removes insoluble material / dirt
ignore large objects
1
chlorine: kills/destroy bacteria/microbes/ germs etc
allow disinfect / sterilise or gets rid of bacteria
ignore purify / clean
1
[3]
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