GCSEScienceWJECScience (Double Award)ChemistryExam QuestionsChemical Substances, Reactions & Essential ResourcesWater

Water (WJEC GCSE Science (Double Award): Chemistry): Exam Questions

Exam code: 3430

2 hours19 questions

2 marks

Some areas of the UK have hard water.

The box contains some advantages of hard water and some advantages of soft water.

uses less soap reduces risk of heart disease does not fur up kettles
strengthens teeth and bones does not cause limescale

From the box, state two advantages of hard water.

.....................................................................................................................................................................
.....................................................................................................................................................................

How did you do?

1 mark

Circle the method that can be used to soften temporary hard water.

freezing

dissolving

boiling

filtering

How did you do?

1 mark

The table shows the concentrations of some common ions in water samples from three areas, X, Y and Z.

Area	Concentration of sodium ions (mg / dm³)	Concentration of calcium ions (mg / dm³)	Concentration of potassium ions (mg / dm³)
X	41	81	0.5
Y	35	68	1.2
Z	13	102	0.8

Give the letter of the area with the hardest water.

......................................................................................................

How did you do?

Was this exam question helpful?

1 mark

The table shows how the solubility of potassium nitrate in water varies with temperature.

Temperature (°C)	Solubility (g per 100 g of water)
0	13
10	21
20	32
30	46
40	64
50	86

Tick (✓) the box that shows approximately how many times more soluble potassium nitrate is at 40 °C than it is at 10 °C.

2 times	$□$
3 times	$□$
4 times	$□$
5 times	$□$

How did you do?

5 marks

(i) Plot the solubility of potassium nitrate against temperature on the grid.

Draw a suitable line.

Figure: Blank grid with x-axis "Temperature (°C)" from 0 to 60 in steps of 10, and y-axis "Solubility (g per 100 g of water)" from 0 to 100 in steps of 10, for the candidate to plot the six data points from the table and draw a smooth curve through them.

[3]

(ii) I. State the solubility of potassium nitrate at 45 °C.

....................................................... g per 100 g of water

[1]

II. Calculate the mass of solid potassium nitrate that forms when a saturated solution in 100 g of water at 45 °C cools to 25 °C.

Mass = ....................................................... g

[1]

How did you do?

Was this exam question helpful?

2 marks

Fluoride ions (mostly from sodium fluoride) are found naturally in the drinking water in some regions of England. The concentration of these fluoride ions is quite low with values being less than 0.5 mg / dm³.

However, water companies in some areas add fluoride ions to drinking water. Areas where this happens include Yorkshire, the North East, the East Midlands and the West Midlands. The mean concentration of fluoride ions added is around 1 mg / dm³.

It is known that a high concentration of fluoride ions in drinking water can be poisonous and can cause a yellowing of teeth – fluorosis. Fluoridation of drinking water is a controversial issue. Some people are opposed to it because it removes the individual's choice to not take fluoride.

The table shows the mean number of decayed, missing and filled teeth (DMFT) in five-year-old children in some areas of England in 2018.

Area	Mean DMFT
South East	0.6
West Midlands	0.7
North West	1.3
London	1.0
South West	0.7
Yorkshire	1.0
North East	1.0
East Midlands	0.9
East England	0.7

Which two of the following statements are correct according to the information given?

Tick (✓) two boxes.

London, Yorkshire and the North West all have a mean DMFT of 1.0	$□$
The South East has the lowest mean DMFT	$□$
The East Midlands has the highest mean DMFT	$□$
East England, the South West and the South East have a mean DMFT of 0.7	$□$
The East Midlands has a lower mean DMFT than Yorkshire	$□$
London, the North West and the South West all have a mean DMFT of 0.9	$□$

How did you do?

2 marks

(i) Which of the following statements supports the argument for fluoridation of drinking water? Tick (✓) one box.

All areas with fluoridated drinking water have lower mean DMFT than areas which do not fluoridate drinking water	$□$
All areas with fluoridated drinking water have the same mean DMFT as non-fluoridated areas	$□$
All areas with fluoridated drinking water have lower mean DMFT than the North West	$□$

[1]

(ii) Which of the following statements could be used to oppose the argument for fluoridation of drinking water? Tick (✓) one box.

It is not possible to decide whether fluoridation of drinking water lowers mean DMFT	$□$
All areas with fluoridated drinking water have higher mean DMFT than areas which do not fluoridate drinking water	$□$
All areas with fluoridated drinking water have a higher mean DMFT than the South West	$□$

[1]

How did you do?

1 mark

Suggest a possible reason why the South East has a low mean DMFT in five-year-old children even though no fluoride is added to drinking water in this area.

....................................................................................................................................

How did you do?

Was this exam question helpful?

13a

2 marks

A student investigates the solubility of ammonium chloride by adding different masses to 10 g of water.

He uses the apparatus shown.

Figure: Diagram of a boiling tube clamped upright, containing a solution with crystals of ammonium chloride visible at the bottom, with a thermometer inserted into the solution to measure its temperature.

10 g of water is placed in a boiling tube and 3.0 g of ammonium chloride is added.

The tube is heated until all the solid dissolves.

The tube is allowed to cool.

The temperature at which solid ammonium chloride first appears is recorded.

The experiment is repeated using different masses of ammonium chloride.

The results are shown in the table.

Mass of ammonium chloride in 10 g of water (g)	3.0	3.3	4.1	5.2	5.9	6.6
Temperature at which solid ammonium chloride first appears (°C)	4	10	30	52	68	80

What practical problem is the student likely to come across in finding the first two results? Suggest how this problem might be overcome.

...................................................................................................................................................................

How did you do?

13b

4 marks

(i) On the grid below, plot the temperature at which solid ammonium chloride first appears against the mass of ammonium chloride in 10 g of water. Draw a suitable line.

Figure: Blank grid with x-axis "Mass of ammonium chloride in 10 g of water (g)" from 0.0 to 8.0, and y-axis "Temperature at which solid ammonium chloride first appears (°C)" from 0 to 80, for the student to plot the 6 data points from the table in part (a) and draw a suitable curve/line of best fit through them.

[3]

(ii) The student is given a boiling tube containing 5.0 g of ammonium chloride in 10 g of water. He stirs the ammonium chloride in the water and heats it to a temperature of 45°C.

State whether all the ammonium chloride dissolves. Give a reason for your answer.

...................................................................................................................................................................

[1]

How did you do?

13c

3 marks

The student is asked to use a different method to find the exact solubility of another compound in water at room temperature. He knows that it has a value of approximately 7 g per 100 g of water at this temperature.

He is given a 5.0 g sample of the compound and common laboratory equipment but no heating apparatus.

Describe how he would carry out his method and how he would find the solubility.

...................................................................................................................................................................

How did you do?

Was this exam question helpful?

18a

4 marks

Most of the tap water in Wales comes from mountain reservoirs. The water from these reservoirs is never pure.

(i) Information about some of the stages used in the treatment of tap water is shown.

Draw a line to connect each stage to the correct description. One has already been completed.

Matching exercise with four stage and description boxes; only screening is connected to “screens are used to remove objects such as leaves, sticks and litter”, while the other three remain unconnected.

(ii) The pie chart shows some of the main uses of water in a typical Welsh home.

Figure: Pie chart showing main uses of water in a typical Welsh home: flushing the toilet 30%, bathing 21%, gardening 17%, showering 12%, washing up 7%, and washing clothes (unlabelled segment, to be calculated).

Use the pie chart to answer parts I and II.

I. Calculate the percentage of water used for washing clothes.

............................................................... %

[1]

II. Give the name of the use that accounts for three times as much water as another use.

...............................................................

[1]

How did you do?

18b

6 marks

5 cm³ of three water samples, labelled A, B and C, were mixed with 10 drops of soap solution and shaken. One of the samples was distilled water. The boiling point of each water sample was also measured. The results obtained are shown.

Figure: Three test tubes labelled A, B and C, each showing a different height of froth/lather formed above the water after shaking with soap solution — A shows the least froth, B shows the most froth, C shows an intermediate amount.

Water sample	Boiling point (°C)
A	102
B	100
C	101

(i) Place the water samples, A, B and C, in order of hardness.

hardest ....................................

....................................

softest ....................................

[1]

(ii) Give the letter of the sample that is distilled water. Give two reasons for your choice.

Sample ....................................

Reasons

............................................................................................
.............................................................................................

[2]

(iii) The volume of each water sample and soap solution was kept the same for each test. State which other variable must also be controlled before measuring the froth height. Describe how you would control this.

[2]

(iv) Hardness in water can be caused by dissolved calcium fluoride. Give the chemical formula for calcium fluoride.

.........................................................................

[1]

How did you do?

Was this exam question helpful?

19a

1 mark

The following information is about hardness in water.

Hardness in water is caused by the presence of dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions come from compounds that are dissolved by the water as it passes through rocks. Because they are dissolved, these ions are not removed during the water treatment processes.

Hardness in water can be identified using soap solution. The relative hardness in different water samples can be determined by measuring the volume of soap solution required to produce a given lather.

Temporary hardness in water can be removed simply by boiling. Permanent hardness can be removed by passing the sample through an ion exchange column.

Three samples of water, A, B and C, were tested for hardness using soap solution. Distilled water was also tested.

Illustration of three water sample containers labelled A, B and C. Text states soap solution volumes before and after boiling: A 8 and 8 cm³, B 12 and 6 cm³, and C 15 and 2 cm³.

Distilled water required 2cm3 of soap solution to form lather both before and after boiling.

Which one of these statements best describes the water samples before boiling?

Tick ( $✓$ ) the correct answer.

samples A, B and C contain magnesium or calcium ions	$□$
only samples A and B contain magnesium or calcium ions	$□$
only samples B and C contain magnesium or calcium ions	$□$
none of the samples contain magnesium or calcium ions	$□$

How did you do?

19b

1 mark

What is the purpose of testing the distilled water? Tick ( $✓$ ) the correct answer.

to show the expected result for permanent hard water	$□$
to show the expected result for temporary hard water	$□$
to act as a control for the experiment	$□$
to make sure the investigation is a fair test	$□$

How did you do?

19c

1 mark

In carrying out the tests on the samples, which variables need to be kept the same each time? Tick ( $✓$ ) the correct answer.

volume of soap solution and number of times shaken	$□$
volume of water sample and volume of soap solution used	$□$
volume of water sample and number of times shaken	$□$
volume of water sample, volume of soap solution and number of times shaken	$□$

How did you do?

19d

3 marks

Which one of these statements best describes water sample B? Tick ( $✓$ ) the correct answer and explain your choice.

sample B contains temporary hardness only	$□$
sample B contains permanent hardness only	$□$
sample B contains a mixture of temporary and permanent hardness	$□$
sample B does not contain hardness	$□$

Explanation .................................................................................................................................................................................

How did you do?

19e

2 marks

In your opinion, do the advantages of living in a hard water area outweigh the disadvantages? Give two reasons to support your answer.

How did you do?

Was this exam question helpful?

Temperature (°C)	Solubility (g / 100 cm³ of water)
0	91
20	98
40	106
60	116
80	128
100	132

Concentration of fluoride (mg / dm³)	Mean DMFT	Percentage of people affected by fluorosis (%)
0.3	7.0	4
0.6	4.5	6
0.9	3.0	15
1.2	2.5	35
1.5	2.3	40
1.8	2.0	45
2.1	2.1	60
2.4	2.1	68
2.7	2.1	75

Location	potassium K⁺	ammonium NH₄⁺	calcium Ca²⁺	fluoride F^-	sulfate SO₄^2-	nitrate NO₃^-
A	0.1	0.4	0.0	0.0	0.4	0.2
B	0.0	0.3	0.4	4.4	0.2	0.0
C	0.2	0.6	2.7	0.4	0.0	0.1
D	3.4	2.1	1.0	2.1	2.5	2.3

Ions present	Ion content in water sample (mg/dm³)
Ions present	X	Y	Z
sodium	29	116	23
potassium	12	15	11
magnesium	31	4	98
calcium	141	2	27
hydrogencarbonate	30	19	219
chloride	17	14	20
sulfate	346	6	27
nitrate	12	15	19

Water sample	Volume of soap solution needed to give a lather (cm³)
Water sample	Peter	Claire	David	Mean
A	18	19	17	.........................
B	8	10	9	9
C	1	1	1	1