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Science questions, chapter 5
Nama / NameKelas / ClassTarikh / Date

Water and solution

41 marks. Use Practice to check each answer as you go, or Exam to answer everything against the clock first.

Section A: objective questions

12 marks
Choose the best answer for each question.
1

Question 1

A daddy longlegs can stand on the surface of a pond without sinking. Which property of water makes this possible?
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B
Cohesive force between the water molecules at the surface gives water a high surface tension, which supports light insects. Capillary action is the movement of water up narrow tubes such as xylem.
For the teacher: Remembering, low difficulty, standard 5.1
Textbook p. 96
2

Question 2

Which of the following describes the gases formed when water is electrolysed?
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A
Hydrogen is produced at the cathode and oxygen at the anode. A water molecule has two hydrogen atoms for one oxygen atom, so the volume of hydrogen is twice the volume of oxygen.
For the teacher: Understanding, low difficulty, standard 5.1
Textbook p. 98
3

Question 3

Table salt is added to distilled water and to ice. Which statement is correct?
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D
Impurities raise the boiling point of water (above 100 °C) and lower the melting point of ice (below 0 °C).
For the teacher: Understanding, low difficulty, standard 5.1
Textbook p. 100
4

Question 4

Three identical wet filter papers are hung up to dry. Paper P is left open, Q is folded in two and R is folded in four. Diagram 1 shows the time each takes to dry. What can be concluded from the results?
Bar chart: filter paper P dries in 12 minutes, Q in 20 minutes and R in 34 minutes
Diagram 1
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C
P has the largest exposed area and dries in the shortest time (12 minutes). R, folded in four, has the smallest area and takes the longest (34 minutes). Humidity and air movement were not changed.
For the teacher: Applying, medium difficulty, standard 5.1
Textbook p. 103
5

Question 5

Why does a towel take longer to dry in a humid room than in a dry room?
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A
The higher the humidity, the lower the rate of evaporation, because air that is already full of water vapour cannot hold many more escaping molecules.
For the teacher: Understanding, low difficulty, standard 5.1
Textbook p. 104
6

Question 6

Nail varnish does not dissolve in water. Which substance can be used to remove it?
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C
Acetone is an organic solvent. Organic solvents dissolve solutes that are insoluble in water, such as nail varnish.
For the teacher: Applying, low difficulty, standard 5.2
Textbook p. 112
7

Question 7

Diagram 2 shows three beakers, each with 50 mL of water, to which copper(II) sulphate crystals were added and stirred. Which statements are correct?
I. P is a dilute solution.
II. Q is more concentrated than P.
III. R is a saturated solution.
Beaker P with 4 dissolved particles, beaker Q with 12 dissolved particles, beaker R with 12 dissolved particles and a heap of undissolved crystals at the bottom
Diagram 2
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D
P holds little solute (dilute). Q holds much more solute, so it is more concentrated. R has excess solute that will not dissolve and settles at the bottom, so it is saturated.
For the teacher: Analysing, medium difficulty, standard 5.2
Textbook p. 106
8

Question 8

Which mixture is a suspension?
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B
Chalk is insoluble in water. The mixture is cloudy, light cannot pass through it, it settles on standing and leaves a residue on filtering. The other three dissolve to form clear solutions.
For the teacher: Understanding, low difficulty, standard 5.2
Textbook p. 108
9

Question 9

Fine sugar dissolves faster in water than a sugar cube of the same mass. What is the reason?
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C
The smaller the size of the solute, the larger the total surface area that is exposed to the solvent particles, so it dissolves faster.
For the teacher: Applying, medium difficulty, standard 5.2
Textbook p. 111
10

Question 10

Which of the following is a colloid?
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D
Milk is a colloid (an emulsion): the particles are spread evenly and do not settle or form a clear solution. Vinegar and salt water are solutions; muddy water is a suspension.
For the teacher: Applying, low difficulty, standard 5.2
Textbook p. 112
11

Question 11

A hiker has only cloudy stream water, a clean cloth and a pot with a fire. Which method is best to make the water safe to drink?
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B
Filtering removes suspended particles and boiling kills microorganisms. Boiling first and filtering after would let the water pick up new microorganisms from the cloth.
For the teacher: Evaluating, high difficulty, standard 5.3
Textbook p. 114
12

Question 12

Which shows the correct order of stages in a water treatment plant?
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A
Large objects are screened out first, oxygen is added, alum and slaked lime cause coagulation, particles settle (sedimentation), sand filters remove what is left, and chlorine and fluoride are added last.
For the teacher: Understanding, low difficulty, standard 5.3
Textbook p. 117

Section B: structured questions

29 marks
Answer all questions. Write your answers in the spaces provided.
13

Question 13

Name the process in each change of state of water.
[1 mark] (a)Ice cubes in a glass change into water.
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Melting
[1 mark] (b)Water vapour in the air changes into droplets on the outside of a cold glass.
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Condensation
[1 mark] (c)Is heat absorbed or released by the water vapour in (b)?
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Released
Condensation is a change that releases heat (blue arrow in the textbook figure).
For the teacher: Remembering, low difficulty, standard 5.1
Textbook p. 97
14

Question 14

Diagram 3 shows the apparatus used to find the composition of water. After 10 minutes, the gas in cylinder K relights a glowing splinter. The gas in cylinder L burns when tested with a burning splinter, and its volume is 20 mL.
Two measuring cylinders K and L over carbon electrodes in a beaker of distilled water and dilute hydrochloric acid with a switch and battery
Diagram 3
[1 mark] (a)Name the gas in cylinder K.
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Tick each point you got.
[1 mark] (b)Name the gas in cylinder L.
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[1 mark] (c)What is the volume of the gas in cylinder K?
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Hydrogen : oxygen = 2 : 1, so oxygen = 20 ÷ 2 = 10 mL.
Tick each point you got.
[1 mark] (d)Why is dilute hydrochloric acid added to the distilled water?
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[1 mark] (e)State the number of hydrogen atoms and oxygen atoms in one water molecule.
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For the teacher: Understanding, low difficulty, standard 5.1
Textbook p. 98
15

Question 15

Two beakers wrapped in towels each contain the same number of ice cubes. One spatula of table salt is added to beaker P only. The temperature of the ice is recorded every 2 minutes.
Time (min)246
Temperature in P, with salt (°C)−3−6−8
Temperature in Q, no salt (°C)000
[1 mark] (a)What is the melting point of the ice in beaker Q?
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[1 mark] (b)State the effect of salt on the melting point of ice.
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[2 marks] (c)Using the kinetic theory of matter, explain how the ice in beaker Q changes into water.
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For the teacher: Analysing, medium difficulty, standard 5.1
Textbook p. 99
16

Question 16

Two microscope slides each carry a piece of cobalt chloride paper with a few drops of water on it. Slide M is placed under a moving fan and slide N is placed away from the fan. After 15 minutes the papers are observed.
[1 mark] (a)What colour is cobalt chloride paper when it is wet?
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[1 mark] (b)State the manipulated variable.
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[1 mark] (c)State the responding variable.
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[2 marks] (d)Which paper turns blue first? Explain your answer.
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For the teacher: Applying, medium difficulty, standard 5.1
Textbook p. 103
17

Question 17

A student pours copper(II) sulphate crystals into 100 mL of water in beaker X, and chalk powder into 100 mL of water in beaker Y. Both are stirred and then observed.
BeakerAppearanceLight from a torchAfter filtering
XClear bluePasses throughNo residue
YCloudy whiteDoes not pass throughWhite residue
[1 mark] (a)Which beaker contains a suspension?
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Y
[2 marks] (b)Name the solute and the solvent in beaker X.
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[1 mark] (c)Why does light not pass through the mixture in beaker Y?
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For the teacher: Understanding, low difficulty, standard 5.2
Textbook p. 108
18

Question 18

Diagram 4 shows the stages in the water supply system of a town.
Flow diagram of a water treatment plant from reservoir through filtration, oxidation, coagulation, sedimentation, filtration and chlorination and fluoridation to homes
Diagram 4
[1 mark] (a)What is added in the coagulation tank to make mud particles stick together?
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[1 mark] (b)State the function of the oxidation stage.
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[1 mark] (c)Why is a fluoride compound added to the water?
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[1 mark] (d)State the function of chlorine.
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For the teacher: Understanding, low difficulty, standard 5.3
Textbook p. 117
19

Question 19

A factory beside a river discharges untreated waste water into it. Fish in the river are dying, and villagers downstream who boil river water for drinking still fall ill.
[1 mark] (a)Name the type of water pollutant from the factory.
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[1 mark] (b)Explain why boiling does not make the river water safe to drink.
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[2 marks] (c)Suggest two actions that can be taken to stop this pollution.
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For the teacher: Creating, high difficulty, standard 5.3
Textbook p. 118