Acids and Bases

28 Grade 10 Chemistry questions on Acids and Bases, with worked marking schemes. 28 questions are available on this topic in full.

1. Question 1

   4 marks

   A maize farmer in Trans Nzoia has applied ammonium sulphate fertiliser to the same plot every season for many years. Explain the effect this has on the soil and suggest what the farmer should do about it.

   (4 marks)

   Marking scheme

   The soil becomes increasingly acidic / its pH falls (1). This is because the fertiliser leaves an acidic residue, releasing hydrogen ions into the soil (1). Strongly acidic soil locks up plant nutrients and harms soil organisms, so crop yields drop (1). The farmer should apply agricultural lime (calcium oxide, calcium hydroxide or calcium carbonate) to neutralise the acidity (1). Accept for the last mark: test the soil pH first and alternate with a non-acidifying fertiliser.

2. Question 2

   1 mark

   Zinc oxide dissolves in dilute hydrochloric acid and also dissolves in hot concentrated sodium hydroxide solution. Zinc oxide is therefore described as

   A. a basic oxide only.

   B. a neutral oxide.

   C. an amphoteric oxide.

   D. an acidic oxide.

   (1 mark)

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3. Question 3

   1 mark

   Dilute sulphuric acid is neutralised with potassium hydroxide solution. The products of the reaction are

   A. potassium sulphite and water.

   B. potassium sulphate and water.

   C. potassium sulphide and water.

   D. potassium sulphate and hydrogen gas.

   (1 mark)

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4. Question 4

   3 marks

   Write word equations for the reactions between: (a) dilute hydrochloric acid and sodium carbonate; (b) dilute nitric acid and copper(II) oxide; (c) dilute sulphuric acid and zinc.

   (3 marks)

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5. Question 5

   1 mark

   A person suffering from acid indigestion swallows a tablet containing magnesium hydroxide, which reacts with the hydrochloric acid in the stomach. The salt formed is

   A. magnesium nitrate.

   B. magnesium carbonate.

   C. magnesium chloride.

   D. magnesium sulphate.

   (1 mark)

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6. Question 6

   3 marks

   Describe how a learner would use universal indicator solution to find out whether a sample of soil from the school garden is acidic.

   (3 marks)

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7. Question 7

   1 mark

   Dilute hydrochloric acid is added to pieces of chalk in a test tube and the gas produced is bubbled through limewater. What observation is expected in the limewater?

   A. The limewater remains colourless and no change is seen.

   B. The limewater turns bright yellow.

   C. The limewater turns from colourless to blue.

   D. The limewater turns milky.

   (1 mark)

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8. Question 8

   3 marks

   Identify the salt formed in each of the following reactions: (a) dilute sulphuric acid and ammonia solution; (b) dilute nitric acid and calcium carbonate; (c) dilute hydrochloric acid and zinc oxide.

   (3 marks)

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9. Question 9

   1 mark

   During a practical lesson, learners shake wood ash from a kitchen jiko with distilled water and filter the mixture. The pH of the filtrate is most likely to be

   A. 4

   B. 11

   C. 1

   D. 7

   (1 mark)

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10. Question 10

    4 marks

    Dry hydrogen chloride gas has no effect on dry blue litmus paper, but moist blue litmus paper turns red in the same gas. Account for this observation.

    (4 marks)

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11. Question 11

    4 marks

    Describe how you would prepare a simple indicator from coloured flower petals and use it to test a sample of lemon juice.

    (4 marks)

    Marking scheme

    Crush or grind the coloured petals (for example hibiscus or bougainvillea) in a mortar with a small amount of water or ethanol (1). Filter or decant the mixture to obtain the coloured extract (1). Add a few drops of the extract to the lemon juice in a test tube and shake (1). Compare the colour produced with the colour the same extract gives in a known acid and in a known alkali, and record the conclusion (1).

12. Question 12

    3 marks

    Fresh milk has a pH of about 6.6, while the same milk after souring into mala has a pH of about 4.5. Explain what this change in pH shows.

    (3 marks)

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13. Question 13

    1 mark

    Which one of the following is a property of a dilute alkaline solution?

    A. It turns methyl orange indicator red.

    B. It feels soapy between the fingers and turns red litmus paper blue.

    C. It has a pH value of less than 7.

    D. It reacts with a metal carbonate to give off carbon dioxide gas.

    (1 mark)

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14. Question 14

    1 mark

    When dilute nitric acid is added slowly to dilute sodium hydroxide solution, the temperature of the mixture rises steadily. What does this show?

    A. The acid used must have been concentrated rather than dilute.

    B. The water formed is evaporating and warming the mixture.

    C. Neutralisation releases heat to the surroundings.

    D. The reaction is endothermic.

    (1 mark)

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15. Question 15

    6 marks

    Describe how you would prepare dry crystals of sodium chloride in the laboratory, starting with dilute hydrochloric acid and dilute sodium hydroxide solution.

    (6 marks)

    Marking scheme

    Measure a known volume of the sodium hydroxide solution into a clean conical flask or beaker and add two to three drops of a suitable indicator, for example methyl orange (1). Add the dilute hydrochloric acid from a measuring cylinder a little at a time, swirling, until the indicator just changes colour, and record the volume of acid used (1). Repeat the procedure using the same volumes of alkali and acid but without adding any indicator, so that the salt is not contaminated by the indicator (1). Pour the neutral mixture into an evaporating dish and heat it gently to evaporate about two thirds of the water, until a saturated solution is obtained (1). Remove the dish from the flame and allow the solution to cool slowly so that crystals form (1). Filter or decant off the remaining liquid and dry the crystals between filter papers (1).

16. Question 16

    1 mark

    Zinc granules are added to dilute hydrochloric acid and the gas given off is collected in a test tube. Which test confirms the identity of this gas?

    A. It turns limewater milky.

    B. It turns moist red litmus paper blue.

    C. It burns with a pop sound when a lighted splint is applied.

    D. It relights a glowing wooden splint.

    (1 mark)

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17. Question 17

    2 marks

    Other than in farming, state two everyday situations in a Kenyan home in which neutralisation is applied.

    (2 marks)

    Marking scheme

    Any two, 1 mark each: taking an antacid tablet (magnesium hydroxide or sodium hydrogencarbonate) to relieve indigestion; brushing teeth with toothpaste to neutralise acid produced by bacteria in the mouth; rubbing baking soda or wood ash on a bee or nettle sting; adding a little wood ash or baking soda to over-sour porridge or mala; treating acidic waste water before pouring it away.

18. Question 18

    1 mark

    A colourless solution conducts electricity and turns blue litmus paper red. Which statement best explains what an acid does when it dissolves in water?

    A. It produces hydroxide ions (OH-) in the solution.

    B. It forms a solution that feels soapy and slippery.

    C. It produces hydrogen ions (H+) in the solution.

    D. It gains electrons from the water molecules.

    (1 mark)

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19. Question 19

    4 marks

    Rain falling near an industrial area is found to have a pH of 4. Explain the effects this rain would have on iron roofing sheets and on a building made from limestone blocks.

    (4 marks)

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20. Question 20

    1 mark

    A few drops of methyl orange indicator are added to dilute sodium hydroxide solution. The colour observed is

    A. yellow.

    B. colourless.

    C. pink.

    D. red.

    (1 mark)

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21. Question 21

    4 marks

    Distinguish between a strong acid and a weak acid, and give one example of each.

    (4 marks)

    Marking scheme

    A strong acid ionises completely (or almost completely) in water, giving a high concentration of hydrogen ions (1). A weak acid ionises only partially in water, so only a small fraction of its molecules release hydrogen ions (1). Example of a strong acid: hydrochloric acid / nitric acid / sulphuric acid (1). Example of a weak acid: ethanoic acid / citric acid / carbonic acid (1).

22. Question 22

    1 mark

    Which statement about a concentrated solution of ethanoic acid is correct?

    A. It has no effect on litmus paper because ethanoic acid is weak.

    B. It is a strong acid because it is concentrated.

    C. It contains a large amount of acid in a given volume but is still only partially ionised.

    D. Its pH must be 7 because ethanoic acid comes from plant material.

    (1 mark)

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23. Question 23

    4 marks

    Distinguish between a base and an alkali. Name one base that is not an alkali and describe how you would show that it is a base.

    (4 marks)

    Marking scheme

    A base is a substance (usually a metal oxide or hydroxide) that neutralises an acid to give a salt and water only (1). An alkali is a base that is soluble in water and produces hydroxide ions in solution (1). Example of a base that is not an alkali: copper(II) oxide (accept iron(III) oxide, lead(II) oxide) (1). Warm the solid with dilute sulphuric acid; it dissolves to give a blue solution (a salt) and water, with no gas evolved, showing it has neutralised the acid (1).

24. Question 24

    1 mark

    An extract prepared from hibiscus petals turns red in lemon juice and green in a solution of washing soda. When a few drops of the extract are added to a solution of bar soap, the mixture turns green. This shows that the soap solution is

    A. alkaline.

    B. acidic.

    C. neutral.

    D. a strong acid that has been diluted.

    (1 mark)

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25. Question 25

    3 marks

    State three observations that would be made when a clean piece of magnesium ribbon is dropped into dilute sulphuric acid in a test tube.

    (3 marks)

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26. Question 26

    1 mark

    Four solutions W, X, Y and Z have pH values of 2, 5, 7 and 12 respectively. Which solution contains the highest concentration of hydrogen ions?

    A. Solution Z

    B. Solution X

    C. Solution Y

    D. Solution W

    (1 mark)

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27. Question 27

    1 mark

    A learner connects a bulb and electrodes to dilute hydrochloric acid and then to ethanoic acid of the same concentration. The bulb glows brightly in the hydrochloric acid but dimly in the ethanoic acid. Which is the correct explanation?

    A. Ethanoic acid contains no hydrogen ions at all.

    B. Ethanoic acid is only partially ionised, so fewer ions are present to carry the current.

    C. Ethanoic acid molecules are too large to move between the electrodes.

    D. The ethanoic acid is more dilute than the hydrochloric acid.

    (1 mark)

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28. Question 28

    5 marks

    A laboratory technician needs to dilute concentrated sulphuric acid. Outline the correct procedure and state the safety precautions to be observed.

    (5 marks)

    Marking scheme

    Add the concentrated acid slowly to the water, never water to the acid (1). This is because dilution is strongly exothermic, and pouring water onto the acid causes violent boiling and spitting of the hot acid (1). Stir the mixture continuously while adding the acid, and allow it to cool before use (1). Wear safety goggles, a laboratory coat and gloves, and work at the bench in a well ventilated room (1). If acid spills on the skin, wash immediately with plenty of running water and then apply dilute sodium hydrogencarbonate solution (1).

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