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Science questions, chapter 6
Nama / NameKelas / ClassTarikh / Date

Acids and alkalis

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

Section A: objective questions

14 marks
Choose the best answer for each question.
1

Question 1

Which pair of properties describes an alkali?
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B
An alkali has a pH value more than 7 and turns red litmus paper blue. It does not react with metals (textbook Table 6.2, p. 128).
For the teacher: Remembering, low difficulty, standard 6.1.1
Textbook p. 128
2

Question 2

A magnesium ribbon is placed in dilute hydrochloric acid. A lighted splinter is put at the mouth of the test tube. What is the observation?
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C
An acid reacts with a metal to produce hydrogen gas. Hydrogen burns with a 'pop' sound when a lighted splinter is put near it.
For the teacher: Understanding, low difficulty, standard 6.1.1
Textbook p. 127
3

Question 3

Which of these is an alkaline substance?
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C
Soap is alkaline. Vinegar, lemon juice and apples are acidic (textbook p. 128 to 129).
For the teacher: Remembering, low difficulty, standard 6.1.2
Textbook p. 128
4

Question 4

What is the colour of phenolphthalein in an alkaline solution?
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D
Phenolphthalein is colourless in acid and neutral solutions but pink in an alkali (Table 6.3).
For the teacher: Remembering, low difficulty, standard 6.1.2
Textbook p. 129
5

Question 5

Dry glacial ethanoic acid is tested with blue litmus paper and there is no change in colour. Which statement explains this?
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B
Acids and alkalis show their properties only when water is present. In water, ethanoic acid turns blue litmus paper red (Figure 6.4).
For the teacher: Understanding, medium difficulty, standard 6.1.1
Textbook p. 128
6

Question 6

Solution X is tested with indicators. It turns red litmus paper blue and methyl orange yellow. What colour is X with universal indicator?
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D
Red litmus turning blue shows X is an alkali. Universal indicator is blue in an alkali (green is neutral and red is acidic).
For the teacher: Applying, medium difficulty, standard 6.1.2
Textbook p. 129
7

Question 7

A student wants to know how strong an acid is. Which is the best indicator?
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D
Universal indicator (or pH paper / pH meter) gives a pH value, so it shows the strength. Litmus paper, methyl orange and phenolphthalein only show whether the solution is acidic or alkaline.
For the teacher: Understanding, medium difficulty, standard 6.1.3
Textbook p. 130
8

Question 8

Diagram 1 shows the pH values of solutions P, Q, R, S and T. Which solution is a weak alkali?
pH scale 0 to 14 with P at pH 1, Q at 5, R at 7, S at 9 and T at 13
Diagram 1
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C
S has pH 9: above 7 but close to it, so it is a weak alkali. T (pH 13) is a strong alkali, Q (pH 5) a weak acid and P (pH 1) a strong acid.
For the teacher: Applying, medium difficulty, standard 6.1.3
Textbook p. 130
9

Question 9

Which arrangement shows decreasing pH value?
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A
Soap water is alkaline (pH above 7), mineral water is neutral (about 7), orange juice is a weak acid and hydrochloric acid is a strong acid with the lowest pH. So the pH decreases in that order.
For the teacher: Applying, medium difficulty, standard 6.1.3
Textbook p. 132
10

Question 10

Which substance is used to make antacid pills?
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B
Antacid pills contain an alkali, magnesium hydroxide, to neutralise excess acid in the stomach (Photograph 6.3).
For the teacher: Remembering, low difficulty, standard 6.1.4
Textbook p. 132
11

Question 11

What is produced when an acid reacts with an alkali?
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A
Acid + alkali gives salt + water. This reaction is neutralisation.
For the teacher: Remembering, low difficulty, standard 6.2.1
Textbook p. 133
12

Question 12

Nitric acid reacts with sodium hydroxide solution. What is the salt formed?
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C
Nitric acid gives a nitrate and sodium hydroxide gives a sodium salt, so the salt is sodium nitrate (textbook p. 133).
For the teacher: Applying, medium difficulty, standard 6.2.1
Textbook p. 133
13

Question 13

A farmer's soil is too acidic for his crops. Which substance should he add?
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B
Slaked lime is alkaline. It neutralises the acid in the soil so that plants grow well.
For the teacher: Applying, medium difficulty, standard 6.2.2
Textbook p. 135
14

Question 14

In a titration, 25 mL of sodium hydroxide solution with phenolphthalein is in a conical flask and hydrochloric acid is added from a burette. At which point should the student stop adding acid?
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A
The solution starts pink in the alkali. The end point is when it just becomes colourless: all the alkali has been neutralised (Activity 6.5).
For the teacher: Applying, medium difficulty, standard 6.2.1
Textbook p. 133

Section B: structured questions

30 marks
Answer all questions.
15

Question 15

Table 1 shows the results of tests on solutions J and K.
TestSolution JSolution K
Blue litmus paperTurns redNo change
Red litmus paperNo changeTurns blue
Magnesium ribbonBubbles of gasNo change
[1 mark] (a)Which solution is an acid?
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J
J turns blue litmus paper red and reacts with magnesium.
[1 mark] (b)Name the gas produced when solution J reacts with magnesium ribbon.
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Tick each point you got.
[2 marks] (c)Describe how the gas in (b) is tested.
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[1 mark] (d)State the pH range of solution K.
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For the teacher: Understanding, low difficulty, standard 6.1.1
Textbook p. 128
16

Question 16

Table 2 shows the pH values of four solutions of the same concentration.
SolutionpH value
Hydrochloric acid1
Ethanoic acid3
Ammonia solution11
Sodium hydroxide solution13
[1 mark] (a)Which solution is the strongest acid?
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Tick each point you got.
[1 mark] (b)Which solution is a weak alkali?
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[1 mark] (c)State the relationship between the pH value and the strength of an alkali.
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[1 mark] (d)Why must all four solutions have the same concentration in this comparison?
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Any 1 points
Tick each point you got.
[1 mark] (e)Salt solution is tested with pH paper. Predict its pH value.
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For the teacher: Applying, medium difficulty, standard 6.1.3
Textbook p. 130
17

Question 17

Grace adds two drops of phenolphthalein to a colourless solution M. The solution stays colourless.
[1 mark] (a)Is solution M an alkali? Explain.
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[2 marks] (b)Can Grace conclude that M is an acid? Explain.
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[1 mark] (c)Suggest one other test to find out whether M is acidic, neutral or alkaline.
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Any 1 points
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For the teacher: Analysing, medium difficulty, standard 6.1.2
Textbook p. 129
18

Question 18

A student carries out a titration. Using a pipette, 25 mL of 0.5 M sodium hydroxide solution is put in a conical flask with three drops of phenolphthalein. 0.5 M hydrochloric acid is added from a burette. The initial burette reading is 2.40 mL and the final reading is 27.80 mL.
[1 mark] (a)Calculate the volume of hydrochloric acid used.
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25.40 mL
Tick each point you got.
[1 mark] (b)What colour change is seen in the conical flask at the end point?
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[2 marks] (c)Write the word equation for the reaction.
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[1 mark] (d)Name this type of reaction.
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For the teacher: Understanding, medium difficulty, standard 6.2.1
Textbook p. 133
19

Question 19

Amran was stung by a jellyfish while swimming. The stung area became red and swollen. The pain became worse when his friend applied soap and toothpaste to it.
[2 marks] (a)Explain why the pain became worse after applying soap and toothpaste.
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[1 mark] (b)Suggest one way to reduce the pain.
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For the teacher: Evaluating, high difficulty, standard 6.2.2
Textbook p. 138
20

Question 20

A farmer's land is not fertile. His son tested a soil sample. When baking soda and water were added to the soil, gas bubbles were seen. When vinegar was added to the soil, no gas bubbles were seen.
[1 mark] (a)What can be concluded about the soil?
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[1 mark] (b)Relate your answer in (a) to the infertility of the soil.
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[2 marks] (c)Suggest and explain one way to solve the farmer's problem.
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For the teacher: Evaluating, high difficulty, standard 6.2.2
Textbook p. 135
21

Question 21

A shop wants to sell a 2 in 1 hair care product. The shampoo is slightly alkaline and the hair conditioner is slightly acidic.
[2 marks] (a)Explain why a slightly acidic hair conditioner is used after shampoo.
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[1 mark] (b)Name the chemical process that occurs in (a).
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Neutralisation
An acid reacts with an alkali and each loses its properties.
[1 mark] (c)Suggest why the alkaline shampoo and the acidic conditioner would not work well if they were mixed in one bottle.
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For the teacher: Creating, high difficulty, standard 6.2.2
Textbook p. 134