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

Acid, Base and Salt

44 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

Which of the following is an alkali?
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C
An alkali is a base that is soluble in water. KOH dissolves in water to give OH⁻ ions. The other three are bases that are insoluble in water.
For the teacher: Remembering, low difficulty, standard 6.1.1
Textbook p. 138
2

Question 2

Which acid is diprotic?
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B
Sulphuric acid produces two H⁺ ions per molecule, so it is diprotic. HNO₃, HCl and CH₃COOH each produce one H⁺ ion.
For the teacher: Remembering, low difficulty, standard 6.1.2
Textbook p. 137
3

Question 3

Dry blue litmus paper stays blue in solid oxalic acid, but turns red when water is added. Why?
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D
An acid shows acidic properties only in the presence of water, which lets its molecules ionise to H⁺ ions.
For the teacher: Understanding, medium difficulty, standard 6.1.3
Textbook p. 140
4

Question 4

What is the pH value of 0.001 mol dm⁻³ nitric acid, HNO₃?
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A
HNO₃ is monoprotic and strong, so [H⁺] = 0.001 = 10⁻³ mol dm⁻³. pH = −log 10⁻³ = 3.
For the teacher: Applying, low difficulty, standard 6.2.2
Textbook p. 144
5

Question 5

What is the pH value of 0.01 mol dm⁻³ sodium hydroxide solution, NaOH?
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C
[OH⁻] = 0.01, so pOH = 2. pH = 14 − 2 = 12.
For the teacher: Applying, medium difficulty, standard 6.2.2
Textbook p. 145
6

Question 6

0.1 mol dm⁻³ ethanoic acid has a higher pH than 0.1 mol dm⁻³ hydrochloric acid. What is the reason?
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B
Ethanoic acid is a weak acid. Only a small fraction of its molecules ionise, giving a lower [H⁺] and a higher pH.
For the teacher: Understanding, medium difficulty, standard 6.3.2
Textbook p. 150
7

Question 7

Which reaction produces a gas that turns limewater cloudy?
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A
Acid + metal carbonate gives salt + water + carbon dioxide, and CO₂ turns limewater cloudy. Zinc with acid gives hydrogen.
For the teacher: Understanding, low difficulty, standard 6.4.1
Textbook p. 155
8

Question 8

4.0 g of sodium hydroxide, NaOH, is dissolved in water to make 500 cm³ of solution. What is its molarity? [Relative atomic mass: H = 1, O = 16, Na = 23]
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D
n = 4.0 ÷ 40 = 0.10 mol. Molarity = 0.10 ÷ 0.500 dm³ = 0.20 mol dm⁻³.
For the teacher: Applying, medium difficulty, standard 6.5.2
Textbook p. 159
9

Question 9

What volume of 2.0 mol dm⁻³ hydrochloric acid is needed to prepare 250 cm³ of 0.40 mol dm⁻³ hydrochloric acid?
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C
M₁V₁ = M₂V₂: 2.0 × V₁ = 0.40 × 250, so V₁ = 50 cm³.
For the teacher: Applying, medium difficulty, standard 6.6.3
Textbook p. 166
10

Question 10

What volume of 0.10 mol dm⁻³ sulphuric acid, H₂SO₄, exactly neutralises 25 cm³ of 0.10 mol dm⁻³ sodium hydroxide solution, NaOH?
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A
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O. n(NaOH) = 0.0025 mol, so n(H₂SO₄) = 0.00125 mol. V = 0.00125 ÷ 0.10 × 1000 = 12.5 cm³.
For the teacher: Applying, medium difficulty, standard 6.7.3
Textbook p. 172
11

Question 11

Which salt does not dissolve in water?
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D
PbSO₄ is one of the insoluble sulphates (Pb, Ba, Ca). All nitrates, ammonium, sodium and potassium salts dissolve.
For the teacher: Understanding, low difficulty, standard 6.9.1
Textbook p. 179
12

Question 12

A salt solution gives a blue precipitate with sodium hydroxide solution that does not dissolve in excess. With ammonia solution it gives a blue precipitate that dissolves in excess to form a dark blue solution. Which cation is present?
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B
Cu²⁺ forms a blue precipitate of Cu(OH)₂, insoluble in excess NaOH but soluble in excess ammonia to give a dark blue solution.
For the teacher: Analysing, high difficulty, standard 6.11.1
Textbook p. 209

Section B: structured questions

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

Question 13

Table 1 shows the pH values of two acids of the same concentration, 0.1 mol dm⁻³.
AcidpH value
Hydrochloric acid, HCl1.0
Ethanoic acid, CH₃COOH2.9
[1 mark] (a)State the meaning of a strong acid.
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[1 mark] (b)Which acid is the weak acid?
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[2 marks] (c)Explain why the two acids have different pH values.
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[1 mark] (d)Write the equation for the ionisation of hydrochloric acid in water.
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For the teacher: Understanding, low difficulty, standard 6.3.2
Textbook p. 150
14

Question 14

Diagram 1 shows the apparatus used to titrate 1.0 mol dm⁻³ nitric acid, HNO₃, against 25.0 cm³ of potassium hydroxide solution, KOH, using phenolphthalein. Table 2 shows the burette readings.
TitrationRough123
Final reading (cm³)20.5020.6040.5020.20
Initial reading (cm³)0.000.5020.600.20
Titration set-up with a burette of nitric acid above a conical flask of potassium hydroxide solution and phenolphthalein on a white tile
Diagram 1
[1 mark] (a)State the colour change of the solution at the end point.
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[1 mark] (b)Calculate the average volume of nitric acid used. Ignore the rough titration.
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[1 mark] (c)Write the balanced chemical equation for the reaction.
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[3 marks] (d)Calculate the molarity of the potassium hydroxide solution.
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For the teacher: Applying, medium difficulty, standard 6.7.2
Textbook p. 171
15

Question 15

Diagram 2 shows the height of the precipitate formed when different volumes of 0.5 mol dm⁻³ potassium iodide solution, KI, are added to 5 cm³ of 0.5 mol dm⁻³ lead(II) nitrate solution, Pb(NO₃)₂.
Graph of precipitate height rising from 0 cm to 4.0 cm at 10 cm³ of KI, then staying constant at 4.0 cm
Diagram 2
[1 mark] (a)What is the volume of potassium iodide solution that reacts completely with 5 cm³ of lead(II) nitrate solution?
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[1 mark] (b)Calculate the number of moles of Pb²⁺ ions in 5 cm³ of the lead(II) nitrate solution.
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[1 mark] (c)Calculate the number of moles of I⁻ ions that react completely with the Pb²⁺ ions.
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[1 mark] (d)Write the ionic equation for the formation of the precipitate.
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[1 mark] (e)State the colour of the precipitate.
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For the teacher: Analysing, high difficulty, standard 6.9.4
Textbook p. 188
16

Question 16

Salt X is a green solid that is insoluble in water. When heated strongly, it turns black and releases a colourless gas that turns limewater cloudy.
[1 mark] (a)Name the gas released.
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[1 mark] (b)Name salt X.
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[1 mark] (c)Write the equation for the decomposition of X by heat.
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[2 marks] (d)State two observations when excess dilute hydrochloric acid is added to X.
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For the teacher: Analysing, medium difficulty, standard 6.10.2
Textbook p. 196
17

Question 17

A white salt Y dissolves in water to form a colourless solution. A white precipitate forms when sodium hydroxide solution is added, and it dissolves in excess. With ammonia solution, a white precipitate forms that does not dissolve in excess. When Y is heated, a brown gas is released.
[2 marks] (a)A student says that Y contains Zn²⁺. Do you agree? Give a reason.
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[2 marks] (b)Describe a test to confirm whether the cation is Pb²⁺ or Al³⁺.
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[1 mark] (c)State the anion in Y and explain your answer.
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For the teacher: Evaluating, high difficulty, standard 6.11.2
Textbook p. 212
18

Question 18

A student wants to prepare dry crystals of zinc sulphate, ZnSO₄, in the laboratory.
[1 mark] (a)Name two suitable chemicals for the preparation.
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[3 marks] (b)Describe how the student obtains dry zinc sulphate crystals from the two chemicals.
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[1 mark] (c)Why is zinc added in excess?
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[1 mark] (d)Write the chemical equation for the reaction.
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For the teacher: Creating, medium difficulty, standard 6.9.2
Textbook p. 183