Chapter 4 Practice Paper: Chemical Calculations — question paper (print)

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Secondary 3 · Combined Science (Chemistry) (G2 / G3)

Chapter 4 Practice Paper

Chemical Calculations

Duration: 40 minutes

Total: 30 marks

Name:

Class:

Date:

READ THESE INSTRUCTIONS FIRST

Answer all questions.
Section A: choose the one correct answer for each multiple-choice question.
Section B: answer in the spaces provided; show all necessary working.
Give numerical answers to 3 significant figures where appropriate, with units.
A copy of the Periodic Table is printed with real Combined Science papers; it is not needed for this paper.
The use of a calculator is permitted.

Original practice material written for the MOE Combined Science (Chemistry) syllabus. It is not an official MOE or school examination paper. Chapter 4 (formulae and equations with state symbols, ionic equations, Ar and Mr, the mole, reacting masses, gas volumes at 24 dm³/mol, limiting reactants, concentrations in mol/dm³ and g/dm³).

For Examiner’s Use
Section A	/ 10
Section B	/ 20
Total	/ 30

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

1
The relative molecular mass of sulfuric acid, H₂SO₄, is (H = 1, S = 32, O = 16)
1. A98
2. B96
3. C100
4. D49
( )
2
What amount, in moles, does 4.4 g of carbon dioxide contain? (Mr of CO₂ = 44)
1. A0.05 mol
2. B0.1 mol
3. C0.2 mol
4. D10 mol
( )
3
One mole of any gas occupies 24 dm³ at room temperature and pressure. The volume of 0.25 mol of oxygen is
1. A6 dm³
2. B12 dm³
3. C24 dm³
4. D96 dm³
( )
4
In the reaction CH₄ + 2O₂ → CO₂ + 2H₂O, 500 cm³ of methane needs what volume of oxygen (same conditions)?
1. A250 cm³
2. B500 cm³
3. C1000 cm³
4. D2000 cm³
( )
5
8 g of sodium hydroxide (Mr = 40) is dissolved in water to make exactly 1 dm³ of solution. The concentration, in mol/dm³, is
1. A0.1 mol/dm³
2. B0.2 mol/dm³
3. C0.5 mol/dm³
4. D8 mol/dm³
( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided. Show all necessary working. Give numerical answers to 3 significant figures where appropriate, with units.

1
Calcium carbonate decomposes on heating: CaCO₃(s) → CaO(s) + CO₂(g). (Ca = 40, C = 12, O = 16; one mole of gas occupies 24 dm³ at r.t.p.)
1. (a)
  Calculate the relative formula mass of CaCO₃.
  Mr =[1]
2. (b)
  Calculate the moles of CaCO₃ in 10 g.
  moles =[1]
3. (c)
  Calculate the mass of CO₂ released when all 10 g decomposes.
  mass =[2]
4. (d)
  Calculate the volume of the CO₂ released at r.t.p.
  volume =[2]
2
Magnesium reacts with dilute hydrochloric acid: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g). (Mg = 24, Cl = 35.5)
1. (a)
  Rewrite the equation as the ionic equation, with state symbols.
  [2]
2. (b)
  Calculate the moles of magnesium in 2.40 g.
  moles =[1]
3. (c)
  Calculate the volume of hydrogen produced at r.t.p. from 2.40 g of magnesium (excess acid).
  volume =[2]
4. (d)
  Calculate the mass of magnesium chloride formed from 2.40 g of magnesium.
  mass =[2]
3
A student adds 100 cm³ of 1.50 mol/dm³ hydrochloric acid to 2.40 g of magnesium. (HCl + Mg data as above; H = 1, Cl = 35.5)
1. (a)
  Calculate the moles of HCl added.
  moles =[1]
2. (b)
  Show by calculation which reactant is limiting.
  [2]
3. (c)
  Calculate the volume of hydrogen produced at r.t.p. in this experiment.
  volume =[2]
4
25.0 cm³ of sodium hydroxide solution is neutralised by 20.0 cm³ of 0.100 mol/dm³ sulfuric acid. H₂SO₄(aq) + 2NaOH(aq) → Na₂SO₄(aq) + 2H₂O(l). (Na = 23, O = 16, H = 1)
1. (a)
  Calculate the concentration of the sodium hydroxide in mol/dm³.
  [2]

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