Topical Hub, IGCSE Chemistry 0620 exam-style questions

Stoichiometry

30 questions: 15 multiple choice, 15 structured.

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1

Core Formulae [1]

Limestone is mainly calcium carbonate. Which formula represents calcium carbonate?

  1. A Ca2CO3
  2. B CaCO2
  3. C CaCO3
  4. D Ca(CO3)2

2

Core Formulae [1]

What does the molecular formula of a compound show?

  1. A The number and type of each atom in one molecule of the compound
  2. B The simplest whole-number ratio of atoms in the compound
  3. C The charges on the ions in one formula unit of the compound
  4. D The percentage by mass of each element in the compound

3

Core Formulae [1]

Magnesium ribbon burns in air to form magnesium oxide. Which symbol equation, including state symbols, correctly represents this reaction?

  1. A Mg(s) + O2(g) → MgO2(s)
  2. B Mg(s) + O(g) → MgO(s)
  3. C 2Mg(s) + O2(g) → MgO(s)
  4. D 2Mg(s) + O2(g) → 2MgO(s)

4

Supplement Formulae [1]

A compound has the molecular formula C4H10. What is its empirical formula?

  1. A C4H10
  2. B C2H5
  3. C CH2
  4. D C2H10

5

Supplement Formulae [1]

Aluminium ions, Al3+, and sulfate ions, SO42−, combine to form an ionic compound. What is the formula of this compound?

  1. A Al2(SO4)3
  2. B AlSO4
  3. C Al2SO4
  4. D Al3(SO4)2

6

Supplement Formulae [1]

Aqueous silver nitrate is added to aqueous sodium chloride, forming a white precipitate. Which ionic equation, with state symbols, correctly represents this reaction?

  1. A AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
  2. B Ag+(aq) + NO3−(aq) → AgNO3(s)
  3. C Ag+(aq) + Cl−(aq) → AgCl(s)
  4. D 2Ag+(aq) + Cl−(aq) → Ag2Cl(s)

7

Core Formulae [4]

Sodium reacts with water to produce sodium hydroxide and hydrogen gas.

(a)

Give the formula of each of the following:

(i)

sodium hydroxide

[1]
(ii)

hydrogen gas

[1]
(b)

Write a balanced symbol equation for this reaction, including state symbols.

[2]

8

Core Formulae [4]

The table shows the number of each type of atom present in one molecule of three compounds, P, Q and R.

Compound Carbon atoms Hydrogen atoms Oxygen atoms
P 1 4 0
Q 2 6 1
R 1 2 1
(a)

Deduce the molecular formula of compound P.

[1]
(b)

Deduce the molecular formula of compound Q.

[1]
(c)

Deduce the molecular formula of compound R.

[1]
(d)

State the meaning of the term molecular formula.

[1]

9

Core Formulae [4]

Calcium carbonate is a solid. When it is heated strongly in an open container, it decomposes into calcium oxide, which is also a solid, and carbon dioxide gas.

(a)

Write a word equation for this reaction.

[1]
(b)

Write a balanced symbol equation for this reaction, including state symbols.

[2]
(c)

Explain, using the equation, why the total mass of solid remaining decreases when calcium carbonate is heated in an open container.

[1]

10

Supplement Formulae [4]

A hydrocarbon molecule contains 6 carbon atoms and 12 hydrogen atoms.

(a)

State the meaning of the term empirical formula.

[1]
(b)

Give the molecular formula of this hydrocarbon.

[1]
(c)

Deduce the empirical formula of this hydrocarbon.

[1]
(d)

A different hydrocarbon has the empirical formula CH2 and its molecule contains 4 carbon atoms. Deduce its molecular formula.

[1]

11

Supplement Formulae [5]

The table gives the formula and charge of four ions.

Ion Formula Charge
Barium Ba 2+
Sulfate SO4 2−
Chloride Cl 1−
Sodium Na 1+
(a)

Deduce the formula of barium sulfate.

[1]
(b)

Deduce the formula of sodium chloride.

[1]
(c)

Aqueous barium chloride is mixed with aqueous sodium sulfate. A white precipitate of barium sulfate forms, leaving sodium chloride in solution. Write a balanced symbol equation for this reaction, including state symbols.

[3]

12

Supplement Formulae [5]

Dilute hydrochloric acid reacts with aqueous sodium hydroxide in a neutralisation reaction, producing water and aqueous sodium chloride.

(a)

Write a full balanced symbol equation for this reaction, including state symbols.

[2]
(b)

Identify the two spectator ions in this reaction.

[1]
(c)

Write the ionic equation for this neutralisation reaction, including state symbols.

[2]

13

Core Relative masses of atoms and molecules [1]

Which statement correctly defines relative atomic mass, Ar?

  1. A The mass of one atom of an element measured in grams
  2. B The average mass of the isotopes of an element compared with 1/12 of the mass of an atom of carbon-12
  3. C The number of protons and neutrons in the nucleus of an atom
  4. D The mass of one mole of atoms of an element

14

Core Relative masses of atoms and molecules [1]

Using Ar: C = 12, O = 16, Ca = 40, what is the relative formula mass, Mr, of calcium carbonate, CaCO3?

  1. A 68
  2. B 84
  3. C 116
  4. D 100

15

Core Relative masses of atoms and molecules [5]

Ar: H = 1, C = 12, N = 14, O = 16.

(a)

Calculate the relative molecular mass, Mr, of carbon dioxide, CO2.

[1]
(b)

Calculate the relative molecular mass, Mr, of glucose, C6H12O6.

[2]
(c)

Calculate the relative formula mass, Mr, of ammonium nitrate, NH4NO3.

[2]

16

Core Relative masses of atoms and molecules [4]

In the reaction 2Mg + O2 → 2MgO, 24 g of magnesium reacts completely with oxygen to form 40 g of magnesium oxide (relative formula mass of MgO = 40).

(a)

Calculate the mass of oxygen that reacts with 24 g of magnesium.

[1]
(b)

Calculate the mass of magnesium oxide formed when 9.6 g of magnesium is completely oxidised, using simple proportion.

[2]
(c)

Calculate the mass of oxygen needed to react completely with 9.6 g of magnesium.

[1]

17

Core Relative masses of atoms and molecules [4]

Copper carbonate decomposes on heating: CuCO3 → CuO + CO2

The relative formula masses are: CuCO3 = 124, CuO = 80, CO2 = 44.

(a)

Show that these three relative formula masses are consistent with conservation of mass in this equation.

[1]
(b)

3.1 g of copper carbonate is heated until it decomposes completely. Calculate the mass of copper oxide formed.

[2]
(c)

Calculate the mass of carbon dioxide gas released in part (b).

[1]

18

Core The mole and the Avogadro constant [1]

Which pair of units can both be used to express the concentration of a solution?

  1. A g/dm3 and mol/dm3
  2. B g/cm3 and mol/g
  3. C mol/dm3 and dm3/mol
  4. D g/mol and mol/dm3

19

Supplement The mole and the Avogadro constant [1]

What is the value of the Avogadro constant, and what does it represent?

  1. A 6.02 × 10^23; the number of moles in one gram of a substance
  2. B 6.02 × 10^-23; the number of particles in one mole of a substance
  3. C 6.02 × 10^23; the number of particles in one mole of a substance
  4. D 6.02 × 10^23; the mass, in grams, of one mole of a substance

20

Supplement The mole and the Avogadro constant [1]

Ar: Na = 23. What amount, in moles, is present in 11.5 g of sodium?

  1. A 0.5 mol
  2. B 0.05 mol
  3. C 2.0 mol
  4. D 5.0 mol

21

Supplement The mole and the Avogadro constant [1]

The molar gas volume is 24 dm3 at room temperature and pressure (r.t.p.). What is the volume occupied by 0.25 mol of a gas at r.t.p.?

  1. A 24 dm3
  2. B 96 dm3
  3. C 0.25 dm3
  4. D 6 dm3

22

Supplement The mole and the Avogadro constant [1]

0.25 mol of solute is dissolved in 250 cm3 of solution. What is the concentration of this solution, in mol/dm3?

  1. A 0.1 mol/dm3
  2. B 1.0 mol/dm3
  3. C 4.0 mol/dm3
  4. D 1000 mol/dm3

23

Supplement The mole and the Avogadro constant [1]

A compound contains 82.4% nitrogen and 17.6% hydrogen by mass. Ar: N = 14, H = 1. What is the empirical formula of this compound?

  1. A NH
  2. B NH2
  3. C NH3
  4. D N3H

24

Supplement The mole and the Avogadro constant [1]

A student expected to obtain 12.0 g of a salt from a reaction but actually obtained 9.6 g. What is the percentage yield?

  1. A 20%
  2. B 80%
  3. C 96%
  4. D 125%

25

Supplement The mole and the Avogadro constant [5]

Ar: Na = 23, O = 16, H = 1.

A solution of sodium hydroxide has a concentration of 8.0 g/dm3.

(a)

Calculate the relative formula mass, Mr, of sodium hydroxide, NaOH.

[1]
(b)

Calculate the concentration of this solution in mol/dm3.

[2]
(c)

Calculate the amount, in moles, of sodium hydroxide present in 250 cm3 of this solution.

[2]

26

Supplement The mole and the Avogadro constant [5]

Ar: Mg = 24.

(a)

Calculate the amount, in moles, of magnesium atoms in 3.0 g of magnesium.

[2]
(b)

Calculate the number of magnesium atoms in this 3.0 g sample.

[2]
(c)

Calculate the mass of 0.60 mol of magnesium atoms.

[1]

27

Supplement The mole and the Avogadro constant [7]

Ar: Mg = 24, H = 1, Cl = 35.5.

Magnesium reacts with hydrochloric acid: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

2.4 g of magnesium is added to 120 cm3 of hydrochloric acid of concentration 2.0 mol/dm3.

(a)

Calculate the amount, in moles, of magnesium used.

[1]
(b)

Calculate the amount, in moles, of hydrochloric acid used.

[2]
(c)

Determine which reactant is in excess. Show your working.

[2]
(d)

Calculate the maximum mass of magnesium chloride, MgCl2, that could form.

[2]

28

Supplement The mole and the Avogadro constant [4]

Ar: Na = 23, C = 12, O = 16.

Excess dilute sulfuric acid reacts with 5.3 g of sodium carbonate:

Na2CO3(s) + H2SO4(aq) → Na2SO4(aq) + H2O(l) + CO2(g)

(a)

Calculate the amount, in moles, of sodium carbonate reacted.

[1]
(b)

Calculate the amount, in moles, of carbon dioxide gas produced.

[1]
(c)

Calculate the volume of carbon dioxide gas produced, measured at r.t.p.

[2]

29

Supplement The mole and the Avogadro constant [6]

In a titration, 25.0 cm3 of a sodium hydroxide solution of unknown concentration was exactly neutralised by 22.5 cm3 of hydrochloric acid of concentration 0.100 mol/dm3.

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

(a)

Calculate the amount, in moles, of hydrochloric acid used.

[1]
(b)

Calculate the amount, in moles, of sodium hydroxide that reacted.

[1]
(c)

Calculate the concentration of the sodium hydroxide solution, in mol/dm3.

[2]
(d)

Ar: Na = 23, O = 16, H = 1. Calculate the concentration of the sodium hydroxide solution in g/dm3.

[2]

30

Supplement The mole and the Avogadro constant [5]

A hydrocarbon contains 85.7% carbon and 14.3% hydrogen by mass. Its relative molecular mass, Mr, is 42.

Ar: C = 12, H = 1.

(a)

Calculate the empirical formula of this hydrocarbon. Show your working.

[3]
(b)

Calculate the molecular formula of this hydrocarbon.

[2]