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CAIE IGCSE Chemistry Mole and Avogadro Constant Questions

Practise moving between mass, moles, particles, gas volume and solution concentration before applying equation ratios to quantitative reactions.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • convert mass to moles with relative formula mass and particles with the Avogadro constant
  • convert gas volume at room conditions or solution volume and concentration into moles
  • apply balanced-equation ratios to reacting masses, limiting reagents, yields and volumes

Covered syllabus points

3.3.1—Concentration can be measured in g/dm33.3.2—Mole, mol, is the unit of amount of3.3.3—Amount of substance relation: amount3.3.4—Molar gas volume, taken as 24 dm3 at3.3.5—Stoichiometric reacting masses3.3.6—Experimental data from a titration to3.3.7—Empirical formulae and molecular3.3.8—Percentage yield, percentage

3.3 The mole and the Avogadro constant question 1

[Maximum number: 2]

Sulfur is a Group VI element.

Question (a)

(a)

A sample of sulfur contains two isotopes, 32 S{ }^{32} \mathrm{~S} and 34 S{ }^{34} \mathrm{~S}.

[ 2 ]

Question (i)

(i)

State the mass of 6.02×10236.02 \times 10^{23} atoms of 34 S{ }^{34} \mathrm{~S}. Include units in your answer.

[ 1 ]

Question (ii)

(ii)

State the name of the amount of substance which contains 6.02×10236.02 \times 10^{23} atoms.

[ 1 ]

3.3 The mole and the Avogadro constant question 2

[Maximum number: 4]

Hydrogen peroxide, H2O2\mathrm{H}_{2} \mathrm{O}_{2}, decomposes into water and oxygen in the presence of a catalyst, manganese(IV) oxide.

2H2O2(aq)→2H2O(l)+O2( g)2 \mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g})

Question (a)

(a)

Calculate the number of moles of hydrogen peroxide used in this experiment.
mol [1]

[ 1 ]

Question (b)

(b)

Use your answer to (c)(i) and the equation to calculate the number of moles of oxygen produced in the reaction.

2H2O2(aq)→2H2O(l)+O2( g)2 \mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g})

mol

[ 1 ]

Question (c)

(c)

Calculate the volume (at r.t.p.) of oxygen produced.
dm3\mathrm{dm}^{3}

[ 1 ]

Question (d)

(d)

Deduce the volume of oxygen that would be produced if 20 cm320 \mathrm{~cm}^{3} of 0.2 mol/dm30.2 \mathrm{~mol} / \mathrm{dm}^{3} hydrogen peroxide was used instead of 20 cm320 \mathrm{~cm}^{3} of 0.1 mol/dm30.1 \mathrm{~mol} / \mathrm{dm}^{3} hydrogen peroxide.
dm3\mathrm{dm}^{3}

[ 1 ]
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