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CAIE IGCSE Chemistry Chemical Formulae Question Bank

Practise constructing ionic and molecular formulae, balancing symbol equations and using composition or particle ratios to determine empirical formulae.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • combine ion charges in the smallest whole-number ratio to construct a neutral formula
  • translate a word or reaction description into correct formulae before balancing the equation
  • derive an empirical formula by converting masses or percentages to a simplest mole ratio

Covered syllabus points

3.1.1—Formulae of the elements and compounds3.1.2—Molecular formula of a compound as the3.1.3—Deduce the formula of a simple3.1.4—Construct word equations and symbol3.1.5—Empirical formula of a compound as the3.1.6—Deduce the formula of an ionic3.1.7—Construct symbol equations with state3.1.8—Deduce the symbol equation with state

3.1 Formulae question 1

[Maximum number: 1]

The Haber process is used to manufacture ammonia.

Ammonia reacts with an acid to form ammonium sulfate, (NH4)2SO4\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}.

State the formula of the acid used.

3.1 Formulae question 2

[Maximum number: 1]

The chemical formulae of two substances, W and X, are given.
W NaAlSi3O8\mathrm{NaAlSi}_{3} \mathrm{O}_{8}
X CaAl2Si2O8\quad \mathrm{CaAl}_{2} \mathrm{Si}_{2} \mathrm{O}_{8}
Which statements are correct?

1 W and X contain the same amount of oxygen.
2 W contains three times as much silicon as X.
3 X contains twice as much aluminium as W.
A1 and 2
B1 and 3
C 2 and 3
D 1, 2 and 3

3.1 Formulae question 3

[Maximum number: 2]

Sulfur is a Group VI element.

Question (a)

(a)

An acid containing sulfur reacts with sodium hydroxide, NaOH , to form a salt and water. The salt has the formula Na2SO3\mathrm{Na}_{2} \mathrm{SO}_{3}.

[ 2 ]

Question (i)

(i)

Deduce the formula of this acid.

[ 1 ]

Question (ii)

(ii)

Deduce the formula of the anion in Na2SO3\mathrm{Na}_{2} \mathrm{SO}_{3}.

[ 1 ]
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