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CAIE IGCSE Chemistry 3.3.7 Empirical formulae & molecular

CAIE IGCSE Chemistry 3.3.7 Empirical formulae & molecular
Cambridge IGCSE Chemistry 0620 syllabus for exams in 2026, 2027 and 20282026–2028

Practise deriving empirical and molecular formulae from percentage composition, masses, mole ratios and relative molecular mass.

How this is tested

  • divide masses or percentages by Ar values, then reduce to the simplest whole-number ratio
  • use empirical formula mass and Mr to scale up to the molecular formula
  • determine x in hydrated salts by comparing moles of anhydrous salt and H2O

Question 7

[Maximum number: 5]

Many organic compounds contain carbon and hydrogen only.

Question 7(a)(i)

(a)

An organic compound A has the following composition by mass.

C,83.33%;H,16.67%\mathrm{C}, 83.33 \% ; \quad \mathrm{H}, 16.67 \%

Calculate the empirical formula of compound A.
empirical formula =

[ 3 ]

Question 7(a)(ii)

(b)

Compound B has the empirical formula C2H5\mathrm{C}_{2} \mathrm{H}_{5} and a relative molecular mass of 58.

Determine the molecular formula of compound B.
molecular formula =

[ 2 ]