Pearson Edexcel IAL Chemistry 1.6 Empirical & molecular formulae

Practise deriving empirical and molecular formulae from percentage composition, combustion data, hydrates and molar-mass evidence.

Exam points

calculate mole ratios from masses or percentages to obtain an empirical formula
use empirical formula mass and molar mass to deduce the molecular formula
determine water of crystallisation from mass loss or percentage water data

[Maximum number: 1]

An organic compound contains 53.3\% carbon, 11.1\% hydrogen and 35.6\% oxygen by mass. The molar mass of this compound is $90.0 \mathrm{~g} \mathrm{~mol}^{-1}$ .
[Data: $A_{\mathrm{r}} \mathrm{H}=1.0 \quad \mathrm{C}=12.0 \quad \mathrm{O}=16.0$ ]
What is the empirical formula of the compound?

$\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}$

$\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}_{2}$

$\mathrm{C}_{4} \mathrm{H}_{5} \mathrm{O}_{2}$

$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}$

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1.6—Experimental data to calculate empirical and molecular formulae question 1