CAIE IGCSE Chemistry 12.4.3 Substances & assess their purity

Practise using melting and boiling point data to identify substances, judge purity and compare pure samples with mixtures.

Exam points

compare melting and boiling points of pure and impure samples against data values
predict lower melting points and higher boiling points when impurities are present

[Maximum number: 2]

The chemical equation for the complete combustion of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ , is shown.

\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}+3 \mathrm{O}_{2} \rightarrow 2 \mathrm{CO}_{2}+3 \mathrm{H}_{2} \mathrm{O}

The energy released when one mole of ethanol undergoes complete combustion is 1280 kJ .
Part of the energy level diagram for this reaction is shown.

Figure for Question 12.4.3—Substances and assess their purity question 1 — CAIE IGCSE Chemistry

Dodecane is an alkane containing 12 carbon atoms. Ethanol can be manufactured from dodecane in a two-stage process.

In stage 1, each molecule of dodecane is converted into three molecules of ethene and one molecule of another hydrocarbon.

Suggest how to test the purity of the ethanol produced.

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12.4.3—Substances and assess their purity question 1