CAIE IGCSE Chemistry Separation and Purification

Practise choosing filtration, crystallisation or distillation from mixture properties and using melting or boiling behaviour to assess purity.

Exam points

choose filtration for an insoluble solid and crystallisation to recover a dissolved solid
choose simple or fractional distillation by considering solvent recovery and boiling points
assess purity from a sharp melting or boiling point compared with the accepted value

Covered syllabus points

12.4.1—Methods of separation and purification 12.4.2—Suggest suitable separation and 12.4.3—Substances and assess their purity

[Maximum number: 3]

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 Separation and purification question 1 — CAIE IGCSE Chemistry

(a)

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.

[ 2 ]

(i)

Suggest how to test the purity of the ethanol produced.

[ 2 ]

(b)

Ethanol can also be manufactured by the fermentation of glucose, $\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}$ .

[ 1 ]

(i)

Suggest the name of a process to obtain ethanol from a mixture of ethanol and water.

[ 1 ]

[Maximum number: 1]

Lead(II) iodide is formed as a precipitate in the reaction shown.

\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{NaI}(\mathrm{aq}) \rightarrow \mathrm{PbI}_{2}(\mathrm{~s})+2 \mathrm{NaNO}_{3}(\mathrm{aq})

Which method is used to separate the lead(II) iodide from the mixture?

crystallisation

distillation

evaporation

filtration

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Covered syllabus points

12.4 Separation and purification question 1

Question (a)

Question (i)

Question (b)

Question (i)

12.4 Separation and purification question 2