Edexcel IGCSEChemistryGeneral Applications9 Marks

This question is about separation techniques. (a) Describe how to obtain pure salt (sodium chloride) from a mixture of salt and sand.

(a)Describe how to obtain pure salt (sodium chloride) from a mixture of salt and sand.[4]
(b)Paper chromatography can be used to separate coloured dyes. (i) State one safety precaution when carrying out paper chromatography.[1]
(b)(ii)Describe how to obtain the pure dyes from the chromatogram.[2]
(b)(iii)Explain why some dyes travel further up the chromatography paper than others.[2]

Mark scheme

Marking points from the official mark scheme. The mark or mark type is shown in brackets.

M1 for (a) add water / dissolve salt
M1 for (a) filter to remove sand
M1 for (a) heat to evaporate water / crystallise
A1 for (a) obtain pure salt crystals / dry crystals
B1 for (b)(i) wear eye protection / use fume cupboard (if volatile solvent) / avoid skin contact with solvent
M1 for (b)(ii) cut out the desired spot/band (from chromatogram)
A1 for (b)(ii) dissolve in a suitable solvent / elute with solvent and evaporate solvent
M1 for (b)(iii) (dyes have) different solubilities (in solvent)
A1 for (b)(iii) (dyes have) different attractions to stationary phase / paper

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