Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

Modern techniques for chemical analysis often depend on interpreting data collected by instrumental methods.
(a)[2]

Electrophoresis and paper chromatography may each be used to separate amino acids from a mixture formed from polypeptides. For each method, give one amino acid property that leads to the separation: electrophoresis; paper chromatography.

(b)[1]

Amino acids have no colour. What method is used to show where the different amino acids are so that measurements can be taken?

(c)[1]

Which measurements must be taken to identify individual amino acids in paper chromatography?

(d)[3]

The diagram shows the outcomes of electrophoresis on a mixture of the amino acids glycine, lysine and glutamic acid at pH $7.0$. The structures of the amino acids at pH $7.0$ are shown: glycine: $\mathrm{H_3N^+CH_2CO_2^-}$ lysine: $\mathrm{H_3N^+CH(CH_2CH_2CH_2CH_2NH_3^+)CO_2^-}$ glutamic\ acid: $\mathrm{H_3N^+CH(CH_2CH_2CO_2^-)CO_2^-}$ Identify the amino acids responsible for the spots labelled $R$, $S$ and $T$.

(e(i))[1]

This diagram shows the results of two-way paper chromatography of a mixture of amino acids. Place a $U$ next to the amino acid that travelled the furthest in solvent $2$.

(e(ii))[1]

Draw a ring around the two amino acids that were not separated in solvent $1$.

(e(iii))[1]

Place a $W$ next to the amino acid that was very soluble in both solvents.

Worked solution & mark scheme

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