Chemistry 9701 · AS & A Level · States of matter

States of matter — practice question

(a)[4]

State the order of basicity for ethanamide, diethylamine and ethylamine in aqueous solution. Explain your answer.

(b)

The amino acid alanine, $\text{H}_2\text{NCH}(\text{CH}_3)\text{COOH}$, is able to act as a buffer.

(b(i))[2]

Define a buffer solution.

(b(ii))[2]

Write two equations to show how an aqueous solution of alanine can behave as a buffer solution.

(c)

Another amino acid that acts as a buffer is glutamic acid.

(c(i))[1]

Draw the skeletal formula of glutamic acid.

(c(ii))[2]

Draw the structure of the dipeptide, ala-glu, made from one molecule of alanine and one molecule of glutamic acid. The peptide bond that forms should be shown.

(d)[3]

The isoelectric point of alanine is $6.0$ and of glutamic acid is $3.2$. A mixture containing the dipeptide, ala-glu, and its two component amino acids, alanine and glutamic acid, is examined by electrophoresis using a buffer at $\text{pH }6.0$. Draw and label three spots on Fig. 7.2 to show the predicted position of each of these three species after electrophoresis. Explain your answer.

(e)

Alanine, $\text{H}_2\text{NCH}(\text{CH}_3)\text{COOH}$, reacts with methanol under suitable conditions to produce the ester G. The proton ($^1\text{H}$) NMR spectrum of G dissolved in $\text{D}_2\text{O}$ is shown in Fig. 7.3.

(e(i))[3]

Complete Table 7.2 for the proton ($^1\text{H}$) NMR spectrum of $G$.

(e(ii))[1]

The proton ($^1\text{H}$) NMR spectrum of $G$ dissolved in $\text{CDCl}_3$ is obtained. Describe the difference between this spectrum and the proton NMR spectrum in $\text{D}_2O$ shown in Fig. 7.3. Explain your answer.

Worked solution & mark scheme

This 18-mark question has a full step-by-step worked solution and mark scheme. One marking point: Basicity sequence: diethylamine > ethylamine > ethanamide

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