Chemistry 9701 · AS & A Level · Nitrogen compounds

Nitrogen compounds — practice question

Alanine and similar amino acids are the key units used to build proteins. They may be made by a general reaction, an example of which is shown below.
(a(i))[1]

In the box above, suggest the structural formula of intermediate compound $E$.

(a(ii))[1]

In the box below, suggest the structural formula of the starting compound required to make phenylalanine by the general reaction above.

(b(i))[1]

What is meant by a protein?

(b(ii))[3]

Using alanine as an example, draw a diagram to show how proteins are formed from amino acids. Include two repeat units in your answer.

(c(i))[1]

State the reagents and conditions required for this hydrolysis.

(c(ii))[3]

Draw the structures of products $G$ and $H$ in the boxes above.

(d(i))[1]

Draw the zwitterionic structure of alanine.

(d(ii))[4]

Suggest the structural formulae of the zwitterions that may be formed from the compounds below.

(e(i))

What is meant by the term buffer?

(e(ii))

Write an equation to show how a solution of alanine, $\\text{CH}_3\\text{CH(NH}_2)\\text{CO}_2\\text{H}$, acts as a buffer in the presence of an acid such as $\\text{HCl(aq)}$.

(e(iii))

Briefly describe how the pH of blood is controlled.

(e(iv))[7]

Calculate the pH of the buffer produced when $10.0\\,\\text{cm}^3$ of $0.100\\,\\text{mol dm}^{-3}$ NaOH is added to $10.0\\,\\text{cm}^3$ of $0.250\\,\\text{mol dm}^{-3}$ $\\text{CH}_3\\text{CO}_2\\text{H}$, where $pK_a = 4.76$.

Worked solution & mark scheme

This 22-mark question has a full step-by-step worked solution and mark scheme. One marking point: The formula of $E$ is $\\mathrm{CH_3CH(NH_2)CN}$.

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