Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

Oxygen-containing organic compounds can include several different functional groups, such as alcohol, aldehyde, carboxylic acid, ester or ketone groups. These groups can be recognised from how they react with particular reagents.
(a)[5]

When compounds containing each of these functional groups are treated with the reagents below, only five of the possible combinations react. Finish the table by putting a tick (✓) in each box where you think a reaction will happen. Do not use more than five ticks in the table.

(b(i))

Compound G has empirical formula $\text{CH}_2\text{O}$ and $M_r$ of $90$. An aqueous solution of G is neutral. G shows no reaction with $\text{NaHCO}_3$. When $0.30\ \text{g}$ of pure G is reacted with excess Na, $80\ \text{cm}^3$ of $\text{H}_2$, measured at room temperature and pressure, is produced. What functional group do these two reactions reveal to be present in G?

(b(ii))

Use the information to calculate the amount, in moles, of hydrogen atoms made from $0.30\ \text{g}$ of G.

(b(iii))[4]

Hence, show that each molecule of G contains two of the functional groups named in (i).

(c(i))

When G is treated with $2,4$-dinitrophenylhydrazine reagent, an orange solid is formed. On warming G with Fehling’s reagent, there is no reaction. What functional group do these reactions reveal to be present in G? Draw the displayed formula of this functional group.

(c(ii))[2]

Use your answers to (b)(i) and (c)(i) to work out the structural formula of G.

(d(i))

Compound G can be both oxidised and reduced. When G is heated under reflux with acidified $\text{K}_2\text{Cr}_2\text{O}_7$, compound H is produced. Give the structural formula of compound H.

(d(ii))[2]

When G is reacted with $\text{NaBH}_4$ under suitable conditions, compound J is formed. Give the structural formula of compound J.

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: Correct ticks showing the reactions of NaHCO$_3$, Na and $\text{Cr}_2\text{O}_7^{2-}/\text{H}^+$ with the appropriate functional groups

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