Chemistry 9701 · AS & A Level · Nitrogen and sulfur

Nitrogen and sulfur — practice question

(a)[2]

$\text{NH}_3(g)$ reacts with $\text{HCl}(g)$ to form $\text{NH}_4\text{Cl}(s)$, as shown. $\text{NH}_3(g) + \text{HCl}(g) \rightarrow \text{NH}_4\text{Cl}(s)$ Draw a diagram that shows the ionic, covalent and coordinate bonding present in one formula unit of $\text{NH}_4\text{Cl}$.

(b(i))[1]

An exothermic reaction occurs when $\text{NH}_4^+(aq)$ is added to $\text{OH}^-(aq)$. Identify the type of reaction.

(b(ii))[1]

Construct an ionic equation for the reaction of $\text{NH}_4^+$ and $\text{OH}^-$.

(c(i))[1]

In substitution reactions of $\text{NH}_3$ and $\text{OH}^-$ with halogenoalkanes, both species use a lone pair of electrons. Name the role of $\text{NH}_3$ and $\text{OH}^-$ in these reactions.

(c(ii))[1]

Suggest which species, $\text{NH}_3$ or $\text{OH}^-$, is more reactive in these reactions. Explain your answer.

(d)[2]

When 2-bromo-2-methylpropane reacts with $\text{OH}^-$, both $\text{S}_N1$ and $\text{S}_N2$ mechanisms take place. The $\text{S}_N2$ mechanism has the slower rate. Fig. 4.1 shows the reaction pathway diagram for the $\text{S}_N1$ mechanism. Sketch a graph on Fig. 4.1 to show the reaction pathway for the $\text{S}_N2$ mechanism.

(e(i))[3]

Complete Fig. 4.2 to show the mechanism for the $\text{S}_N1$ reaction that happens when $\mathrm{CH_3CHBrC_2H_5}$ reacts with $\text{NH}_3$ to form $\mathrm{CH_3CH(NH_2)C_2H_5}$. Include charges, dipoles, lone pairs of electrons and curly arrows, where relevant.

(e(ii))[1]

Identify the inorganic product produced in the reaction shown in Fig. 4.2.

(e(iii))[1]

Give the systematic name of the organic product $\text{CH}_3\text{CH(NH}_2\text{)C}_2\text{H}_5$.

(f(i))[1]

Complete Table 4.1 by drawing the structural formula of the intermediate formed when 2-bromo-2-methylpropane reacts in an $\text{S}_\text{N}1$ reaction.

(f(ii))[2]

Identify the halogenoalkane in Table 4.1 that has the greater tendency to react by the $\text{S}_\text{N}1$ mechanism. Explain your answer.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: Accurate display of the ionic bond between $\mathrm{NH_4^+}$ and $\mathrm{Cl^-}$ together with four $\mathrm{N-H}$ covalent bonds

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