Chemistry 9701 · AS & A Level · Nitrogen and sulfur

Nitrogen and sulfur — practice question

Group 15 elements form halides such as $\text{PCl}_5$, $\text{PCl}_3$ and $\text{NCl}_3$.
(a(i))[1]

Phosphorus can react with chlorine to make $\text{PCl}_5$. Write the equation for forming $\text{PCl}_5$ from phosphorus and chlorine.

(a(ii))[1]

State the type of structure and bonding present in liquid $\text{PCl}_5$.

(b(i))[1]

A small amount of $\text{PCl}_5$ is added to excess water. The $\text{PCl}_5$ reacts vigorously to form a colourless solution. Give one other observation you would make when $\text{PCl}_5$ reacts with excess water.

(b(ii))[1]

Write the equation for the reaction between $\text{PCl}_5$ and excess water.

(b(iii))[1]

Estimate the pH of the solution formed.

(c(i))[1]

$\text{PCl}_3$ is used to change alcohols into chloroalkanes, including compound T. One possible route to T is shown. Identify a reagent that could be used in reaction 1.

(c(ii))[2]

T shows optical isomerism. Explain the meaning of optical isomer and circle any atom(s) in T that cause optical isomerism.

(c(iii))[1]

T is a minor product in the reaction of compound S with excess $\text{HCl}$. Draw the structure of the major product from the reaction of S with excess $\text{HCl}$.

(d(i))[2]

$\text{NCl}_3$ is a yellow liquid used to bleach flour. Predict the shape of the $\text{NCl}_3$ molecule and the $\text{Cl-N-Cl}$ bond angle.

(d(ii))[2]

$\text{NCl}_3$ reacts with water to form $\text{HOCl}$, a weak Brønsted-Lowry acid. Explain fully what is meant by weak Brønsted-Lowry acid.

(d(iii))[4]

$\text{NCl}_3(l)$ decomposes according to the equation shown: $2\text{NCl}_3(l) \rightarrow \text{N}_2(g) + 3\text{Cl}_2(g)$. A sealed container with volume $250\,\text{cm}^3$ initially contains an unreactive gas at a pressure of $1.00 \times 10^5\,\text{Pa}$. $0.241\,\text{g}$ of $\text{NCl}_3(l)$ is injected into the sealed container. The container is heated so that the $\text{NCl}_3(l)$ decomposes completely and is then cooled to $20^\circ\text{C}$. Calculate the final total pressure inside the sealed container at $20^\circ\text{C}$ after all the $\text{NCl}_3(l)$ has decomposed.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: Balanced equation: $\mathrm{P_4 + 10Cl_2 \rightarrow 4PCl_5}$

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