Chemistry 9701/42 — May/June 2011

Cambridge A-Level · A Level Structured Questions · worked solutions for every part, with the mark scheme

questions

100

marks

120

minutes

Topics Transition Elements · Nitrogen Compounds · Carboxylic Acids and Derivatives · Reaction Kinetics · Electrochemistry · Introduction to A Level Organic Chemistry · +7 more

Q1EquilibriaTransition ElementsNitrogen CompoundsChemical EnergeticsFree sample

(a)

Hydrogen fluoride, HF, behaves as a weak acid in water, with $K_a = 5.6 \times 10^{-4} \text{ mol dm}^{-3}$ .

Calculate the pH of a $0.050 \text{ mol dm}^{-3}$ solution of HF.

(b)

Gaseous ammonia and hydrogen fluoride react together to give solid ionic ammonium fluoride.

\text{NH}_3(\text{g}) + \text{HF}(\text{g}) \rightleftharpoons \text{NH}_4\text{F}(\text{s}) \quad \Delta H = -147 \text{ kJ mol}^{-1}

(i)

What type of reaction is this?

(ii)

Draw dot-and-cross diagrams (outer shells only) describing the bonding in the three compounds involved in this reaction.

Fig. 1.1

(iii)

There are three types of bonding in $\text{NH}_4\text{F}$ .

Give the names of each of the three types, and state where in the compound each type occurs.

(iv)

The reaction between $\text{NH}_3$ and $\text{HF}$ is reversible. What conditions of temperature and pressure would favour the reverse reaction, i.e. the dissociation of $\text{NH}_4\text{F}$ ? Explain your answer.

(c)

Many commercial copper and brass polishes contain ammonia. The tarnish that forms on the surface of copper is often copper sulfide, CuS. In the presence of $\text{O}_2$ from the air, $\text{NH}_3$ can combine with this copper sulfide to produce the soluble cuprammonium sulfate, $[\text{Cu}(\text{NH}_3)_4]\text{SO}_4$ .

(i)

Construct an equation for this reaction.

(ii)

State the colour of cuprammonium sulfate solution.

(iii)

Describe what you would see if a solution of cuprammonium sulfate was diluted with water. Explain your answer.

(d)

When sulfuric acid is added to $\text{Cu}^{2+}(\text{aq})$ , no colour change occurs, but when concentrated hydrochloric acid is added to $\text{Cu}^{2+}(\text{aq})$ , the solution turns yellow-green. The solution reverts to its original colour when it is diluted with water.

Suggest the type of reaction occurring with $\text{HCl}(\text{aq})$ , suggest what is formed during the reaction, and write an equation for the change.

The rest of this paper

7 more questions

Q2Transition Elements · Group 2 · Carboxylic Acids and Derivatives · Reaction Kinetics10M
Q3Electrochemistry15M
Q4Polymerisation · Carboxylic Acids and Derivatives · Introduction to A Level Organic Chemistry15M
Q5Hydroxy Compounds · Organic Synthesis13M
Q6Nitrogen Compounds · Reaction Kinetics10M
Q7Analytical Techniques10M
Q8Introduction to A Level Organic Chemistry · Transition Elements · Electrochemistry10M

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