Chemistry 9701/42 — May/June 2022

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

questions

100

marks

120

minutes

Topics Equilibria · Nitrogen Compounds · Group 2 · Transition Elements · Chemical Energetics · Carboxylic Acids and Derivatives · +6 more

Q1Group 2EquilibriaTransition ElementsFree sample

(a)

The solubility of the Group 2 hydroxides increases down the group.

Explain this trend.

(b)

The solubility of $\text{Be(OH)}_2$ in water is $2.40 \times 10^{-6}\text{ g}\,\text{dm}^{-3}$ at $298\text{ K}$ .

(i)

Write an expression for the solubility product, $K_{\text{sp}}$ , of $\text{Be(OH)}_2$ and state its units.

$K_{\text{sp}} =$

$\text{units} = \text{..............................}$

(ii)

Calculate the numerical value of $K_{\text{sp}}$ for $\text{Be(OH)}_2$ at $298\text{ K}$ .

$K_{\text{sp}} = \text{..............................}$

(c)

$\text{Be(OH)}_2$ is soluble in aqueous solutions containing an excess of hydroxide ions and forms the complex ion $[\text{Be(OH)}_4]^{2-}$ . This complex ion has a similar shape to that of $[\text{CuCl}_4]^{2-}$ .

(i)

Define the term complex ion.

(ii)

Draw a three-dimensional diagram to show the structure of the complex ion $[\text{Be(OH)}_4]^{2-}$ .
Name the shape of the $[\text{Be(OH)}_4]^{2-}$ complex ion.

$\text{shape ..................................................................................................}$

(d)

(i)

Explain why transition elements can form complex ions.

(ii)

Complete Table 1.1 to show the coordination number of each metal ion, and the shapes and overall polarities of the complex ions listed.

Table 1.1

complex ion	shape	coordination number	polar or non-polar
$\text{cis-}[\text{Pt}(\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2)\text{Cl}_2]$	square planar
$[\text{Ag}(\text{NH}_3)_2]^+$			non-polar
$[\text{Fe}(\text{C}_2\text{O}_4)_3]^{3-}$		6

(e)

(i)

Define stability constant, $K_{\text{stab}}$ .

(ii)

Nickel can form complexes with the ligands $\text{en}$ , $\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2$ , and $\text{tn}$ , $\text{H}_2\text{NCH}_2\text{CH}_2\text{CH}_2\text{NH}_2$ , as shown.

\begin{aligned} \text{equilibrium 1} \quad & [\text{Ni}(\text{H}_2\text{O})_6]^{2+} + 3\text{en} \rightleftharpoons [\text{Ni}(\text{en})_3]^{2+} + 6\text{H}_2\text{O} && K_{\text{stab}} = 6.76 \times 10^{17} \\[6pt] \text{equilibrium 2} \quad & [\text{Ni}(\text{H}_2\text{O})_6]^{2+} + 3\text{tn} \rightleftharpoons [\text{Ni}(\text{tn})_3]^{2+} + 6\text{H}_2\text{O} && K_{\text{stab}} = 1.86 \times 10^{12} \end{aligned}

Construct an expression for the stability constant, $K_{\text{stab}}$ , for equilibrium 1.

State the units for $K_{\text{stab}}$ .

$K_{\text{stab}} =$ ..............................

units = ..............................

(iii)

Describe what the $K_{\text{stab}}$ values indicate about the position of equilibrium for equilibrium 1 and 2. Use the $K_{\text{stab}}$ values to deduce which complex, $[\text{Ni}(\text{en})_3]^{2+}$ or $[\text{Ni}(\text{tn})_3]^{2+}$ , is more stable.

The rest of this paper

8 more questions

Q2Transition Elements · Equilibria9M
Q3Chemical Energetics9M
Q4Chemical Energetics · Group 2 · Equilibria14M
Q5Electrochemistry8M
Q6Hydrocarbons · Nitrogen Compounds16M
Q7Analytical Techniques · Introduction to A Level Organic Chemistry8M
Q8Hydroxy Compounds · Carboxylic Acids and Derivatives · Polymerisation · Nitrogen Compounds11M
Q9Nitrogen Compounds · Carboxylic Acids and Derivatives9M

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