AS & A Level Chemistry - 9701 Paper 4 2022 Summer Zone 2

(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 $2.40 \times 10^{-6} \text{ g dm}^{-3}$ at 298 K.
(i) Write an expression for the solubility product, $K_{sp}$, of $\text{Be(OH)}_2$ and state its units.
$K_{sp} =$ ..............................................
units = ............................
(ii) Calculate the numerical value of $K_{sp}$ for $\text{Be(OH)}_2$ at 298 K.
$K_{sp} =$ ..............................................

(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.
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]

(a) Explain why transition elements have variable oxidation states. ....................................................................................................................... ....................................................................................................................... [1]

(b) Sketch the shape of a 3d$_{xy}$ orbital. [1]

(c) Explain why transition elements form coloured compounds. ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... [3]

(d) Aqueous solutions of copper(II) salts contain [Cu(H$_2$O)$_6$]$^{2+}$ ions.
Equilibrium 3 and equilibrium 4 show two reactions of these ions.
equilibrium 3  [Cu(H$_2$O)$_6$]$^{2+}$(aq) + 2OH$^-$(aq) $\rightleftharpoons$ Cu(OH)$_2$(s) + 6H$_2$O(l)
equilibrium 4  [Cu(H$_2$O)$_6$]$^{2+}$(aq) + 4NH$_3$(aq) $\rightleftharpoons$ [Cu(NH$_3$)$_4$(H$_2$O)$_2$]$^{2+}$(aq) + 4H$_2$O(l)
(i) State the colour of Cu(OH)$_2$(s) and [Cu(NH$_3$)$_4$(H$_2$O)$_2$]$^{2+}$(aq).
colour of Cu(OH)$_2$(s) ..................................................................................................................
colour of [Cu(NH$_3$)$_4$(H$_2$O)$_2$]$^{2+}$(aq) .................................................................................................................. [1]
(ii) Use Le Chatelier’s principle to explain why a precipitate is formed when NaOH(aq) is added dropwise to [Cu(H$_2$O)$_6$]$^{2+}$(aq).
.......................................................................................................................... .......................................................................................................................... .......................................................................................................................... [1]

(e) There are two possible stereoisomers with the formula [Cu(NH$_3$)$_4$(H$_2$O)$_2$]$^{2+}$.
Draw three-dimensional diagrams to show the two stereoisomers. [2]

(a) (i) Define first electron affinity.
...................................................................................................................................................
...................................................................................................................................................
................................................................................................................................................... [2]

(ii) The first electron affinity of an atom is usually an exothermic process, whereas the second electron affinity is an endothermic process. Suggest why.
...................................................................................................................................................
................................................................................................................................................... [1]

(iii) Describe the general trend in first electron affinities for Cl, Br and I. Explain your answer.
...................................................................................................................................................
................................................................................................................................................... [2]

(b) Table 3.1 shows energy changes to be used in this question and in (c).

[Table_1]

Calculate the first electron affinity for iodine. Use relevant data from Table 3.1 in your working. It may be helpful to draw a labelled energy cycle. Show all working.

first electron affinity for iodine = ................................. kJ mol⁻¹ [3]

(c) Predict how $\Delta H^\circ_{\text{latt}}$ of CdI₂(s) differs from $\Delta H^\circ_{\text{latt}}$ of ZnI₂(s). Place a tick (✓) in the appropriate box in Table 3.2.

[Table_2]

Explain your answer.
...................................................................................................................................................
................................................................................................................................................... [1]

[Total: 9]

(a) Calcium carbonate decomposes on heating.

CaCO$_3$(s) → CaO(s) + CO$_2$(g)

Table 4.1 shows the values of the Gibbs free energy change, ΔG°, for this reaction at various temperatures.

[Table_1]

Assume the standard enthalpy change, ΔH°, and the standard entropy change, ΔS°, for this reaction remain constant over this temperature range.

(i) Use the data in Table 4.1 to plot a graph of ΔG° against T on the grid.

[Graph Image]

(ii) Calculate the gradient of your graph. Determine the ΔS° in JK$^{-1}$mol$^{-1}$ for this reaction. Show all working.

ΔS° = ................................. JK$^{-1}$mol$^{-1}$ [2]

(b) Group 1 hydrogencarbonates, MHCO$_3$, decompose on gentle heating to give the corresponding metal carbonate, carbon dioxide and water vapour.

(i) Write an ionic equation for the decomposition of the hydrogencarbonate ion.
.............................................................................................................................................................. [1]

(ii) The thermal stability of Group 1 hydrogencarbonates increases down the group.

Suggest an explanation for the trend in thermal stability of the Group 1 hydrogencarbonates.
............................................................................................................................................................
............................................................................................................................................................
............................................................................................................................................................
............................................................................................................................................................ [2]

(c) The buffer system in seawater contains a mixture of HCO$_3^-$ and H$_2$CO$_3$.

equilibrium 5 H$_2$CO$_3$ + H$_2$O ⇌ HCO$_3^-$ + H$_3$O$^+$

(i) Define a buffer solution.
............................................................................................................................................................
............................................................................................................................................................
............................................................................................................................................................ [2]

(ii) Construct two equations to show how equilibrium 5 acts as a buffer solution.
............................................................................................................................................................
............................................................................................................................................................ [2]

(iii) The [HCO$_3^-$]/[H$_2$CO$_3$] ratio in a sample of seawater is 14.1.

Calculate the pH of this sample.
[pK$_a$: H$_2$CO$_3$, 6.35]

pH = ................................ [3]

(a) Complete Table 5.1 to predict the substance liberated at each electrode during electrolysis of the indicated electrolyte with inert electrodes.

Table 5.1

[Table_1]

electrolyte | substance liberated at the anode | substance liberated at the cathode
PbBr$_2$(l)
concentrated NaCl(aq)
Cu(NO$_3$)$_2$(aq)

[3]

(b) An electrolytic cell is set up to determine a value for the Avogadro constant, $L$. The electrolyte is dilute sulfuric acid and both electrodes are copper.

When a current of 0.600A is passed through the acid for 30.0 minutes, the anode decreases in mass by 0.350g.

(i) State the relationship between the Faraday constant, $F$, and the Avogadro constant, $L$.
.................................................................................................................................................. [1]

(ii) Use the experimental information in (b) and data from the table on page 23 to calculate a value for the Avogadro constant, $L$.

Show all working.

Avogadro constant, $L$ = .............................. [4]

[Total: 8]

(a) The reagent and conditions required for the nitration of benzene, benzoic acid and phenol are shown in Table 6.1.

Table 6.1

[Table_1]

Concentrated HNO\(_3\) reacts with concentrated H\(_2\)SO\(_4\) to generate the electrophile NO\(_2^+\).

(i) Complete Fig. 6.1 to show the mechanism of the reaction between benzene and NO\(_2^+\). Include all relevant curly arrows and charges.



[3]

(ii) Write an equation to show how H\(_2\)SO\(_4\) is regenerated.
..............................................................................................................................................................................
............................................................................................................................................................... [1]

(b) Draw the major products from the mononitration of benzoic acid and of phenol.



[2]

(c) Compare the relative ease of nitration of benzene, benzoic acid and phenol. Explain your reasoning; include reference to the structures of the three compounds in your answer.

............................................................... > ............................................................... > ...............................................................
easiest least easy
..................................................................................................................................................................
..................................................................................................................................................................
..................................................................................................................................................................
..................................................................................................................................................................
[4]

(d) The azo compound Congo Red is used as an acid–base indicator and can be made by the route shown in Fig. 6.2.

In step 3 of this synthesis, compound Y reacts with compound Z. Compound Z is made from compound X. Assume that the –SO\(_3^-\)Na\(^+\) groups do not react.



(i) Suggest structures for compounds X, Y and Z and draw them in the boxes in Fig. 6.2. [3]

(ii) Give the reagents and conditions for step 1 and step 2.
step 1 .......................................................................................................................................................................
step 2 .......................................................................................................................................................................
[3]

[Total: 16]

(a) State the uses of TMS and $D_2O$ in NMR spectroscopy.

TMS ..........................................................................................................................................
$D_2O$ .........................................................................................................................................

(b) The three isomeric ketones with molecular formula $C_5H_{10}O$ are:
• pentan-2-one
• pentan-3-one
• 3-methylbutanone.

(i) Complete Table 7.1 to show the number of peaks observed in the proton ($^1H$) NMR spectrum and in the carbon-13 NMR spectrum for each compound listed.

[Table 7.1]
- ketone
- number of peaks observed in the proton ($^1H$) NMR spectrum
- number of peaks observed in the carbon-13 NMR spectrum

(ii) State all the ketones with molecular formula $C_5H_{10}O$ that have:

a doublet in their proton ($^1H$) NMR spectrum
.....................................................................................................................................................

a singlet in their proton ($^1H$) NMR spectrum.
.....................................................................................................................................................

(c) Cortisone, $C_{21}H_{28}O_5$, is a naturally occurring chemical that contains chiral carbon atoms.


(i) Deduce the number of chiral carbon atoms in one molecule of cortisone.
.....................................................................................................................................................

(ii) Cortisone is reacted with an excess of $NaBH_4$.
State the molecular formula of the organic compound formed.
.....................................................................................................................................................

(iii) Cortisone is an optically active molecule.
Explain what is meant by optically active.
.....................................................................................................................................................
.....................................................................................................................................................
.....................................................................................................................................................

(a) Compare the relative acidities of ethanol, ethanoic acid, chloroethanoic acid and phenol. Explain your reasoning.
.............................. > .............................. > .............................. > .............................. > ..............................
most acidic
least acidic
[4]

(b) An excess of ethanedioic acid, HOOCCOOH(aq), is reacted with warm acidified KMnO₄(aq).
State the type of reaction undergone by ethanedioic acid.
Describe what you would observe.
Write an equation for this reaction.
Your equation can use [O] or [H] as necessary.
type of reaction .......................................................................................................................................
observations ...........................................................................................................................................
equation ..................................................................................................................................................
[2]

(c) A section of a polyester is shown.
[Image_1: Fig. 8.1]
Draw the structures of the two monomers that form this polyester.
[2]

(d) Serine can polymerise to form two different types of condensation polymer; a polyester and a polypeptide.
[Image_2: Fig. 8.2]
Draw the structure of the polypeptide showing two repeat units. The peptide linkage should be shown displayed.
[2]

(e) Explain why condensation polymers normally biodegrade more readily than addition polymers.
.........................................................................................................................................................
.........................................................................................................................................................
[1]

The structure of cyclohexylamine is shown in Fig. 9.1.

(a) Compare the relative basicities of ammonia, cyclohexylamine and phenylamine. Explain your reasoning.
............................................. > ............................................. > .............................................
most basic    least basic
.........................................................................................................................................................................................
.........................................................................................................................................................................................
.........................................................................................................................................................................................
.........................................................................................................................................................................................
......................................................................................................................................................................................... [3]
(b) Cyclohexylamine reacts with ethanoyl chloride to form the corresponding amide, L.

(i) Name the mechanism for the reaction shown in Fig. 9.2.
......................................................................................................................................................................................... [1]
(ii) Complete the mechanism of the reaction between cyclohexylamine and $\text{CH}_3\text{COCl}$.
R$-$NH$_2$ is used to represent cyclohexylamine.
Include all relevant lone pairs of electrons, curly arrows, charges and partial charges.

R$-$NH$_2$

products [4]
(iii) The reaction between cyclohexylamine and an excess of $\text{CH}_3\text{COCl}$ forms compound M. Compound M has the molecular formula C$_{10}$H$_{17}$NO$_2$.
Suggest and draw the structure of M. [1]
[Total: 9]