科目：化学 Chemistry (9701)
年份：2022 夏季
试卷：Paper 42
总页数：18
章节：19 Lattice energy, 20 Electrochemistry, 21 Further aspects of equilibria, 23 Entropy and Gibbs free energy, 24 Transition elements, 25 Benzene and its compounds, 26 Carboxylic acids and their derivatives, 27 Organic nitrogen compounds, 28 Polymerisation, 29 Organic synthesis, 30 Analytical chemistry
Answer all the questions in the spaces provided.
1. (a) The solubility of the Group 2 hydroxides increases down the group.
Explain this trend.
(b) The solubility of Be(OH)$_2$ in water is $2.40 \times 10^{-6}$ g dm$^{-3}$ at 298 K.
(i) Write an expression for the solubility product, $K_{sp}$, of Be(OH)$_2$ and state its units.
$$K_{sp} =$$
units = ..... [2]
(ii) Calculate the numerical value of $K_{sp}$ for Be(OH)$_2$ at 298 K.
$$K_{sp} =$$ ... [2]
(c) Be(OH)$_2$ is soluble in aqueous solutions containing an excess of hydroxide ions and forms the complex ion $[Be(OH)_4]^{2-}$. This complex ion has a similar shape to that of $[CuCll_4]^{2-}$.
(i) Define the term complex ion.
..... [1]
(ii) Draw a three-dimensional diagram to show the structure of the complex ion $[Be(OH)_�]^{2-}$. Name(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 |
| :--- | :---: | :---: | :---: |
| $cis-[\text{Pt}(\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2)\text{Cl}_2]$ | 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 $en$, $\text{H}_2\text{NCH}_{2}\text{CH}_{2}\text{NH}_{2}$, and $tn$, $\text{H}_2\text{ NCH}_{2}\text{CH}_{2} \text{CH}_{2} \text{NH}_{2}$, as shown.
$$\begin{array}{l}
\tex2 (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.(d) Aqueous solutions of copper(II) salts contain $[\text{Cu(H}_2\text{O})_6]^{2+}$ ions.
Equilibrium 3 and equilibrium 4 show two reactions of these ions.
equilibrium 3 $[\text{Cu(H}_2\text {O})_6]^{2+}(\text{aq}) + 2\text{OH}^-(\text{aq}) \rightleftharpoons \text{Cu(OH)}_2(\text{s}) + 6\text{H}_2\text{O}(\text{l})$
equilibrium 4 $[\text{Cu(H}_2\text{array}{O})_6]^{2+}(\mathrm{aq}) + 4\text{NH}_3(\mathrm{aq}) \rightleftharpoonup [\text{Cu(NH}_3)_4(\text{H}_2\text{array}{O})_2]^{2+}(\mathrm{aq})+4\text{H}_2\text{array}{O}(\mathrm{I})$
(i) State the colour of $\text{Cu(OH)}_2(\mathrm{s})$ and $[\text{Cu(NH}_3)_4 (\text{H}_2\text{array}{O} )_2]^{2+}(\mathrm{aq})$.
colour of $\text{Cu(OH)}_�(\mathrm{s})$ ..... [1]
colour of $[\text{Cu(NH}_3)_{4}(\text{H}_2\text{array}{O })_2]^{2+}(\math3 (a) (i) Define first electron affinity.
(ii) The first electron affinity of an atom is usually an exothermic process, whereas the second electron affinity is an endothermic process.
Suggest why.
(iii) Describe the general trend in first electron affinities for Cl, Br and I. Explain your answer.
(b) Table 3.1 shows energy changes to be used in this question and in (c).
Table 3.1
| energy change | value/kJ mol$^{-1}$ |
| :--- | :--- |
| standard enthalpy change of atomisation of zinc | +131 |
| first ionisation energy of zinc | +906 |
| second ionisation energy of zinc | +1733 |
| standard enthalpy change of formation of ZnI$_2$(s) | –208 |
| lattice energy, $\Delta H_{\text{latt}}$, of zinc iodide, ZnI$_2$(s) | −2605 |
| first ionisation energy of iodine | +1008 |
| second ionisatioCalculate 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_{\text{latt}}^{\circ}$ of CdI$_2$(s) differs from $\Delta H_{\text{latt}}^\circ$ of ZnI$_2$(s).
Place a tick ($\checkmark$) in the appropriate box in Table 3.2.
Table 3.2
| $\Delta H_{\text{latt}}^{ \circ} $ of CdI$_2$(s) is less negative than $\Delta H_{\text{latt}}^ { \circ} $ of ZnI$_2$(s) | $\Delta H_{\text{latt}} ^ {\circ} $ of CdI$_�$(s) is the same as $\Delta H_{\text{latt}} ^{ \circ} $ of ZnI}_2$(s) | $\Delta H_{\mathrm{latt}} ^ {\circ} $
of CdI$_2$(s) is more negative than $\Delta H_{\mathrm{latt}}^ {\circ} $ of ZnI$_�$(s) |
4 (a) Calcium carbonate decomposes on heating.
$$\text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g)$$
Table 4.1 shows the values of the Gibbs free energy change, $\Delta G^\circ$, for this reaction at various temperatures.
| $T/K$ | $\Delta G^\circ/\text{kJ mol}^{-1}$ |
| :---: | :---: |
| 1050 | 9.9 |
| 1085 | 4.3 |
| 1120 | -1.3 |
| 1148 | -5.8 |
| 1176 | -10.3 |
Assume the standard enthalpy change, $\Delta H^\circ$, and the standard entropy change, $\Delta S^\circ$, for this reaction remain constant over this temperature range.
(i) Use the data in Table 4.1 to plot a graph of $\Delta G^\circ$ against $T$ on the grid.
(ii) Calculate the gradient of your graph. Determine the $\Delta S^\circ$ in JK$^{-1}$mol$^{-1}$ for this reaction. Show all working.
$$\Delta S^\circ = \do(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. (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. (c) The buffer system in seawater contains a mixture of HCO$_3^-$ and H$_2$CO$_3$. Equilibrium 5: $H_2CO_3 + H_2O \rightleftharpoons HCO_3^- + H_3O^+$ (i) Define a buffer solution. (ii) Construct two equations to show how equilibrium 5 acts as a buffer solution. (iii) The $[HCO_3^-]/[H_2CO_3]$ ratio in a sample of seawater is 14.1. Calculate the pH of this sample. $pK_a: H_2CO_3, 6.35$ $p
5 (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
| electrolyte | substance liberated at the anode | substance liberated at the cathode |
| :--- | :---: | :---: |
| $PbBr_2(l)$ | | |
| concentrated NaCl(aq) | | |
| $\text{Cu(NO}_3)_2(\text{aq})$ | | |
(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 0.350 g.
(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 6 (a) The reagent and conditions required for the nitration of benzene, benzoic acid and phenol are shown in Table 6.1. Table 6.1 | compound | reagents and conditions for nitration | | :--- | :--- | | benzene | concentrated HNO$_3$, 50 °C, concentrated H$_2$SO$_4$ catalyst | | benzoic acid | concentrated HNO$_3$, 100 °C, concentrated H$_2$ SO$_4$ catalyst | | phenol | dilute HNO$_3$(aq), 20 °C | 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. Fig. 6.1 (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.
(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 $-\text{SO}_3^-$-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 ..... [Total: 16]7 (a) State the uses of TMS and D$_2$O in NMR spectroscopy.
TMS ... [1]
(b) The three isomeric ketones with molecular formula C$_5$H$_{10}$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 ($^1\text{H}$) NMR spectrum and in the carbon-13 NMR spectrum for each compound listed.
Table 7.1
| ketone | number of peaks observed in the proton ( $^1\text{H}$ ) NMR spectrum | number of peaks observed in the carbon-13 NMR spectrum |
| :--- | :---: | :---: |
| pentan-2-one | | |
| pentan-3-one | | |
| 3-methylbutanone | | |
(ii) State all the ketones with molecular formula C$_5$$H_{10}$$\textcircled{O}$ that have:
a doublet in their proton ( $^1\text{H}$( $^1\text{H}$) NMRpectrum
a singlet in their proton ( $^1\t(c) Cortisone, $C_{21}H_{28}O_5$, is a naturally occurring chemical that contains chiral carbon atoms.
**Fig. 7.1**
(i) Deduce the number of chiral carbon atoms in one molecule of cortisone.
[1]
(ii) Cortisone is reacted with an excess of NaBH$_4$.
State the molecular formula of the organic compound formed.
[1]
(iii) Cortisone is an optically active molecule.
Explain what is meant by optically active.
[1]
[Total: 8]8 (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 KMnO$_4$(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.
$$\text{polyester}$$
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.
$$\text{serine}$$
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.
[Total: 11]9 The structure of cyclohexylamine is shown in Fig. 9.1. cyclohexylamine 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. Fig. 9.2 (i) Name the mechanism for the reaction shown in Fig. 9.2. [1] (ii) Complete the mechanism of the reaction between cyclohexylamine and CH₃COCl. R–NH₂ is used to represent cyclohexylamine. Include all relevant lone pairs of electrons, curly arrows, charges and partial charges. H₃C—CCl products R—NH₂ (iii) The reaction between cyclohexylamine and an excess of CH₃COCl forms compound M. Compound M has the molecular formula C₁₀H₁₇NO₂. Suggest and draw the structure of M. [Total: 9]