科目：化学 Chemistry (9701)
年份：2025 冬季
试卷：Paper 42
总页数：23
章节：19 Lattice energy, 20 Electrochemistry, 21 Further aspects of equilibria, 22 Reaction kinetics, 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
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1 Magnesium nitrate, Mg(NO$_3$)$_2$, and strontium nitrate, Sr(NO$_3$)$_2$, both decompose when heated to form the metal oxide and a mixture of gases. (a) Write an equation for the thermal decomposition of Mg(NO$_3$)$_2$. [1] (b) State which of Mg(NO$_3$)$_�$ or Sr(NO$_3$)$_�$ decomposes at a lower temperature. Explain your answer. Compound that decomposes at a lower temperature explanation [2] (c) Magnesium oxide, MgO, and strontium oxide, SrO, both react with dilute sulfuric acid. MgO forms a soluble salt, A. SrO forms an insoluble salt, B. (i) Identify the products formed when MgO reacts with dilute sulfuric acid. [1] (ii) Explain why A is more soluble than B. [3] Total: 7
2 Ethanal, CH$_3$CHO, reacts with nitrogen dioxide, NO$_2$. The products of the first step of this reaction are a CH$_3$C=O radical and a molecule of nitrous acid, HNO$_2$.
$$\text{CH}_3\text{CHO} + \text{NO}_2 \rightarrow \text{CH}_3\text{C}=\text{O} + \text{HNO}_2$$
(a) (i) Use two words to complete the sentence.
This reaction involves ... of the single covalent bond between a hydrogen atom and a carbon atom in CH$_3$CHO.
(ii) The hydrogen atom mentioned in (a)(i) forms a covalent bond with one of the oxygen atoms of an NO$_2$ molecule. An NO$_2$ molecule has a single, unpaired electron on the nitrogen atom. All electrons are paired in an HNO$_2$ molecule.
Draw dot-and-cross diagrams of NO$_2$ and HNO$_2$ in the boxes. Show outer shell electrons only.
(iii) Use VSEPR theory to pred(c) The reaction mixture described in (b) is monitored over a period of time.
Predict whether the graph of $[NO_2]$ against time shows a constant half-life.
Explain your answer.
prediction ..... [1]
(d) NO$_2$ also reacts with ozone, O$_3$.
The rate equation is shown.
$$\text{rate} = k_1[NO_2]$$
Under certain conditions, the value of $k_1$ is 0.0848 s$^{-1}$.
The reaction has a constant half-life under these conditions.
Calculate the half-life in seconds.
$$\text{half-life} = \dots\dots\dots\dots\square$$ [1]
(e) NO$_2$ is present in the exhaust gases of cars. It can react with carbon monoxide, CO, on the surface of a heterogeneous catalyst in the car’s catalytic converter.
Describe the mode of action of this heterogeneous catalyst.
[Total: 9](a) (i) Define conjugate acid–base pair.
(ii) Give the formulas of the conjugate acid and the conjugate base of the hydrogen phosphate ion, HPO$_4^{2-}$.
conjugate acid of HPO$_4^{2-}$ .....
conjugate base of HPO$_4^{2-}$ ... [1]
(b) The $K_a$ of propanoic acid, CH$_3$CH$_2$COOH, is $1.35 \times 10^{-5} \text{ mol dm}^{-3}$ at 298 K.
Solution C is a solution of CH$_3$CH$_2$COH with a pH of 3.60 at 298 K.
(i) Calculate the concentration of CH$_3$CH$_2$ COOH in solution C.
$$[\text{CH}_3\text{CH}_2\text{COOH}] = \dots\dots\dots\dots\mathrm{mol dm}^{-3}$$
(ii) Calculate the concentration of hydroxide ions in solution C.
$$[\text{OH}^-] = \dots\dots\dotted\dots\mathrm{mol dm^{-3}}$$
(iii) Calculate the concentration of a solution of hydrochloric acid with the same pH as solution C.
(iv) Table 3.1 shows three possible values of the $K_a$ of dimethylpropanoic acid, $(\text{CH}_3)_3\text{CCOOH}$.
Place a tick in Table 3.1 to show the correct value. Explain your answer.
Table 3.1
| value of $K_a$/mol dm$^{-3}$ | place one tick (✓) in this column |
| :--- | :--- |
| $9.33 \times 10^{-6}$ | |
| $1.35 \times 10^{-5}$ | |
| $3.35 \times 10^{-4}$ | |
explanation ..... [3]
(c) Solution D is made by mixing $100\text{cm}^3$ of $0.100\text{mol}\text{dm}^{-3}\text{CH}_3\text{CH}_2\text{COOH}$ and $100\text{cm}^3$
of $0.100\text{mol}$$\text{dm}^{-3}\text{NaCl}$.
The pH of solution D is measured as small amounts of $\text{H}_2\text{SO}_4$(aq) are added to it, and when small amounts of NaOH(aq) are added to it.
Solution D only acts as a buffer solution when one of these soluti(d) Manganese(II) hydroxide, $Mn(OH)_2$, is only slightly soluble in water.
The solubility of $Mn(OH)_2$ in water is $3.28 \times 10^{-3} \text{ g dm}^{-3}$ at 298 K.
(i) Calculate the concentration of a saturated solution of $Mn(OH)_2$ at 298 K.
$$[Mn(OH)_2] = \dots\dots\dots\dots\mathrm{mol}\,\mathrm{dm}^{-3}$$
(ii) Write an expression for the $K_{sp}$ of $Mn(OH)_2$. Give the units of $K_{sp}$.
$$K_{sp} = \quad \text{units} = \dots\dots\dottots\dots\dots\dot\dots\dots$$
(iii) Use your answers to (d)(i) and (d)(ii) to calculate the value of $K_{sp}$ of $Mn(\text{OH})_2$ at 298 K.
$$K_{sp} = \dots\dots\ddots\ddots\dots\dots\dotted\dots\dots\dots$$
[Total: 15](a) Define enthalpy change of atomisation, $\Delta H_{\text{at}}$.
[1]
(b) Define first electron affinity, EA.
[1]
(c) Explain why the first electron affinity of chlorine is more exothermic than the first electron affinity of iodine.
[2]
(d) The enthalpy change for the reaction $C l_2(g) + 2e^- \rightarrow 2 C l^-(g)$ is $-486\text{ kJ mol}^{-1}$. The first electron affinity of chlorine is $-364\text{ kJ mol}^{-1}$.
Calculate the enthalpy change of atomisation of chlorine.
$$\Delta H_{\text{at}} \text{ of chlorine} = \dots\dots\dots\dots\kappa J \text{ mol}^{-1}$$
[Total: 6]5 Cobalt is a transition element which forms compounds containing Co$^{2+}$ and Co$^{3+}$ ions. Cobalt(II) sulfate dissolves in water to form a solution containing the $[\text{Co(H}_2\text{O})_6]^{2+}$ complex ion.
(a) (i) Complete the electronic configurations of a Co$^{2+}$ ion and a Co$^{3+}$ ion.
$$\text{Co}^{2+} = [\text{Ar}] \quad .....$$
$$\text{Co}^{3+} = [\text{Ar}]$$
[1]
(ii) Explain why transition elements can form complex ions.
...
[1]
(iii) An excess of concentrated HCl is added to a solution containing $[\text{Co(H}_2\text {O})_6]^{2+}$.
Describe the colour change observed and the state of the cobalt-containing product.
The colour changes from ... to ...
The state of the cobalt-containing product is ... .
[2]
(iv) Write an equation for the reaction occurring in (a)(iii(b) Cobalt metal can be oxidised by acidified K$_2$Cr$_2$O$_7$. The relevant half-equations, and their $E^\circ$ values, are shown.
$$\text{Co}^{2+} + 2\text{e}^- \rightleftharpoons \text{Co}$$
$$\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6\text{e}^- \rightlefsharpoons 2\text{Cr}^{3+} + 7\text{H}_2\text{O}$$
(i) A Co$^{2+}/\text{Co}$ electrode is constructed in which [Co$^{2+}$] is 0.020 mol dm$^{-3}$ at 298 K.
Use the Nernst equation to show that the $E^\circ$ value for this Co$^{2+}/\text{CO}$ electrode is –0.33 V.
[2]
(ii) An electrochemical cell is constructed using the Co$^{2+}/\text{ CO}$ electrode described in (b)(i) and a Cr$_2\text{O}_7^{2-}/\text{Cr}^{3+}$ electrode in which all conditions are standard.
Calculate the value of $E_{\text{cell}}$.
$$E_{\text{cell}} = ...$$
[1(a) Nickel forms complexes.
(i) Give the formula and charge of the tetrahedral complex formed by Ni atoms with carbon monoxide molecules. Carbon monoxide is a monodentate ligand. This is complex E.
$$E = \ldots$$
(ii) Give the formula and charge of the octahedral complex formed by Ni$^{2+}$ ions with ethanedioate ions. This is complex F.
$$F = \ldots$$
(iii) Identify which complex, E or F, exists as a mixture of two stereoisomers and the type of stereoisomerism involved.
The complex which exists as a mixture of two stereoisomERS is ...
The type of stereoisomerism involved is ...
(b) Cadmium forms complexes with methylamine, CH$_3$NH$_2$, and 1,2-diaminoethane, en. The values of the stability constants, $K_{\text{stab}}$, of these complex ions are given in Table 6.1.
| complex | $K_{\t7 P, Q, R, S, T, U, and V are the seven structural isomers with molecular formula $C_5H_{10}O$ that have a carbonyl group.
P $\text{CH}_3(\text{CH}_2)_3\text{CHO}$
Q $\text{CH}_3\text{CH}_2\text{CH}(\text{CH}_3)\text{CHO}$
R $(\text{CH}_3)_2\text{CHCH}_2\text{CHO}$
S $(\text{CH}_3)_3\text{CCHO}$
T $\text{CH}_3\text{CH}_{2}\text{CH}_2\text{COCH}_3$
U $\text{CH}_3\text{CH}_{\2}\text{COCH}_2\text{CH}_3$
V $(\text{CH}_3)_2\text{CHCOCH}_3$
(a) Only one of these seven compounds has stereoisomers.
Draw three-dimensional diagrams of the two stereoisomers of this compound.
(b) P, Q, R, S, T，U，and V are treated separately with alkaline $I_2$(aq) and the product mixture is acidified.
(i) Identify the two compounds that give a positive result with alkaline $I_2$(aq).
... and ... [1]
(c) The proton (1H) NMR spectra of P, Q, R, S, T, U, and V are compared. (i) Identify the only compound that gives a spectrum with two singlets and no other peaks. Fig. 7.1 shows the spectrum obtained from one of the compounds. Fig. 7.1 (ii) Identify the compound that gives this spectrum. [1] (iii) Name the splitting pattern of the peak at $\delta = 1.1$ in Fig. 7.1. Give the reason for this splitting. name ..... reason ..... [1] (iv) Identify the substance that gives the small peak at $\delta = 0$ in Fig. 7.1. [1]
(d) The carbon-13 NMR spectra of R, S, T and U are compared.
Complete Table 7.1 to state the number of peaks in the spectrum of each compound.
| compound | number of peaks |
| :--- | :--- |
| $R$ $(\text{CH}_3)_2\text{CHCH}_2\text{CHO}$ | |
| $S$ $(\text{CH}_3)_3\text{CCHO}$ | |
| $T$ $\text{CH}_3\text{CH}_2\text{CH}_2\text{COCH}_3$ | |
| $U$ $\text{CH}_3\text{Ch}_2\text{COCH}_2\text{CH}_3$ | |
[Total: 11]8 Asparagine and aspartic acid are two naturally occurring amino acids. Their structures and isoelectric points are shown in Table 8.1. Table 8.1 | amino acid | structure | isoelectric point | | :--- | :---: | :---: | | asparagine | HOOCCH(NH₂)CH₂CONH₂ | 5.41 | | aspartic acid | HOOCCH(NH₂)Ch₂COOH | 2.77 | (a) Define isoelectric point. [1] (b) Draw the structures of asparagine and aspartic acid at pH2. [2] (c) Asparagine and aspartic acid are treated separately with an excess of LiAlH₄. Draw the structures of the organic products of these reactions. [2]
(d) Propanedioic acid, HOOCCH$_2$COOH, is treated with an excess of thionyl chloride, SOC$_l_2$. Propanedioyl chloride, C$_l$OCCH$_2$COC$_l$, is formed.
(i) Write an equation for this reaction.
(ii) Propanedioyl chloride reacts with an excess of asparagine to form compound G with molecular formula C$_{11}$H$_{16}$N$_4$O$_8$.
Each molecule of compound G has four amide groups.
Draw the structure of compound G.
Compound G, C$_{11}$H$_{{16}}$N$_4$O$_8$
(e) Asparagine is hydrolysed with an excess of hot NaOH(aq).
Draw the structure of the organic product of this reaction.
(f) A polymer can form from asparagine, HOOCCH(NH$_2$)CH$_2$CONH$_2$, as the only monomer.
Draw a length of the polymer chain containing three monomer residues.
Clearly label the repeat unit of the polymer on your di(g) Aspartic acid exists in two optically active forms. (i) Plane polarised light is passed through pure samples of these two optically active forms in solutions of the same concentration. Describe **two** similarities and **one** difference in their effect on the plane polarised light. similarities ... difference ... [2] (ii) Give the term used to describe a mixture of equal amounts of the two optically active forms. [1] [Total: 16]
Question 9 starts on page 20.
9 Compound X is made from benzene by the route shown in Fig. 9.1. benzene Fig. 9.1 (a) Describe the bonding in benzene, $C_6H_6$. Your answer should include: • the hybridisation of the six carbon atoms • the types of bond between the carbon atoms • the orbitals that overlap to produce the bonds between the carbon atoms • the type of bond between the carbon atoms and the hydrogen atoms • the orbitals that overlap to producethe bonds between the carbon atoms and the hydrogen atoms. [3] (b) Describe the reagents and conditions required for step 1 in Fig. 9.1. [1]
(c) In step 1 of Fig. 9.1 benzene reacts with $^+CH_3$. Complete Fig. 9.2 to show the mechanism for this reaction, including: • the movement of electron pairs using curly arrows • the structure of the intermediate involved. Fig. 9.2 (d) Describe the reagents and conditions required for step 2 of Fig. 9.1. [2] (e) Identify the reagents required for step 3 of Fig. 9.1. Compound W is the product of this step. [1] (f) Name compound W. [1] (g) The reagents commonly used for step 4 will not reduce the –COOH group. Identify the reagents and conditions required for step 4 of Fig. 9.1. [1]
(h) Benzene can also be used as a starting material to make compound Y. compound Y Describe how the route described in Fig. 9.1 (repeated below) can be changed to give compound Y instead of compound X. Explain your answer. [2] benzene step 1 CH₃ step 2 NO₂ CH₃ step 3 W NO₂ COOH step 4 NH₂ COOH Fig. 9.1 [Total: 14]
Important values, constants and standards
| | |
| :--- | :--- |
| molar gas constant | $R = 8.31 \text{ JK}^{-1} \text{mol}^{-1}$ |
| Faraday constant | $F = 9.65 \times 10^4 \text{ C mol}^{-1}$ |
| Avogadro constant | $L = 6.02 \times 10^{23} \text{ mol}^{-1}$ |
| electronic charge | $e = -1.60 \times 10^{-19} \text{ C}$ |
| molar volume of gas | $V_m = 22.4 \text{ dm}^3 \text{ mol}^{-1}$ at s.t.p. (101 kPa and 273 K)
$V_m = 24.0 \text{ dm}^3 \text {mol}^{-1}$ at room conditions |
| ionic product of water | $K_w = 1.00 \times 10^{-14} \text{ mol}^2 \text{dm}^{-6}$ (at 298 K (25 °C)) |
| specific heat capacity of water | $c = 4.18 \text{ kJ kg}^{-1} \text{K}^{-1}$ (4.18 Jg}^{-1} \text{K}^{−1}) |The Periodic Table of Elements Group 1 2 3 Li lithium 6.9 4 Be beryllium 9.0 11 Na sodium 23.0 12 Mg magnesium 24.3 Key atomic number atomic symbol name relative atomic mass 1 H hydrogen 1.0 2 He helium 4.0 3 B boron 10.8 4 C carbon 12.0 5 N nitrogen 14.0 6 O oxygen 16.0 7 F fluorine 19.0 8 F fluorine 19.0 13 Al aluminium 27.0 14 Si silicon 28.1 15 P phosphorus 31.0 16 S sulfur 32.1 17 Cl chlorine 35.5 18 Ar argon 39.9 19 K potassium 39.1 20 Ca calcium 40.1 21 Sc scandium 45.0 22 Ti titanium 47.9 23 V vanadium 50.9 24 Cr chromium 52.0 25 Mn manganese 54.9 26 Fe iron 55.8 27 Co cobalt 58.9 28 Ni nickel 58.7 29 Cu copper 63.5 30 Zn zinc 65.4 31 Ga gallium 69.7 32 Ge germanium 72.6 33 As arsenic 74.9 34 Se selenium 79.0 35 Br bromine 79.9 36 Kr krypton 83.8 37 Rb rubidium 85.5 38 Sr st