科目：化学 Chemistry (9701)
年份：2025 夏季
试卷：Paper 42
总页数：20
章节：19 Lattice energy, 20 Electrochemistry, 21 Further aspects of equilibria, 22 Reaction kinetics, 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, 30 Analytical chemistry
1. (a) (i) Calcium nitrate, Ca(NO$_3$)$_2$, decomposes on heating. Write an equation for the decomposition of calcium nitrate. [1] (ii) Describe the trend in the decomposition temperature of the Group 2 nitrates. Explain your answer. [3] (b) A sample of 0.333 g of strontium oxide, SrO, is completely dissolved in distilled water to form a solution of strontium hydroxide, Sr(OH)$_2$. The resulting solution is added to a volumetric flask and made up to 250.0 cm$^3$ with distilled water. Calculate the pH of this solution at 298 K. Give your answer to two decimal places. pH = ..... [4] [Total: 8]
2 (a) When cobalt(II) sulfate, CoSO$_4$, is dissolved in distilled water, solution A is formed.
The reaction scheme in Fig. 2.1 shows some reactions of solution A.
Fig. 2.1
(i) Complete Table 2.1 to show the formula and colour of each of the cobalt-containing species present in A, B and C. Identify the type of reaction forming each of B and C.
Table 2.1
| | formula of cobalt-containing species | colour of cobalt-containing species | type of reaction |
| :--- | :---: | :---: | :---: |
| A | | | |
| B | | | |
| C | | | |
(ii) Suggest a suitable reagent for the formation of [CoCl$_4$]$^{2-}$ from solution A.
[1]
(b) The complex ion [CoCl$_4$]$^{2-$} has tetrahedral geometry.
The 3d orbitals in an isolated Co$^{2+}$ ion are degenerate.
(i) Complete Fig. 2.2 to show the relative energ(ii) Draw a three-dimensional diagram to show the structure of the complex ion $[\text{CoCl}_4]^{2-}$.
(c) $\text{H}_2\text{O}_2$ can act as an oxidising agent or a reducing agent when reacting with species that contain manganese.
Table 2.2 shows electrode potentials, $E^\ominus$, for some electrode reactions.
| electrode reaction | $E^\ominus/\text{V}$ |
| :--- | :--- |
| $\text{MnO}_2 + 2\text{H}_2\text{O} + 2\text{e}^-$ $\rightleftharpoons \text{Mn(OH)}_2 + 2\text{OH}^-$ | $-0.04$ |
| $\text{MnO}_� + 4\text{H}^+ + 2\text{e}^-$ $\leftarrow \text{Mn}^{2+} + 2\text{H}_2\text{\text{O}}$ | $+1.22$ |
| $\text{H}_2\text{O}_{2} + 2\text{H}^+ + 2\text{\text{e}}^-$ $\rightleftharpoons 2\text{H}_2\text{\mathrm{O}}$ | $+1.78$ |
| $\text{H}_2\mathrm{O}_2 + \text{OH}^- + 2\text{\text{e}}^{-}$ $\ri(d) Acidified manganate(VII) ions, MnO$_4^-$, can be used to analyse the content of iron tablets by titration.
Two identical iron tablets are crushed and dissolved in distilled water.
The resulting solution is made up to 150.0 cm$^3$ with distilled water.
25.0 cm$^3$ of this solution requires 18.60 cm$^3$ of 0.0500 mol dm$^{-3}$ acidified MnO$_4^-$ to reach the end-point. All the Fe$^{2+}$ ions are oxidised.
The relevant half-equations are shown.
$$\text{MnO}_4^- + 8\text{H}^+ + 5\text{e}^- \rightleftharpoons \text{Mn}^{2+} + 4\text{H}_2\text{O}$$
$$\text{Fe}^{2+} \rightleftharpoons \text {Fe}^{3+} + \text{e}^-$$
(i) Describe the colour change observed at the end-point of this titration.
from ... to ... [1]
(ii) Calculate the mass, in mg, of iron in one tablet.
Assume that all the (a) Define entropy. (b) Fig. 3.1 shows how the entropy, $S$, of a pure substance changes with temperature, $T$. Fig. 3.1 (i) Identify the process occurring at each of the temperatures $T_1$ and $T_2$. $$T_1 \quad T_2$$ [1] (ii) Explain why the entropy change, $\Delta S$, at $T_2$ is bigger than the entropy change at $T_1$.
(c) The equation for the reduction of iron(III) oxide by carbon monoxide at 450 °C is shown.
$$\text{Fe}_2\text{O}_3(s) + 3\text{CO}(g) \rightarrow 2\text{Fe}(s) + 3\text{CO}_2(g) \quad \Delta G^\ominus = -36.2 \text{kJ mol}^{-1}$$
Table 3.1 shows the enthalpy of formation, $\Delta H_f^\ominus$, and the entropy, $S^\ominus$, for some substances.
| | Fe$_2$O$_3$(s) | CO(g) | Fe(s) | CO$_2$(g) |
| :---: | :---: | :---: | : ---: | :---: |
| $\Delta H_f^\ominus / \text{kJ mol}^{-1}$ | −824.2 | −110.5 | 0.0 | −393.5 |
| $S^\ominus / \text{J K}^{-1} \text{mol}^{-1}$ | 87.4 | to be calculated | 27.3 | 213.8 |
Use the data in Table 3.1 to calculate the entropy, $S^\ominus}$, of carbon monoxide at 450°C.
Show your working.
$$S^\ominus \text{ of CO}(g) = \dots\dots\dots\dots\mathrm{JK}^{-1} \t4 (a) In aqueous solution, iodide ions react with acidified hydrogen peroxide, as shown in reaction 1.
$$2I^- + H_2O_2 + 2H^+ \rightarrow I_2 + 2H_2O$$
The rate equation for reaction 1 is shown.
$$\text{rate} = k [I^-][H_2O_2]$$
(i) Explain what is meant by order of reaction.
[1]
(ii) Complete Table 4.1.
Table 4.1
| the order of reaction with respect to $[H^+]$ | |
| :--- | :--- |
| the order of reaction with respect to $[\text{I}^-]$ | |
| the order of reaction with respect to $$[H_2O_2]}$$ | |
| overall order of the reaction | |
[2]
(iii) Sketch a line on Fig. 4.1 to show the relationship between $[I^-]$ and time.
Fig. 4.1(b) Nitrogen dioxide, NO₂, reacts with ozone, O₃, as shown in reaction 2.
reaction 2 $\quad$ $2\text{NO}_2 + \text{O}_3 \rightarrow \text{O}_2 + \text{N}_2\text{O}_5$
The rate equation for reaction 2 is shown.
$$\text{rate} = k [\text{NO}_2][\text{O}_3]$$
(i) Two experiments are carried out to measure the rate of reaction 2.
In the first experiment, the initial rate is measured starting with known concentrations of NO₂ and O₃. In the second experiment, the concentrations of NO₂ and O₃ are both increased by a factor of four.
Predict how the initial rate for reaction 2 would change.
[1]
(ii) The reaction mechanism for reaction 2 has two steps.
Define rate-determining step.
[1]
(iii) Suggest equations for the two steps of the reaction mechanism for reaction 2.
step 1 ...
step 2 .(c) Dinitrogen pentoxide, $N_2O_5$, can decompose to NO$_2$ and O$_2$.
The rate equation for this decomposition is shown.
$$\text{rate} = k [N_2O_5]$$
Fig. 4.2 shows the graph of rate against $[N_2O_5]$ for this decomposition.
**Fig. 4.2**
(i) Use Fig. 4.2 to calculate a value for the rate constant, $k$, for this decomposition.
$$k = \dots\dots\dots\dots\ldots\ldots\ldots\ldotp$$
(ii) Use your answer to (c)(i) to calculate the half-life, $t_{\frac{1}{2}}$, in seconds, for this decomposition.
$$t_{\frac{1}{2}} = \dots\dots\dottp s$$
[Total: 10]5 (a) Chloric(I) acid, HClO, is a weak Brønsted–Lowry acid.
When chloric(I) acid is added to aqueous sodium hydroxide, an acid–base reaction takes place, as shown.
$$\text{HClO} + \text{NaOH} \rightarrow \text{NaClO} + \text{H}_2\text{O}$$
(i) Identify the two conjugate acid–base pairs in this reaction.
- acid I: HClO
- conjugate base of acid I:
- acid II: .....
- conjugate base of acid II:
[1]
(ii) The value for the acid dissociation constant, $K_a$, of HClO(aq) is $3.70 \times 10^{-8}$.
Calculate the concentration, in mol dm$^{-3}$, of HClO(aq) at a pH of 4.51.
$$\text{concentration of HClO} = \dots\dots\dots\dots\mathrm{mol}\,\mathrm{dm}^{-3}$$
(iii) When a solution of HClO(aq) is heated, chloric(V) acid and a strong acid not containing oxygen are formed as the only products.
Wr(c) Some fertilisers contain calcium dihydrogenphosphate, Ca(H₂PO₄)₂.
An aqueous solution containing dihydrogenphosphate ions, H₂PO₄⁻, can act as a buffer solution.
Write two equations to show how H₂PO₄⁻ ions can act as a buffer.
equation 1 ... [2]
(d) The solubility of calcium phosphate, Ca₃(PO₄)₂, is $1.14 \times 10^{-7}$ mol dm³ at 25°C.
(i) The expression for the solubility product, K_sp, of Ca₃(PO₄)�2 is shown.
$$K_{sp} = [Ca^{2+}]^3[PO_4^{3-}]^2$$
Calculate the value of K_sp for Ca₃(PO₄)�２. Include units.
$$K_{sp} = \text{units}$$
(ii) Some solid sodium phosphate is added to a saturated solution of Ca₃(PO₄)².
Predict the effect, if any, on the solubility of Ca₃(PO₄)②.
Explain your answer.
[Total: 12]6 (a) Methylbenzene reacts readily with nitronium ions, NO$_2^+$. NO$_2^+$ ions are generated by the reaction between concentrated nitric acid and concentrated sulfuric acid. (i) Write an equation for the formation of the NO$_2^+$ ion. (ii) Complete the mechanism in Fig. 6.1 for the nitration of methylbenzene to form 1-methyl-2-nitrobenzene. Include all relevant curly arrows and charges.  (b) Phenol can be nitrated with dilute nitric acid. Explain why the nitration of phenol occurs under milder conditions than the nitration of benzene. [2] (c) A sample of 2-nitrophenol is reacted with sodium. Complete the equation in Fig. 6.2 for the reaction of 2-nitrophenol with sodium. [1]
(d) 2-nitrophenol can undergo different reactions as shown in Fig. 6.3. Fig. 6.3 (i) Suggest reagents and conditions for reaction 1. [1] (ii) Name the type of reaction for reaction 1. [1] (iii) Reaction 2 is carried out at room temperature. Draw the structure of the organic product from reaction 2 in Fig. 6.3.[1] (iv) Name the mechanism for reaction 2. [1] (e) The NO$_2$ group in 2-nitrophenol is electron withdrawing. Suggest the relative acidities of ethanol, 2-nitrophenol, phenol and water. Explain your answer. most acidic least acidic
(f) Salbutamol is a pharmaceutical drug that contains a phenol functional group.
Fig. 6.4
(i) Name and classify the three other functional groups in salbutamol in Table 6.1.
Table 6.1
| name of functional group | classification of functional group |
| :--- | :--- |
| | |
(ii) Salbutamol reacts with Br$_2$(aq) to form organic product X.
Draw the structure of X.
(iii) Salbutamol reacts with an excess of SOC$l_2$ to form organic product Y.
The molecular formula of Y is C$_{13}$H$_{19}$Cl$l_2$NO.
Draw the structure of Y.7 (a) 2-aminobutane, CH$_3$CH(NH$_2$)CH$_2$CH$_3$, exists as a mixture of two enantiomers.
Define enantiomers.
[1]
(b) (i) Explain why an aqueous solution of 2-aminobutane has a pH greater than 7.
Include an equation in your answer.
[2]
(ii) A $0.10 \text{ mol dm}^{-3}$ solution of diethylamine, $(\text{CH}_3\text{CH}_2)_2\text{NH}$, has a higher pH than a $0.10 \text{ mol } \text{dm}^{-3}$ solution of 2-aminobutane, $\text{CH}_3\text{CH}(\text{NH}_2)\text{CH}_2\text{CH}_3$.
Suggest why.
[2]
(iii) $(\text{CH}_3\text{Ch}_2)_2\text{NH}$ reacts with ethanoic acid, $\text{CH}_3\text{COOH}$.
Complete the equation for this reaction.
$(\text{CH}_3\text{Ch}^2)_2\text{NH} + \text{CH}_3\text{COOH} \rightarrow$ [1]
(iv) $(\text{CH}_3\text {Ch}_2)_2\text{NH}$ reacts with ethanoyl chloride, (c) Table 7.1 shows monomers that can undergo polymerisation. (i) Complete Table 7.1. Table 7.1 | monomer | type of polymerisation | | :--- | :--- | | CH$_2$C(CH$_3$)COOH | | | Chemical structure for CH$_2$C(CH$_3$-)COOH | | | CH$_3$CH(NH$_2$)COOH | | (ii) Ethanedioic acid, HOOCCOOH, can react with propane-1,3-diamine, H$_2$NCH$_2$CH$_2$CH$_2$NH$_2$, to form polymer W. Draw a section of polymer W showing only one repeat unit. The new functional group formed should be displayed. (iii) Poly(alkenes) biodegrade very slowly. Explain why. [Total: 11]
(a) Compound A is analysed by carbon-13 NMR and proton (¹H) NMR spectroscopy. Fig. 8.1 State the reference substance and a solvent that can be used in NMR spectroscopy. reference ... solvent ... [1] (b) Predict the number of peaks in the carbon-13 NMR spectrum of A. ... [1] (c) The proton (¹H) NMR spectrum of A shows peaks in four different chemical environments. Complete Table 8.1 for the proton (¹H) NMRpectrum of A. Table 8.1 | chemical shift $\delta$/ppm | splitting pattern | number of protons on adjacent carbon atoms | number of $^1$H atoms responsible for the peak | | :--- | :--- | :--- | :--- | | 1.10 | | | | | 1.50 | | | 6 | | 2.85 | | | | | 3.75 | | | | [Total: 6]
Table 8.2
| environment of proton | example | chemical shift range $\delta$/ppm |
| :--- | :--- | :--- |
| alkane | $-CH_3$, $-CH_2^{-}$, $>CH^{-}$ | 0.9–1.7 |
| alkyl next to C=O | $CH_3-C=O$, $-CH_2-C=O$, $>CH-C=O$ | 2.2–3.0 |
| alkyl next to aromatic ring | $CH_3-Ar$, $-CH_2-Ar$, $>CH-Ar$ | 2.3–3.0 |
| alkyl next到 electronegative atom | $CH_3-O$, $-CH_2-O$, $-CH_2-Cl$ | 3.2–4.0 |
| attached to alkene | =CHR | 4.5–6.0 |
| attached to aromatic ring | H–Ar | 6.0–9.0 |
| aldehyde | HCOR | 9.3–10.5 |
| alcohol | ROH | 0.5–6.0 |
| phenol | Ar–OH | 4.5–7.0 |
| carboxylic acid | RCOOH | 9.0–13.0 |
| alkyl amine | R-NH- | 1.0–5.0 |
| aryl amine | Ar-NH$_2$ | 3.0–6.0 |
| amide | RCONHR | 5.0–12.0 |9 (a) The structures of the amino acids serine and lysine are shown in Fig. 9.1.
serine
$$\text{CH}_2\text{OH}$$
$$\text{H}_2\text{N} \longrightarrow \text{C} \longrightarrow \text{COOH}$$
lysine
$$\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\nu_{2}$$
$$\text{H}_2\text{N} \longrightarrow \text C \longrightarrow \text{COOH}$$
Fig. 9.1
Draw the structure for the dipeptide, ser–lys, with molecular formula $C_9H_{19}N_3O_4$. The peptide functional group formed should be displayed.
[2]
(b) The isoelectric point of serine is 5.7 and of lysine is 9.7.
(i) State what is meant by isoelectric point.
[1]
(ii) A mixture of serine, lysine and ser–lys is analysed by electrophoresis using a buffer at pH 5.7.
Fig. 9.2
Draw and label three spots on Fig. 9.2 to indicate the predicted position o(c) Fig. 9.3 shows the synthesis of compound R from compound P. (i) Draw the structure of Q in Fig. 9.3. [1] (ii) State the reagents and conditions for steps 1 and 2 in Fig. 9.3. step 1 ... step 2 ... [2] [Total: 9]