科目：化学 Chemistry (9701)
年份：2025 冬季
试卷：Paper 43
总页数：25
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, 29 Organic synthesis, 30 Analytical chemistry
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1. (a) Solutions of Group 2 hydrogencarbonates, $M(HCO_3)_2$, decompose on heating to give the corresponding metal carbonate, carbon dioxide and water. (i) Write an equation for the decomposition of strontium hydrogencarbonate, $Sr(HCO_3)_2$. [1] (ii) The thermal stability of Group 2 carbonates increases down the group. Explain this trend. [2] (b) The hydroxides and fluorides of Group 2 elements show similar trends in solubility. Describe the trend in the solubility of the fluorides of calcium, strontium and barium. Explain your answer. least soluble most soluble explanation ...
(c) (i) Define enthalpy change of hydration, $\Delta H_{\text{hyd}}$.
[1]
(ii) State the main factors that affect the magnitude of enthalpy change of hydration. Explain your answer.
[2]
(d) Table 1.1 shows various energy changes.
| energy change | value / kJ mol$^{-1}$ |
| :--- | :---: |
| lattice energy of MgF$_2$ | $-2957$ |
| enthalpy change of hydration, $\delta H_{\text{hyd}}$, of Mg$^{2+}$ | $-1926$ |
| enthalpy change of hydation, $\Delta H_{\text{hyd}}$, of F$^-$ | $-505$ |
Use data from Table 1.1 to calculate the enthalpy change of solution, $\Delta H_{\text{sol}}$, for MgF$_2$(s).
It may be helpful to draw a labelled energy cycle. Show your working.
$\Delta H_{\text{sol}}$ of MgF$_2$(s) = ... kJ mol$^{-1}$ [2](e) Mercury(I) fluoride, Hg$_2$F$_2$, is sparingly soluble in water.
The cation in Hg$_2$F$_2$ exists as the diatomic ion Hg$_2^{2+}$ with a covalent Hg–Hg bond.
(i) Write the expression for the solubility product, $K_{sp}$, of Hg$_2$F$_2$. Include the units.
$$K_{sp} = \text{units}$$
(ii) The solubility of Hg$_2$F$_2$ is 9.20 $\times 10^{-3}$ mol dm$^{-3}$ at 298 K.
Calculate the value of $K_{sp}$ of Hg$_2$F$_2$-at 298 K.
$$K_{sp} = \text{\ldots}$$
[Total: 15]2 (a) Iron can form stable ions in the +2 and +3 oxidation states.
Explain why transition elements have variable oxidation states.
[1]
(b) Aqueous solutions of iron(II) salts contain the complex ion $[\text{Fe}(\text{H}_2\text{O})_6]^{2+}$.
Define complex ion.
[1]
(c) $[\text{Fe}(\text{H}_{2}\text{O})_6]^{2+} \text{ can be converted into } [\text{Fe}(\text{H}_2\text{O})_4(\text{OH})_2]$.
(i) Suggest a suitable reagent for this conversion. State the type of reaction.
reagent ..... type of reaction ..... [1]
(ii) $[\text{Fe}(\text{ H}_2\text{O})_4(\text{OH })_2]$ is a green precipitate that turns brown on standing in air.
Table 2.1 shows electrode potentials for some electrode reactions.
| electrode reaction | $E^\ominus / V$ |
| :--- | :--- |
| $\text{Fe}(\text{H}_2{\text{O}})_3((d) The complex $[\text{Co}(\text{NH}_3)_6]^{2+}$ reacts with hydrogen peroxide as shown.
$$\text{reaction 1} \quad 2[\text{Co}(\text{NH}_�)_6]^{2+} + \text{H}_2\text{O}_2 \rightarrow 2[\text{Co}(\text{Nh}_�)_6]^{3+} + 2\text{OH}^- \quad E_{\text{cell}} = +1.67\text{V}$$
Calculate $\Delta G^\ominus$, in kJ mol$^{-1}$, for reaction 1.
$\Delta G^\ominus = \dots\dots\dots\dots\mathrm{kJ mol}^{-1}$ [2]
[Total: 8]3 (a) Solid manganese(IV) oxide, MnO$_2$, catalyses the decomposition of hydrogen peroxide.
$$2\text{H}_2\text{O}_2(\text{aq}) \rightarrow 2\text{H}_2\text{O}(\text{l}) + \text{O}_2(\text{g})$$
State the type of catalysis for this reaction. Explain your answer.
[1]
(b) Hydrogen peroxide reacts with iodide ions in acidic conditions as shown.
$$\text{H}_2\text{O}_2 + 2\text{I}^- + 2\text{H}^+ \rightarrow 2\text{H}_�\text{O} + \text{I}_2$$
The initial rate of this reaction is investigated with different concentrations of H$_2$O$_2$, I$^-$ and H$^{+}$. The results obtained are shown in Table 3.1.
Table 3.1
| experiment | $[\text{H}_2\text{O}_6]/\text{mol dm}^{-3}$ | $[\text{I}^-]/\text{mol dm}^{-3}$ |
| :--- | :---: | :---: |
| 1 | 0.0450 | 0.0300 |
| 2 | 0.0225 | 0.0600 |
| 3 | 0.0225(c) The rate of the thermal decomposition of azomethane, CH$_3$N=NCH$_3$, is investigated.
$$\text{CH}_3\text{N}=\text{NCH}_3 \rightarrow \text{N}_2 + \text{C}_2\text{H}_6$$
Fig. 3.1 shows the results obtained. The reaction is first order with respect to CH$_3$N=NCH$__3$.
**Fig. 3.1**
(i) Use Fig. 3.1 to calculate two half-lives, $t_{\frac{1}{2}}$, to show that the reaction is first order.
[2]
(ii) Use your answer to (c)(i) to calculate the rate constant, $k$, for the decomposition of azomethane.
$$k = \dots\dots\dots\dots\ dm^{-1}$$
(d) Describe the effect of increasing temperature on the rate constant and on the rate of a reaction.
[Total: 11]4 (a) Define standard cell potential, $E_{\text{cell}}$. Include a description of standard conditions.
[2]
(b) The Daniell cell is an electrochemical cell consisting of a Cu$^{2+}$(aq)/Cu(s) electrode and a Zn$^{2+}$(aq)/Zn(s) electrode.
(i) Draw a labelled diagram of this electrochemical cell.
Include all necessary substances and relevant pieces of apparatus needed to measure the $E_{\text{cell}}$.
It is not necessary to state the conditions used.
[3]
(ii) State the charge carriers that transfer current through the solutions and through the wire. the solutions ... the wire ... [1]
(iii) The standard electrode potential, $E^{\ominus}$, for the Zn$^{2+}$(aq) / Zn(s) electrode is –0.76 V.
Water is added to a standard Zn$^{2+}$(aq/Zn(s)) electrode.
The new concentration of Zn$^{2+}$(c) An electrochemical cell consists of a ZnO/Zn electrode and a MnO$_2$/Mn$_2$O$_3$ electrode in an alkaline electrolyte.
The standard cell potential, $E^\ominus_{\text{cell}}$, for this cell is +1.47 V.
The half-equation at each electrode when this cell is discharging is shown.
$$\text{Zn} + 2\text{OH}^- \rightarrow \text{ZnO} + \text{H}_2\text{O} + 2\text{e}^-$$
$$2\text{MnO}_2 + \text{H}_2\text{О} + 2\text{е}^- \rightarrow \text{Mn}_2\text{O}_3 + 2\text{OH}^-$$
(i) Use this information to determine the change in oxidation state of manganese when this cell is discharging.
from ... to ... [1]
(ii) Write the equation for the overall reaction that occurs when this cell is discharging.
... [1]
(iii) The $E^\ominus_{\text{for the ZnO/Zn electrode is } -1.28\text{V}}$.
Calculate the5 (a) Copper shows typical properties of transition elements, including its behaviour as a catalyst.
Complete Table 5.1 to show the total number of unpaired electrons in the 3d and 4s orbitals of an isolated gaseous Cu atom and a Cu$^{2+}$ ion.
Table 5.1
| species | number of unpaired electrons |
| :--- | :--- |
| 3d | 4s |
| Cu | |
| Cu$^{2+}$ | |
(b) The 3d orbitals in an isolated Cu$^{2+}$ ion are degenerate.
Complete the diagram to show the relative energies of the 3d orbitals in an isolated Cu${}^{2+}$ ion and in Cu${}^{2+}$ in a tetrahedral complex.
[energy]
isolated Cu${}^{2+}$ ion
Cu${}^{2+}$ in a tetrahedral complex
[c] Explain why transition elements behave as catalysts.
...(d) CN$^{-}$ is a monodentate ligand.
Table 5.2 shows information about two complex ions that contain only CN$^{-}$ ions as ligands.
Complete Table 5.2.
| metal ion | coordination number | formula of complex ion | charge of complex ion |
| :---: | :---: | :---: | :---
| Ag$^{+}$ | 2 | | |
| Fe$^{2+}$ | | | 4– |
(e) The complex ion $[\text{Au(CN)}_2\text{Br}_2]^-$ displays geometrical (cis/trans) isomerism.
Draw the structure of trans-[$\text{Au(CN)}_2\text {Br}_2]^-$. State its shape and the Br-Au-Br bond angle.
shape ..... Br-Au-Br bond angle = ... [2](f) An impure sample of a vanadium(V) compound of mass 0.250 g is dissolved in aqueous acid. This solution contains $VO_3^-$ ions.
An excess of zinc is added to this solution. All the $VO_3^-$ ions are reduced to $V^{2+}$ ions and Zn atoms are oxidised to $Zn^{2+}$ ions.
The unreacted zinc is removed and the resulting solution is titrated with acidified $MnO_4^-$.
The end-point is reached when 22.5 cm$^3$ of 0.0750 mol dm$^{-3}$ $MnO_4^-$ is added.
A redox reaction takes place and all the $V^{2+}$ reacts forming $VO_3^-$.
$$3MnO_4^- + 5V^{2+} + 3H_2O \rightarrow 3Mn^{2+} + 5VO_3^- + 6H^+$$
(i) Calculate the percentage by mass of vanadium in the 0.250 g of impure sample.
Assume the impurities do not contain any vanadium ions.
Show your working.
percentage of vanadium = ..... [3]
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6 (a) Thin-layer and gas/liquid chromatography can be used to separate mixtures into their individual components. (i) Define the following terms used in chromatography. $R_f$ value ... [2] retention time ... [2] (ii) Each type of chromatography makes use of a stationary phase and a mobile phase. Complete Table 6.1 with a description of each of these. Table 6.1 | | stationary phase | mobile phase | | :--- | :---: | :---: | | thin-layer chromatography | | | | gas/liquid chromatography | | | (b) A mixture of two substances $A$ and $B$ is analysed by thin-layer chromatography. The $R_f$ value of substance $A$ is larger than that of substance $B$. Suggest why substance $A$ has a larger $R_f$ value. ... [1]
(c) The two isomeric compounds Y and Z are analysed by proton (¹H) NMR spectroscopy. (i) Complete Table 6.2 to predict the number of peaks observed in the proton (¹H) NMR spectrum for Y and Z. Table 6.2 | compound | number of peaks observed | | :--- | :--- | | Y | | | Z | | (ii) Name all the different splitting patterns observed in the proton (¹H] NMR spectra for Y and Z. Y ..... [2] Z ..... [Total: 7]
7 (a) State the relative acidities of bromoethanoic acid, BrCH$_2$COOH, chloroethanoic acid, ClCH$_2$COOH, ethanoic acid, CH$_3$COOH and ethanol, CH$_3$CH$_2$OH. Explain your answer. most acidic least acidic [4] (b) Fig. 7.1 shows the reaction of methylbenzene and ethanedioic acid with KMnO$_4$. Predict the major carbon-containing product for each of these reactions. methylbenzene hot alkaline KMnO$_4$ ethanedioic acid hot acidified KMnO$_4$ Fig. 7.1 [2]
(c) Polyamide X can be synthesised from ethanedioic acid and benzene-1,4-diamine. benzene-1,4-diamine (i) Draw the repeat unit of polyamide X in the box. The new functional group formed should be shown displayed. polyamide X (ii) Benzene-1,4-diamine can be formed by reduction of 1,4-dinitrobenzene. Complete the equation for this reduction. [H] represents one atom of hydrogen from a reducing agent. + ..... [H] → H₂N + NH₂ + ...
(d) Fig. 7.2 shows the two-step synthesis of the azo compound W. Fig. 7.2 (i) Suggest structures for compounds V and W and draw them in the boxes in Fig. 7.2. [2] (ii) Give the reagents and conditions for step 1. [Total: 12]
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8 (a) In the electrophilic substitution of arenes, different substituents can direct to different ring positions.
(i) Describe the directing effect of the $-\text{NO}_2$ group. Explain your answer.
[1]
(ii) The nitration of arenes uses a mixture of concentrated $\text{HNO}_3$ and concentrated $\text{H}_2\text{SO}_4$ to generate the $\text{NO}_2^+$ electrophile.
Write an equation for the formation of the $\text{NO}_2^+$-electrophile.
[1]
(b) Carbon-carbon bond formation is an important reaction in organic synthesis.
Fig. 8.1 shows the synthesis of compound Q from benzene in two reaction steps.
(i) Draw the structure of compound P in the box in Fig. 8.1.
[1]
(ii) Suggest reagents and conditions for reactions 1 and 2 in Fig. 8.1.
reaction 1
reaction 2
[2](c) Separate samples of C$_6$H$_5$Br and C$_6$H$_5$CH$_2$Br are added to warm AgNO$_3$(aq). State the expected observations, if any. Explain your answer. C$_6$H$_5$Br with AgNO$_3$(aq) C$_6$H$_5$CH$_�$Br with AgNO$_3$(aq) explanation [3] (d) Acyl bromides, RCOBr, react readily with H$_2$O. The mechanism of this reaction is similar to that of the reaction of H$_2$O with acyl chlorides, RCOCl. (i) Name the mechanism of this reaction. [1] (ii) Complete the mechanism in Fig. 8.2 for the reaction of RCOBr with H$_2$O. Include all relevant lone pairs of electrons, curly arrows, charges and dipoles. Draw the structure of the intermediate. Fig. 8.2 [Total: 13]
9 (a) Explain why amides are much weaker bases than amines. [2] (b) Fig. 9.1 shows the preparation of 2-phenylethylamine, C$_6$H$_5$CH$_2$CH$_2$NH$_2$, by three different routes. Fig. 9.1 (i) Suggest structures for compounds M and N and draw them in the boxes in Fig. 9.1. [2] (ii) Give the reagents and conditions for reaction 1. [1]
(c) Fig. 9.2 shows compound H which is a useful starting material in organic synthesis. Fig. 9.2 H contains an alkene and an amine functional group. Name the other functional group and give the classification of the amine group in H. other functional group in H ..... classification of amine ..... [1] (d) Ozonolysis involves the oxidative cleavage of a C=C bond in alkenes using ozone, $O_3$, as shown in Fig. 9.3. Fig. 9.3 Fig. 9.4 shows the first step in this reaction which involves the formation of an ozonide intermediate. Fig. 9.4 (i) On Fig. 9.4, draw three curly arrows to complete the mechanism of this step. [2]
(ii) L is formed from alkene K, C₈H₁₄, by a similar reaction to that shown in Fig. 9.3. Suggest the structure of K. K C₈H₁₄ [1] [Total: 9]