科目：化学 Chemistry (9701)
年份：2021 夏季
试卷：Paper 42
总页数：21
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
Answer all the questions in the spaces provided.
1. (a) An aqueous solution of chromium(III) contains the green $[\text{Cr}(\text{H}_2\text{O})_6]^{3+}$ complex ion.
(i) Complete the electronic configuration of an isolated, gaseous Cr$^{3+}$ ion.
$$1s^2$$ ... [1]
(ii) Define the term complex ion.
..... [1]
(b) $[\text{Cr}(\text{H}_{2}\text{O})_6]^{3+}$(aq) shows some similar chemical properties to $[\text{Co}(\text{H}_{2}\text{ O})_6]^{2+}$(aq).
Samples of $[\text{Cr}(\text{H_{2}O})_6]^{3+}$ are reacted separately with either NaOH(aq), H$_2$O$_2$(aq), or excess NH$_3$(aq).
Use this information and the Data Booklet to suggest the formula of the chromium species formed. State the type of reaction taking place in each case.
| reagent added to $[\text{(d) The structure of $[\text{Cr}_2(\text{O}_2\text{CCH}_3)_4(\text{H}_2\text{O})_2]$ is shown. Ethanoate ions act as ligands in this complex.
The ethanoate ligand, $\text{CH}_3\text{CO}_2^-$, is shown as
(i) Water and ethanoate ions behave as different types of ligand in this complex.
Suggest an explanation for this statement.
[1]
(ii) Deduce the coordination number of Cr and the geometry around each Cr atom in this structure.
coordination number ...
geometry around Cr atom ...
[1]
(iii) State the type of bond between the two atoms in the Cr–Cr bond.
[1]
(e) The $[\text{Cr}_2(\text(O}_2\text{CCH}_3)_�(\text{H}_2\text{O))}_2]$ complex reacts with aqueous acid to form $\text{Cr}^{2+}(\text{aq})$ ions.
$\text{Cr}^{2+}(\text{aq})$ ions react with $\text{O}_2(\text{aq})$ under acidi2 (a) State and explain the trend observed in the thermal stability of the Group 2 nitrates. [3] (b) (i) Lead(II) nitrate, Pb(NO$_3$)$_2$, decomposes on heating in a similar manner to the Group 2 nitrates. Write an equation for the decomposition of lead(II) nitrate. [1] (ii) Suggest how the ease of decomposition of Pb(NO$_3$)$_�$ would compare to that of Ba(NO$_3$)$_2$. Explain your answer. You may find it useful to refer to the Data Booklet. [1] (c) (i) Barium ethanedioate, BaC$_2$O$_4$, decomposes on heating to produce barium oxide and a mixture of two different gases. Construct an equation for the decomposition of barium ethanedioate. [1]
(ii) An impure sample of BaC$_2$O$_4$, of mass 0.500 g, is added to 50.0 cm$^3$ of 0.0200 mol dm$^{-3}$ acidified MnO$_4^-$ (aq), an excess. A redox reaction takes place and all the BaC$_2$O$_4$ reacts.
The resulting solution, containing unreacted acidified MnO$_4^-$, is titrated with 0.0500 mol dm$^{-3}$ Fe$^{2+}$ (aq).
The end-point is reached when 30.40 cm$^3$ of 0,0500 mol dm$^{-1}$ Fe$^{2+}$ (aq) has been added.
$$\text{C}_2\text{O}_4^{2-} \rightleftharpoons 2\text{CO}_2 + 2\text{e}^-$$
$$\text{MnO}_4^- + 8\text{H}^+ + 5\text{e}^- \rightleftharpoons \text{Mn}^{2+} + 4\text{H}_2\text{O}$$
$$\text{Fe}^{2+} \rightleftharpoons \text {Fe}^{3+} + \text{e}^-$$
Calculate the percentage by mass of BaC$_2$O$_4$ in the 0.500 g impure sample. Show your working.
[M$_r$: BaC$_2$O$_4$, 225.3]3 (a) (i) Define the term standard electrode potential.
Three redox systems, A, B and C, are shown. The ligand 1,2-diaminoethane, H$_2$NCH$_2$CH$_2$NH$_2$, is represented by en.
$$\begin{array}{l}
\text{A} \quad [\text{Ru(H}_2\text{O)}_6]^{3+} + e^- \rightleftharpoons [\text{Ru(H}_2\text {O)}_6]^{2+} \\
\text{B} \quad [\text{Ru(NH}_3)_6]^{3+} + e^-) \rightleftharpoons [\mathrm{Ru(NH}_3)_6]^2+ \\
\text{C} \quad [\mathrm{Ru(en)}_3]^{3+} + e^-) = [\mathrm{Ru(en)}_6]^{2+}
\end{array}$$
Two electrochemical cells are set up to compare the standard electrode potentials, $E^\circ$, of three half-cells. The diagrams show the relative potential of each electrode.
(ii) Use this information to complete the table by adding the labels A, B and C to deduce the order of $E^\circ$ for the three half-ce(iii) The complex $[\text{Ru}(en)_3]^{3+}$ shows stereoisomerism. The ligand en is bidentate.
Draw three-dimensional diagrams to show the two isomers of $[\text{Ru}(en)_3]{3+}$. Represent the ligand en by using a chemical structure with N and N' atoms.
Name the type of stereoisomerism.
type of stereoisomerism ... [3]
(b) (i) An electrochemical cell consists of a Br$_2$/Br$^-$ half-cell and a Ag$^+$/Ag half-cell, under standard conditions.
Use the Data Booklet to calculate the $E^\circ_{\text{cell}}$. Deduce the direction of electron flow in the wire through the voltmeter between these two half-cells.
$$E^\circ_{\text{cell}} = \text{V}$$
direction of electron flow from ... to ... [1]
(ii) Water is added to the Ag$^+$/Ag half-cell in (b)(i).
Suggest the effect of this addition on th(c) Silver bromide, AgBr, dissolves in an aqueous solution of S$_2$O$_3^{2-}$ ions to form the complex ion [Ag(S$_2$O$_3$)$_2$]$^3-$. The S$_2$O$_3^{2-$} ions act as monodentate ligands.
equilibrium 1 $\text{AgBr(s)} + 2\text{S}_2\text{O}_3^{2-}(\text{aq}) \rightleftharpoons [\text{Ag(S}_2\text{O}_3)_2]$$^3-(\text{aq}) + \text{Br}^-(\text{aq})
(i) Define the term ligand.
[1]
(ii) Write an expression for the equilibrium constant, $K_c$, for equilibrium 1.
$$K_c =$$
[1]
(iii) Some additional data are given about the dissolution of AgBr in S$_2$O$_3^{2$-}(aq).
| equilibrium constant | numerical value |
| :--- | :--- |
| solubility product, $K_{sp}$, of AgBr | $5.4 \times 10^{-13}$ |
| stability constant, $K_{stab}$, of [Ag(S$_2$O$_3)_2]$^3-$ | $2.9 \times 10^{13}$ |
Use your answer t4 (a) (i) Define the term lattice energy.
(ii) Use the following data to calculate a value for the enthalpy change of solution of copper(II) chloride, CuCl$_2$(s). You might find it helpful to construct an energy cycle.
enthalpy change of hydration of Cl$^{-}$ = $-378 \text{ kJ mol}^{-1}$
enthalpy change of hydration of Cu$^{2+}$ = $-2099 \text{ kJ mol}^{-1$
lattice energy of CuCl$_2$(s) = $-2824 \text{ kJ mol}^{-1$
enthalpy change of solution of CuCl$_2$(s) = ... kJ mol$^{-1}$ [2]
(iii) The enthalpy change of hydration of Ca$^{2+}$ is $-1579 \text{ kJ mol}^{- 1}$.
Use the Data Booklet to suggest why there is a big difference in the values of $\Delta H_{\text{hyd}}$ for Ca$^{2+}$ and Cu$^{2+}$.
(b) (i) Identify the substances formed at the anode and at the cathode during the electrol(c) (i) Explain what is meant by the term entropy of a system. (ii) Place one tick ($\checkmark$) in each row of the table to show the sign of each entropy change, $\Delta S$. | process | $\Delta S$ is negative | $\Delta S$ is zero | $\Delta S$ is positive | | :---: | :---: | :---: | :--- | NaCl dissolving in water | | | | | water solidifying to ice | | | | (iii) The evaporation of one mole of water has a standard Gibbs free energy change, $\Delta G^\circ$, of +8.6 kJ at 25°C. Sketch a graph on the axes to show how $\Delta G^\circ$ changes for this process between 25°C and 150°C at 101 kPa. (d) The reaction between A and B is feasible at low temperatures but is not feasible at high temperatures. $$A + B \rightleftharpoons C + D$$ Deduce the signs of $\Delta H$ and $\Delta S$ for thi
5 (a) Describe and explain the relative basicities of phenylamine, ethylamine and 4-nitrophenylamine.
most basic > least basic
(b) The dye R can be synthesised from 4-nitrophenylamine in two steps.
$$\text{4-nitrophenylamine} \xrightarrow{\text{step 1}} \text{Q}$$
$$\text{R} \xrightarrow{\text{step2}} \text{O}_2\text{N}-\text{N}=\text{N}-\text{OH}$$
(i) Deduce and draw the structure of the organic salt Q in the box. [1]
(ii) Suggest reagents and conditions for step 1 and 2 in (b).
step 1 ..... [2]
step 2 ..... [2](c) Compound G can be synthesised from methylbenzene in three steps. (i) Give the systematic name of compound G. [1] (ii) Deduce the identities of E and F and draw their structures in the boxes. [2] (iii) Suggest reagents and conditions for each of steps 1 to 3 in (c). step 1 ... step 2 ... step 3 ... [Total: 13]
6 (a) There are four possible structural isomers of $C_8H_{10}$ that contain a benzene ring.
Draw the skeletal formulae of the four structural isomers in the appropriate boxes. The number of peaks observed in the carbon-13 ($^{13}\text{C}$) NMR spectrum of each compound is given.
isomer 1
three peaks in $^{13}\text{C}$ NMR
isomer 2
four peaks in $^{13}\text {C}$ NMR
isomer 3
five peaks in $^{13}\text C$ NMR
isomer 4
six peaks in $^{13}\textC$ NMR(b) A three-step synthesis of X (C\textsubscript{10}H\textsubscript{10}O) from benzene is suggested as shown.
(i) Step 1 is the alkylation of benzene by electrophilic substitution. Use R–Cl to represent Cl(CH\textsubscript{2})\textsubscript{3CO}_2H.
Write an equation for the formation of an electrophile from R–Cl and AlCl\textsubscript{3}.
[1]
(ii) Deduce and draw the structures of W and X in the boxes.
[2]
(iii) Suggest the reagents and conditions for step 2.
[1](iv) Complete the mechanism for the reaction of benzene with the electrophile formed in (b)(i). Include all relevant charges and curly arrows showing the movement of electron pairs. Draw the structure of the intermediate.
7 (a) In aqueous solution, chlorine dioxide, $ClO_2$, reacts with hydroxide ions as shown.
$$2ClO_2 + 2OH^- \rightarrow ClO_3^- + ClO_2^- + H_2O$$
A series of experiments is carried out using different concentrations of $ClO_2$ and $\text{OH}^-$. The table shows the results obtained.
| experiment | $[ClO_2] / \text{mol dm}^{-3}$ | $[\text{OH}^-] / \text{mol dm}^{−3}$ | initial rate / $\text{mol dm}^{−3}\text{min}^{−1}$ |
| :--- | :---: | :---: | :---: |
| 1 | 0.020 | 0.030 | $7.20 \times 10^{-4}$ |
| 2 | 0.020 | 0.120 | $2.88 \times 10^{-3}$ |
| 3 | 0.050 | 0.030 | $4.50 \times 10^{-3}$ |
(i) Explain the term order of reaction.
(ii) Use the data in the table to determine the order of reaction with respect to each reactant, $ClO_2$ and $\text{\text{OH}}^-$.
Explain your reasoning.
Question 7 continues on the next page.
(b) The decomposition of benzenediazonium ions, $C_6H_5N_2^+$, using a large excess of water, is a first-order reaction.
The graph shows the results obtained.
(i) Draw the structure of the organic product formed in this reaction.
[1]
(ii) Use the graph to determine the rate of reaction at 100 s. Show your working.
rate = ..... mol dm$^{-3}$ s$^{-1}$ [1](c) Sketch a concentration–time graph for a zero-order reaction. Use your graph to suggest how successive half-lives for a zero-order reaction vary as the concentration of a reactant decreases. Indicate this by placing a tick ($\checkmark$) in the appropriate box in the table. | successive half-lives decrease | no change in successive half-lives | successive half-lives increase | | :--- | :---: | :---: | | | | | [Total: 9]
8 (a) State and explain the relative rate of hydrolysis of acyl chlorides, alkyl chlorides and aryl chlorides. fastest > slowest [3]
(b) The drug remifentanil is shown. Remifentanil is completely hydrolysed under acidic conditions. Three different organic compounds are formed. Draw the structures for these organic compounds in the boxes.
(c) Compound Y, C$_5$H$_{10}$O$_2$, reacts with Na$_2$CO$_3$(aq) to evolve bubbles of gas. The proton (^1H) NMR spectrum of compound Y in D$_2$O is shown.
(i) Use this information to suggest a structure for Y.
[1]
(ii) Use the Data Booklet, the proton (^1H) NMR spectrum and your answer to (c)(i) to complete the table.
| chemical shift ($\delta$) | environment of proton | splitting pattern | number of ^1H atoms responsible for the peak |
| :--- | :--- | :--- | :--- |
| 0.95 | | | |
| 1.90 | | | |
| 2.20 | | | |
[Total: 10]