科目：化学 Chemistry (9701)
年份：2016 夏季
试卷：Paper 43
总页数：16
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, 30 Analytical chemistry
Answer all the questions in the spaces provided. 1. (a) Limewater is a saturated solution of Ca(OH)$_2$ in water. It is used to test for the presence of CO$_2$ in a gaseous mixture. (i) Write an equation for the reaction between limewater and CO$_2$. [1] A saturated solution of Ba(OH)$_2$ can be used instead of Ca(OH)$_2$ to test for CO$_2$. A saturated solution of Mg(OH)$_2$ cannot be used for this test. (ii) Explain why a saturated solution of Ba(OH)$_�$ can be used to test for CO$_2$. [1] (iii) Explain why a saturated solution of Mg(OH)$_�$ cannot be used to test for CO$_2$。 [2] (b) Describe and explain the trend in the thermal stabilities of the carbonates down Group 2. [3] (c) Nickel carbonate, NiCO$_3$, decomposes on heating. Use the Data Booklet to explain whether NiCO$_
2 (a) (i) Complete the following electronic configurations.
• the cobalt atom, Co $1s^2 2s^2 2p^6$
• the cobalt(II) ion, $\text{Co}^{2+}$ $1s^2 2s^3 2p^6$
[1]
(ii) State the colours you would observe when concentrated HCl(aq) is added to an aqueous solution of cobalt(II) nitrate, $\text{Co}(\text{NO}_3)_2$. Give the formulae and geometry of the complexes formed.
[5]
(b) There are two isomers with the formula $\text{Ni}(R_3\text{P})_2\text{I}_2$, but only one structure with the formula $\text{Co}(R_3\text{P})_4\text{I}_2$. ($\text{R} = \text{alkyl}$, $R_3\text{P}$ is a monodentate ligand)
Draw diagrams showing the structure of $\text{Co}(R_3\text {P})_2\text{I}_2$ and the two isomers of $\text{Ni}(R_3\text {P})_4\text{I}_2$.
[3]
[Total: 9]3 One method of producing hydrogen from natural gas is the reaction between hydrogen sulfide and methane.
$$2H_2S(g) + CH_4(g) \rightleftharpoons CS_2(g) + 4H_2(g)$$
(a) Write the expression for $K_p$ for this reaction, and state its units.
$$K_p =$$
units ..... [2]
(b) The initial partial pressures of the two gases in a mixture at 1000 K are recorded.
$$H_2S(g) \quad 200\text{ atm} \quad CH_4(g) \quad 100\text{ atm}$$
The mixture is left to reach equilibrium.
It is found that the equilibrium partial pressure of $CS_2(g)$ is 2 atm and that of the remaining $CH_4(g)$ is 98 atm.
(i) Calculate the equilibrium partial pressures of $H_2S(g)$ and $H_2(g).
$$p(H_2S) = \text{atm}$$
$$p(H_2) = \text{atm}$$
[2]
(ii) Calculate the value of $K_p$ at this temperature.
$$K_p = \text{atm}$$
(c) (i) Predict the sign of $\Delta S^\circ$ for this reaction. Explain your answer.
$$2H_2S(g) + CH_4(g) \rightleftharpoons CS_2(g) + 4H_2(g) \quad \Delta H^\circ = +241\text{ kJ mol}^{-1}$$
[1]
The free energy change, $\Delta G^\circ$, for this reaction at 1000 K is $+51\text{ kJ mol}^{-1}$.
(ii) Calculate the value of $\Delta S^\circ$ forthis reaction, stating its units.
$\Delta S^\circ =$ units [2]
(d) How would the value of $\Delta G^\circ$, and hence the spontaneity (feasibility) of this reaction change as the temperature increases? Explain your answer.
[Total: 10]4 (a) (i) Define the term standard cell potential, $E_{\text{cell}}^{\circ}$.
The following incomplete diagram shows the apparatus that can be used to measure the $E_{\text{cell}}^{\circe}$ for a cell composed of the Fe$^{3+}$/Fe$^{2+}$ and Ag$^+$/Ag half-cells.
(ii) Complete the diagram, labelling the components you add. [1]
(iii) Identify the components A-D.
A ... B ... C D ... [3]
(b) (i) Use $E^\circ$ values to write an equation for the cell reaction that takes place if the two electrodes in (a) are connected by a wire and the circuit is completed.
[1]
(ii) Another electrochemical cell was set up using 0.31 mol dm$^{-3}$ Ag$^+$(aq) instead of the standard Ag solution.
Use the Nernst equation, $E = E^\circ + 0.059 \log[\text{Ag}^+(aq)]$, and the relevant $E^\circ$ values to calc5 Dicarboxylic acids dissociate in stages.
$$\text{HO}_2\text{C}(\text{CH}_2)_n\text{CO}_2\text{H} \xrightleftharpoons[\text{stage 1}]{\text{}} \text{HO}_2\text{C}(\ text{CH}_2)_n\text{CO}^- + \text{H}^+ \xrightleftharpoons[\mathrm{stage 2}]{\text{-}}\text{O}_2\text{C}(\text{CH}_{2})_n\text{CO}^- + 2\text{H}^+$$
(a) The $pK_a$ values for stage 1 and stage 2 for some dicarboxylic acids are listed below.
| n in $\text{HO}_2\text{C}(\mathrm{CH}_2)_n\text{CO}_{2}\text{H}$ | p$K_a$(1) for stage 1 | p$K_a$(2) for stage 2 |
| :--- | :---: | :---: |
| 1 | 2.83 | 5.69 |
| 2 | 4.16 | 5.61 |
| 3 | 4.31 | 5.41 |
For comparison, the $pK_a$ of ethanoic acid, $\text{CH}_3\text{CO}_2\text{H}$, is 4.76.
(i) State the mathematical relationship between $pK_a$ and the acid dissociation constant $K_a$.
(6 Nitrobenzene, $C_6H_5NO_2$, can be reduced to phenylamine, $C_6H_5NH_2$, in acid solution in a two step process.
(a) (i) Balance the half-equation for this reaction to work out how many moles of electrons are needed to reduce one mole of nitrobenzene.
$$C_6H_5NO_2 + e^- + H^+ \rightarrow C_6H_5NH_2 + H_2O$$
(ii) The reducing agent normally used is granulated tin and concentrated hydrochloric acid. In the first step, the reduction of nitrobenzene to phenylammonium chloride can be represented by the equation shown.
Use oxidation numbers or electrons transferred to balance this equation. You might find your answer to (i) useful.
$$C_6H_5NO_{2} + HCl + Sn \rightarrow C_6H_5 NH_{3} Cl + SnCl_{4} + H_2O$$
(b) When 5.0 g of nitrobenzene was reduced in this reaction, 4.2 g of phenylammoniu(d) How does the basicity of phenylamine compare to that of ethylamine? Explain your answer. (e) Phenol can be synthesised from phenylamine in two steps. (i) State the reagents and conditions for steps 1 and 2. step 1 ... step 2 ..... [2] (ii) Draw the structure of the intermediate compound E in the box above. [1] [Total: 13]
7 (a) (i) Use the Data Booklet to draw the structure of the tripeptide Ala-Ser-Gly showing its peptide bonds in full. Ala-Ser-Gly (ii) Calculate the relative molecular mass, $M_r$, of Ala-Ser-Gly. $$M_r = \dots\dots\dots\dots\ldots\ldots\ldots\ldotp$$ (b) Electrophoresis can be used to separate mixtures of amino acids and peptides. A mixture of the tripeptide Ala-Ser_Gly and its three constituent amino acids was subjected to electrophoresis in a buffer at pH 11. (i) Draw the structure of serine at pH 11.
At the end of the experiment the following results were seen. (ii) Identify the components labelled F-I in the above diagram. F ... [4] G ... [3] H ... [3] I ... [3] (iii) Suggest the identities of the species responsible for spot P, spot S. Explain your answers. ... [3] (c) (i) State the reagents and conditions needed for converting the tripeptide into its three constituent amino acids. ... [1] (ii) Name the type of reaction in (i). ... [1] [Total: 13]
8 (a) Chromyl chloride, CrO$_2$Cl$_2$, can be prepared by heating a mixture of potassium dichromate(VI) and potassium chloride with concentrated sulfuric acid.
$$\text{K}_2\text{Cr}_2\text{O}_7 + 4\text{KCl} + 3\text{H}_2\text{SO}_4 \rightarrow 2\text{CrO}_2\text{Cl}_2 + 3\text{K}_2\text{SO}_4 + 3\text{H}_2\text O}$$
Use the following data to complete the Hess’ Law cycle and calculate the enthalpy change of the reaction, $\Delta H_r$.
| compound | enthalpy change of formation, $\Delta H_f^\circ$/kJ mol$^{-1}$ |
| :--- | :--- |
| $K_2\text{Cr}_2\text{O}_{7}$ | -2061 |
| KCl | -437 |
| $H_2\text{SO}_4$ | -814 |
| CrO$_2$Cl$_2$ | -580 |
| $K_2\text{SO}_4$ | −1438 |
| $H_2\text{O}$ | −286 |
$$\text{K}_2\text{CR}_2\text{O}_7 + 4\text{KCl} + 3\text{H}_2\text{ SO}_4 \xrightarrow{\Delta H_r}(b) There are two isomeric complex ions with the formula $[\text{Cr}(\text{NH}_3)_4\text{Cl}_2]^+$. One is green and the other is violet.
(i) Suggest the type of isomerism shown by these complex ions.
[1]
(ii) Explain why these two complex ions
- are coloured,
- have different colours.9 The anti-inflammatory drug ketoprofen can be synthesised from benzene via the following five steps. (a) Suggest the structures of compounds T and U and draw them in the boxes above. [2] (b) Suggest reagents and conditions for steps 1-5. step 1 ... step 2 ... step 3 ... step 4 ... step 5 ... [5] (c) What types of reaction are steps 1 and 5? step 1 ... step 5 ... [2] [Total: 9]
10 (a) Ethanedioic acid, $C_2O_4H_2$, occurs in many vegetables. The amount that occurs in spinach can be estimated as follows.
- 40.0g of spinach leaves are crushed and mixed with distilled water, using a mortar and pestle.
- The mixture is filtered, and the leaves are washed with a little more water.
- The combined filtrate and washings are made up to 100.0 cm$^3$ with water.
- A 25.0 cm$^3$ portion of the resulting solution is added to a conical flask, along with an excess of dilute sulfuric acid.
- The acidified solution is warmed, and then titrated with 0.0200 mol dm$^{-3}$ KMnO$_4$.
The equation for the reaction between ethanedioic acid and acidified manganate(VII) ions is shown.
$$2\text{MnO}_4^{−} + 6\text{H}^+ + 5\text{C}_2\text{O}_4\text{H}_2 \rightarrow 2\text{Mn}^{2+} + 10\t(b) Ethanedioic acid can be converted into ethanedioyl chloride:
$$\text{HO}_2\text{CCO}_2\text{H} \rightarrow \text{ClOCCOCl}$$
(i) State a suitable reagent for this reaction.
(ii) For the reactions of ethanedioyl chloride below, suggest the structures of compounds J and K and draw them in the boxes.
(c) When ethanedioyl chloride is reacted with silver ethanedioate, $\text{AgO}_2\text{CCO}_2\text{\text{Ag}}$, in ethoxyethane at $-30^{\circ}\text{C}$, an oxide of carbon, L, is formed. The molecule of L has no overall dipole and has molecular formula $\text{C}_4\text{O}_6$.
The carbon-13 NMR spectrum of a solution of L in ethoxyethane, $\text{CH}_3\text{CH}_2\text{OCH}_2\text{CH}_3$, is shown below.
(i) Use the Data Booklet to state in the boxes below the $\delta$ values for the peaks(d) When pure L is reacted with an excess of CH$_3$OH, a mixture of three compounds is formed.
$$\text{L and } \text{CH}_3\text{OH} \rightarrow \text{M and N and O}$$
$$(\text{C}_4\text{O}_6) \quad (\text{C}_2\text{H}_2\text{O}_4) \quad (\text{C}_3\text{H}_4\text{O}_4) \quad (\mathrm{C}_4\text{H}_6\text{O}_4)$$
M is formed as one of the products when either N or O is heated with aqueous acid.
The table gives information of the peaks recorded in the carbon-13 NMR spectra of M, N and O.
| compound | peaks recorded in carbon-13 NMR spectrum |
| :--- | :--- |
| M | $\delta 162$ |
| N | $\delta 53, \delta 160, \delta 162$ |
| O | $\delta 53, \delta160$ |
(i) Suggest the structures of M, N and O.
[3]
(ii) Suggest a structure for L that fits all the data given in (c) and (d).
[1]