科目：化学 Chemistry (9701)
年份：2017 夏季
试卷：Paper 42
总页数：19
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) (i) Describe and explain the variation in the thermal stabilities of the carbonates of the Group 2 elements. [3] (ii) Suggest and explain a reason why sodium carbonate is more stable to heat than magnesium carbonate. [1] (b) Sodium hydrogencarbonate, NaHCO$_3$, and potassium hydrogencarbonate, KHCO$_3$, decompose on heating to produce gases and the solid metal carbonate. (i) Write an equation for the decomposition of KHCO$_3$. [1] (ii) Predict which of NaHCO$_3$ or KHCO$_3$ will decompose at the lower temperature. Explain your answer. [1]
(c) (i) Use the data in the table below, and relevant data from the Data Booklet, to calculate the lattice energy, $\Delta H_{\text{latt}}^{\circ}$, of potassium oxide, $K_2O(s)$.
| energy change | value/kJ mol$^{-1}$ |
| :--- | :--- |
| enthalpy change of atomisation of potassium, $\Delta H_{\text{at}}^{\circ} K(s)$ | +89 |
| electron affinity of O(g) | –141 |
| electron affinity of O$^-$(g) | +798 |
| enthalpy change of formation of potassium oxide, $\Delta H_f^{\circ} K_2O(s)$ | –361 |
$\Delta H_{\text{latt}}^{\odot} = \dots\dots\dots\dots\kappa J \text{mol}^{-1}$ [3]
(ii) State whether the lattice energy of Na$_2$O would be more negative, less negative or the same as that of K$_2$O. Give reasons for your answer.
[Total: 10]2 (a) Complete the table to show how both AgNO$_3$(aq) and NH$_3$(aq) could be used to distinguish between solutions of NaCl(aq) and NaI(aq).
| test performed | observation with NaCl | observation with NaI |
| :--- | :---: | :---: |
Important information for this question
- In this question (pr) means ‘a solution in propanone’.
- Sodium iodide is soluble in propanone giving Na$^+$(pr) and I$^{-}$(pr).
- Sodium chloride is insoluble in propanone.
The reaction between 2-chlorobutane and sodium iodide in propanone is shown:
$$\text{CH}_3\text{CH}_2\text{CHCl}_3(\text{pr}) + \text{Na}^+(\text{pr}) + \text{I}^{-}(\text{pr}) \rightarrow \text{CH}_3\text{CH}_�\text{CHICH}_3(\text{pr}) + \mathrm{NaCl}(s)$$
The rate of this reaction can be investigated by measuring the electrical conductivity(c) The rate of this reaction was measured at different initial concentrations of the two reagents. The table shows the results obtained.
| experiment | $[\text{CH}_3\text{CH}_2\text{CHCl}\text{CH}_3]$ / mol dm$^{-3}$ | $[I^-]$/mol dm$^{-3}$ | relative rate |
| :--- | :---: | :---: | :---: |
| 1 | 0.06 | 0.03 | 3 |
| 2 | 0.10 | 0.03 | 5 |
| 3 | 0.06 | 0,05 | 5 |
| 4 | 0.08 | 0.04 | to be calculated |
(i) Deduce the order of reaction with respect to each of $[\text{CH}_3\text{ CH}_2\text{ CHC l} \text{ CH}_3]$ and $[I^-]$. Explain your reasoning.
order with respect to $[\text{CH}_3\text{ Ch}_2\text{ ChC l} \text{ Ch}_3]$ ..... [2]
order with respect to $[I^-$] ..... [2]
(ii) Write the rate equation for this reaction, stating the units of the rate constant, $k$.
rate = ... mol dm$^{-3}(d) (i) Suggest the mechanism for the reaction of 2-chlorobutane with iodide ions. Draw out the steps involved, including the following. - all relevant lone pairs and dipoles - curly arrows to show the movement of electron pairs - the structure of any transition state or intermediate (ii) This reaction was carried out using a single optical isomer of 2-chlorobutane. Use your mechanism in (i) to predict whether the product will be a single optical isomer or a mixture of two optical isomers. Explain your answer. [1] (e) (i) State the number of peaks that would be seen in the carbon-13 NMR spectrum of CH$_3$CH$_2$CHClCH$_3$. [1] (ii) There are two isomers of CH$_3$CH$_2$ChClCH$_3$ that have fewer peaks in their carbon-13 NMR spectra than CH$_3$CH$_2$ChCllCH$_3$. Draw the structures of
Question 3 starts on the next page.
3 (a) In a molecule of $SOCl_2$ the sulfur atom has four bonds.
Draw a 'dot-and-cross' diagram of $SOCl_2$. Show the outer shell electrons only.
[2]
(b) When $SOCl_2$ is reacted with a carboxylic acid to produce an acyl chloride, two acidic gases are formed.
$$SOCl_2(l) + RCO_2H(l) \rightarrow RCOCl(l) + SO_2(g) + HCl(g)$$
A 1.00 g sample of a carboxylic acid $RCO_2H$ was treated in this way, and the gases were absorbed in 60.0 cm$^3$ of 0.500 mol dm$^{-3}$ NaOH(aq), an excess.
(i) Write equations for the reactions between
NaOH and $HCl$, ...
NaOH and $SO_2$, ...
[2]
The excess NaOH was titrated with 0.500 mol dm${}^{-3}$ H$^{+}$(aq). It required 10.8 cm$^3$ of the H$^{+}$(aq) solution to reach the end-point.
(ii) Calculate the total number of moles of NaOH that reacted with the(iv) Hence calculate the $M_r$ of the carboxylic acid, $\text{RCO}_2\text{H}$.
$$M_r \text{RCO}_2\text{H} = ...$$
(v) The R group contains carbon and hydrogen only.
Suggest the molecular formula of $\text{RCO}_2\text{H}$$.
... [1]
(c) The following synthetic route shows how a carboxylic acid can be converted into an amine.
$$\text{CH}_3\text{CO}_2\text{H} \xrightarrow{\text{SOCl}_2} \text{CH}_3\text{COC l} \xrightarrow{\text{NH}_3} \text{CH}_3\text{CONH}_2 \xrightarrow{\text{step 3}} \text{CH}_3\text{CH}_2\text{NH}_2$$
(i) Suggest a reagent for step 3.
... [1]
Angelic acid, $\text{C}_5\text{H}_8\text{O}_2$, is a natural product isolated from the roots of the angelica plant.
- Angelic acid reacts with $\text{H}_2 + \text{Ni}$ to form T, $\text{C}_5\text{ H}_{10}\text{O}_2$.
- T und4 (a) A number of isomers with the formula Cr(H₂O)₆Cl₃ exist. Their general formula is [Cr(H₂O)₆nClₙ]Cl₃-n·nH₂O.
Each isomer contains a six co-ordinated Cr(III) ion in an octahedral complex.
Water molecules not directly bonded with the Cr atom are held in the crystal lattice as water of crystallisation.
The Cr–Cl bond is not easily broken and so chloride bonded with the Cr(III) ion in the complex does not react.
1.00 g samples of three of the isomers, A, B and C, were dissolved in separate samples of water. An excess of AgNO₃(aq) was added to each and the mass of AgCl(s) formed was measured.
$$\text{Ag}^+(\text{aq}) + \text{Cl}^-(\text{aq}) \rightarrow \text{AgCl}(\text{s})$$
The number of moles of AgCl(s) formed was calculated. The table shows the results.
| isomer | moles of AgCl for(b) Two isomers have the same shape and their formula is $Ni(R_3P)_2(CN)_2$, where $R = CH_3$. Only one of these isomers has a dipole moment. (i) Name the type of isomerism shown by $Ni(R_3P)_2(C_N)_2$. (ii) Draw structures of these two isomers. (iii) State which isomer has a dipole moment. Explain your answer. [Total: 6]
5 (a) 1,2-diaminoethane, en, H$_2$NCH$_2$CH$_2$NH$_2$, is a bidentate ligand.
(i) What is meant by the terms bidentate and ligand?
bidentate ...
ligand ...
(ii) There are three isomeric complex ions with the formula [Cr(en)$_2$Cl$_2$]$^+$.
Complete the three-dimensional diagrams of the isomers in the boxes.
You may use $N-N$ to represent en.
(b) Copper forms complexes with NH$_3$ and en according to equilibria 1 and 2.
equilibrium 1 $\text{Cu}^{2+}(\text{aq}) + 4\text{NH}_3(\text{aq}) \rightleftharpoons [\text{Cu(NH}_3)_4]^{2+}(\text{aq})$
equilibrium 2 $\text{Cu}^{2+}(\text {aq}) + 2\text{en}(\text {aq}) \rightleftharpoons[\text{Cu(en)}_2]^{2+}(\text{aq})$
(i) Write the expressions for the stability constants, $K_{\text{stab1}}$ and $K_{\text{stab2}}$, for equilibria 1 and 2. Include(ii) An equilibrium is set up when both en and NH$_3$ ligands are added to a solution containing Cu$^{2+}$ (aq) as shown in equilibrium 3.
$$\text{equilibrium 3} \quad [\text{Cu(NH}_3)_4]^{2+}(\text{aq}) + 2\text{en}(\text{aq}) \rightleftharpoons [\text{Cu}(en)_2]^{2+}(\text{aq})+4\text{NH}_3(\text{aq})$$
Write an expression for the equilibrium constant, $K_{\text{eq3}}$, in terms of $K_{\text{stab1}}$ and $K_{\text{stab2}}$.
$$K_{\text{eq3}} = ...$$
(iii) The numerical values for these stability constants are shown.
$$K_{\text{stab1}} = 1.2 \times 10^{13} \quad K_{\text{stab2}} = 5.3 \times 10^{19}$$
Calculate the value of $K_{\text{eq3}}$ stating its units.
$$K_{\text{eq3}}=... \text{unit}=...$$
(c) $\Delta S^\circ$ values for equilibria 1 and 2 differ greatly, as can be seen in 6 The table lists some organic acids and their $pK_a$ values.
| acid | formula | $pK_a$ |
| :--- | :---: | :---: |
| ethanoic acid | $\text{CH}_3\text{CO}_2\text{H}$ | 4.76 |
| chloroethanoic acid | $\text{ClCH}_2\text{CO}_2\text{H}$| 2.86 |
| aminoethanoic acid (glycine) | $\text{H}_2\text{NCH}_2\text{CO}_2\text H$ | 9.87 |
(a) (i) State the relationship between $pK_a$ and the strength of an acid.
[1]
(ii) State the mathematical relationship between $pK_a$ and the acidity constant $K_a$.
[1]
(iii) Give reasons for why the $pK_a$ value for chloroethanoic acid is smaller than that for ethanoic acid.
[2]
(b) (i) Use the zwitterionic structure for aminoethanoic acid (glycene) in aqueous solution to write an equation for its dissociation giving $H^+$(aq) ions.
[1]
(ii) Calculate the pH oA 10.0 cm$^3$ sample of 0.100 mol dm$^{-3}$ aminoethanoic acid (glycine) was titrated with 0.100 mol dm $^{-3}$ NaOH. After 20.0 cm$^3$ of NaOH, an excess had been added, the pH was found to be 12.5.
(iii) Using the following axes, sketch a graph showing how the pH changes during this titration.
[3]
[Total: 10]7 Compounds W, X, Y and Z are isomers of each other with the molecular formula $C_8H_7ClO$. All four isomers contain a benzene ring. Only one of the isomers contains a chiral centre. The results of six tests carried out on W, X, Y and Z are shown in the table. | test | observations with each isomer | | :--- | :---------------------------------| | | W X Y Z | | 1 add cold AgNO$_3$(aq) | white ppt. forms immediately none white ppt. forms very slowly none | | 2 heat with NaOH(aq), then add dilute HNO$_3$ + AgNO$_3$(aq) | white ppt. none white ppt. none | | 3 add NaOH(aq) + I$_2$(aq) | none pale yellow ppt. none none | | 4 warm with Fehling’s solution | none none red ppt. none | | 5 add cold, dilute, acidified KMnO$_4$(aq) | no change no change no change decolourises
(b) Isomers W, X, Y and Z all have the molecular formula $C_8H_7ClO$. (i) Use the information in (a) to suggest a structure for each of these isomers and draw these in the boxes. (ii) Draw a circle around the chiral centre in one of the above structures. [1] [Total: 10]
8 (a) The amino acid tyrosine can be synthesised from phenol by the route shown. (i) Name the mechanism occurring in the following steps. step 1 ... step 2 ... [2] (ii) What type of reaction is occurring in step 3? ... [1] (iii) Suggest reagents and conditions for each of the following steps. step 1 ... step
(iv) Draw the structures of the products of the reactions of tyrosine with an excess of each of the following reagents. with NaOH(aq) with HCl(aq) with Br₂(aq) Question 8 continues on the next page.
(b) The dipeptide phe-tyr has the following structure. A mixture of this dipeptide (phe-tyr) and its two constituent amino acids (phe and tyr) was subjected to electrophoresis in a buffer at pH12. At the end of the experiment the following results were seen. Spots R and S remained very close together. The three spots are due to the three species phe, tyr and phe-tyr. (i) Which species is responsible for spot P? Explain your answer. [2] (ii) Suggest why the other two species give spots R and S that are so close together. [1] [Total: 15]