科目：化学 Chemistry (9701)
年份：2021 冬季
试卷：Paper 42
总页数：19
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, 27 Organic nitrogen compounds, 29 Organic synthesis, 30 Analytical chemistry
Answer all the questions in the spaces provided.
1 Radium is a Group 2 element.
The predicted lattice energy, $\Delta H_{\text{latt}}$, of radium sulfide, RaS, is $-2612 \text{ kJ mol}^{-1}$.
(a) Define $\Delta H_{\text{latt}}$.
Some data relating to radium and sulfur are listed. Select relevant data from this list for use in your answers to parts (b) to (e).
| process | value/kJmol$^{-1}$ |
| :--- | :--- |
| enthalpy change for Ra(s) $\rightarrow$ Ra$^{2+}(\text{g}) + 2\text{e}^-$ | $+1619$ |
| first ionisation energy of sulfur | $+1000$ |
| second ionisation energy of sulfur | $+2260$ |
| first electron affinity of sulfur | $-200$ |
| second electron affinity of sulfur | $+532$ |
| enthalpy change for $\frac{1}{8} S_8(\text{s}) + 2\text{e}^- \rightarrow S^2-(\text{g})$ | $+555$ |
| l(d) Calculate the standard enthalpy change of formation, $\Delta H_{\text{f}}^{\circ}$, of radium sulfide.
standard enthalpy change, $\Delta H_{\text{f}}^\circ = \dots\dots\dots\dots\kappa\text{J mol}^{-1}$ [2]
(e) (i) State the two major factors that affect the numerical magnitude of a lattice energy.
[2]
(ii) For each factor you have identified in (e)(i), state whether it tends to make the lattice energy of radium sulfide more or less exothermic than that of sodium chloride.
Explain your answer.
[2]
(iii) The lattice energies of sodium chloride, NaCl, and radium sulfide, RaS, are $-771\text{ kJ mol}^{-1}$ and $-2612\text{ kJ mol}^{-1}$, respectively.
Identify the dominant factor in determining the relative numerical magnitudes of the lattice energies of radium sulfide and sodium 2 Ethoxyethane, $C_2H_5OC_2H_5$, can dissolve both in water and in octan-1-ol. The expression and numerical value for the partition coefficient of ethoxyethane between water and octan-1-ol are given. Water and octan-1-ol are immiscible.
$$K_{pc} = \frac{\text{concentration of } C_2H_5OC_2H_{5} \text{ in octan-1-ol}}{\text{concentration of } C_{2}H_{5}OCl_{2}H_{5} \text{ in water}} = 6.760 \text{ at } 20^{\circ}\text{C}$$
(a) In an experiment, octan-1-ol at $20^{\circ}\text{C}$ is added to a solution of ethoxyethane in water at $20^{\circ}\text.C$. The mixture is analysed immediately and a value of $K_{pc}$ is calculated.
The calculation is performed correctly; the value calculated is 5.625.
Explain why the value calculated is less than 6.760.
[2]
(b) A second experiment is performed (c) An aqueous solution of lead(II) nitrate is mixed with an aqueous solution of sodium iodide. A yellow precipitate of lead(II) iodide is formed and is filtered out, leaving solution X.
The concentration of Pb$^{2+}$ in solution X is $5.68 \times 10^{-3} \text{ mol dm}^{-3}$.
The concentration of I$^-$ in solution X is $4.20 \times 10^{-4} \text{ mol dm}^{-2}$.
(i) Use these data to calculate a value for the solubility product, $K_{sp}$, of lead(II) iodide.
State the units of $K_{sp}$.
$$K_{sp} = \dots\dots\dots\dots\quad\text{units} = \dots\dots\ddots\ddots\quad[2]$$
(ii) Potassium iodide is very soluble in water.
Describe and explain what is seen if a few drops of saturated potassium iodide solution are added to a portion of solution X.
[Total: 10]3 Pure water is a very poor conductor of electricity. However, when hydrogen chloride gas is dissolved in water, ions are formed and a current flows during electrolysis.
$$\text{HC}l(g) + \text{aq} \rightarrow \text{H}^+(\text{aq}) + \text{Cl}^-(\text{aq})$$
The overall change after electrolysis is that hydrogen chloride gas is converted into hydrogen and chlorine.
$$2\text{HC}l(g) \rightarrow \text{H}_2(g) + \text{Cl}_2(g)$$
When a current of 3.10A is passed through the solution for $Y$ minutes, $351\text{ cm}^3$ of chlorine are produced at the anode, measured under room conditions.
(a) Calculate the number of chlorine molecules produced during the electrolysis.
number of chlorine molecules = ..... [2]
(b) Calculate the total number of electrons transferred to produce this number o(e) The standard entropies, $S^\circ$, of three species are given in the table.
| species | $S^\circ$/JK$^{-1}$mol$^{-1}$ |
| :---: | :---: |
| HCl(g) | +187 |
| H$_2$(g) | +131 |
| Cl$_2$(g) | +223 |
(i) Calculate $\Delta S^\circ$ for the reaction 2HCl(g) $\rightarrow$ H$_2$(g) + Cl$_2$(g).
$$\Delta S^\circ = \text{JK}^{-1}\text{mol}^{-1}$$
(ii) $\Delta H^\circ$ for the reaction 2HCl(g) $\rightarrow$ H$_2$(g) + Cl$_2$(g) is +185 kJ mol$^{-1}$. Calculate $\Delta G^\circ$ for this reaction at 298 K.
$$\Delta G^\circ = \text{kJ mol}^{-1}$$
(iii) Predict the effect of increasing temperature on the spontaneity of this reaction. Explain your answer.
[Total: 9]4 Separate samples of 0.01mol of magnesium nitrate and 0.01mol of strontium nitrate are heated until completely decomposed to the metal oxide, nitrogen dioxide and oxygen. (a) State which of these two Group 2 nitrates requires the higher temperature before it begins to decompose. Explain your answer. [2] (b) After decomposition is complete the 0.01mol sample of magnesium oxide is taken and increasing amounts of water are added to it, with stirring, until no solid remains. This procedure is repeated with the 0.01mol sample of strontium oxide. Identify the sample to which most water must be added to cause all the solid to dissolve. Explain your answer by reference to the solubilities of the products formed when water is added to the oxides. You should refer to relevant energy terms in y
(ii) The HNO$_3$ present in 25.0 cm$^3$ of this solution is neutralised using $0.125 \text{ mol dm}^{-3} \text{ NaOH(aq)}$.
Calculate the minimum volume, in cm$^3$, of NaOH(aq) needed. Give your answer to three significant figures.
volume = ..... cm$^3$ [1]
[Total: 7]5 Transition elements form complexes.
(a) Molybdenum, Mo, forms an octahedral complex consisting of one Mo atom surrounded by carbon monoxide, CO, molecules. CO is a monodentate ligand. Iron forms an octahedral complex consisting of one Fe$^{3+}$ and a number of cyanide, CN$^{-}$, ions. CN$^{-}$ is a monodentate ligand.
(i) Define the term monodentate ligand.
[1]
(ii) Complete the table by stating the formulae and charges of the complexes described.
| | formula | charge |
| :--- | :---: | :---: |
| molybdenum complex | | |
| iron(III) complex | | |
[2]
(iii) Draw a three-dimensional diagram to show the shape of this iron(III) complex.
Label one $180^\circ$ bond angle on your diagram.
[1]
(b) An excess of aqueous ammonia is added to dilute copper(II) sulfate(ii) Explain the origin of colour in copper(II) complexes.
(c) An excess of concentrated hydrochloric acid is added to the dark blue solution of $[\text{Cu(NH}_3)_4(\text{H}_2\text{O})_2]^{2+}$. A new complex, Z, is formed. The colour of the solution changes.
(i) Write an equation for the formation of Z from the solution of $[\text{Cu(NH}_{3})_{4}(\text{H}_{2}\text{O})_{2}]^{2+}$. Include the formula and charge of Z.
(ii) Name the type of reaction when Z forms from $[\text{Cu(NH}_{3 })_{4}(\text{H}_{2}\mathrm{O})_{2}]^{2+}.$
(iii) State the geometry of Z.
(iv) State the colour of a solution of Z.
(v) Explain why the colour of a solution of $[\text{Cu(NH_{3}})_4(\text{H}_{2}\text{O })_2]^{2+}$ is different from the colour of a solution of Z. You should refer to the energies of the orb6 An excess of aqueous ammonia is added to a solution containing the complex ion $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$.
$$[\text{Co}(\text{H}_�\text{O})_6]^{2^+} + 6\text{NH}_3 \rightleftharpoons [\text{Co}(\text{NH}_3)_6]^{2^+} + 4\text{H}_2\text{O}$$
(a) Complete the sentence to describe the colour change that will be seen during this reaction. The colour changes from ..... to ..... . [1]
(b) Write an expression for the stability constant, $K_{\text{stab}}$, of $[\text{Co}(\text{NH}_3)]_{6}^{2+}$.
$$K_{\text{stab}} =$$
[1]
(c) The numerical value of $K_{\text{stab}}$ of $[\text{Co}(\text{ NH}_3 )_6 ]^{2^+}$ is $7.7 \times 10^4$. What deduction about the properties of $[\text{Co}(\text{ N H}_3 )_6 ]^{2^+"}$ and $[\text{Co}(\text{ H}_2\text{ O})_6 ]^{2^+}$ can be made from this $K7 The structure of benzene-1,3-dicarboxylic acid is shown.
benzene-1,3-dicarboxylic acid
(a) State the empirical formula of benzene-1,3-dcarboxylic acid.
[1]
(b) Benzene-1,3-dicarboxyolic acid is an isomer of benzene-1,4-dicarboxylic acid. These two isomers can be distinguished by carbon-13 ($^{13}$C) NMR spectroscopy.
State the number of peaks in the carbon-13 ($^{13}$С) NMR spectrum of each compound.
| benzene-1,3-dicar boxylic acid | |
| :--- | :--- |
| benzene-1,4-dicar boxylic acid | |
(c) Benzene-1,3-d-carboxylic acid can be made by the two-step synthesis shown below.
compound P $\rightarrow$ compound Q $\rightarrow$ benzene-1,3-dicar_boxylic acid
(i) Name compound P.
[1]
(ii) Explain why the major product of this two-step synthesis is benzene-1,3-dicarBoxylic acid and not(iii) The reagents used for step 1 are CH$_3$COCl and AlCl$_3$. These reagents give rise to CH$_3$C=O ions which react with compound P. Name the mechanism of this reaction. [1] (iv) Draw the mechanism of the reaction of CH$_3$C=O ions with compound P. Include all relevant curly arrows and charges, the structure of the intermediate and the structure of compound Q. intermediate compound Q [3] (v) Suggest a reagent and conditions to convert compound Q into benzene-1,3-dicarboxylic acid, in step 2. [1] [Total: 10]
8 Alanine, H$_2$NCH(CH$_3$)CO$_2$H, and glutamic acid, H$_2$NCH(CH $_2 $CH$_2 $CO$_2 $H)CO$_2$H, are two naturally occurring amino acids. (a) H$_2$NCH(CH$_�$)CO$_2$H exists as two optical isomers. Draw three-dimensional structures of these two optical isomers. (b) The proton (^1H) NMR spectrum of either alanine in D$_2$O or glutamic acid in D$_2$O is shown. State whether this is the spectrum of alanine in D$_2$O or the spectrum of glutamic acid in D$_2$О. Explain your answer by reference to the number of peaks and splitting patterns. [3]
(c) The mass spectrum of glutamic acid, H$_2$NCH(CH$_2$CH$_2$CO$_2$H)CO$_2$H, is obtained. (i) State the $m/e$ value of the molecular ion peak in this spectrum. (ii) The spectrum has peaks with $m/e$ values of 88 and 131. Draw the structures of the ions responsible for these peaks. | $m/e$ | structure of ion | | :---: | :---: | | 88 | | | 131 | | (d) At pH 11 alanine exists as H$_2$NCH(CH$_3$)CO$_2^-$ ions and glutamic acid exists as H$_2$NCH(Ch$_2$CH$_2$CO$_�^-)$CO_2^-$ ions. A mixture of alanine and glutamic acid at pH 11 is subjected to electrophoresis. (i) State how the mixture can be maintained at pH 11 during electrophoresis. (ii) Draw a fully labelled diagram for the apparatus that would be used to carry out this electrophoresis. Your diagram should include the position of the
(iii) Identify the electrode that each amino acid travels towards during electrophoresis at pH 11. alanine ..... glutamic acid ..... [1] (iv) In a particular electrophoresis experiment at pH 11, the glutamic acid travels 3.4 cm. Alanine travels a shorter distance. Explain the factors that account for the difference in the distances travelled. [Total: 14]
9 Butylamine, CH$_3$CH$_2$CH$_2$CH$_2$NH$_2$, can be synthesised from different organic compounds by using suitable reagents. Each reaction involves one step. (a) Complete the table to describe three different syntheses. - One of the three syntheses should involve a nucleophilic substitution reaction. - The starting organic compound for each synthesis should contain a different functional group. - A different reagent should be used for each synthesis. | starting organic compound | reagent and conditions | | :--- | :--- | | | | [6] (b) Compare and explain the relative basicities of ammonia, butylamine and phenylamine. ... > ... > ... most basic least basic [Total: 10]
10 (a) Complete the table to show the structure of the organic product from each reaction of phenol, $C_6H_5OH$.
| reaction | reaction mixture | structure of organic product |
| :--- | :---: | :---: |
| 1 | phenol + NaOH(aq) | |
| 2 | phenol + Na(s) | |
| 3 | $\text{phenol} + \text{N}^{+}\text{N}=\text{N}$ (aq) + NaOH, at 4°C | |
| 4 | an excess of phenol + $\text{Cl}_2\text{O}$ | |
(b) Identify two reactions from the table in which ethanol would behave in a similar way to phenol. [1]
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