科目：化学 Chemistry (9701)
年份：2017 冬季
试卷：Paper 42
总页数：18
章节：19 Lattice energy, 20 Electrochemistry, 21 Further aspects of equilibria, 22 Reaction kinetics, 24 Transition elements, 25 Benzene and its compounds, 26 Carboxylic acids and their derivatives, 27 Organic nitrogen compounds, 28 Polymerisation, 30 Analytical chemistry
Answer all the questions in the spaces provided.
1. The compound chlorine dioxide, $ClO_2$, can be prepared by the reaction shown.
$$NaClO_2 + \frac{1}{2}Cl_2 \rightarrow ClO_2 + NaCl$$
(a) Using oxidation numbers, explain why this reaction is a redox reaction.
[2]
(b) The central atom in the molecule of $ClO_2$ is chlorine.
Draw the ‘dot-and-cross’ diagram for $ClO_2$. Show outer electrons only.
[2]
(c) The reaction between $ClO_2$ and $F_2$ is shown.
$$2ClO_2 + F_2 \rightarrow 2ClO_2F$$
The rate of the reaction was measured at various concentrations of the two reactants and the following results were obtained.
| experiment | $[ClO_2]/mol dm^{-3}$ | $[F_2]/mol dm^{-3}$ |
| :---: | :---: | :---: |
| 1 | 0.010 | 0.060 | $2.20 \times 10^{-3}$ |
| 2 | 0.025 | 0.060 | to be calculated(ii) Use the results of experiment 1 to calculate the rate constant, $k$, for this reaction. Include the units of $k$.
$$\text{rate constant}, k = \dots\dots\dots\dots\quad\text{units}$$
(iii) Use the data in the table to calculate
- the initial rate in experiment 2,
$$\text{initial rate} = \dots\dots\dottots\dots\quad\text{mol dm}^{-3}\text{s}^{-1}$$
- $\left[\text{ClO}_2\right]$ in experiment 3.
$$\left[\text{ClO}_2\right] = \dots\dots\dittots\dots\quad\text{mol}\text{dm}^{-3}$$
(d) (i) What is meant by the term *rate-determining step*?
[1]
(ii) The equation for the reaction between $\text{ClO}_2$ and $\text{F}_2$ is shown.
$$2\text{ClO}_2 + \text{F}_2 \rightarrow 2\text{ClO}_2\text{F}$$
$$\text{rate} = k\left[\text{ClO}_2\right]\left[\text{F}_2\right]$$
The mechanism for thi2 (a) When water is added to magnesium nitride, Mg$_3$N$_2$, the products are a white suspension of Mg(OH)$_2$ and an alkaline gas.
(i) Write an equation for this reaction.
[1]
(ii) A 2.52 g sample of Mg$_3$N$_2$ is added to an excess of water.
Calculate the mass of Mg(OH)$_2$ formed.
mass of Mg(OH)$_2$ = ..... g [2]
(b) State and explain how the solubility of the Group 2 hydroxides varies down the group.
[4]
(c) Magnesium hydroxide is sparingly soluble in water. The concentration of its saturated solution at 298 K is $1.7 \times 10^{-4}$ mol dm$^{-3}$.
(i) Write an expression for the solubility product, $K_{sp}$, of Mg(OH)$_2$.
$$K_{sp} =$$
[1]
(ii) Calculate the value of $K_{sp}$ for Mg(OH)$_2$ at 298 K and state its units.
$$K_{sp} =$$ units ... [2](d) The temperature at which the Group 2 hydroxides and carbonates start to decompose increases down the group. Suggest an explanation for this trend in the decomposition temperature of the Group 2 hydroxides. [Total: 12]
3 Serotonin can be synthesised from the amino acid tryptophan in two steps. (a) (i) In a buffer solution at pH 5.9, a sample of tryptophan does not move during electrophoresis. Draw the structures of the ions formed by tryptophan at pH 1.0 and pH 5.9. (ii) Tryptophan can combine with valine to form a dipeptide. Use the Data Booklet to draw the structure of this dipeptide.
(b) Complete the following table to show the structures of the products formed and the type of reaction occurring when serotonin reacts with the four reagents in separate reactions. | reagent | structure of product | type of reaction | | :--- | :---: | :---: | | Na | | | | excess Br₂(aq) | | | | excess CH₃COCl | | | | excess H₂/Pt catalyst | | [8]
(c) Serotonin is converted by enzymes in the liver to compound M. (i) By reference to the Data Booklet, suggest how the infra-red spectrum of M would differ from that of serotonin. [1] (ii) The proton NMR spectrum of M dissolved in CDCl$_3$ shows eight peaks due to the eight different types of proton present in the molecule. The proton NMR spectrum of M dissolved在D$_2$O was recorded. Predict the number of peaks that would be seen in the proton NMR spectrum of M in D$_2$O. Explain your answer. number of peaks ... explanation ... [2] (d) Compound M can be polymerised under certain conditions to form polymer N, shown. Polymer N is biodegradable, unlike polyethene which is not. Explain why N is biodegradable. [1] [Total: 16]
4 An electrochemical cell consists of a half-cell containing $V^{3+}(aq)$ and $V^{2+}(aq)$ ions and another half-cell containing $VO_{2}^{+}(aq)$ and $VO_{2}^{2+}(aq)$ ions.
(a) (i) Use data from the Data Booklet to calculate a value for the $E_{\text{cell}}^{\circ}$.
$$E_{\text{cell}}^{\circ} = \dots\dots\dots\dots\ V$$
(ii) Write the ionic equation for the cell reaction.
[1]
(iii) Draw a fully labelled diagram of the apparatus you could use to measure the potential of this cell. Include the necessary chemicals.
[4](b) Use data from the Data Booklet to predict whether a reaction might take place when the following pairs of aqueous solutions are mixed. If a reaction occurs, write an equation for it and calculate the $E_{\text{cell}}^{\circ}$.
- $V^{2+}(\text{aq})$ and $\text{Sn}^{4+}(\text{aq})$
Does a reaction occur? .....
equation .....
$E_{\text{cell}}^{\circ}$
- $\text{VO}^{2+}(\text{aq})$ and $$\text{Fe}^{3+}(\text{aq})$$
Does a reaction occur? .....
equaction .....
$E_{\text{cell }}^{\circ}$
[Total: 9]5 (a) The arrangement of the anions around a cation is called the geometry of the cation; e.g. in $[\text{CuCl}_4]^{2-}$ the geometry of copper is tetrahedral and the co-ordination number of copper is 4.
The geometry of a cation in an ionic compound can be predicted from the ratio of the ionic radii of the cation and anion involved.
| cation radius / anion radius | geometry of cation |
| :--- | :--- |
| 0.155–0.225 | trigonal planar |
| 0.225–0.414 | tetrahedral |
| 0.414–0.732 | octahedral |
Use data from the Data Booklet to predict the geometry of, and hence the co-ordination number of, the cation for
• sodium chloride, $\text{NaCl}$,
geometry of $\text{Na}^+ = \dots\dots\dots\dots\ldots$ co-ordination number of $\text{Na}^+ = \ldots\dots\dots\ldotsss$
• magnesium chloride, $\text{(c) (i) The equation for which $\Delta H$ is the lattice energy for MgCl$_l$ is shown.
$$\text{Mg}^{+}(\text{g}) + \text{Cl}^{-}(\text{g}) \rightarrow \text{MgCl}_l(\text{s})$$
Use the equation, the following data, and relevant data from the Data Booklet to calculate a value for the lattice energy of MgCl$_l$. You might find it helpful to construct an energy cycle.
electron affinity of Cl($\text{g}$) = $-349\text{ kJ mol}^{-1}$
enthalpy change of atomisation of Mg($\text{s}$) = $+147\text{ kJ mol}^{-1}$
enthalpy change of formation of MgCl$_l$(s) = $-106\text{ kJ mol}^{-1}$
lattice energy MgCl$_l$ = ... kJ mol$^{-1}$ [3]
(ii) Suggest how the lattice energies of MgCl$_2$ and NaCl will compare to that of MgCl$_l$.
Explain your answers.
MgCl$_2$ and MgCl ..... [3]
NaCl and MgCl..... [6 (a) Define the term transition metal complex.
[1]
(b) Platinum can form the compound $[\text{Pt}(\text{NH}_3)_4\text{Cl}_2][\text{PtCl}_4]$.
State the co-ordination numbers and the oxidation numbers of the platinum in the two ions of this compound.
| | co-ordination number | oxidation number |
| :--- | :---: | :---: |
| $[\text{Pt}(\text{NH}_{3})_4\text{Cl}_2]^{2+}$ | | |
| $[\text{PtCl}_4]^{2-}$ | | |
(c) Draw three-dimensional diagrams to show the structures of the two isomers of $[\text{Pt}(\text{NH} _ {3 })_{4}\text{Cl}_{2}]^{2+}$.
[2]
(d) Solutions of the compounds $[\text{Pt}(\text{NH } _{3 })_{4}\text{Cl}_{�}] \text{Br}_{2}$ and $[\text{Pt}(\text{NH}^{3 })_{4}\text{Br}_{2}] \text{Cl}_{2}$ can be distinguished from each other by a simple chemical test. Assume that any specie(e) In this question you should consider geometrical and optical isomerism.
What type of isomerism is shown by the following complexes?
You should answer geometrical, optical, both or neither.
octahedral [Co(NH$_2$CH$_2$CH$_2$NH$_2)$_2Cl$_2]$^+ ... [3]
square planar [Ni(CN)$_2$Cl$_2$]^{2-} ... [3]
tetrahedral [CuBr$_2$Cl$_2$]^{2−} ... [3]
(f) Many enzymes contain transition metal complexes.
Describe, with the aid of a suitably labelled diagram, how an enzyme catalyses the breakdown of a substrate molecule.7 (a) Calcium carbide, CaC$_2$, reacts readily with water, forming ethyne, C$_2$H$_2$, and a sparingly soluble white ionic compound.
(i) Write an equation for the reaction of CaC$_2$ with water.
[1]
(ii) Draw a ‘dot-and-cross’ diagram for the carbide ion, C$_2^{2-}$. Show outer electrons only.
[1]
(b) Ethyne is the simplest member of the alkyne homologous series.
$$\text{H} \longrightarrow \text{C} = \text{C} - \text{H}$$
ethyne
Propyne, C$_3$H$_4$, and butyne, C$_4$H$_6$, are the next two members of the series.
Deduce the general formula for the alkynes.
[1]
(c) Ethyne can be polymerised into poly(acetylene), which is a conducting polymer.
$$\text{poly(acetylene)}$$
(i) Suggest why this polymer conducts electricity.
[1]
(ii) State the empirical formula of poly(acetylene).
[(d) Alkynes can react with carbonyl compounds under basic conditions as shown in reaction 1. (i) The first step of the mechanism of reaction 1 involves the alkyne anion reacting with the carbonyl compound. Complete the first step of the mechanism and draw the intermediate for this reaction. Include all relevant dipoles, charges and curly arrows. (ii) Suggest the name of the mechanism in reaction 1. [1]
(iii) An alkyne, Q, and a carbonyl compound, R, react together to form compound P as shown.
$$\text{2Q} + \text{R} \rightarrow \text{P}$$
Use reaction 1 to suggest the structures of Q and R.
(e) A series of twelve separate experiments is carried out as shown in the table.
Complete the table by writing in each box a tick (✓) if a reaction occurs, or a cross (x) if no reaction occurs.
| | CH$_3$CHO | HCO$_2$H | CH$_3$COCH$_3$ | HO$_2$CCO$_2$H |
| :--- | :---: | :---: | :---: | ---: |
| hot, acidified MnO$_4^-$(aq) | | | | |
| alkaline I$_2$(aq) | | | | |
| warm Tollens’ reagent | | | | |
[Total: 16]8 (a) Compound A can be produced from a plant hormone.
(i) Compound A shows optical and geometrical isomerism.
On the structure of A above,
• draw a line through the bond(s) that give rise to geometrical isomerism,
• circle all chiral carbon atoms. [2]
(ii) Give the names of four functional groups present in A.
[2]
(iii) A molecule of A has 17 carbon atoms.
State the number of carbon atoms that are sp, sp² and sp³ hybridised in A.
sp carbons = ... sp² carbons = ... sp³ carbons = ... [1]
(iv) When A is reacted with an excess of hot, concentrated manganate(VII) ions, a mixture of three organic compounds is formed.
$$\text{A} \rightarrow \text{X} \quad \text{and} \quad \text{Y} \quad \text{and} \tag{C_{10}\text{H}_{14}\text{O}_7}$$
$$\text{(C_3\text{H}_4\text{O}_3)} \quad \text{(C_3\te(b) A mixture of three different compounds, J, K and L, was analysed by thin layer chromatography using a polar stationary phase and a non-polar mobile phase. The three compounds all have similar molecular masses. The resulting chromatogram is shown.
(i) Identify which spot corresponds to each compound.
| compound | spot |
| :--- | :--- |
| $J$ $\text{CH}_3\text{COCO}_2\text{H}$ | |
| $K$ $\text{HO}_2\text{CCO}_2\text{H}$ | |
| $\text{L}$ $\text{CH}_3\text{CH}_2\text{COCH}_2\text{CH}_3$ | |
[1]
(ii) Explain your answers to (b)(i).
... [1]
(iii) What is meant by the term $R_f$ value?
... [1]
[Total: 10]