科目：化学 Chemistry (9701)
年份：2020 春季
试卷：Paper 42
总页数：23
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, 29 Organic synthesis, 30 Analytical chemistry
Answer all the questions in the spaces provided.
1 Iron is a transition element in the fourth period. Iron forms compounds containing the ions Fe$^{2+}$ and Fe$^{3+}$.
(a) (i) Define the term transition element.
[1]
(ii) Compare the melting point and density of iron with those of calcium, an s-block element in the fourth period.
melting point ... density ... [1]
(iii) Complete the electronic configuration of an isolated gaseous Fe$^{2+}$ ion.
1s$^2$ ... [1]
(iv) Aqueous Fe$^{3+}$ ions form coloured complexes.
Explain the origin of the colour in transition element complexes.
[4](b) When an excess of CN⁻(aq) ions is added to green [Fe(H₂O)₆]²⁺(aq) ions, yellow [Fe(CN)₆]⁴− complex ions are formed.
Heating [Fe(CN)₆]ⴴ− with dilute nitric acid and then neutralising the product with Na₂CO₃(aq) produces red crystals, containing the [Fe(CN)₅NO]²⁻ complex ion.
NO is a neutral, monodentate ligand.
(i) State the shape of the [Fe(H₂O)₆](2+)(aq) complex ion.
[1]
(ii) Write the equation for the reaction between [Fe(H₂O)₆][2+](aq) ions and an excess of CN⁻(aq)sion.
[1]
(iii) Deduce the oxidation states of iron in:
[Fe(CN)₆]ⴾ ... [Fe(CN)₅NO]³⁻. [1]
(iv) Define the term monodentate ligand.
[2]
(v) Complete the diagram to show the three-dimensional structure of the [Fe(CN)₅NO][2−] complex ion.
(vi) The two complex ions [Fe(CN)₆]ℴ− and [Fe(CN)₅NO]^{2−(c) E is a complex ion, $[\text{Fe}(\text{C}_2\text{O}_4)_2\text{Cl}_2]^{4-}$, containing Fe$^{2+}$ with a coordination number of 6.
(i) Define the term coordination number.
(ii) E shows both optical isomerism and cis-trans isomerism.
One isomer of E is shown. The C$_2$O$_4^{2-}$ ion is represented as $\text{ox}$.
In the boxes, draw three-dimensional diagrams to show:
• the trans isomer of E
• the optical isomer of E.
$$\begin{array}{c}
\text{E} \\
[ \text{Fe} ] [ \text{Cl} ] [ \text{Cl} ] \\
\text{cis isomer}
\end{array}$$
$$\begin{array}{c}
\text{trans isomer} \\
[ \text{Fe} ]
\end{array}$$
$$\begin{array}{l}
\text{optical isomer} \\
[ \text{FE} ]
\end{array}$$(iii) $[\text{Fe}(\text{C}_2\text{O}_4)_2\text{Cl}_2]^{4-}$ contains ligands which are anions of ethanedioic acid, $\text{HO}_2\text{CCO}_2\text{H}$.
Complete the table to show any observations for the reactions of $\text{HO}_2\text{CCCO}_2\text{H}$ with the named reagents.
Where no change is observed, write ‘none’.
| reagent | observations with $\text{HO}_2\text{CC CO}_2\text{H}$ |
| :--- | :--- |
| warm acidified manganate(VII) | |
| 2,4-dinitrophenylhydrazine | |
| warm Tollens’ reagent | |
[Total: 20]2 (a) Group 2 metals form stable carbonates and sulfates. (i) State and explain the trend in the thermal stability of the Group 2 carbonates down the group. [3] (ii) The sulfates of Group 2 elements become less soluble down the group. Explain this trend. [3]
(b) Aluminium is extracted from $Al_2O_3$ by electrolysis. $Al_2O_3$ is dissolved in cryolite in this process.
(i) The half-equation for the reaction at the anode is shown.
$$O^{2-} + C \rightarrow CO + 2e^-$$
Use this half-equation to write the ionic equation for the electrolysis of $Al_2O_3$.
(ii) Aluminium oxide is electrolysed for 3.0 hours using carbon electrodes and a current of $3.5 \times 10^5$ A.
Calculate the mass of aluminium that is formed.
mass of aluminium = ..... g [3]
(iii) Cryolite can be made from $\text{SiF}_4$.
The first step in this conversion is the reaction of $\text{SiF}_4$ with $H_2O$, forming $H_2\text{SiF}_6$ and $\text{SiO}_2$.
Write an equation for this reaction.
[Total: 11]3 Gold is an unreactive metal that can only be oxidised under specific conditions.
(a) The standard electrode potential, $E^\circ$, of Au$^{3+}$(aq)/Au(s) is +1.50 V.
(i) Define the term standard electrode potential.
[2]
(ii) Draw a fully labelled diagram of the apparatus that should be used to measure the standard cell potential, $E^\circ_{\text{cell}}$, of Au$^{3+}$(aq)/Au(s) and HNO$_3$(aq)/NO(g).
Include all necessary chemicals.Some relevant half-equations and their standard electrode potentials are given.
| half-equation | $E^\circ$/V |
| :--- | :--- |
| $\text{Au}^{3+}(\text{aq}) + 3\text{e}^- \rightleftharpoons \text{Au(s)}$ | +1.50 |
| $[\text{AuCl}_4]^{-}(\text{aq}) + 3\text e^- \rightleftharpoons \mathrm{Au(s)} + 4\text{Cl}^-(\text{aq})$ | +1.00 |
| $\text{NO}_3^-(\text{aq}) + 4\text{H}^+(\text{aq}) + 3\text{е}^- \rightleftharpoons (\mathrm{NO(g)} + 2\text{H}_2\mathrm{O(l)})$ | +0.96 |
(iii) Write an ionic equation to show the spontaneous reaction that occurs when an electric current is drawn from the cell in (a)(ii).
[1]
(iv) Calculate the $E^\circ_{\text{cell}}$ of the reaction in (a)(iii).
$$E^\circ_{\text{cell}} = \dots\dots\dots\dots\ V$$ [1]
(v) Gold can be oxidised by a mixture of concentrated (b) Aqueous gold(III) chloride, AuCl$_3$, reacts with aqueous hydrogen peroxide, H$_2$O$_2$, under certain conditions, forming Au, O$_2$ and HCl.
A student carries out separate experiments using different initial concentrations of AuCl$_3$ and H$_2$O$_2$. The initial rate of each reaction is measured.
The table shows the results that are obtained.
| experiment | [AuCl$_3$] / mol dm$^{-3}$ | [H$_2$O$_2$] / mol dm$^{-3}$$\cdot$$10^{-2}$ | rate of production of O$_2$(g) / dm$^3$ minute$^{-1}$ |
| :--- | :---: | :---: | :---: |
| 1 | 0.05 | 0.50 | $7.66 \times 10^{-2}$ |
| 2 | 0.10 | 0.50 | $1.53 \times 10^{-1}$ |
| 3 | 0.15 | 1.00 | $4.60 \times 10^{-1}$ |
(i) Write an equation for the reaction of AuCl$_3$ with H$_2$O$_2$.
[1]
(ii) Determine the rate equation of the reaction.
Show your(c) $AlF_3$ is an ionic compound.
The Born–Haber cycle for the formation of $AlF_3$ is shown.
(i) Name the enthalpy changes labelled $\Delta H_4$ and $\Delta H_6$.
$$\Delta H_4 = \text{...}$$
$$\Delta H_6 = \text{...}$$
[2]
(ii) Use the data in the table and data from the Data Booklet to calculate the lattice energy of $AlF_3$.
| process | enthalpy change /kJ mol^{-1} |
| :--- | :---:|
| $Al(s) \rightarrow Al(g)$ | +326 |
| $Al(g) \rightarrow Al^{3+}(g)$ | +5137 |
| $F(g) \rightarrow F^- (g)$ | -328 |
| $Al(s) + 1.5F_2(g) \rightarrow AlF_3(s)$ | -1504 |
lattice energy of $AlF_3 = \text{... kJ mol}^{-1}$ [2](iii) Scandium fluoride, $ScF_3$, is an ionic compound.
Use data from the Data Booklet to suggest how the lattice energy of $AlF_3$ compares with the lattice energy of $ScF_3$.
Explain your answer.
[2]
(d) $AlF_3$ is sparingly soluble in water. The concentration of its saturated solution at 298K is $6.5 \times 10^{-2} \text{ mol dm}^{-3}$.
(i) Write an expression for the solubility product, $K_{\text{sp}}$, of $AlF_3$.
$$K_{\text{sp}} = ...$$
[1]
(ii) Calculate the numerical value of $K_{\text{sp}}$ for $AlF_3$ at 298K.
$$K_{\text{sp}} =...$$
[1]
[Total: 25]4 Compound F has been found in small quantities in some cereals and dried fruit. (a) (i) Give the name of the functional groups labelled A and B. A ... [2] B ... [1] (ii) State the number of chiral carbon atoms in one molecule of F. ... [1]
(b) F can be hydrolysed by heating with an excess of dilute hydrochloric acid, as shown. Three products are formed: G and two others. Draw the structures of the other products of the reaction in the boxes provided. (c) Compound H is formed in one step of a different synthesis, as shown. (i) State the role of FeCl$_3$ in this step. [1]
(ii) Use the Data Booklet to suggest two reasons why the chlorine atom in compound H substitutes into the ring at the position shown, instead of the other positions in the ring. 1 .... 2 .... [2] (d) Compound J, $C_xH_yO_z$, is also found in some cereals. Part of the mass spectrum of J is shown. The M and M+1 peaks are labelled, along with their relative intensities. (i) Calculate the number of carbon atoms, x, present in J. $$x = \dots\dots\dots\dots\quad [2]$$ (ii) The mass spectrum has a peak at $m/e = 205$. Suggest the identity of the fragment lost from J to form this peak. [Total: 12]
5 Gallic acid, $C_7H_6O_5$, is a naturally occurring aromatic molecule.
(a) Gallic acid contains the carboxylic acid and phenol functional groups. State and explain the relative acid strength of these two functional groups.
[2]
(b) A buffer solution was prepared by dissolving 2.04 g of gallic acid in 250 cm$^3$ of a solution containing 0.0600 mol dm$^{-3}$ of gallate ions, $C_7H_5O_5^-$. $$C_7H_6O_5 \rightleftharpoons C_7H_5O_5^-$ + $H^+$$ $K_a = 3.89 \times 10^{-5} \text{mol dm}^{-3}$ at 298 K
(i) Define the term buffer solution.
[2]
(ii) Calculate the pH of this buffer solution.
pH = ..... [3](iii) Write two equations to show how a solution containing gallic acid, $C_7H_6O_5$, and gallate ions, $C_7H_5O_5^-$, acts as a buffer. (c) Compound K is used as the starting material in a synthesis of gallic acid. A student suggested the first two steps of the synthesis could be as shown. Nitronium ions, $NO_2^+$, are generated by the reaction between concentrated sulfuric acid and concentrated nitric acid. (i) Construct an equation for the formation of $NO_2^+$ by this method. [1] (ii) Complete the mechanism and draw the intermediate of step 1. Include all relevant charges and curly arrows to show the movement of electron pairs. [2] (iii) State the name of the mechanism in (c)(ii).
Compound M is converted into compound P as shown.
(iv) State the reagents and conditions for step 4.
P reacts with an excess of sodium nitrite, NaNO$_2$, and dilute HCl at 5°C to form compound Q, C$_{9}$H$_{7}$N$_{6}$O$_{2}$Cl$_{3}$.
Compound Q is then converted into gallic acid.
(v) Suggest the structure of compound Q in the box provided.
(vi) State the reagents and conditions for step.(d) (i) State the number of peaks that would be observed in the $^{13}$C NMR spectrum of gallic acid.
gallic acid
[1]
(ii) The proton NMR spectrum of gallic acid dissolved in D$_2$O is recorded.
- Predict the number of peaks observed and any expected splitting pattern.
- State the expected chemical shift range ($\delta$) of each peak predicted.
[Total: 21]6 Valinol can be synthesised by the following reactions. Reaction 1 uses valine as the starting material. (a) (i) Write an equation for reaction 1, using [H] to represent the reducing agent. [1] (ii) Suggest a suitable reagent for reaction 1. [1] (iii) Name the mechanism for reaction 2. [1] (b) Valine and glycine, H$_2$NCH$_2$COOH, form the tripeptide Gly–Val–Gly. Draw the structure of this tripeptide. Show the peptide bonds fully displayed. [2]
(c) (i) Valine exists as two stereoisomers.
Draw three-dimensional diagrams to show the two stereoisomers of valine. In your diagrams, the $-\text{CH}(\text{CH}_3)_2$ group can be represented by $-R$.
State the type of stereoisomerism shown.
type of stereoisomerism ... [2]
(ii) Valine is an amino acid.
Draw the zwitterion of valine. [1](iii) Valinate, $Val^{-}$, is the anion of valine. It takes part in a ligand substitution reaction with hexaaquanickel(II) ions. Complex $Z$ is formed.
$$[Ni(H_2O)_6]^{2+}(aq) + 2Val^{-}(aq) \rightleftharpoons [Ni(H_2O)_2(Val)_2](aq) + 4H_2O(I)$$
Write an expression for $K_{stab}$ for this equilibrium.
$$K_{stab} =$$
[1]
(iv) At room temperature, the numerical value of $K_{stab}$ is $2.34 \times 10^5$. Explain what this value indicates about the equilibrium and the stability of complex $Z$.
[1]
(v) $Z$ is an octahedral complex with formula $$[Ni(H_2O)_2(Val)]_2$$. Use this information to state the type of ligand that the valinate ion is acting as in this complex.
[1]
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