AS & A Level Chemistry - 9701 Paper 4 2023 Winter Zone 1

Fluorine reacts with chlorine dioxide, $ClO_2$, as shown.

$$F_2(g) + 2ClO_2(g) \rightarrow 2FClO_2(g)$$
The rate of the reaction is first order with respect to the concentration of $F_2$ and first order with respect to the concentration of $ClO_2$. No catalyst is involved.

(a) (i) Suggest a two-step mechanism for this reaction.

step 1 $\rightarrow$
step 2 $\rightarrow$
[2]

(ii) Identify the rate-determining step in this mechanism. Explain your answer.
.........................................................................................................................................................................
......................................................................................................................................................................... [1]

(b) When the rate of the reaction is measured in $mol\ dm^{-3}\ s^{-1}$ the numerical value of the rate constant, $k$, is 1.22 under certain conditions.

(i) Complete the rate equation for this reaction, stating the overall order of the reaction.
rate =
overall order of reaction =
[1]

(ii) Use your rate equation in (i) to calculate the rate of the reaction when the concentrations of $F_2$ and $ClO_2$ are both $2.00 \times 10^{-3} mol\ dm^{-3}$.
rate = ............................... $mol\ dm^{-3}\ s^{-1}$ [1]

(c) Under different conditions, and in the presence of a large excess of $ClO_2$, the rate equation is as shown.
$$rate = k_1[F_2]$$
The half-life, $t_{1/2}$, of the concentration of $F_2$ is 4.00 s under these conditions.

(i) Calculate the numerical value of $k_1$, giving its units.
Give your answer to three significant figures.
$$k_1 = .......................... units ..........................$$ [2]

(ii) An experiment is performed under these conditions in which the starting concentration of $F_2$ is $0.00200 mol\ dm^{-3}$.
Draw a graph on the grid in Fig. 1.1 to show how the concentration of $F_2$ changes over the first 12 s of the reaction.

!(here)
Fig. 1.1
[1]

(iii) Use your graph in Fig. 1.1 to find the rate of the reaction when the concentration of $F_2$ is $0.00100 mol\ dm^{-3}$. Show your working on the graph.
rate = ............................... $mol\ dm^{-3}\ s^{-1}$ [1]

(a) Define $K_w$ mathematically by completing the expression.

$K_w = \text{........................................................................................................................................}$ [1]

(b) Two solutions, V and W, are described.

• V is HCl(aq).
• W is NaOH(aq).
• The concentration of HCl in V is the same as the concentration of NaOH in W.
• The pH values of V and W differ by exactly 11.00 at 298 K.

(i) Calculate the concentration of HCl in V.

concentration of HCl in V = .............................. mol dm$^{-3}$ [2]

(ii) Equal volumes of the two solutions V and W are mixed, giving solution X.

Name solution X and state its pH.

solution X .............................. pH .............................. [1]

(iii) A 1 cm$^3$ sample of 1.0 mol dm$^{-3}$ HNO$_3$ is added to 100 cm$^3$ of solution X, forming mixture Y.
A 1 cm$^3$ sample of 1.0 mol dm$^{-3}$ KOH is added to 100 cm$^3$ of solution X, forming mixture Z.
Estimate the pH of mixtures Y and Z. No calculations are required.

mixture Y .............................. mixture Z .............................. [1]

(c) (i) CH$_3$CH$_2$COOH, CH$_3$CCl$_2$COOH and H$_2$SO$_4$ are all acidic.

Suggest the trend in the relative acid strength of these three compounds.

Explain your answer.

.............................. .............................. ..............................
strongest acid weakest acid
explanation .......................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
................................................................................................................................................... [3]

(ii) When concentrated H$_2$SO$_4$ is added to water a series of acid-base reactions occurs.
There are three conjugate acid-base pairs that can be identified during this series of reactions.
Write the formulae of these three conjugate acid-base pairs.

conjugate acid 1 .............................. conjugate base 1 ..............................
conjugate acid 2 .............................. conjugate base 2 ..............................
conjugate acid 3 .............................. conjugate base 3 .............................. [2]

(d) The partition coefficient, $K_{pc}$, of a substance, Q, between hexane and water is 7.84 at 298 K.

Q is more soluble in hexane than it is in water.

(i) Define partition coefficient, $K_{pc}$.

...................................................................................................................................................
................................................................................................................................................... [1]

(ii) 5.00 g of Q is shaken with a mixture of 100.0 cm$^3$ of water and 100.0 cm$^3$ of hexane at 298 K and left until there is no further change in concentrations.
Calculate the mass of Q dissolved in the water.

mass of Q = .............................. g [1]

(iii) A sample of Q is shaken with a different mixture of water and hexane and left until there is no further change in concentrations.
It is found that the mass of Q dissolved in each solvent is the same.
Use the $K_{pc}$ value to suggest possible values for the volume of water used and the volume of hexane used.

volume of water = .............................. cm$^3$
volume of hexane = .............................. cm$^3$ [1]

(iv) Q is more soluble in hexane than it is in water.
It is suggested that Q is one of KCl, CH$_3$(CH$_2$)$_4$OH or HCOOH.
Identify Q. Explain your answer.

...................................................................................................................................................
................................................................................................................................................... [1]

(a) (i) Define entropy.
................................................
[1]

(ii) Predict the sign of the standard entropy change of reaction 1.
Explain your answer.
sign ..........................................
explanation ................................
................................................
[1]

(b) Some bond energy data are shown in Table 3.1.

Table 3.1


Use the data in Table 3.1 to show that the enthalpy change of the following reaction is −196 kJ mol⁻¹.

$2H_2O_2(g) \rightarrow 2H_2O(g) + O_2(g)$
[1]

(c) Some standard entropies, $S^{\circ}$, are shown in Table 3.2.

Table 3.2


The enthalpy change and Gibbs free energy change for the following reaction are shown.

$2H_2O_2(l) \rightarrow 2H_2O(l) + O_2(g)$
$\Delta H^{\circ} = −196$ kJ mol⁻¹
$\Delta G^{\circ} = −238$ kJ mol⁻¹

Use the data given to calculate the standard entropy of oxygen, $S^{\circ}$, $O_2(g)$.

$S^{\circ}$, $O_2(g) = ................................... $ JK⁻¹ mol⁻¹ [3]

(d) The decomposition of $H_2O_2(aq)$ is catalysed by aqueous iron(III) chloride and by silver metal.
Identify which of these two catalysts is acting as a homogeneous catalyst.
Explain your answer.
homogeneous catalyst .......................
explanation .........................................
[1]

(e) The $E^{\circ}$ values for two electrode reactions are given.

$H_2O_2 + 2H^+ + 2e^- \rightarrow 2H_2O \quad E^{\circ} = +1.77$ V
$Cr^{3+} + e^- \rightarrow Cr^{2+} \quad E^{\circ} = −0.41$ V

(i) An electrochemical cell is constructed with the following half-cells (electrodes):
• an acidified solution of $H_2O_2$, a platinum wire
• $Cr^{2+}$ mixed with $Cr^{3+}$, a platinum wire.
Identify the positive half-cell and calculate the standard cell potential, $E^{\circ}_{cell}$.
positive half-cell ...........................
$E^{\circ}_{cell} = .............................$ V [1]

(ii) Calculate the value of $\Delta G^{\circ}$ for the cell reaction that occurs, per mole of $H_2O_2$.
$\Delta G^{\circ}$ = .......................... kJ mol⁻¹ [2]

(f) The $E^{\circ}$ values for two electrode reactions are given.

$H_2O_2 + 2H^+ + 2e^- \rightarrow 2H_2O \quad E^{\circ} = +1.77$ V
$Co^{3+} + e^- \rightarrow Co^{2+} \quad E^{\circ} = +1.82$ V

An electrochemical cell is constructed with the following half-cells.

half-cell 1 an acidified solution of $H_2O_2$ under standard conditions, a platinum wire
half-cell 2 a solution containing $0.020$ mol dm⁻³ Co³⁺ and $2.0$ mol dm⁻³ Co²⁺, a platinum wire

(i) Use the Nernst equation to calculate the value of $E$, the electrode potential of half-cell 2 under these conditions.
$E = ..............................$ V [2]

(ii) Write an equation for the cell reaction that occurs in this cell under these conditions.
..................................................
[1]

(g) (i) Define enthalpy change of hydration, $\Delta H_{hyd}^{\circ}$.
..................................................
[1]

(ii) Aluminium fluoride, $AlF_3$, is an ionic solid.
Complete and label the energy cycle to show the relationship between:
• the enthalpy change of solution of $AlF_3$, $\Delta H_{sol}^{\circ}$
• the lattice energy of $AlF_3$, $\Delta H_{latt}^{\circ}$
• the enthalpy changes of hydration of $Al^{3+}$ and $F^-$, $\Delta H_{hyd}^{\circ}$.
Include state symbols for all substances and ions.

[2]

(iii) Relevant data for this question are given.

$\Delta H_{sol}^{\circ} AlF_3 = −209$ kJ mol⁻¹
$\Delta H_{hyd}^{\circ} Al^{3+} = −4690$ kJ mol⁻¹
$\Delta H_{hyd}^{\circ} F^- = −506$ kJ mol⁻¹

Use these data and your energy cycle in (g)(ii) to calculate the $\Delta H_{latt}^{\circ}$ of $AlF_3$.

$\Delta H_{latt}^{\circ} of AlF_3 = .....................$ kJ mol⁻¹ [1]

(a) Cobalt(II) nitrate, Co(NO_3)_2, is a reddish-brown crystalline solid. It dissolves in water to form a solution containing [Co(H_2O)_6]^{2+} complex ions.
(i) Complete Table 4.1 giving the formula of the cobalt-containing species that is formed in each of the three reactions described.
[Table_4.1]
(ii) Describe the colour change seen in reaction 3.
original colour of [Co(H_2O)_6]^{2+}(aq) ..............................................................
final colour after addition of an excess of conc. HCl(aq) ..............................................

(b) Calcium nitrate, Ca(NO_3)_2, is a white crystalline solid. When heated, it starts to decompose at approximately 500°C.
(i) Write an equation for the decomposition of Ca(NO_3)_2. ..................................................................................................................
(ii) Suggest temperatures at which Mg(NO_3)_2 and Ba(NO_3)_2 start to decompose. Explain your answer.
temperature at which Mg(NO_3)_2 starts to decompose ..............................°C
temperature at which Ba(NO_3)_2 starts to decompose ......................................°C
explanation ..............................................................................................................................

Transition elements behave as catalysts and can form complex ions.
(a) Explain why transition elements behave as catalysts.
............................................................................................................................................................
............................................................................................................................................................
............................................................................................................................................................

(b) Silver forms the linear complex ion $[Ag(CN)_2]^-$.
Copper forms the tetrahedral complex ion $[Cu(CN)_4]^{3-}$.
Titanium forms the complex $[TiCl_4(diars)_2]$, where diars is a neutral bidentate ligand.
(i) State the oxidation state and the coordination number of titanium in $[TiCl_4(diars)_2]$.
oxidation state ...............................
coordination number ............................... [1]
(ii) Draw three-dimensional diagrams to show the shapes of $[Ag(CN)_2]^-$ and $[Cu(CN)_4]^{3-}$, in the boxes.
Label one bond angle on each diagram.



(c) The numerical value of the stability constant, $K_{stab}$, of the copper(I) complex $[Cu(CN)_4]^{3-}$ is $2.0 \times 10^{27}$.
(i) Write an expression for the $K_{stab}$ of $[Cu(CN)_4]^{3-}$.
$K_{stab}$ = ................................................................................................................. [1]
(ii) In a solution the concentrations of $CN^-$ and $[Cu(CN)_4]^{3-}$ are both $0.0010 \text{mol}\text{dm}^{-3}$.
Use your expression from (c)(i) and the value of $K_{stab}$ to calculate the concentration of $Cu^+(aq)$ in this solution.
concentration of $Cu^+(aq)$ = ........................................... $\text{mol}\text{dm}^{-3}$ [1]

(d) A piece of a copper-containing alloy has a mass of $0.567\,\text{g}$. It is dissolved in an acid giving $100.0\,\text{cm}^3$ of a blue solution in which all the copper is present as $Cu^{2+}$ ions.
An excess of $KI(aq)$ is added to a $25.0\,\text{cm}^3$ sample of this solution.
All of the copper is precipitated as white $CuI(s)$.
$Cu^{2+}$ ions are the only component in the solution that react with $KI(aq)$. This is reaction 1.
reaction 1 $\quad 2Cu^{2+} + 4I^- \rightarrow 2CuI + I_2$
The liberated $I_2$ is then titrated with $0.0200\,\text{mol}\text{dm}^{-3} S_2O_3^{2-}$. This is reaction 2.
reaction 2 $\quad I_2 + 2S_2O_3^{2-} \rightarrow 2I^- + S_4O_6^{2-}$
The titration requires $20.10\,\text{cm}^3$ of $0.0200\,\text{mol}\text{dm}^{-3} S_2O_3^{2-}$ to reach the end-point.
(i) Calculate the number of moles of $I_2$ that are reduced in this titration.
number of moles of $I_2$ = ......................................... $\text{mol}$ [1]
(ii) Calculate the number of moles of copper in the original piece of alloy.
number of moles of copper = ......................................... $\text{mol}$ [1]
(iii) Calculate the percentage of copper in the alloy.
percentage of copper = ......................................... % [1]
(iv) Suggest why a solution of $Cu^{2+}$ is coloured but solid $CuI$ is white.
..........................................................................................................................
.......................................................................................................................... [2]

(a) Five ligands are listed in Table 6.1.

Table 6.1
[Table_1]

(i) Complete Table 6.1 using the words monodentate, bidentate and polydentate only. Each of these three words may be used once, more than once, or not at all. [2]

(ii) The molecule $\text{H}_2\text{NCH}_2\text{CH}_2\text{NCH}_2\text{CH}_2\text{NH}_2$ is a tridentate ligand. Suggest the meaning of tridentate ligand.

.............................................................................................................................
............................................................................................................................. [1]

(iii) Suggest how $\text{H}_2\text{NCH}_2\text{CH}_2\text{NCH}_2\text{CH}_2\text{NH}_2$ acts as a tridentate ligand.

.............................................................................................................................
............................................................................................................................. [1]

(b) Nickel forms the octahedral complex $[\text{Ni(en)}_2(\text{H}_2\text{O})_2]^{2+}$. This complex can exist in three isomeric forms, listed in Table 6.2.

One of these forms is a trans isomer, the other forms are two different cis isomers.

Table 6.2
[Table_2]

(i) Complete Table 6.2 using the terms polar or non-polar. Each term may be used once, more than once, or not at all. [1]

(ii) Describe the difference between cis isomer 1 and cis isomer 2.

.............................................................................................................................
............................................................................................................................. [1]

(a) State the molecular formula of the Sunset Yellow anion.
................................................................................................................................. [1]
(b) Deduce the structures of E, F and G and draw them in the boxes in Fig. 7.1. [3]
(c) Suggest suitable reagents and conditions for step 1 and 2.
step 1 .........................................................................................................................
step 2 ......................................................................................................................... [3]
(d) Predict the number of peaks in the carbon-13 NMR spectrum of the Sunset Yellow anion.
................................................................................................................................. [1]
[Image_1: Diagram of Sunset Yellow synthesis route, including molecules E, F, G with Sunset Yellow anion.]

Capsaicin is found in chilli peppers.

You should assume the C H_3 O group is unreactive in the reactions involved in this question.

(a) Name all the functional groups in capsaicin in addition to the C H_3 O group.
.............................................................................................................................................................

(b) Complete the equation for the reaction of capsaicin with an excess of Br_2(aq) in the dark.
Draw the structure of the organic product in the labelled box.

+ ..........Br_2 →

+ .....................

(c) Capsaicin is heated with an excess of hydrogen gas in the presence of platinum metal.
The six-membered ring reacts in the same way as benzene under these conditions.
Draw the structure of the organic product formed.

(d) When capsaicin is treated with reagent J under suitable conditions one of the products is methylpropanoic acid, C H_3 C H (C H_3) C O O H.
(i) Identify reagent J and any necessary conditions.
.............................................................................................................................................................

(ii) There are three different peaks in the proton ((1)H) NMR spectrum of C H_3 C H (C H_3) C O O H in C D C l_3.

[Table_1]

Use Table 8.1 to complete Table 8.2 and state:
• the typical proton ((1)H) chemical shift values (δ) for the protons
• the splitting pattern (singlet, doublet, triplet, quartet or multiplet) shown by each peak
• the explanation for the splitting patterns of the CH_3 protons and the CH proton.

[Table_2]

(e) (i) Capsaicin is heated with an excess of hot aqueous NaOH.

Draw the structures of the two organic products H and K.

H C_8 H_10 N O_2 Na
K C_10 H_17 O_2 Na

(ii) Name the two types of reaction occurring in (e)(i).
.............................................................................................................................................................

(f) Draw the structure of the organic product L formed when capsaicin is treated with LiAlH_4 in dry ether.

(a) Benzoyl chloride, $C_6H_5COCl$, can be made from ethyl benzene in a two-step process. A reaction scheme is shown.

(i) Draw the intermediate organic compound M in the box. [1]
(ii) Suggest suitable reagents and conditions for step 1 and step 2.
step 1 ..............................................................................................................................
step 2 .............................................................................................................................. [2]
(iii) Identify the type of reaction in step 1 and step 2.
step 1 ..............................................................................................................................
step 2 .............................................................................................................................. [2]

(b) $C_6H_5COCl$ reacts with phenol, $C_6H_5OH$, to give the ester phenyl benzoate, $C_6H_5COOC_6H_5$. An incomplete description of the mechanism of this reaction is shown in Fig. 9.1.

(i) Complete the mechanism in Fig. 9.1 and include:
• all relevant dipoles ($\delta+$ and $\delta-$) and full electric charges (+ and –) on the species in box one and in box two
• all relevant lone pairs on the species in box one and in box two
• all relevant curly arrows to show the movement of electron pairs in box one and in box two
• the formula of the second product in box three. [4]
(ii) Name this mechanism.
............................................................................................................................... [1]

(c) Benzoyl chloride, chlorobenzene and chloroethane differ in their rates of hydrolysis when each compound is added separately to water at 25 °C.
Suggest the relative ease of hydrolysis of these three compounds.
Explain your answer.
................................. .................................. ..................................
hardest to hydrolyse easiest to hydrolyse
explanation ...................................................................................................................
.................................................................................................................................
.................................................................................................................................
................................................................................................................................. [3]