AS & A Level Chemistry - 9701 Paper 4 2023 Winter Zone 3

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]

(a) (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]

(b) (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]

(c) (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.
Fig. 1.1 [1]

(c) (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 298K.

(i) Calculate the concentration of HCl in \(V\).

concentration of HCl in \(V\) = \text{..........................} 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 \(X\) \text{...........................} pH \text{...........................}
[1]

(iii) A $1 cm^{3}$ sample of $1.0 mol dm^{-3}$ HNO₃ 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 \(Y\) \text{..........................} mixture \(Z\) \text{..........................}
[1]

(c)(i) $\text{CH}_3\text{CH}_2\text{COOH}$, $\text{CH}_3\text{CCl}_2\text{COOH}$ and $\text{H}_2\text{SO}_4$ are all acidic.
Suggest the trend in the relative acid strength of these three compounds.
Explain your answer.
\text{...............................................} \text{.....................................................} \text{.....................................................}
strongest acid weakest acid
explanation \text{..............................................................................................................................}
\text{..................................................................................................................................................}
\text{..................................................................................................................................................}
\text{..................................................................................................................................................}
[3]

(ii) When concentrated $\text{H}_2\text{SO}_4$ is added to water a series of acid-base reactions occur.
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 \text{...........................................} conjugate base 1 \text{...........................................}
conjugate acid 2 \text{...........................................} conjugate base 2 \text{...........................................}
conjugate acid 3 \text{...........................................} conjugate base 3 \text{...........................................}
[2]

(d) The partition coefficient, $K_{pc}$, of a substance, \(Q\), between hexane and water is 7.84 at 298K.
\(Q\) is more soluble in hexane than it is in water.
(i) Define partition coefficient, $K_{pc}$.
\text{......................................................................................................................................................}
\text{......................................................................................................................................................}
[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 298K and left until there is no further change in concentrations.
Calculate the mass of \(Q\) dissolved in the water.
mass of \(Q\) = \text{...........................} 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 = \text{...........................} $cm^{3}$
volume of hexane = \text{...........................} $cm^{3}$
[1]

(iv) \(Q\) is more soluble in hexane than it is in water.
It is suggested that \(Q\) is one of KCl, $\text{CH}_3(\text{CH}_2)_4\text{OH}$ or HCOOH.
Identify \(Q\). Explain your answer.
\text{..................................................................................................................................................}
[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, $S^⦵$, are shown in Table 3.2.

[Table 3.2]

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

$2H_2O_2(l) \rightarrow 2H_2O(l) + O_2(g)$
∆H^⦵ = −196 kJ mol^−1
∆G^⦵ = −238 kJ mol^−1

Use the data given to calculate the standard entropy of oxygen, $S^⦵$, O_2(g).

$S^⦵$, O_2(g) = ............................... J K^−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 $E^⦵$ values for two electrode reactions are given.

$H_2O_2 + 2H^+ + 2e^− \rightleftarrows 2H_2O$ $E^⦵ = +1.77 V$
$Cr^{3+} + e^− \rightleftarrows Cr^{2+}$ $E^⦵ = −0.41 V$

(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, $E^⦵_{cell}$
positive half-cell ............................... $E^⦵_{cell}$ = ............................... V [1]

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

(f) The $E^⦵$ values for two electrode reactions are given.

$H_2O_2 + 2H^+ + 2e^− \rightleftarrows 2H_2O$ $E^⦵ = +1.77 V$
$Co^{3+} + e^− \rightleftarrows Co^{2+}$ $E^⦵ = +1.82 V$

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 $Co^{3+}$ and 2.0 mol dm^−3 $Co^{2+}$, 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, ∆H^⦵_hyd.
................................................................................................................................................................
................................................................................................................................................................ [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 $AlF_3$, ∆H^⦵_sol
• the lattice energy of $AlF_3$, ∆H^⦵_latt
• the enthalpy changes of hydration of $Al^{3+}$ and $F^−$, ∆H^⦵_hyd.
Include state symbols for all substances and ions.

[Energy cycle diagram]

[2]

(iii) Relevant data for this question are given.
∆H^⦵_sol $AlF_3$ = −209 kJ mol^−1
∆H^⦵_hyd $Al^{3+}$ = −4690 kJ mol^−1
∆H^⦵_hyd $F^−$ = −506 kJ mol^−1
Use these data and your energy cycle in (g)(ii) to calculate the ∆H^⦵_latt of $AlF_3$.
∆H^⦵_latt of $AlF_3$ = ............................... kJ mol^−1 [1]

(a) Cobalt(II) nitrate, Co(NO3)2, is a reddish-brown crystalline solid. It dissolves in water to form a solution containing $[Co(H2O)_6]^{2+}$ 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_1]

| reaction | reagent added to $[Co(H2O)_6]^{2+}$(aq) | cobalt-containing species formed |
|-----------|---------------------------------------|-------------------------------------|
| 1 | NaOH(aq) | |
| 2 | an excess of NH3(aq) | |
| 3 | an excess of conc. HCl(aq) | |

[2]
(ii) Describe the colour change seen in reaction 3.
original colour of $[Co(H2O)_6]^{2+}$(aq) ............................................................
final colour after addition of an excess of conc. HCl(aq) ...............................
[1]
(b) Calcium nitrate, Ca(NO3)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(NO3)2.
.................................................................................................................................
[1]
(ii) Suggest temperatures at which Mg(NO3)2 and Ba(NO3)2 start to decompose.
Explain your answer.
temperature at which Mg(NO3)2 starts to decompose ................................. °C
temperature at which Ba(NO3)2 starts to decompose ................................. °C
explanation .......................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
[3]

(a) Explain why transition elements behave as catalysts.
............................................................................................................................................................
............................................................................................................................................................
............................................................................................................................................................

(b) Silver forms the linear complex ion $[\text{Ag(CN)}_2]^-$.
Copper forms the tetrahedral complex ion $[\text{Cu(CN)}_4]^{3-}$.
Titanium forms the complex $[\text{TiCl}_4(diars)_2]$, where $diars$ is a neutral bidentate ligand.
(i) State the oxidation state and the coordination number of titanium in $[\text{TiCl}_4(diars)_2]$.
oxidation state ...............................
coordination number ............................ [1]
(ii) Draw three-dimensional diagrams to show the shapes of $[\text{Ag(CN)}_2]^-$ and $[\text{Cu(CN)}_4]^{3-}$, 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 $[\text{Cu(CN)}_4]^{3-}$ is $2.0 \times 10^{27}$.
(i) Write an expression for the $K_{stab}$ of $[\text{Cu(CN)}_4]^{3-}$.
$K_{stab} =$ [1]

(ii) In a solution the concentrations of $\text{CN}^-$ and $[\text{Cu(CN)}_4]^{3-}$ are both $0.0010 \text{mol dm}^{-3}$.
Use your expression from (c)(i) and the value of $K_{stab}$ to calculate the concentration of $\text{Cu}^+ (\text{aq})$ in this solution.
concentration of $\text{Cu}^+ (\text{aq}) = ..................................... \text{mol dm}^{-3}$ [1]

(d) A piece of a copper-containing alloy has a mass of 0.567 g. It is dissolved in an acid giving 100.0 cm³ of a blue solution in which all the copper is present as $\text{Cu}^{2+}$ ions.
An excess of $\text{KI (aq)}$ is added to a 25.0 cm³ sample of this solution.
All of the copper is precipitated as white $\text{CuI (s)}$.
$\text{Cu}^{2+}$ ions are the only component in the solution that react with $\text{KI (aq)}$. This is reaction 1.
reaction 1            2$\text{Cu}^{2+}$ + 4$\text{I}^{-}$ → 2$\text{CuI}$ + $\text{I}_2$
The liberated $\text{I}_2$ is then titrated with $0.0200 \text{mol dm}^{-3} \text{S}_2\text{O}_3^{2-}$. This is reaction 2.
reaction 2            $\text{I}_2$ + 2$\text{S}_2\text{O}_3^{2-}$ → 2$\text{I}^{-}$ + $\text{S}_4\text{O}_6^{2-}$
The titration requires 20.10 cm³ of $0.0200 \text{mol dm}^{-3} \text{S}_2\text{O}_3^{2-}$ to reach the end-point.
(i) Calculate the number of moles of $\text{I}_2$ that are reduced in this titration.
number of moles of $\text{I}_2 =$ .............................. mol [1]
(ii) Calculate the number of moles of copper in the original piece of alloy.
number of moles of copper = .............................. mol [1]
(iii) Calculate the percentage of copper in the alloy.
percentage of copper = ............................. % [1]
(iv) Suggest why a solution of $\text{Cu}^{2+}$ is coloured but solid $\text{CuI}$ is white.
............................................................................................................................................................
............................................................................................................................................................

(a) Five ligands are listed in Table 6.1.

[Table_1]
The table shows:
| ligand | type of ligand |
|--------------------------|----------------|
| NH₃ | |
| EDTA⁴⁻ | |
| CN⁻ | |
| H₂NCH₂CH₂NCH₂CH₂NH₂ | tridentate |
| C₂O₄²⁻ | |

(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 H₂NCH₂CH₂NCH₂CH₂NH₂ is a tridentate ligand.
Suggest the meaning of tridentate ligand.
...............................................................................................................................
............................................................................................................................... [1]

(iii) Suggest how H₂NCH₂CH₂NCH₂CH₂NH₂ acts as a tridentate ligand.
...............................................................................................................................
............................................................................................................................... [1]

(b) Nickel forms the octahedral complex [Ni(en)₂(H₂O)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_2]
The table shows:
| isomer | polarity |
|------------ |-----------|
| trans isomer| |
| cis isomer 1| |
| cis isomer 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]

Capsaicin is found in chilli peppers.



You should assume the CH₃O group is unreactive in the reactions involved in this question.

(a) Name all the functional groups in capsaicin in addition to the CH₃O group.
.............................................................................................................................................. [1]

(b) Complete the equation for the reaction of capsaicin with an excess of Br₂(aq) in the dark. Draw the structure of the organic product in the labelled box.


capsaicin + ..........Br₂ →


organic product + .....................
.............................................................................................. [3]

(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.
........................................................................................................... [2]

(d) When capsaicin is treated with reagent J under suitable conditions one of the products is methylpropanoic acid, CH₃CH(CH₃)COOH.

(i) Identify reagent J and any necessary conditions.
.............................................................................................................................................. [1]

(ii) There are three different peaks in the proton (¹H) NMR spectrum of CH₃CH(CH₃)COOH in CDCl₃.

[Table_1]

Use Table 8.1 to complete Table 8.2 and state:
• the typical proton (¹H) 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 CH₃ protons and the CH proton.

[Table_2]
.............................................................................................. [3]

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


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

H C₈H₁₀NO₂Na
K C₁₀H₁₇O₂Na
................................................................................................... [2]

(ii) Name the two types of reaction occurring in (e)(i).
.............................................................................................................................................. [1]

(f) Draw the structure of the organic product L formed when capsaicin is treated with LiAlH₄ in dry ether.

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

(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]