AS & A Level Chemistry - 9701 Paper 4 2024 Winter Zone 1

(a) Disodium phosphate, $(\text{Na}^+)_{2}(\text{HPO}_4^{2-})$, reacts with an acid to form monosodium phosphate, $\text{Na}^+(\text{H}_2\text{PO}_4^-)$.
(i) Identify the ions that are a conjugate acid–base pair in this reaction, using the formulae of the species involved.
conjugate acid                           conjugate base
.......................................................... ................................................................................. [1]
(ii) Define buffer solution.
.................................................................................................................................................... [2]
(iii) Write two equations to show how a mixture of $(\text{Na}^+)_{2}(\text{HPO}_4^{2-})$ and $\text{Na}^+(\text{H}_2\text{PO}_4^-)$ can act as a buffer solution.
equation 1 ....................................................................................................................................................
equation 2 ....................................................................................................................................................
.................................................................................................................................................... [2]
(iv) Identify one inorganic ion that acts as a buffer in blood.
.................................................................................................................................................... [1]

(b) Compound E is the hydroxide of a Group 2 element. Compound E is a strong alkali.
2.63 g of E is dissolved in water to make $250\text{ cm}^3$ of solution F. Solution F has a pH of 13.09 at 298 K.
(i) Show that the concentration of hydroxide ions in solution F is $0.123\text{ mol dm}^{-3}$.
....................................................................................................................................................
(ii) Explain why the concentration of compound E in solution F is $0.0615\text{ mol dm}^{-3}$.
.................................................................................................................................................... [2]
(iii) Use the concentration given in (ii) to identify compound E.
compound E ................................................................................................................................................. [1]

(c) Compound E is much more soluble than magnesium hydroxide.
A saturated solution of magnesium hydroxide in water has a concentration of $1.40 \times 10^{-4}\text{ mol dm}^{-3}$ at 298 K.
Calculate the solubility product, $K_{sp}$, of magnesium hydroxide. Include units.
$K_{sp} = \text{...................... units ..........................}$ [3]

(d) Explain why compound E is much more soluble than magnesium hydroxide.
.................................................................................................................................................... [3]

(a) Predict and explain the variation in enthalpy change of hydration for the ions F^−, Cl^−, Br^− and I^−.
................................................................................................................................. [2]
(b) Fig. 2.1 shows an incomplete energy cycle involving calcium fluoride, CaF₂.


(i) Complete line D. Include state symbols. [1]
(ii) The value of the enthalpy change for process 1 can be calculated using the values of five other enthalpy changes which are not referred to in Fig. 2.1.

process 1: Ca(s) + F₂(g) → Ca^2+(g) + 2F^−(g)

Identify these five other enthalpy changes, using either names or symbols.
................................................................................................................................. [2]
(iii) Define lattice energy, ΔH_latt.
................................................................................................................................. [2]
(iv) Complete the expression to give the mathematical relationship between ΔH_latt of calcium fluoride and the enthalpy changes for processes 1 and 3.
ΔH_latt = ................................................................................................................................. [1]
(c) Use data from Table 2.1 to calculate a value for the hydration energy, ΔH_hyd, of fluoride ions, F^−(g).

[Table_1]
ΔH_hyd F^−(g) = ......................................... kJ mol^−1 [2]
(d) Define entropy.
................................................................................................................................. [1]
(e) At 298 K, the Gibbs free energy change, ΔG, for the solution of compound T is +6.00 kJ mol^−1.
The enthalpy change of solution, ΔH_sol, of compound T is +30.0 kJ mol^−1 at 298 K.
Calculate the value of the entropy change, ΔS, for the solution of compound T at 298 K.
ΔS = ......................................... JK^−1 mol^−1 [2]
(f) Predict whether compound T becomes more or less soluble as the water is heated from 298 K to 360 K. Explain your answer.
................................................................................................................................. [1]
[Total: 14]

(a) A and B react together to give product AB.
A + B → AB

When the concentrations of A and B are both 0.0100 mol dm⁻³, the rate of formation of AB is 7.62 × 10⁻⁴ mol dm⁻³ s⁻¹. When the concentrations of A and B are both 0.0200 mol dm⁻³, the rate of formation of AB is 3.05 × 10⁻³ mol dm⁻³ s⁻¹.

(i) Complete the three possible rate equations that are consistent with these data.
rate = ............................................................................................................................
rate = ............................................................................................................................
rate = ............................................................................................................................ [2]

(ii) Choose one of the rate equations you have written in (i), and calculate the value of the rate constant, k. Include the units of k.
k = .............................. units .............................. [2]

(iii) Explain why it is not possible to calculate a value for the half-life, $t_{\frac{1}{2}}$, of this reaction using the value of the rate constant $k$ calculated in (ii) and the equation $k = 0.693 / t_{\frac{1}{2}}$.
............................................................................................................................. [1]

(b) Catalysts may be homogeneous or heterogeneous.

(i) Identify two metals that act as heterogeneous catalysts in the removal of NO₂ from the exhaust gases of car engines.
.............................................................. and .............................................................. [1]

(ii) Iron acts as a heterogeneous catalyst in the Haber process.
Describe the mode of action of this iron catalyst.
..................................................................................................................... [2]

(iii) Fe²⁺ ions act as a homogeneous catalyst in the reaction between I⁻(aq) and S₂O₈²⁻(aq).
Write equations for the two reactions that occur when Fe²⁺(aq) is added to a mixture of I⁻(aq) and S₂O₈²⁻(aq).
equation 1 S₂O₈²⁻ + ..............................................................
equation 2 ..................................................................................................................... [2]

(iv) Explain the difference between a homogeneous catalyst and a heterogeneous catalyst.
..................................................................................................................... [1]

(c) Fe²⁺ ions can be oxidised to Fe³⁺ ions under alkaline conditions by suitable oxidising agents.

(i) Iron is a transition element. Explain why iron forms stable compounds in both the +2 and the +3 oxidation states.
...................................................................................................................... [1]

(ii) The half-equation for the reduction of Fe³⁺ under alkaline conditions, and its E^⦵ value, are shown.
Fe(OH)₃ + e⁻ ⇌ Fe(OH)₂ + OH⁻   E^⦵ = −0.56 V
Four more half-equations for reactions under alkaline conditions, and their E^⦵ values, are shown.
Al(OH)₄⁻ + 3e⁻ ⇌ Al + 4OH⁻   E^⦵ = −2.35 V
ClO⁻ + H₂O + 2e⁻ ⇌ Cl⁻ + 2OH⁻   E^⦵ = +0.89 V
O₂ + 2H₂O + 4e⁻ ⇌ 4OH⁻   E^⦵ = +0.40 V
Zn(OH)₄²⁻ + 2e⁻ ⇌ Zn + 4OH⁻   E^⦵ = −1.22 V
Select two oxidising agents that can oxidise Fe²⁺ ions to Fe³⁺ ions under alkaline conditions.
Write an equation, and give the E^⦵_cell value, for each of the two reactions that occur.
oxidising agent 1: .....................................
equation: .............................................................................................................
E^⦵_cell = .......................... V

oxidising agent 2: .....................................
equation: .............................................................................................................
E^⦵_cell = .......................... V [4]

(a) Explain why transition elements form complex ions.
............................................................................................................................. [1]
(b) $\text{Co}^{2+}$ ions form complex ion $G$.
Each $G$ ion contains \textbf{two} $\text{Co}^{2+}$ ions, both of which are octahedrally coordinated.
Each $G$ ion contains one $\text{O}_2$ molecule, which donates one pair of electrons to \textbf{each} $\text{Co}^{2+}$ ion, and one $\text{NH}_2^-$ ion, which donates one pair of electrons to \textbf{each} $\text{Co}^{2+}$ ion.
The remaining ligands are $\text{NH}_3$ molecules.
(i) Deduce the formula of complex ion $G$. Include its overall charge.
formula of $G$ ............................................................... [2]
(ii) The d-orbitals of the $\text{Co}^{2+}$ ions present in complex ion $G$ are split. State the number of d-orbitals that are at a higher energy level and the number of d-orbitals that are at a lower energy level in \textbf{each} $\text{Co}^{2+}$ ion.
$$\begin{array}{|c|c|} \hline \text{number of d-orbitals at a higher energy level} \\ \hline \text{number of d-orbitals at a lower energy level} \\ \hline \end{array}$$ [1]
(iii) $\text{Co}^{2+}$ ions form a different complex ion, $M$.
Each $M$ ion contains \textbf{two} $\text{Co}^{2+}$ ions, both of which are octahedrally coordinated, but the ligands are different from the ligands in $G$.
Explain why $G$ and $M$ have different colours.
............................................................................................................................. [2]

(c) Cadmium forms complex ion $X$, $[\text{Cd}(\text{NH}_3)_4]^{2+}$.
When a solution containing $\text{CN}^-$ ions is added to an aqueous solution of $X$, a ligand exchange reaction takes place, forming complex ion $Y$. $Y$ contains no $\text{NH}_3$ ligands and no $\text{H}_2\text{O}$ ligands.
$Y$ is in a much higher concentration in the mixture than $X$.
The oxidation state and coordination number of cadmium do \textbf{not} change in this reaction.
(i) Write an ionic equation for this reaction, using the formulae of the complex ions.
............................................................................................................................. [2]
(ii) Cadmium forms complex ion $Z$ in the same oxidation state and with the same coordination number as in $X$. All the ligands in $Z$ are $\text{Cl}^-$ ions.
When $\text{NaCl}(\text{aq})$ is added to a solution of $X$, very little $Z$ forms.
Write the \textbf{three} cadmium complexes, $X, Y$ and $Z$, in order of increasing stability constant, $K_{stab}$.
.............................................................................................................................
smallest value of $K_{stab}$ .............................................................. largest value of $K_{stab}$ [1]

(d) Ethanedioate ions, $\text{C}_2\text{O}_4^{2-}$, form complexes with transition element ions.
The concentration of $\text{C}_2\text{O}_4^{2-}$ ions can be found by reaction with acidified $\text{Cr}_2\text{O}_7^{2-}$ ions. $\text{C}_2\text{O}_4^{2-}$ ions are protonated and form $\text{HOOC-COOH}$ molecules which are oxidised by $\text{Cr}_2\text{O}_7^{2-}$.
The half-equations are shown.
$$\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6e^- \rightleftharpoons 2\text{Cr}^{3+} + 7\text{H}_2\text{O}$$
$$2\text{CO}_2 + 2\text{H}^+ + 2e^- \rightleftharpoons \text{HOOC-COOH}$$
(i) Construct an equation for the reaction between acidified $\text{Cr}_2\text{O}_7^{2-}$ and $\text{HOOC-COOH}$.
............................................................................................................................. [1]
(ii) A 25.0 cm$^3$ sample of a solution of $\text{Na}_2\text{C}_2\text{O}_4$ reacts with exactly 16.20 cm$^3$ of an acidified solution of 0.0500 mol dm$^{-3}$ $\text{K}_2\text{Cr}_2\text{O}_7$.
Calculate the concentration of the solution of $\text{Na}_2\text{C}_2\text{O}_4$.
$[\text{Na}_2\text{C}_2\text{O}_4] = ................................................ \text{ moldm}^{-3}$ [2]

The shapes of four different complexes, P, Q, R and S, are shown in Table 5.1.
The symbol J represents an atom or ion of a transition element.
The symbol L is used to represent a monodentate ligand.

[Table_5.1]

(a) Label one bond angle on each of complexes P, Q, R and S, and identify the size of the angle in degrees. [2]

(b) Identify the shapes of complexes P, Q, R and S.
P ..................................................................................................................................................................................
Q ..................................................................................................................................................................................
R ..................................................................................................................................................................................
S .................................................................................................................................................................................. [2]

(c) Two L ligands are exchanged with two different monodentate ligands X and Y in each of complexes P, Q, R and S.
Identify all the complexes which form new complexes that show geometrical isomerism. .................................................................................................................................................................................. [1]

(d) Three L ligands are exchanged with three different monodentate ligands X, Y and Z in each of complexes P, Q and R.
Identify all the complexes which form new complexes that show optical isomerism. .................................................................................................................................................................................. [1]

[Total: 6]

Benzene, $C_6H_6$, reacts with chloroethane, $C_2H_5Cl$, in the presence of a suitable catalyst to form ethylbenzene, $C_6H_5C_2H_5$. In the presence of the catalyst, the ion $C_2H_5^+$ is formed. This ion reacts with benzene.
(a) Complete the equation for the reaction of $C_2H_5Cl$ with this catalyst to form $C_2H_5^+$ as one product.
$C_2H_5Cl + ext{.......................} \rightarrow C_2H_5^+ + ext{......................}$ [1]
(b) Ethylbenzene reacts with more $C_2H_5Cl$, forming a mixture containing 1,2-diethylbenzene and 1,4-diethylbenzene.
(i) Draw the structures of 1,2-diethylbenzene and 1,4-diethylbenzene.

[1]
(ii) Explain why there is very little 1,3-diethylbenzene in the product mixture.
.........................................................
[1]
(c) 1,2-diethylbenzene can be oxidised to benzene-1,2-dioic acid, $C_6H_4(COOH)_2$.
benzene-1,2-dioic acid

(i) State the reagent and conditions used for this reaction.
.........................................................
[1]
(ii) Complete the overall equation for this reaction.
An atom of oxygen from the oxidising agent is represented as [O].
All of the atoms in the two ethyl groups are fully oxidised in this reaction.
$.................................. + ext{..................} [O] \rightarrow C_6H_4(COOH)_2 + ext{....................} + ext{....................}$ (1,2-diethylbenzene) [2]
(iii) Predict the number of peaks in the carbon-13 NMR spectrum of benzene-1,2-dioic acid.
..........................................
[1]
(d) The proton ($^1H$) NMR spectra of ethylbenzene, $C_6H_5C_2H_5$, in $CDCl_3$ and of benzene-1,2-dioic acid, $C_6H_4(COOH)_2$, in $CDCl_3$ are shown. They have not been identified.

(i) Explain the use of $CDCl_3$, instead of $CHCl_3$, as the solvent when obtaining these spectra.
........................................
[1]
(ii) Identify the substance shown by the spectrum in Fig. 6.1, and complete Table 6.1.
substance ...................................................
Table 6.1
peak at $\delta = 1.2$ | peak at $\delta = 2.6$
name of splitting pattern |
group responsible for peak |
explanation of splitting pattern |
[3]
(iii) Identify the substance shown by the spectrum in Fig. 6.2, and complete Table 6.2.
substance ...................................................
Table 6.2
peak at $\delta = 7.8$ | peak at $\delta = 13.1$
group responsible for peak |
[1]
(iv) When $D_2O$ is used as a solvent, the spectrum obtained is different from the spectrum in Fig. 6.2.
Describe this difference and explain your answer.
........................................
[1]
(e) Benzene-1,2-dioic acid can be used to produce K.

Suggest the name of this type of reaction.
........................................
[1]

(a) Identify compound U which contains only three elements.
........................................................... [1]
(b) Describe the reagents and conditions for reaction 1.
........................................................... [1]
(c) Identify compound V.
........................................................... [1]
(d) Complete the equation for reaction 3.
$\text{CH}_3\text{COOH} + \text{SOCl}_2 \rightarrow $ ..................................... [1]
(e) Identify compound W.
........................................................... [1]
(f) Describe the conditions for reaction 4.
........................................................... [1]
(g) Suggest the reagent needed for reaction 6.
........................................................... [1]
(h) Complete Table 7.1 by adding the reaction numbers, 1, 2, 3, 4, 5 and 6, to the right-hand column. Use the reaction numbers given in Fig. 7.1.
Each of the numbers 1, 2, 3, 4, 5 and 6 should be used once only.
[Table_1]
[4]
(i) Compare the basicities of $\text{C}_2\text{H}_5\text{NHCOCH}_3$, $\text{C}_2\text{H}_5\text{NHC}_2\text{H}_5$ and $\text{NH}_3$.
Explain your answer.
......................................... ......................................... .........................................
most basic least basic
........................................................................................
[4]
[Total: 15]

(a) An aqueous solution of phenol, $C_6H_5OH$, is acidic at 298K.
Explain why phenol is more acidic than water.
............................................................................................................................ [2]

(b) (i) Name the \textbf{two} products formed when phenol reacts with an excess of $Br_2(aq)$.
..................................................... and ...................................................... [1]
(ii) Draw the structures of the \textbf{two} isomeric organic products, with $M_r = 139$, that are formed when phenol reacts with $HNO_3(aq)$ at room temperature.
[1]
(iii) Write the equation for the reaction between phenol, $C_6H_5OH$, and sodium metal.
............................................................................................................................ [1]

(c) Phenol can be produced from phenylamine in a two-step synthesis.
\begin{align*}
\text{step one} & \rightarrow \text{intermediate compound} \rightarrow \text{step two}\rightarrow \text{phenol}
\end{align*}
Describe the reagents and conditions needed in each step.

step one:
reagents .......................................................................................................................
conditions ....................................................................................................................

step two:
reagents ......................................................................................................................
conditions .................................................................................................................... [2]

[Total: 7]