2025 Cambridge IAL Chemistry (9701) 模擬試題連答案詳解

The Born-Haber cycle for magnesium fluoride, \(\text{MgF}_2(s)\), can be constructed using the experimental data below:

- Enthalpy of formation of \(\text{MgF}_2(s) = -1124\text{ kJ mol}^{-1}\)
- Atomisation enthalpy of \(\text{Mg}(s) = +148\text{ kJ mol}^{-1}\)
- First ionisation energy of \(\text{Mg}(g) = +738\text{ kJ mol}^{-1}\)
- Second ionisation energy of \(\text{Mg}(g) = +1451\text{ kJ mol}^{-1}\)
- Atomisation enthalpy of fluorine, \(\frac{1}{2}\text{F}_2(g) \rightarrow \text{F}(g) = +79\text{ kJ mol}^{-1}\)
- First electron affinity of fluorine, \(\text{F}(g) \rightarrow \text{F}^-(g) = -328\text{ kJ mol}^{-1}\)

What is the lattice energy, \(\Delta H_{latt}^\ominus\), of \(\text{MgF}_2(s)\)?

An electrochemical cell is set up at 298 K under non-standard conditions:

\(\text{Cu}(s) | \text{Cu}^{2+}(aq, 0.10\text{ mol dm}^{-3}) || \text{Ag}^{+}(aq, 0.010\text{ mol dm}^{-3}) | \text{Ag}(s)\)

The standard electrode potentials are:

\(\text{Cu}^{2+} + 2\text{e}^- \rightleftharpoons \text{Cu}(s) \quad E^\ominus = +0.34\text{ V}\)
\(\text{Ag}^+ + \text{e}^- \rightleftharpoons \text{Ag}(s) \quad E^\ominus = +0.80\text{ V}\)

Using the Nernst equation, \(E = E^\ominus + \frac{0.059}{z}\log_{10}[\text{ion}]\), what is the non-standard cell potential, \(E_{cell}\), of this cell?

Initial rates of reaction data were collected for the reaction:

\(\text{A} + \text{B} + \text{C} \rightarrow \text{products}\)

| Experiment | \([\text{A}] / \text{mol dm}^{-3}\) | \([\text{B}] / \text{mol dm}^{-3}\) | \([\text{C}] / \text{mol dm}^{-3}\) | Initial rate / \(10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\) |
| :--- | :---: | :---: | :---: | :---: |
| 1 | 0.10 | 0.10 | 0.10 | 2.0 |
| 2 | 0.20 | 0.10 | 0.10 | 8.0 |
| 3 | 0.10 | 0.20 | 0.10 | 2.0 |
| 4 | 0.20 | 0.10 | 0.20 | 16.0 |

What is the initial rate of reaction when \([\text{A}] = 0.30\text{ mol dm}^{-3}\), \([\text{B}] = 0.30\text{ mol dm}^{-3}\), and \([\text{C}] = 0.15\text{ mol dm}^{-3}\) at the same temperature?

A buffer solution is prepared by mixing \(50.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) propanoic acid (\(K_a = 1.35 \times 10^{-5}\text{ mol dm}^{-3}\)) with \(20.0\text{ cm}^3\) of \(0.150\text{ mol dm}^{-3}\) sodium hydroxide.

What is the pH of the resulting buffer solution at 298 K?

Which statement best explains why aqueous copper(II) ions, \([\text{Cu}(\text{H}_2\text{O})_6]^{2+}\), are blue?

Methylbenzene is subjected to two different reaction conditions:

- **Condition 1**: Boiled with chlorine gas in the presence of anhydrous iron(III) chloride catalyst, in the dark.
- **Condition 2**: Boiled with chlorine gas under ultraviolet (UV) light.

Which row correctly describes the type of mechanism occurring and the major monosubstituted organic product formed for each condition?

| Row | Condition 1 mechanism | Condition 1 product | Condition 2 mechanism | Condition 2 product |
| :--- | :--- | :--- | :--- | :--- |
| **A** | Electrophilic substitution | 4-chlorotoluene | Free-radical substitution | (chloromethyl)benzene |
| **B** | Electrophilic addition | (chloromethyl)benzene | Electrophilic substitution | 2-chlorotoluene |
| **C** | Electrophilic substitution | (chloromethyl)benzene | Free-radical substitution | 4-chlorotoluene |
| **D** | Free-radical substitution | 4-chlorotoluene | Electrophilic substitution | (chloromethyl)benzene |

What is the major ionic species of the amino acid lysine, \(\text{H}_2\text{N-(CH}_2)_4\text{-CH(NH}_2)\text{-COOH}\), present in an aqueous solution of pH 1?

An organic compound, Z, contains carbon, hydrogen, and one halogen atom.

In the mass spectrum of Z:
- The ratio of the abundance of the molecular ion peak \([\text{M}]^+\) to the \([\text{M}+1]^+\) peak is \(100 : 6.6\).
- The ratio of the abundance of the \([\text{M}]^+\) peak to the \([\text{M}+2]^+\) peak is approximately \(3 : 1\).

What is the molecular formula of Z?

The table shows kinetic data for a reaction between reactants X and Y at constant temperature. Experiment 1: [X] = 0.10 mol dm\(^{-3}\), [Y] = 0.10 mol dm\(^{-3}\), Initial rate = 2.0 \(\times\) 10\(^{-4}\) mol dm\(^{-3}\) s\(^{-1}\). Experiment 2: [X] = 0.20 mol dm\(^{-3}\), [Y] = 0.10 mol dm\(^{-3}\), Initial rate = 4.0 \(\times\) 10\(^{-4}\) mol dm\(^{-3}\) s\(^{-1}\). Experiment 3: [X] = 0.10 mol dm\(^{-3}\), [Y] = 0.30 mol dm\(^{-3}\), Initial rate = 1.8 \(\times\) 10\(^{-3}\) mol dm\(^{-3}\) s\(^{-1}\). What is the value and units of the rate constant, k, for this reaction?

How many stereoisomers (including cis-trans and optical isomers) exist for the octahedral complex ion [Co(en)\(_2\)Cl\(_2\)]\(^+\) (where 'en' represents the bidentate ligand ethane-1,2-diamine)?

A standard silver electrode has a potential of E\(^\ominus\) = +0.80 V for the half-reaction Ag\(^+\)(aq) + e\(^-\) \(\rightleftharpoons\) Ag(s). What is the electrode potential of this half-cell at 298 K when the concentration of Ag\(^+\)(aq) is decreased to 0.010 mol dm\(^{-3}\)? Use the Nernst equation: E = E\(^\ominus\) + (0.059/z) log[M\(^{z+}\)]

A buffer solution contains [HA] = 0.100 mol dm\(^{-3}\) of a weak acid and [A\(^-\)] = 0.200 mol dm\(^{-3}\) of its conjugate base. The acid dissociation constant, K\(_a\), of HA is 2.00 \(\times\) 10\(^{-5}\) mol dm\(^{-3}\) at 298 K. What is the pH of this buffer solution? (Assume log\(_{10}\) 2.00 = 0.301)

Which statement correctly describes and explains the trend in the lattice energy values of the Group 2 oxides, MgO, CaO, and SrO?

Methylbenzene (toluene) is reacted with chlorine under two different sets of conditions. Reaction 1: chlorine gas in the presence of ultraviolet (UV) light. Reaction 2: chlorine gas in the dark, with an anhydrous AlCl\(_3\) catalyst. What are the major organic products for Reaction 1 and Reaction 2?

Which list shows ammonia, ethylamine, and phenylamine in order of increasing basic strength in aqueous solution (weakest base first)?

Which statement correctly describes the reaction that occurs when phenol is treated with aqueous bromine (bromine water) at room temperature?

The rate equation for a reaction between \(P\) and \(Q\) is shown below.

$$\text{Rate} = k[P][Q]^2$$

In a series of experiments, the initial concentration of \(P\) is doubled and the initial concentration of \(Q\) is halved.

What is the ratio of the new initial rate of reaction to the original initial rate of reaction?

The bidentate ligand ethylenediamine, \(\text{en}\), reacts with aqueous nickel(II) ions to form a complex ion as shown in the equilibrium below.

$$\text{[Ni(H}_2\text{O)}_6\text{]}^{2+}(aq) + 3\text{en}(aq) \rightleftharpoons \text{[Ni(en)}_3\text{]}^{2+}(aq) + 6\text{H}_2\text{O}(l)$$

What are the units of the stability constant, \(K_{\text{stab}}\), for this complex-formation reaction?

A half-cell is set up with a copper electrode dipped in a solution of \(\text{Cu}^{2+}(aq)\) at \(298\text{ K}\).

$$\text{Cu}^{2+}(aq) + 2e^- \rightleftharpoons \text{Cu}(s) \quad E^\ominus = +0.34\text{ V}$$

If the concentration of \(\text{Cu}^{2+}(aq)\) is changed to \(0.010\text{ mol dm}^{-3}\), what is the electrode potential, \(E\), of this half-cell?

[Use the Nernst equation: \(E = E^\ominus + \frac{0.059}{z}\log[\text{oxidised species}]\)]

Equal amounts of four different Period 3 chlorides are added to separate, equal volumes of water at \(298\text{ K}\).

The chlorides used are:
1. \(\text{NaCl}\)
2. \(\text{MgCl}_2\)
3. \(\text{AlCl}_3\)
4. \(\text{SiCl}_4\)

Which sequence shows these chlorides in order of the decreasing pH (from highest pH to lowest pH) of their resulting mixtures?

Some enthalpy data for calcium and oxygen are given below:

* Enthalpy change of atomisation of \(\text{Ca}(s) = +178\text{ kJ mol}^{-1}\)
* First ionisation energy of \(\text{Ca}(g) = +590\text{ kJ mol}^{-1}\)
* Second ionisation energy of \(\text{Ca}(g) = +1145\text{ kJ mol}^{-1}\)
* Enthalpy change of atomisation of oxygen, \(\Delta H_{\text{at}}^\ominus [\frac{1}{2}\text{O}_2(g)] = +249\text{ kJ mol}^{-1}\)
* First electron affinity of \(\text{O}(g) = -141\text{ kJ mol}^{-1}\)
* Second electron affinity of \(\text{O}(g) = +798\text{ kJ mol}^{-1}\)
* Standard enthalpy change of formation of \(\text{CaO}(s) = -635\text{ kJ mol}^{-1}\)

What is the lattice energy of calcium oxide, \(\text{CaO}(s)\)?

Methylbenzene is treated with bromine under two different reaction conditions.

* **Reaction 1:** Methylbenzene is reacted with bromine at room temperature in the dark in the presence of an anhydrous \(\text{AlBr}_3\) catalyst.
* **Reaction 2:** Methylbenzene is heated to boiling with bromine in the presence of ultraviolet (UV) light.

Which row correctly identifies the type of reaction and the major organic product formed in each case?

| | Reaction 1 Type | Reaction 1 Major Product | Reaction 2 Type | Reaction 2 Major Product |
|---|---|---|---|---|
| **A** | Electrophilic substitution | 1-bromo-4-methylbenzene | Free-radical substitution | (bromomethyl)benzene |
| **B** | Electrophilic substitution | (bromomethyl)benzene | Free-radical substitution | 1-bromo-4-methylbenzene |
| **C** | Nucleophilic substitution | 1-bromo-4-methylbenzene | Free-radical substitution | (bromomethyl)benzene |
| **D** | Electrophilic addition | 1-bromo-2-methylbenzene | Electrophilic substitution | (bromomethyl)benzene |

Three chlorine-containing compounds are added separately to equal volumes of aqueous silver nitrate at \(50^\circ\text{C}\).

1. benzoyl chloride, \(\text{C}_6\text{H}_5\text{COCl}\)
2. (chloromethyl)benzene, \(\text{C}_6\text{H}_5\text{CH}_2\text{Cl}\)
3. chlorobenzene, \(\text{C}_6\text{H}_5\text{Cl}\)

What is the correct order of the ease of hydrolysis of these compounds, from easiest (fastest precipitate formation) to hardest (slowest or no precipitate formation)?

Phenylamine is reacted with a mixture of sodium nitrite and dilute hydrochloric acid at \(5^\circ\text{C}\) to form compound \(X\).

An alkaline solution of phenol is then added to compound \(X\) at \(5^\circ\text{C}\) to form an azo dye, compound \(Y\).

What are the formulas of compound \(X\) and compound \(Y\)?

| | Compound \(X\) | Compound \(Y\) |
|---|---|---|
| **A** | \(\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^-\)| \(\text{C}_6\text{H}_5\text{N}=\text{NC}_6\text{H}_4\text{OH}\) |
| **B** | \(\text{C}_6\text{H}_5\text{NHNO}_2\) | \(\text{C}_6\text{H}_5\text{N}=\text{NC}_6\text{H}_4\text{OH}\) |
| **C** | \(\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^-\)| \(\text{C}_6\text{H}_5\text{NHNHC}_6\text{H}_4\text{OH}\) |
| **D** | \(\text{C}_6\text{H}_5\text{NH}_3^+\text{Cl}^-\)| \(\text{C}_6\text{H}_5\text{N}=\text{NC}_6\text{H}_5\) |

The Born-Haber cycle for lithium oxide, \(\text{Li}_2\text{O(s)}\), includes the following steps:

- Standard enthalpy change of formation of \(\text{Li}_2\text{O(s)} = -598\text{ kJ mol}^{-1}\)
- Standard enthalpy change of atomisation of lithium, \(\text{Li(s)} \rightarrow \text{Li(g)} = +159\text{ kJ mol}^{-1}\)
- First ionisation energy of lithium = \(+520\text{ kJ mol}^{-1}\)
- Standard enthalpy change of atomisation of oxygen, \(\frac{1}{2}\text{O}_2\text{(g)} \rightarrow \text{O(g)} = +249\text{ kJ mol}^{-1}\)
- First electron affinity of oxygen = \(-141\text{ kJ mol}^{-1}\)
- Second electron affinity of oxygen = \(+798\text{ kJ mol}^{-1}\)

What is the lattice energy, \(\Delta H_{\text{latt}}^\ominus\), of \(\text{Li}_2\text{O(s)}\)?

The reaction between three reactants, A, B, and C, was investigated at a constant temperature. The initial rates of reaction were measured for various starting concentrations:

| Experiment | \([\text{A}] / \text{mol dm}^{-3}\) | \([\text{B}] / \text{mol dm}^{-3}\) | \([\text{C}] / \text{mol dm}^{-3}\) | Initial rate / \(\text{mol dm}^{-3}\text{ s}^{-1}\) |
|---|---|---|---|---|
| 1 | 0.10 | 0.10 | 0.10 | \(1.2 \times 10^{-3}\) |
| 2 | 0.20 | 0.10 | 0.10 | \(4.8 \times 10^{-3}\) |
| 3 | 0.10 | 0.20 | 0.20 | \(2.4 \times 10^{-3}\) |
| 4 | 0.10 | 0.20 | 0.10 | \(2.4 \times 10^{-3}\) |

What is the value and units of the rate constant, \(k\), for this reaction?

The following standard electrode potentials are given:

- \(\text{IO}_3^- + 6\text{H}^+ + 5\text{e}^- \rightleftharpoons \frac{1}{2}\text{I}_2 + 3\text{H}_2\text{O} \quad E^\ominus = +1.19\text{ V}\)
- \(\text{Fe}^{3+} + \text{e}^- \rightleftharpoons \text{Fe}^{2+} \quad E^\ominus = +0.77\text{ V}\)
- \(\text{S}_2\text{O}_8^{2-} + 2\text{e}^- \rightleftharpoons 2\text{S}\text{O}_4^{2-} \quad E^\ominus = +2.01\text{ V}\)
- \(\text{Cl}_2 + 2\text{e}^- \rightleftharpoons 2\text{Cl}^- \quad E^\ominus = +1.36\text{ V}\)

Which reaction will occur spontaneously under standard conditions?

The stability constants, \(K_{\text{stab}}\), for two complex ions of copper(II) are given:

1. \([\text{Cu}(\text{H}_2\text{O})_6]^{2+} + 4\text{Cl}^- \rightleftharpoons [\text{CuCl}_4]^{2-} + 6\text{H}_2\text{O} \quad K_{\text{stab}} = 4.0 \times 10^5\text{ dm}^{12}\text{ mol}^{-4}\)
2. \([\text{Cu}(\text{H}_2\text{O})_6]^{2+} + 4\text{NH}_3 \rightleftharpoons [\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+} + 4\text{H}_2\text{O} \quad K_{\text{stab}} = 1.0 \times 10^{13}\text{ dm}^{12}\text{ mol}^{-4}\)

What is the value of the equilibrium constant, \(K_c\), for the ligand exchange reaction shown below?

\([\text{CuCl}_4]^{2-} + 4\text{NH}_3 + 2\text{H}_2\text{O} \rightleftharpoons [\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+} + 4\text{Cl}^-\)

Four organic compounds are listed below:

- I: Phenol
- II: 4-Nitrophenol
- III: 4-Methylphenol
- IV: 2,4,6-Trichlorophenol

What is the correct order of increasing acid strength (weakest acid first)?

Ethanol is oxidised to ethanoic acid by acidified potassium dichromate(VI). The unbalanced ionic equation for the reaction is shown below:

\(p\text{ Cr}_2\text{O}_7^{2-} + q\text{ CH}_3\text{CH}_2\text{OH} + r\text{ H}^+ \rightarrow s\text{ Cr}^{3+} + t\text{ CH}_3\text{COOH} + u\text{ H}_2\text{O}\)

What is the stoichiometric coefficient of \(\text{H}^+\), \(r\), when this equation is balanced using the lowest whole-number coefficients?

Paracetamol (4-acetamidophenol) has the structure shown below:

\(\text{CH}_3\text{CONH}-\text{C}_6\text{H}_4-\text{OH}\)

A sample of paracetamol is heated under reflux with an excess of aqueous sodium hydroxide. Which pair of organic ions is present in the resulting reaction mixture?

An organic compound \(Y\) with molecular formula \(\text{C}_5\text{H}_{10}\text{O}\) is analysed by mass spectrometry. The mass spectrum shows a prominent peak at \(m/z = 57\) but no significant peak at \(m/z = 43\).

What is the identity of compound \(Y\)?

For the reaction \(2\text{X} + \text{Y} \rightarrow \text{Z}\), the rate equation is \(\text{rate} = k[\text{X}]^2[\text{Y}]\). When the concentration of \(\text{X}\) is increased by a factor of 3 and the concentration of \(\text{Y}\) is halved, by what factor does the initial rate of reaction change?

Phenylamine is reacted with nitrous acid at \(5\ ^\circ\text{C}\) to form benzenediazonium chloride. This intermediate is then reacted with alkaline phenol to produce an azo dye. Which row correctly identifies the formula of the azo dye and the type of mechanism occurring in the coupling step?

The standard electrode potential for the \(\text{Cu}^{2+}/\text{Cu}\) half-cell is \(E^\ominus = +0.34\text{ V}\). What is the electrode potential, \(E\), of this half-cell at \(298\text{ K}\) when the concentration of \(\text{Cu}^{2+}\text{(aq)}\) ions is \(0.010\text{ mol dm}^{-3}\)?

Which statement correctly explains why the transition metal complex \([\text{Cu}(\text{H}_2\text{O})_6]^{2+}\) is light blue whereas \([\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+}\) is a very deep blue-violet?

Using the following thermodynamic data, what is the lattice energy, \(\Delta H_{\text{latt}}\), of lithium fluoride, \(\text{LiF(s)}\)?

- Enthalpy change of formation of \(\text{LiF(s)}\) = \(-617\text{ kJ mol}^{-1}\)
- Enthalpy change of atomisation of \(\text{Li(s)}\) = \(+159\text{ kJ mol}^{-1}\)
- First ionisation energy of \(\text{Li(g)}\) = \(+520\text{ kJ mol}^{-1}\)
- Enthalpy change of atomisation of fluorine, \(\frac{1}{2}\text{F}_2\text{(g)} \rightarrow \text{F(g)}\) = \(+79\text{ kJ mol}^{-1}\)
- First electron affinity of \(\text{F(g)}\) = \(-328\text{ kJ mol}^{-1}\)

How many stereoisomers exist for the compound 4-chlorohex-2-ene?

A buffer solution is prepared by mixing \(50.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) propanoic acid (\(K_a = 1.35 \times 10^{-5}\text{ mol dm}^{-3}\)) with \(50.0\text{ cm}^3\) of \(0.050\text{ mol dm}^{-3}\) sodium propanoate. What is the pH of this buffer solution?

An organic compound \(\text{Y}\) contains carbon, hydrogen, and a single chlorine atom. In the mass spectrum of \(\text{Y}\), the molecular ion peak \([\text{M}]^+\) is at \(m/z = 78\) with a relative abundance of 51.0%. What is the predicted relative abundance of the \([\text{M}+2]^+\) peak, and what is the molecular formula of \(\text{Y}\)?

This question is about atomic structure and ionisation energies.

(a) Define the term first ionisation energy of an element. [3]

(b) Explain why the first ionisation energy of sulfur is lower than that of phosphorus, even though sulfur has a higher nuclear charge. [3]

(c) An element, X, is in Period 3 of the Periodic Table. The successive ionisation energies (in \(\text{kJ mol}^{-1}\)) for X are given below:
- \(I_1 = 1012\)
- \(I_2 = 1903\)
- \(I_3 = 2912\)
- \(I_4 = 4957\)
- \(I_5 = 6274\)
- \(I_6 = 21269\)
- \(I_7 = 25430\)

(i) Identify element X and justify your choice using the data. [3]
(ii) Write the equation, including state symbols, for the process corresponding to the fourth ionisation energy of X. [1]

This question is about chemical energetics and enthalpy determinations.

(a) Define the standard enthalpy change of combustion, \(\Delta H_c^\ominus\). [2]

(b) A student carried out a laboratory experiment to determine the enthalpy change of combustion of propan-1-ol (\(M_r = 60.1\)). A spirit burner containing propan-1-ol was weighed and used to heat \(150.0\text{ g}\) of water in a copper calorimeter.

The following measurements were recorded:
- Initial mass of burner + propan-1-ol = \(120.45\text{ g}\)
- Final mass of burner + propan-1-ol = \(119.85\text{ g}\)
- Initial temperature of water = \(19.5\text{ }^\circ\text{C}\)
- Final temperature of water = \(48.1\text{ }^\circ\text{C}\)
- Specific heat capacity of water, \(c = 4.18\text{ J g}^{-1}\text{ K}^{-1}\)

(i) Calculate the heat energy released, \(q\), in kJ. [2]
(ii) Calculate the number of moles of propan-1-ol burned. [1]
(iii) Calculate the experimental standard enthalpy change of combustion of propan-1-ol, in \(\text{kJ mol}^{-1}\). Give your answer to 3 significant figures and include a sign. [2]

(c) Suggest two reasons, other than student misreadings, why this experimental value is significantly less exothermic than the data book value of \(-2021\text{ kJ mol}^{-1}\). Explain how these reasons lead to a smaller temperature rise. [3]

This question is about reversible reactions and dynamic chemical equilibria.

(a) State two characteristics of a system in dynamic equilibrium. [2]

(b) A mixture of \(2.00\text{ mol}\) of \(\text{H}_2(\text{g})\) and \(1.50\text{ mol}\) of \(\text{I}_2(\text{g})\) is placed in a closed vessel of volume \(V\text{ dm}^3\) at a constant temperature of \(700\text{ K}\). The mixture is allowed to reach equilibrium according to the equation:

\[\text{H}_2(\text{g}) + \text{I}_2(\text{g}) \rightleftharpoons 2\text{HI}(\text{g})\]

At equilibrium, \(2.40\text{ mol}\) of \(\text{HI}(\text{g})\) is found to be present.

(i) Construct an expression for the equilibrium constant, \(K_c\), for this reaction. [1]
(ii) Calculate the equilibrium amounts, in moles, of \(\text{H}_2(\text{g})\) and \(\text{I}_2(\text{g})\). [2]
(iii) Calculate the value of \(K_c\) at \(700\text{ K}\). Show your working. [2]
(iv) Deduce the units of \(K_c\) for this reaction. [1]

(c) Predict, with a reason, the effect of increasing the pressure on the position of equilibrium at constant temperature. [2]

This question is about Period 3 elements and their compounds.

(a) Sodium reacts vigorously with water.
- State two observations during this reaction. [1]
- Write a balanced chemical equation for this reaction, including state symbols. [2]

(b) Phosphorus(V) oxide, \(\text{P}_4\text{O}_{10}\), is a molecular covalent oxide.
(i) Write a balanced chemical equation for the reaction of \(\text{P}_4\text{O}_{10}\) with water. [1]
(ii) State the pH of the resulting solution and classify the acid-base nature of \(\text{P}_4\text{O}_{10}\). [2]

(c) Silicon(IV) chloride, \(\text{SiCl}_4\), reacts rapidly with water.
(i) Describe what is observed during the reaction of \(\text{SiCl}_4\) with water. [1]
(ii) Write a balanced chemical equation for the reaction of \(\text{SiCl}_4\) with water. [1]
(iii) Explain why silicon(IV) chloride hydrolyses in water whereas tetrachloromethane, \(\text{CCl}_4\), does not. [2]

This question is about alkenes and addition reactions.

(a) Alkenes react with hydrogen halides via electrophilic addition.
(i) Define the term electrophile. [1]
(ii) Propene reacts with hydrogen bromide, \(\text{HBr}\), to yield a major and a minor product. Identify the major organic product and draw its structural formula. [1]
(iii) Outline the mechanism for the reaction of propene with \(\text{HBr}\) to form the major product. Include curly arrows to show the movement of electron pairs, and indicate all relevant dipoles and charges. [4]

(b) Explain, in terms of the stability of the carbocation intermediates, why the major product is formed in preference to the minor product. [2]

(c) Propene can also undergo polymerisation.
(i) State the type of polymerisation reaction that propene undergoes. [1]
(ii) Draw the repeat unit of the polymer formed. [1]

This question is about the carbonyl compounds propanal and propanone.

(a) Propanal and propanone are structural isomers.
(i) State the specific type of structural isomerism shown by propanal and propanone. [1]
(ii) Give a chemical test, including reagent and observations, that can be used to distinguish between propanal and propanone. [3]

(b) Propanal reacts with hydrogen cyanide, \(\text{HCN}\), in the presence of a sodium cyanide, \(\text{NaCN}\), catalyst.
(i) Identify the mechanism of this reaction. [1]
(ii) Draw the structural formula of the organic product formed. [1]
(iii) The product molecule exhibits optical isomerism. Explain why the product exhibits optical isomerism, and why the reaction mixture produced is optically inactive. [2]

(c) Propanone can be reduced to an alcohol.
- State the necessary reagent and conditions for this reduction. [1]
- State the IUPAC name of the organic product formed. [1]

In this experiment, you will determine the number of water molecules of crystallisation, \(x\), in a sample of hydrated iron(II) sulfate, \(\text{FeSO}_4 \cdot x\text{H}_2\text{O}\), by redox titration with potassium manganate(VII).

FA 1 is a solution prepared by dissolving \(13.90\text{ g}\) of the hydrated iron(II) sulfate in dilute sulfuric acid and making up to \(1.00\text{ dm}^3\) with distilled water.
FA 2 is \(0.0100\text{ mol dm}^{-3}\) potassium manganate(VII), \(\text{KMnO}_4\).

Method
1. Pipette \(25.0\text{ cm}^3\) of FA 1 into a clean conical flask.
2. Add about \(10\text{ cm}^3\) of \(1.0\text{ mol dm}^{-3}\) sulfuric acid using a measuring cylinder.
3. Titrate this solution with FA 2 until a permanent pale pink colour is obtained.
4. Record your results in a suitable table below and calculate the mean titre.

Results
Assume that your average concordant titre of FA 2 is \(25.00\text{ cm}^3\).

Calculations
Show all your working. State your answers to 3 significant figures where appropriate.

(a) Present your titration results in a table, showing initial and final burette readings and volume of FA 2 added for rough and accurate runs, with appropriate headings and units. Calculate your mean titre.
(b) Calculate the number of moles of \(\text{MnO}_4^-\right.\) ions in your mean titre.
(c) Use the ionic equation below to determine the number of moles of \(\text{Fe}^{2+}\) ions present in \(25.0\text{ cm}^3\) of FA 1:
\(5\text{Fe}^{2+}(\text{aq}) + \text{MnO}_4^-(\text{aq}) + 8\text{H}^+(\text{aq}) \rightarrow 5\text{Fe}^{3+}(\text{aq}) + \text{Mn}^{2+}(\text{aq}) + 4\text{H}_2\text{O}(\text{l})\)
(d) Calculate the concentration of \(\text{Fe}^{2+}\) ions in \(\text{mol dm}^{-3}\) in FA 1.
(e) Calculate the formula mass (\(M_r\)) of the hydrated iron(II) sulfate, assuming the sample was pure, and use this to determine the integer value of \(x\).
(f) Calculate the percentage error in measuring the volume of FA 1 using the \(25.0\text{ cm}^3\) pipette (absolute error of pipette = \(\pm 0.06\text{ cm}^3\)).

In this experiment, you will determine the enthalpy change of hydration of anhydrous copper(II) sulfate, \(\text{CuSO}_4\), to form hydrated copper(II) sulfate, \(\text{CuSO}_4 \cdot 5\text{H}_2\text{O}\).

FA 1 is anhydrous copper(II) sulfate powder, \(\text{CuSO}_4\).
FA 2 is hydrated copper(II) sulfate crystals, \(\text{CuSO}_4 \cdot 5\text{H}_2\text{O}\).

Method
Experiment 1: Enthalpy change of solution of anhydrous copper(II) sulfate
1. Measure \(50.0\text{ cm}^3\) of distilled water into a polystyrene cup.
2. Measure and record the initial temperature of the water to the nearest \(0.1\text{ }^\circ\text{C}\).
3. Weigh a sample bottle containing \(4.79\text{ g}\) of FA 1.
4. Add FA 1 to the water in the cup, stir continuously, and record the maximum temperature reached.
5. Weigh the empty bottle.

Experiment 2: Enthalpy change of solution of hydrated copper(II) sulfate
1. Measure \(50.0\text{ cm}^3\) of distilled water into a polystyrene cup.
2. Measure and record the initial temperature of the water to the nearest \(0.1\text{ }^\circ\text{C}\).
3. Weigh a sample bottle containing \(7.49\text{ g}\) of FA 2.
4. Add FA 2 to the water, stir, and record the minimum temperature reached.
5. Weigh the empty bottle.

Results
Assume the following experimental results are obtained:
- Experiment 1: Mass of FA 1 used = \(4.79\text{ g}\); initial temperature = \(21.5\text{ }^\circ\text{C}\); maximum temperature = \(30.8\text{ }^\circ\text{C}\).
- Experiment 2: Mass of FA 2 used = \(7.49\text{ g}\); initial temperature = \(22.0\text{ }^\circ\text{C}\); minimum temperature = \(20.2\text{ }^\circ\text{C}\).

Calculations
Assume the specific heat capacity of the solution is \(4.18\text{ J g}^{-1}\text{ K}^{-1}\) and its density is \(1.00\text{ g cm}^{-3}\).

(a) Present the results of both experiments clearly in a single table, showing the masses used, temperature changes, and appropriate units.
(b) Calculate the heat energy change, \(q\), in joules for both Experiment 1 and Experiment 2.
(c) Calculate the number of moles of copper(II) sulfate dissolved in both experiments.
(d) Calculate the enthalpy change of solution for anhydrous \(\text{CuSO}_4\) (\(\Delta H_1\)) and for hydrated \(\text{CuSO}_4 \cdot 5\text{H}_2\text{O}\) (\(\Delta H_2\)) in \(\text{kJ mol}^{-1}\). Include the correct signs.
(e) Use Hess's Law and your values from (d) to calculate the enthalpy change of hydration, \(\Delta H_{\text{hydration}}\), for the reaction: \(\text{CuSO}_4(\text{s}) + 5\text{H}_2\text{O}(\text{l}) \rightarrow \text{CuSO}_4 \cdot 5\text{H}_2\text{O}(\text{s})\).

FA 6 is an aqueous solution containing two cations and two anions, all of which are listed in the standard Qualitative Analysis Notes. Carry out the following tests and record your observations. (a) Carry out these four tests and record your detailed observations: (i) Test 1: To a 1 cm depth of FA 6 in a test-tube, add aqueous sodium hydroxide dropwise until in excess. Then, warm the mixture gently and test any gas evolved using damp red litmus paper. (ii) Test 2: To a 1 cm depth of FA 6 in a test-tube, add aqueous ammonia dropwise until in excess. (iii) Test 3: To a 1 cm depth of FA 6 in a test-tube, add a 1 cm depth of aqueous barium nitrate, followed by dilute nitric acid. (iv) Test 4: To a 1 cm depth of FA 6 in a test-tube, add a 1 cm depth of aqueous silver nitrate, followed by aqueous ammonia. (b) Identify the two cations and two anions present in FA 6. For each ion, state its formula and provide the specific evidence from your observations in (a) that supports your identification.

The reaction between peroxodisulfate(VI) ions, \(\text{S}_2\text{O}_8^{2-}\), and iodide ions, \(\text{I}^-\), is represented by the following equation:

\[ \text{S}_2\text{O}_8^{2-}(\text{aq}) + 2\text{I}^-(\text{aq}) \rightarrow 2\text{SO}_4^{2-}(\text{aq}) + \text{I}_2(\text{aq}) \]

(a) Define the term *order of reaction* with respect to a given reactant. [1]

(b) The following initial rate data were obtained at \(298 \text{ K}\):

- **Run 1**: \([\text{S}_2\text{O}_8^{2-}] = 0.0100 \text{ mol dm}^{-3}\), \([\text{I}^-] = 0.0200 \text{ mol dm}^{-3}\), Initial Rate = \(1.50 \times 10^{-5} \text{ mol dm}^{-3}\text{ s}^{-1}\)
- **Run 2**: \([\text{S}_2\text{O}_8^{2-}] = 0.0100 \text{ mol dm}^{-3}\), \([\text{I}^-] = 0.0400 \text{ mol dm}^{-3}\), Initial Rate = \(3.00 \times 10^{-5} \text{ mol dm}^{-3}\text{ s}^{-1}\)
- **Run 3**: \([\text{S}_2\text{O}_8^{2-}] = 0.0200 \text{ mol dm}^{-3}\), \([\text{I}^-] = 0.0400 \text{ mol dm}^{-3}\), Initial Rate = \(6.00 \times 10^{-5} \text{ mol dm}^{-3}\text{ s}^{-1}\)

Deduce the order of reaction with respect to both \(\text{S}_2\text{O}_8^{2-}\) and \(\text{I}^-\), showing your reasoning clearly. [3]

(c) Write the rate equation for this reaction and calculate the value of the rate constant, \(k\), including its units. [3]

(d) A student proposed a mechanism for this reaction:

- **Step 1 (slow)**: \(\text{S}_2\text{O}_8^{2-} + \text{I}^- \rightarrow \text{IS}_2\text{O}_8^{3-}\)
- **Step 2 (fast)**: \(\text{IS}_2\text{O}_8^{3-} + \text{I}^- \rightarrow 2\text{SO}_4^{2-} + \text{I}_2\)

Explain how this mechanism is consistent with your rate equation. [2]

(e) State how the rate constant, \(k\), changes, if at all, when the temperature is increased. [1]

Cobalt forms several different complex ions.

(a) Define the terms:
(i) *Ligand* [1]
(ii) *Coordination number* [1]

(b) An aqueous solution of cobalt(II) chloride is pink due to the presence of octahedral \([\text{Co}(\text{H}_2\text{O})_6]^{2+}\) ions. When excess concentrated hydrochloric acid is added, the solution turns a deep blue color as the tetrahedral complex ion \([\text{CoCl}_4]^{2-}\) is formed.
(i) Write a balanced equation for this ligand substitution reaction. [1]
(ii) Explain, in terms of ligand size, why there is a change in the coordination number of cobalt in this reaction. [1]
(iii) Describe how the split d-orbitals differ in energy level arrangement between an octahedral complex like \([\text{Co}(\text{H}_2\text{O})_6]^{2+}\) and a tetrahedral complex like \([\text{CoCl}_4]^{2-}\). [2]

(c) Cobalt(III) forms an octahedral complex with the bidentate ligand ethane-1,2-diamine, \(\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2\) (abbreviated as 'en').
(i) Complete the formula of the complex ion containing cobalt(III) and three 'en' ligands, including its charge. [1]
(ii) State the type of stereoisomerism exhibited by this complex ion, and draw 3D representations of both isomers to show their relationship. [3]

Standard electrode potentials can be used to predict the feasibility of redox reactions.

(a) Describe the three essential features of a Standard Hydrogen Electrode (SHE). [3]

(b) A student constructs an electrochemical cell under standard conditions. One half-cell consists of a platinum electrode in a mixture of \(1.0 \text{ mol dm}^{-3} \text{ Fe}^{3+}(\text{aq})\) and \(1.0 \text{ mol dm}^{-3} \text{ Fe}^{2+}(\text{aq})\). The other half-cell consists of a silver electrode in \(1.0 \text{ mol dm}^{-3} \text{ Ag}^+(\text{aq})\).

Standard potentials:
- \(\text{Fe}^{3+}(\text{aq}) + \text{e}^- \rightleftharpoons \text{Fe}^{2+}(\text{aq}) \quad E^\ominus = +0.77 \text{ V}\)
- \(\text{Ag}^+(\text{aq}) + \text{e}^- \rightleftharpoons \text{Ag}(\text{s}) \quad E^\ominus = +0.80 \text{ V}\)

(i) Calculate the standard cell potential, \(E^\ominus_{\text{cell}}\). [1]
(ii) Write the overall ionic equation for the spontaneous cell reaction. [1]
(iii) State the direction of electron flow in the external circuit. [1]

(c) The concentration of \(\text{Fe}^{2+}(\text{aq})\) in the iron half-cell is decreased to \(0.010 \text{ mol dm}^{-3}\) while all other concentrations remain at \(1.0 \text{ mol dm}^{-3}\) at \(298 \text{ K}\).
(i) State and explain the effect of this change on the electrode potential of the iron half-cell. [2]
(ii) Calculate the new non-standard electrode potential, \(E\), of the iron half-cell using the Nernst equation:

\[ E = E^\ominus + \frac{0.059}{z} \log\left(\frac{[\text{oxidised}]}{[\text{reduced}]}\right) \] [2]

Propanoic acid, \(\text{CH}_3\text{CH}_2\text{COOH}\), is a weak monoprotic acid with \(K_{\text{a}} = 1.35 \times 10^{-5} \text{ mol dm}^{-3}\) at \(298 \text{ K}\).

(a) Write the expression for the acid dissociation constant, \(K_{\text{a}}\), of propanoic acid. [1]

(b) Calculate the \(\text{pH}\) of a \(0.150 \text{ mol dm}^{-3}\) solution of propanoic acid at \(298 \text{ K}\). State two assumptions you made in this calculation. [4]

(c) A buffer solution is prepared by mixing \(60.0 \text{ cm}^3\) of \(0.150 \text{ mol dm}^{-3}\) propanoic acid with \(40.0 \text{ cm}^3\) of \(0.100 \text{ mol dm}^{-3}\) sodium hydroxide, \(\text{NaOH}\).
(i) Calculate the amount, in moles, of propanoic acid and sodium propanoate present in the resulting buffer solution. [2]
(ii) Calculate the \(\text{pH}\) of this buffer solution. [2]
(iii) Explain how this buffer solution is able to resist changes in pH when a small amount of dilute acid is added. [1]

Benzene and methylbenzene undergo electrophilic substitution reactions.

(a) Benzene can be nitrated using a mixture of concentrated nitric acid and concentrated sulfuric acid at \(50^\circ\text{C}\).
(i) Write a chemical equation for the generation of the active electrophile, \(\text{NO}_2^+\), from the acid mixture. [1]
(ii) Draw the complete mechanism for the nitration of benzene by this electrophile. Include all necessary curly arrows, the positive charge on the intermediate, and the loss of the proton. [3]
(iii) Write an equation to show how the sulfuric acid catalyst is regenerated. [1]

(b) Methylbenzene reacts significantly faster than benzene when nitrated.
(i) Explain why the methyl group increases the rate of electrophilic substitution. [2]
(ii) Draw the structural formulas of the two major organic isomers formed when methylbenzene is mononitrated. [2]

(c) State the reagent and conditions required to oxidize the methyl group of methylbenzene to form benzoic acid. [1]

This question concerns nitrogen-containing organic compounds.

(a) Phenylamine, ammonia, and ethylamine are all weak bases.
(i) Arrange these three bases in order of increasing basic strength (weakest base first). [1]
(ii) Explain this order of basic strength in terms of their electronic structures. [3]

(b) Phenylamine can be converted into a benzenediazonium salt at low temperatures using nitrous acid, \(\text{HNO}_2\).
(i) State the reagents and conditions needed to generate nitrous acid *in situ* and carry out this reaction. [2]
(ii) Explain why the temperature of this reaction must be kept between \(0^\circ\text{C}\) and \(10^\circ\text{C}\). [1]

(c) The benzenediazonium salt can be reacted with an alkaline solution of phenol to form an azo dye.
(i) State the type of reaction that occurs. [1]
(ii) Draw the structure of the azo dye formed. [2]

Acyl chlorides are versatile intermediates in organic synthesis.

(a) Explain why acyl chlorides are much more reactive towards nucleophilic substitution than alkyl chlorides. [2]

(b) Write balanced equations for the reaction of propanoyl chloride, \(\text{CH}_3\text{CH}_2\text{COCl}\), with:
(i) Ethanol, and name the organic product. [2]
(ii) Excess concentrated ammonia, and name the organic product. [2]

(c) The relative ease of hydrolysis of halogen-containing compounds varies dramatically.
(i) Arrange the following compounds in order of their ease of hydrolysis (most rapid first):

\[ \text{CH}_3\text{CH}_2\text{Cl}, \quad \text{CH}_3\text{COCl}, \quad \text{C}_6\text{H}_5\text{Cl} \] [1]

(ii) Explain the resistance of chlorobenzene, \(\text{C}_6\text{H}_5\text{Cl}\), to hydrolysis. [2]

(d) State the reagent needed to prepare propanoyl chloride from propanoic acid. [1]

Lattice energy values provide a measure of ionic bond strength.

(a) (i) Define the term *lattice energy*. [2]
(ii) Explain why lattice energy cannot be measured directly. [1]

(b) Use the following thermodynamic data to construct a Born-Haber cycle and calculate the standard lattice energy, \(\Delta H^\ominus_{\text{latt}}\), of calcium chloride, \(\text{CaCl}_2(\text{s})\).

- Enthalpy change of formation of \(\text{CaCl}_2(\text{s}) = -796 \text{ kJ mol}^{-1}\)
- Enthalpy change of atomisation of \(\text{Ca}(\text{s}) = +178 \text{ kJ mol}^{-1}\)
- First ionisation energy of \(\text{Ca}(\text{g}) = +590 \text{ kJ mol}^{-1}\)
- Second ionisation energy of \(\text{Ca}(\text{g}) = +1145 \text{ kJ mol}^{-1}\)
- Bond enthalpy of \(\text{Cl-Cl}(\text{g}) = +242 \text{ kJ mol}^{-1}\)
- First electron affinity of \(\text{Cl}(\text{g}) = -349 \text{ kJ mol}^{-1}\)

Show your working clearly. [4]

(c) Standard lattice energies of sodium chloride, \(\text{NaCl}\), and magnesium chloride, \(\text{MgCl}_2\), are \(-787 \text{ kJ mol}^{-1}\) and \(-2526 \text{ kJ mol}^{-1}\) respectively. Explain why the lattice energy of magnesium chloride is much more exothermic than that of sodium chloride. [3]

An electrochemical cell is set up to study the effect of concentration on electrode potential.

(a) Define the term standard electrode potential, \(E^\theta\). [2]

(b) The cell consists of a standard \(\text{Ag}^+/\text{Ag}\) electrode (\(E^\theta = +0.80\text{ V}\)) connected via a salt bridge to a non-standard \(\text{Cu}^{2+}/\text{Cu}\) electrode (\(E^\theta = +0.34\text{ V}\)). The concentration of \(\text{Cu}^{2+}(aq)\) in this half-cell is \(0.0050\text{ mol dm}^{-3}\) at \(298\text{ K}\).

(i) State the Nernst equation for the \(\text{Cu}^{2+}/\text{Cu}\) half-cell. [1]

(ii) Calculate the electrode potential, \(E\), of this non-standard \(\text{Cu}^{2+}/\text{Cu}\) electrode at \(298\text{ K}\). [2]

(iii) Calculate the cell potential, \(E_{\text{cell}}\), for this combined cell under these conditions and state which electrode acts as the anode. [2]

(c) Explain, with reference to the position of equilibrium, why the electrode potential of the copper electrode changes when the concentration of \(\text{Cu}^{2+}(aq)\) is decreased. [3]

Azo dyes are manufactured via a two-stage process. Compound X, 4-methylaniline, is converted into an intense orange azo dye, Compound Y, using phenol as a coupling agent.

(a) Stage 1 involves the conversion of 4-methylaniline into a diazonium salt.

(i) State the reagents and temperature condition required for Stage 1. [2]

(ii) Draw the structural formula of the diazonium cation intermediate formed in Stage 1. [1]

(iii) Explain why the temperature in Stage 1 must be kept below \(10\text{ }^\circ\text{C}\). [1]

(b) In Stage 2, the diazonium salt is reacted with an alkaline solution of phenol to form the azo dye, Compound Y.

(i) Draw the skeletal structure of Compound Y and state the name of the reaction type. [3]

(ii) Outline the mechanism for this coupling reaction. In your answer, show the curly arrows representing the initial attack on the phenoxide ion, the structure of the intermediate formed, and the subsequent loss of a proton to restore aromaticity. [3]

An elegant clock reaction can be used to study the kinetics of the reaction between peroxodisulfate ions, \(\text{S}_2\text{O}_8^{2-}\), and iodide ions, \(\text{I}^-\):

\[\text{S}_2\text{O}_8^{2-}(\text{aq}) + 2\text{I}^-(\text{aq}) \rightarrow 2\text{SO}_4^{2-}(\text{aq}) + \text{I}_2(\text{aq})\]

In the presence of a small, fixed amount of sodium thiosulfate, \(\text{Na}_2\text{S}_2\text{O}_3\), and starch indicator, the iodine produced is immediately reduced back to iodide:

\[2\text{S}_2\text{O}_3^{2-}(\text{aq}) + \text{I}_2(\text{aq}) \rightarrow \text{S}_4\text{O}_6^{2-}(\text{aq}) + 2\text{I}^-(\text{aq})\]

Once all the thiosulfate ions are consumed, the excess iodine reacts with starch, turning the solution blue-black. The time, \(t\), for this color change to occur is measured.

You are to plan an experiment to determine the activation energy, \(E_a\), of this reaction by varying the temperature, \(T\).

**(a) Hazard and Safety**
(i) Potassium peroxodisulfate, \(\text{K}_2\text{S}_2\text{O}_8\), is used to prepare the reactant solution. State one hazard associated with \(\text{K}_2\text{S}_2\text{O}_8\) and a specific safety precaution (other than wearing eye protection or a laboratory coat) that must be taken. [1]
(ii) Suggest why heating the reaction mixture directly using a Bunsen burner flame above \(60\ ^\circ\text{C}\) should be avoided, and suggest a safer heating method to maintain temperature control. [2]

**(b) Experimental Planning**
You are required to prepare \(250\text{ cm}^3\) of a \(0.150\text{ mol dm}^{-3}\) standard solution of potassium peroxodisulfate, \(\text{K}_2\text{S}_2\text{O}_8\), from solid \(\text{K}_2\text{S}_2\text{O}_8\).
(i) Calculate the mass of solid potassium peroxodisulfate, \(\text{K}_2\text{S}_2\text{O}_8\), required to prepare this solution. Show your working. [1]
(ii) Describe the precise laboratory procedure you would use to prepare this \(250\text{ cm}^3\) standard solution using your calculated mass of solid. [4]

**(c) Data Analysis and Processing**
The rate of the reaction is assumed to be proportional to \(1/t\).
The Arrhenius equation can be expressed as:

\[\ln(1/t) = -\frac{E_a}{RT} + \text{constant}\]

(i) In one of the trials, the reaction was carried out at \(45.0\ ^\circ\text{C}\) (\(318.1\text{ K}\)) and the blue-black color appeared at \(28.0\text{ s}\). Calculate the values of \(\frac{1}{T}\) (with its appropriate unit) and \(\ln(1/t)\). State both values to 3 significant figures. [2]
(ii) State the quantities that should be plotted on the x-axis and y-axis of a linear graph to determine the activation energy, \(E_a\). [1]
(iii) Explain how the activation energy, \(E_a\), is calculated from the gradient of this graph. State the value and unit of the gas constant, \(R\), that should be used. [2]

**(d) Evaluation and Improvement**
At higher temperatures (e.g. above \(55\ ^\circ\text{C}\)), the blue-black color appears very rapidly (\(t < 5\text{ s}\)), leading to a high percentage uncertainty in the time measured using a manual stopwatch.
(i) Suggest a modification to the apparatus to obtain a more accurate start-to-finish time measurement. [1]
(ii) Suggest a modification to the reaction mixture that would increase the time taken, \(t\), for the blue-black color to appear without changing the total volume of the reaction mixture. Explain your answer. [2]

An investigation is carried out into the rate of decomposition of aqueous benzenediazonium chloride, \(\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^-(aq) \rightarrow \text{C}_6\text{H}_5\text{OH}(aq) + \text{N}_2(g) + \text{HCl}(aq)\), at different temperatures.

The rate constant, \(k\), for this first-order reaction was determined at several temperatures, \(T\). The results of the experiment are shown in the table below.

| Temperature, \(T / \text{K}\) | Reciprocal temperature, \(1/T / \text{K}^{-1}\) | Rate constant, \(k / \text{s}^{-1}\) | \(\ln(k / \text{s}^{-1})\) |
|---|---|---|---|
| 293 | \(3.41 \times 10^{-3}\) | \(2.9 \times 10^{-5}\) | -10.45 |
| 303 | **(a)** | \(1.3 \times 10^{-4}\) | -8.95 |
| 313 | \(3.19 \times 10^{-3}\) | \(5.3 \times 10^{-4}\) | **(b)** |
| 323 | \(3.10 \times 10^{-3}\) | \(1.4 \times 10^{-3}\) | -6.57 |
| 333 | \(3.00 \times 10^{-3}\) | \(6.7 \times 10^{-3}\) | -5.01 |
| 343 | \(2.92 \times 10^{-3}\) | \(2.1 \times 10^{-2}\) | -3.86 |

**(a)** Calculate the missing values for **(a)** and **(b)** in the table. Ensure your answers are written to an appropriate number of significant figures and decimal places. [2]

**(b)** To determine the activation energy, \(E_a\), a graph of \(\ln(k / \text{s}^{-1})\) against \(1/T\) is plotted.
(i) Identify which variable should be plotted on the x-axis and which on the y-axis. [1]
(ii) Identify the anomalous data point from the table. State whether the rate constant at this temperature is faster or slower than expected. Explain your reasoning. [2]

**(c)** A line of best fit is drawn through the non-anomalous points. Two points on this line of best fit are selected:
- Point 1: \((2.95 \times 10^{-3} \text{ K}^{-1}, -4.30)\)
- Point 2: \((3.40 \times 10^{-3} \text{ K}^{-1}, -10.30)\)

Calculate the gradient of this line. Show your working and state the units of the gradient. [3]

**(d)** Use your gradient from **(c)** to calculate the activation energy, \(E_a\), of the reaction in \(\text{kJ mol}^{-1}\). (The gas constant, \(R = 8.31 \text{ J K}^{-1} \text{ mol}^{-1}\)). [3]

**(e)** (i) Explain why a thermostatically controlled water bath is used to heat the reaction mixtures rather than direct heating with a Bunsen burner. [1]
(ii) The reaction progress can be monitored by measuring the volume of \(\text{N}_2(g)\) evolved over time. State how the total, maximum volume of gas collected at the completion of the reaction would change, if at all, if the experiment was repeated at 313 K instead of 293 K at the same pressure using the same starting amount of reactant. Explain your answer. [2]