2024 Cambridge IAL Chemistry (9701) 模擬試題連答案詳解

A 1.00 g sample of a mixture of calcium carbonate (\(\text{CaCO}_3\), \(M_{\text{r}} = 100.1\)) and magnesium carbonate (\(\text{MgCO}_3\), \(M_{\text{r}} = 84.3\)) is reacted with an excess of dilute hydrochloric acid. The volume of carbon dioxide gas released is \(267\text{ cm}^3\) (measured at room temperature and pressure, r.t.p.). What is the percentage by mass of \(\text{CaCO}_3\) in the mixture? [Assume 1 mol of gas occupies \(24.0\text{ dm}^3\) at r.t.p.]

A buffer solution is prepared by mixing \(50.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) propanoic acid (\(K_{\text{a}} = 1.35 \times 10^{-5}\text{ mol dm}^{-3}\)) with \(25.0\text{ cm}^3\) of \(0.0800\text{ mol dm}^{-3}\) sodium hydroxide. What is the pH of the resulting buffer solution at \(298\text{ K}\)?

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

The reaction between propanone and iodine in acidic solution is investigated: \(\text{CH}_3\text{COCH}_3 + \text{I}_2 \xrightarrow{\text{H}^+} \text{CH}_3\text{COCH}_2\text{I} + \text{H}^+ + \text{I}^-\) The rate equation is found to be: \(\text{rate} = k[\text{CH}_3\text{COCH}_3][\text{H}^+]\) Under certain conditions, the initial rate of reaction is \(1.2 \times 10^{-5}\text{ mol dm}^{-3}\text{ s}^{-1}\). The concentration of propanone is doubled, the concentration of \(\text{H}^+\) is halved, and the concentration of \(\text{I}_2\) is tripled. What is the new initial rate of reaction, in \(\text{mol dm}^{-3}\text{ s}^{-1}\)?

Which statement about the reaction of methylbenzene with a mixture of concentrated nitric acid and concentrated sulfuric acid is correct?

The structure of 2-aminopropanoic acid (alanine) is shown: \(\text{CH}_3\text{CH}(\text{NH}_2)\text{COOH}\) Which species is the major component present in an aqueous solution of alanine at \(\text{pH} = 12\)?

Two Period 3 elements, \(X\) and \(Y\), form oxides \(X\text{O}_3\) and \(Y_2\text{O}_3\) respectively. Oxide \(X\text{O}_3\) reacts vigorously with water to form a solution of \(\text{pH} \approx 2\). Oxide \(Y_2\text{O}_3\) is insoluble in water but reacts with both dilute hydrochloric acid and aqueous sodium hydroxide. What are elements \(X\) and \(Y\)?

Sulfur dioxide is oxidised to sulfur trioxide in the atmosphere, catalysed by nitrogen monoxide (\(\text{NO}\)). Which equation represents a step in this catalytic cycle?

A sample of \(10\text{ cm}^3\) of a gaseous hydrocarbon \(C_xH_y\) was exploded with \(80\text{ cm}^3\) of oxygen (an excess). After cooling to room temperature, the total volume of gas remaining was \(70\text{ cm}^3\). After shaking the mixture with excess aqueous sodium hydroxide, the remaining volume of gas was \(30\text{ cm}^3\). What is the formula of the hydrocarbon?

A buffer solution is prepared by mixing \(50.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) propanoic acid, \(CH_3CH_2COOH\) (\(K_a = 1.35 \times 10^{-5}\text{ mol dm}^{-3}\)), with \(50.0\text{ cm}^3\) of \(0.050\text{ mol dm}^{-3}\) sodium hydroxide, \(NaOH\). What is the pH of the resulting buffer solution at \(298\text{ K}\)?

Two ligand-exchange reactions of aqueous cobalt(II) ions are shown below. Reaction 1: \([Co(H_2O)_6]^{2+}(aq) + 4Cl^-(aq) \rightleftharpoons [CoCl_4]^{2-}(aq) + 6H_2O(l)\) (stability constant \(K_1\)). Reaction 2: \([Co(H_2O)_6]^{2+}(aq) + 6NH_3(aq) \rightleftharpoons [Co(NH_3)_6]^{2+}(aq) + 6H_2O(l)\) (stability constant \(K_2\)). Given that \(K_2 > K_1 > 1\\, which statement is correct?

The reaction between reactants \(P\) and \(Q\) is investigated, and the initial rate of reaction is measured at \(298\text{ K}\) for various initial concentrations. Experiment 1: \([P] = 0.10\text{ mol dm}^{-3}\), \([Q] = 0.10\text{ mol dm}^{-3}\), Initial Rate = \(2.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\). Experiment 2: \([P] = 0.20\text{ mol dm}^{-3}\), \([Q] = 0.10\text{ mol dm}^{-3}\), Initial Rate = \(8.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\). Experiment 3: \([P] = 0.20\text{ mol dm}^{-3}\), \([Q] = 0.20\text{ mol dm}^{-3}\), Initial Rate = \(1.6 \times 10^{-3}\text{ mol dm}^{-3}\text{ s}^{-1}\). What are the units of the rate constant, \(k\), for this reaction?

Which statement about the reaction of methylbenzene with a mixture of concentrated nitric acid and concentrated sulfuric acid at \(30^\circ\text{C}\) is correct?

Alanine is 2-aminopropanoic acid. What is the major organic species present when alanine is dissolved in a buffer solution of pH 12?

Three oxides of Period 3 elements, \(X\), \(Y\), and \(Z\), have the following properties. Oxide \(X\) is insoluble in water but dissolves in both dilute hydrochloric acid and dilute sodium hydroxide. Oxide \(Y\) reacts with water to form a strongly acidic solution of pH 1-2. Oxide \(Z\) is insoluble in water and only dissolves in hot, concentrated sodium hydroxide. What are the identities of elements \(X\), \(Y\), and \(Z\)?

Which equation represents a step in the catalytic cycle where nitrogen monoxide, \(NO\), acts as a catalyst in the oxidation of atmospheric sulfur dioxide to sulfur trioxide?

A \(10\text{ cm}^3\) sample of a gaseous hydrocarbon, \(\text{C}_x\text{H}_y\), was completely combusted in \(100\text{ cm}^3\) of oxygen (an excess). After cooling to room temperature, the total volume of gas remaining was \(80\text{ cm}^3\). After passing this remaining gas through excess aqueous potassium hydroxide, the volume of gas decreased to \(40\text{ cm}^3\). What is the molecular formula of the hydrocarbon?

A buffer solution is prepared at \(25\ ^\circ\text{C}\} by mixing \)50.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) propanoic acid (\(K_a = 1.35 \times 10^{-5}\text{ mol dm}^{-3}\)) and \(50.0\text{ cm}^3\) of \(0.050\text{ mol dm}^{-3}\) sodium propanoate. What is the pH of the resulting buffer solution?

Which statement best explains why transition metal complexes, such as aqueous cobalt(II) ions, are coloured?

The table shows experimental rate data for the reaction: \(2\text{A} + \text{B} + 2\text{C} \to \text{D} + 2\text{E}\). Exp 1: [A]=0.10, [B]=0.10, [C]=0.10, Rate=\(2.0 \times 10^{-4}\text{ mol dm}^{-3}\text{s}^{-1}\). Exp 2: [A]=0.20, [B]=0.10, [C]=0.10, Rate=\(4.0 \times 10^{-4}\text{ mol dm}^{-3}\text{s}^{-1}\). Exp 3: [A]=0.10, [B]=0.20, [C]=0.10, Rate=\(2.0 \times 10^{-4}\text{ mol dm}^{-3}\text{s}^{-1}\). Exp 4: [A]=0.10, [B]=0.10, [C]=0.30, Rate=\(1.8 \times 10^{-3}\text{ mol dm}^{-3}\text{s}^{-1}\). What is the value and units of the rate constant, \(k\), for this reaction?

Methylbenzene undergoes nitration when reacted with a mixture of concentrated nitric acid and concentrated sulfuric acid. Which statement about this reaction is correct?

An aqueous solution of the amino acid alanine (2-aminopropanoic acid) is adjusted to pH 12. Which chemical species is the major form of alanine present at this pH?

Which statement correctly describes the behavior of phosphorus(V) chloride and silicon(IV) chloride when added separately to excess water at room temperature?

Catalytic converters in car exhaust systems contain transition metal catalysts (such as Pt, Pd, and Rh) to reduce harmful emissions. Which chemical reaction does NOT take place on the surface of the catalyst in a catalytic converter?

A sample of 1.50 g of an impure metal carbonate, \(M\text{CO}_3\) (where the \(M_r\) of \(M\text{CO}_3\) is 84.3), is reacted with excess dilute hydrochloric acid. This reaction produces 360 cm\(^3\) of carbon dioxide gas, measured at room temperature and pressure (r.t.p.). Assuming the impurity is completely unreactive, what is the percentage purity of the metal carbonate sample? [Take the molar gas volume at r.t.p. as 24.0 dm\(^3\) mol\(^{-1\)}]

A buffer solution is prepared by mixing 40.0 cm\(^3\) of 0.150 mol dm\(^{-3}\) propanoic acid (\(K_a = 1.35 \times 10^{-5}\) mol dm\(^{-3}\)) with 60.0 cm\(^3\) of 0.100 mol dm\(^{-3}\) sodium propanoate. What is the pH of this buffer solution?

Consider the two ligand exchange equilibria shown below: 1) \([\text{Cu}(\text{H}_2\text{O})_6]^{2+}(aq) + 4\text{Cl}^-(aq) \rightleftharpoons [\text{CuCl}_4]^{2-}(aq) + 6\text{H}_2\text{O}(l)\) with stability constant \(K_1\) 2) \([\text{Cu}(\text{H}_2\text{O})_6]^{2+}(aq) + 4\text{NH}_3(aq) \rightleftharpoons [\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+}(aq) + 4\text{H}_2\text{O}(l)\) with stability constant \(K_2\) Given that \(K_2 \gg K_1\), which statement correctly describes what happens when a concentrated aqueous solution of ammonia is added to an equilibrium mixture containing both complexes?

The reaction \(2A + B + C \rightarrow D + E\) was studied and the following initial rate data were obtained: Experiment 1: \([A] = 0.10, [B] = 0.10, [C] = 0.10\), Rate = \(2.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\) Experiment 2: \([A] = 0.20, [B] = 0.10, [C] = 0.10\), Rate = \(4.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\) Experiment 3: \([A] = 0.10, [B] = 0.20, [C] = 0.10\), Rate = \(8.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\) Experiment 4: \([A] = 0.10, [B] = 0.10, [C] = 0.20\), Rate = \(2.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\) What is the overall order of the reaction and the correct units of the rate constant, \(k\)?

Methylbenzene is reacted with a cold mixture of concentrated nitric acid and concentrated sulfuric acid. Which statement about this reaction is correct?

Alanine, \(\text{CH}_3\text{CH(NH}_2)\text{COOH}\), is an amino acid. Which structures represent the major ionic species of alanine in aqueous solutions at pH 1 and pH 13?

An oxide of a Period 3 element, \(X\), is a white solid that reacts with both dilute hydrochloric acid and aqueous sodium hydroxide. Another Period 3 element, \(Y\), forms an oxide that reacts with water to give an acidic solution with a pH of approximately 2. What are the identities of elements \(X\) and \(Y\)?

In the atmosphere, sulfur dioxide (\(\text{SO}_2\)) is oxidized to sulfur trioxide (\(\text{SO}_3\)) in a process catalyzed by nitrogen dioxide (\(\text{NO}_2\)). Which chemical equation represents the step in this catalytic cycle in which the \(\text{NO}_2\) catalyst is regenerated?

An anhydrous metal carbonate, \( \text{M}_2\text{CO}_3 \), where \( \text{M} \) is a Group 1 metal, has a mass of \( 1.325\text{ g} \). It is completely dissolved in water and the solution is made up to \( 250.0\text{ cm}^3 \) in a volumetric flask. A \( 25.0\text{ cm}^3 \) portion of this solution is titrated against \( 0.125\text{ mol dm}^{-3} \) hydrochloric acid, \( \text{HCl}(\text{aq}) \). It requires \( 20.0\text{ cm}^3 \) of the acid for complete neutralisation. What is the identity of metal \( \text{M} \)?

A monoprotic weak acid, \( \text{HA} \), has a relative molecular mass of \( 60.0 \). A solution is prepared by dissolving \( 1.80\text{ g} \) of \( \text{HA} \) in distilled water and diluting to a final volume of \( 250\text{ cm}^3 \). The pH of this solution is \( 2.88 \) at \( 298\text{ K} \). What is the acid dissociation constant, \( K_a \), of \( \text{HA} \) at \( 298\text{ K} \)?

Which statement correctly explains why transition metal complexes are coloured?

For the gaseous reaction: \( 2\text{X}(\text{g}) + \text{Y}(\text{g}) + \text{Z}(\text{g}) \rightarrow \text{products} \), the following initial rate data were obtained at constant temperature:

| Experiment | Initial \( [\text{X}] \) / \( \text{mol dm}^{-3} \) | Initial \( [\text{Y}] \) / \( \text{mol dm}^{-3} \) | Initial \( [\text{Z}] \) / \( \text{mol dm}^{-3} \) | Initial Rate / \( \text{mol dm}^{-3}\text{ s}^{-1} \) |
|---|---|---|---|---|
| 1 | 0.10 | 0.10 | 0.10 | \( 4.0 \times 10^{-4} \) |
| 2 | 0.20 | 0.10 | 0.10 | \( 8.0 \times 10^{-4} \) |
| 3 | 0.10 | 0.20 | 0.10 | \( 1.6 \times 10^{-3} \) |
| 4 | 0.10 | 0.10 | 0.20 | \( 4.0 \times 10^{-4} \) |

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

Which statement correctly explains both the relative rate of nitration of methylbenzene compared to benzene, and the directing effect of the methyl group?

What is the structure of the predominant ionic species present when 2-aminobutanedioic acid (aspartic acid), \( \text{HOOC-CH}_2\text{-CH(NH}_2\text{)-COOH} \), is dissolved in an aqueous solution of pH 12?

A white solid Period 3 oxide, \( \text{X} \), reacts vigorously with water to form a solution that turns blue litmus paper red. Another Period 3 oxide, \( \text{Y} \), is a white solid that is insoluble in water, but dissolves in both dilute hydrochloric acid and hot aqueous sodium hydroxide. What are the identities of \( \text{X} \\ and \) \\text{Y} \)?

In the atmosphere, sulfur dioxide can be oxidised to sulfur trioxide in the presence of nitrogen dioxide.

The following reactions occur:
Reaction 1: \( \text{SO}_2(\text{g}) + \text{NO}_2(\text{g}) \rightarrow \text{SO}_3(\text{g}) + \text{NO}(\text{g}) \)
Reaction 2: \( \text{NO}(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{NO}_2(\text{g}) \)

Which statement about this process is correct?

An organic compound, **X**, is a gaseous hydrocarbon with the empirical formula \(\text{CH}_2\). At a temperature of \(150\ ^\circ\text{C}\) and a pressure of \(1.01 \times 10^5\ \text{Pa}\), a \(0.295\ \text{g}\) sample of **X** occupies a volume of \(244\ \text{cm}^3\).

(a) Define the term *relative molecular mass*, \(M_r\). [2]

(b) (i) Use the general gas equation, \(pV = nRT\), to calculate the relative molecular mass, \(M_r\), of **X**. Show your working. \((R = 8.31\ \text{J K}^{-1}\ \text{mol}^{-1})\) [3]
(ii) Deduce the molecular formula of **X**. [1]

(c) Compound **Y** contains only carbon, hydrogen, and oxygen. Complete combustion of \(1.18\ \text{g}\) of **Y** produces \(1.76\ \text{g}\) of carbon dioxide and \(0.540\ \text{g}\) of water.
(i) Calculate the empirical formula of **Y**. Show your working. [4]
(ii) In the mass spectrum of **Y**, the molecular ion peak is at \(m/z = 118\). Deduce the molecular formula of **Y**. [1]

(d) **Y** is an aliphatic dicarboxylic acid. It reacts with excess aqueous sodium hydrogencarbonate.
(i) State the observation for this reaction. [1]
(ii) Write a balanced chemical equation for the reaction of **Y** with excess sodium hydrogencarbonate, using the molecular formula of **Y**. [2]
(iii) Identify a chemical test, including reagent and positive observation, to show that **Y** does not contain a carbon-carbon double bond. [1]

The elements in Period 3 show distinct trends in their physical and chemical properties.

(a) Period 3 elements react with oxygen to form oxides.
(i) Write a balanced equation for the reaction of phosphorus with excess oxygen to form phosphorus(V) oxide. [1]
(ii) Describe the reaction of sodium oxide, \(\text{Na}_2\text{O}\), with water, including the pH of the resulting solution. [2]
(iii) Describe the reaction of phosphorus(V) oxide, \(\text{P}_4\text{O}_{10}\), with water, write an equation for this reaction, and state the pH of the resulting solution. [3]

(b) (i) Aluminium oxide, \(\text{Al}_2\text{O}_3\), is described as amphoteric. Define this term by writing two equations: one for its reaction with hot aqueous hydrochloric acid, and one for its reaction with hot concentrated aqueous sodium hydroxide. [3]
(ii) Silicon dioxide, \(\text{SiO}_2\), does not react with water, but does react with hot concentrated sodium hydroxide. Explain this difference in reactivity. [2]

(c) Period 3 chlorides also show trends in their reactions with water.
(i) Contrast the behaviour of sodium chloride, \(\text{NaCl}\), and silicon tetrachloride, \(\text{SiCl}_4\), when they are separately added to water. Write a balanced chemical equation for the reaction of silicon tetrachloride with water. [3]
(ii) State and explain the difference in the pH of the resulting mixtures when \(\text{NaCl}\) and \(\text{SiCl}_4\) are separately added to water. [1]

Nitrogen and sulfur play vital roles in biological systems, but their oxides are also major environmental pollutants.

(a) Nitrogen gas, \(\text{N}_2\), is chemically unreactive under normal conditions, whereas nitrogen monoxide, \(\text{NO}\), is highly reactive.
(i) Explain the unreactivity of nitrogen gas in terms of its bonding. [2]
(ii) Explain how nitrogen oxides, \(\text{NO}_x\), are formed in internal combustion engines, and write a balanced chemical equation for the formation of nitrogen monoxide. [3]

(b) Nitrogen monoxide acts as a homogeneous catalyst in the atmospheric oxidation of sulfur dioxide, \(\text{SO}_2\), to sulfur trioxide, \(\text{SO}_3\).
(i) Write two equations to show how \(\text{NO}\) catalyses this oxidation. [2]
(ii) Explain why \(\text{NO}\) acts as a catalyst in this reaction. [1]
(iii) State one environmental consequence of acid rain on the aquatic ecosystem and one on buildings or structures. [2]

(c) Ammonium sulfate, \((\text{NH}_4)_2\text{SO}_4\), is a synthetic nitrogenous fertiliser.
(i) Write a balanced chemical equation for the preparation of ammonium sulfate from ammonia and sulfuric acid. [1]
(ii) Explain why adding calcium hydroxide (slaked lime) to soil that has recently been treated with ammonium sulfate fertiliser reduces the effectiveness of the fertiliser, and write a chemical equation for the reaction that occurs. [3]
(iii) Explain how the discharge of agricultural fertilisers into rivers can lead to eutrophication. [1]

Compound **A** has the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\). It exists as several structural and stereoisomers.

(a) Isomer **A1** is a straight-chain compound that reacts with:
- sodium metal to produce hydrogen gas.
- acidified potassium dichromate(VI) to form a compound that does not react with Tollens' reagent.
- alkaline aqueous iodine to give a yellow precipitate.

(i) Identify the functional group in **A1** responsible for the reaction with sodium. [1]
(ii) Identify the functional group produced when **A1** reacts with acidified potassium dichromate(VI), and explain why this product does not react with Tollens' reagent. [2]
(iii) State the identity of the yellow precipitate formed in the reaction of **A1** with alkaline aqueous iodine. [1]
(iv) Deduce the structure of **A1**. Explain your reasoning based on the reactions described. [3]

(b) Isomer **A2** is a structural isomer of **A1** that contains a chiral carbon atom. Like **A1**, it reacts with sodium metal and gives a positive reaction with alkaline aqueous iodine.
(i) Explain what is meant by a chiral carbon atom. [1]
(ii) Draw the structural formula of **A2**. Mark the chiral carbon with an asterisk (*). [1]
(iii) Draw three-dimensional structures of the two optical isomers of **A2**, showing clearly the spatial relationship between them. [2]

(c) Isomer **A3** is an ester.
(i) Draw the skeletal structure of an ester with molecular formula \(\text{C}_4\text{H}_8\text{O}_2\) that can be hydrolysed to produce methanol as one of the products. [1]
(ii) Write an equation for the acid-catalysed hydrolysis of this ester. [2]
(iii) Name the other organic product of this hydrolysis. [1]

Propanoic acid is a weak Brønsted-Lowry acid.

(a) Define a Brønsted-Lowry acid and write the expression for the acid dissociation constant, \(K_a\), of propanoic acid, \(CH_3CH_2COOH\). [2.5]

(b) Calculate the pH of a 0.150 mol dm\(^{-3}\) aqueous solution of propanoic acid. The \(K_a\) of propanoic acid is \(1.35 \times 10^{-5}\) mol dm\(^{-3}\) at 298 K. [3]

(c) A buffer solution is prepared by mixing 50.0 cm\(^3\) of 0.150 mol dm\(^{-3}\) propanoic acid with 25.0 cm\(^3\) of 0.100 mol dm\(^{-3}\) sodium hydroxide.
(i) Calculate the concentration of both propanoic acid and propanoate ions in this buffer mixture. [4]
(ii) Show by calculation that the pH of this buffer mixture is 4.57. [3]

Transition elements form a wide variety of coloured complex ions with different geometries.

(a) Explain why transition metal complexes are coloured, making reference to d-orbital splitting, light absorption, and d-d electron transitions. [4.5]

(b) Cobalt(II) forms an octahedral complex with water, \([Co(H_2O)_6]^{2+}\), and a tetrahedral complex with chloride ions, \([CoCl_4]^{2-}\).
(i) Draw 3D diagrams of both \([Co(H_2O)_6]^{2+}\) and \([CoCl_4]^{2-}\), showing their 3D shapes clearly. [3]
(ii) State the coordination number and geometry for each complex ion. [2]

(c) Explain why cobalt(II) forms a tetrahedral complex with chloride ligands, but an octahedral complex with water ligands, in terms of ligand size and steric hindrance. [3]

Electrochemical cells can be used to measure standard electrode potentials and predict the feasibility of reactions.

(a) Describe and draw a labeled diagram of an electrochemical cell designed to measure the standard electrode potential, \(E^\theta\), of the \(Fe^{3+}/Fe^{2+}\) half-cell relative to the standard hydrogen electrode (SHE). Label all electrodes, solution compositions, concentrations, and physical conditions. [5]

(b) The standard electrode potentials for two half-cells are given below:
- \(Ag^+(aq) + e^- \rightleftharpoons Ag(s)\) \(E^\theta = +0.80\) V
- \(Fe^{3+}(aq) + e^- \rightleftharpoons Fe^{2+}(aq)\) \(E^\theta = +0.77\) V

(i) Write the overall ionic equation for the reaction that occurs when these two half-cells are connected under standard conditions, and calculate the standard cell potential, \(E^\theta_{\text{cell}}\). [2.5]
(ii) Use the Nernst equation, \(E = E^\theta + \frac{0.059}{z}\log\frac{[\text{oxidised}]}{[\text{reduced}]}\), to calculate the electrode potential, \(E\), of the \(Fe^{3+}/Fe^{2+}\) half-cell at 298 K when \([Fe^{3+}] = 0.010\) mol dm\(^{-3}\) and \([Fe^{2+}] = 0.500\) mol dm\(^{-3}\). [3]
(iii) Predict and explain how this change in concentration affects the cell potential, \(E_{\text{cell}}\), and the thermodynamic feasibility of the reaction in (b)(i). [2]

Benzene undergoes electrophilic substitution reactions, such as nitration, due to its stable delocalised \(\pi\) system.

(a) Benzene is reacted with a mixture of concentrated nitric acid and concentrated sulfuric acid at 50 °C.
(i) Write an equation for the generation of the electrophile, \(NO_2^+\), showing the role of H\(_2\)SO\(_4\) as a catalyst. [2]
(ii) Outline the mechanism for the nitration of benzene, using curly arrows to show the movement of electron pairs. Draw the structure of the intermediate clearly. [5]

(b) Methylbenzene undergoes nitration much faster than benzene.
(i) Explain why methylbenzene is more reactive towards electrophiles than benzene. [2.5]
(ii) Identify the major organic mono-nitrated products formed when methylbenzene reacts with the nitrating mixture, and explain the directing effect of the methyl group. [3]

The reaction between peroxodisulfate(VI) ions, \(S_2O_8^{2-}\), and iodide ions, \(I^-\), is catalysed by \(Fe^{2+}\)(aq):
\(S_2O_8^{2-}(aq) + 2I^-(aq) \rightarrow 2SO_4^{2-}(aq) + I_2(aq)\)

(a) Initial rate experiments were carried out at 298 K, giving the following results:
- Expt 1: \([S_2O_8^{2-}] = 0.010\) mol dm\(^{-3}\), \([I^-] = 0.010\) mol dm\(^{-3}\), Initial Rate = \(1.2 \times 10^{-5}\) mol dm\(^{-3}\) s\(^{-1}\)
- Expt 2: \([S_2O_8^{2-}] = 0.020\) mol dm\(^{-3}\), \([I^-] = 0.010\) mol dm\(^{-3}\), Initial Rate = \(2.4 \times 10^{-5}\) mol dm\(^{-3}\) s\(^{-1}\)
- Expt 3: \([S_2O_8^{2-}] = 0.010\) mol dm\(^{-3}\), \([I^-] = 0.020\) mol dm\(^{-3}\), Initial Rate = \(2.4 \times 10^{-5}\) mol dm\(^{-3}\) s\(^{-1}\)

(i) Deduce the order of reaction with respect to both reactants, explaining your reasoning. [3]
(ii) Write the rate equation and calculate the rate constant, \(k\), at 298 K, including appropriate units. [3.5]

(b) (i) Define the term activation energy, \(E_a\). [1]
(ii) The rate constant \(k\) was determined at different temperatures. A plot of \(\ln k\) against \(1/T\) yielded a straight line with a gradient of \(-6130\) K. Calculate the activation energy, \(E_a\), for this reaction in kJ mol\(^{-1}\). (\(R = 8.31\) J K\(^{-1}\) mol\(^{-1}\)). [3]
(iii) Explain how the addition of \(Fe^{2+}\)(aq) catalyses the reaction. [2]

Amino acids are bifunctional organic compounds that exhibit unique properties depending on pH.

(a) Glycine (H\(_2\)NCH\(_2\)COOH) is the simplest amino acid.
(i) Draw the zwitterionic structure of glycine. [1.5]
(ii) Explain how glycine acts as a buffer solution when small amounts of acid or alkali are added. [3]

(b) When a mixture of glycine and alanine (H\(_2\)NCH(CH\(_3\))COOH) is heated in the presence of a suitable catalyst, condensation polymerisation can occur.
(i) Draw the structures of the two possible dipeptides formed by the reaction between one molecule of glycine and one molecule of alanine. [3]
(ii) State the name of the reaction type and the name of the functional group linking the two amino acid residues. [2]

(c) Electrophoresis can be used to separate a mixture of amino acids.
Explain how the direction and rate of movement of amino acids during electrophoresis depend on the pH of the buffer solution and the structure of the amino acids. [3]

The properties of elements in Period 3 show distinct periodic trends across the period.

(a) Consider the three Period 3 oxides: \(Na_2O\), \(Al_2O_3\), and \(SO_3\).
(i) Describe the reaction, if any, of each oxide with water. Write chemical equations for any reactions that occur and state the approximate pH of the resulting mixture. [5]
(ii) Explain the variation in pH of these resulting solutions in terms of the structure and bonding of the three oxides. [3]

(b) (i) Describe what is observed when water is added separately to solid \(NaCl\) and liquid \(SiCl_4\). Write chemical equations for any reactions that occur. [3.5]
(ii) Explain why \(SiCl_4\) is readily hydrolysed by water, whereas \(NaCl\) simply dissolves, in terms of the electronic structure of silicon. [1.5]

The ideal gas equation can be used to find the relative molecular mass of volatile organic compounds.

(a) A gaseous hydrocarbon, X, has a density of 2.11 g dm\(^{-3}\) at a temperature of 323 K and a pressure of \(1.01 \times 10^5\) Pa.
(i) Use the ideal gas equation, \(pV = nRT\), to calculate the relative molecular mass, \(M_r\), of X. (\(R = 8.31\) J K\(^{-1}\) mol\(^{-1}\)). [3.5]
(ii) Combustion analysis of 1.20 g of X shows that it contains 1.03 g of carbon and the remainder is hydrogen. Calculate the empirical formula of X. [3]
(iii) Deduce the molecular formula of X. [2]

(b) (i) Write a balanced chemical equation for the complete combustion of X. [2]
(ii) Calculate the volume of carbon dioxide gas, in dm\(^3\), produced at 298 K and \(1.01 \times 10^5\) Pa when 2.50 g of X is completely combusted. (Assume that the molar volume of gas under these conditions is 24.0 dm\(^3\) mol\(^{-1}\)). [2]

A student conducts an experiment to determine the Faraday constant, \(F\), by electrolyzing aqueous copper(II) sulfate using copper electrodes.

(a) Draw a labelled diagram of the apparatus that the student should use to carry out this electrolysis. Your diagram should include the electrical circuit showing how current is measured and controlled. Describe how the cathode should be prepared, washed, and dried before and after the electrolysis to ensure accurate mass measurements. (5 marks)

(b) The student runs the electrolysis at a constant current of \(0.500\text{ A}\) for various time periods, \(t\). After each run, the cathode is washed, dried, and weighed to determine the mass of copper deposited, \(m\).
The table below shows the results obtained.

| Run | Time, \(t\) / s | Mass of copper deposited, \(m\) / g |
|:---:|:---:|:---:|
| 1 | 600 | 0.099 |
| 2 | 1200 | 0.198 |
| 3 | 1800 | 0.297 |
| 4 | 2400 | 0.352 |
| 5 | 3000 | 0.495 |
| 6 | 3600 | 0.594 |

(i) Plot a graph of mass of copper deposited, \(m\) (y-axis), against time, \(t\) (x-axis). Describe the shape of the graph, identify the anomalous point, and suggest a physical reason for this anomaly. (4 marks)

(ii) Use your graph to determine the gradient of the line of best fit. Show your working and state the units of the gradient. (2 marks)

(iii) The relationship between the mass of copper deposited, \(m\), and time, \(t\), is given by:
\( m = \frac{I \cdot M_r \cdot t}{z \cdot F} \)
where:
- \(I\) is the current (\(0.500\text{ A}\))
- \(M_r\) is the relative atomic mass of copper (\(63.5\))
- \(z\) is the number of electrons transferred per copper ion (\(z = 2\))
- \(F\) is the Faraday constant

Use your gradient from (b)(ii) to calculate the value of the Faraday constant, \(F\). (2 marks)

(c) Explain why using a higher current (e.g., \(5.0\text{ A}\)) in the same experimental setup might lead to a less accurate value for the Faraday constant. (2 marks)

A student investigates the kinetics of the reaction between peroxodisulfate(VIII) ions, \(\text{S}_2\text{O}_8^{2-}\), and iodide ions, \(\text{I}^-\):
\[ \text{S}_2\text{O}_8^{2-}(\text{aq}) + 2\text{I}^-(\text{aq}) \to 2\text{SO}_4^{2-}(\text{aq}) + \text{I}_2(\text{aq}) \]
This reaction is monitored using an 'iodine clock' technique. A small, fixed amount of sodium thiosulfate, \(\text{Na}_2\text{S}_2\text{O}_3\), and starch indicator are added to the reaction mixture.
The thiosulfate ions immediately react with any iodine produced:
\[ \text{I}_2(\text{aq}) + 2\text{S}_2\text{O}_3^{2-}(\text{aq}) \to 2\text{I}^-(\text{aq}) + \text{S}_4\text{O}_6^{2-}(\text{aq}) \]
Once all the thiosulfate ions are consumed, the iodine remaining in solution reacts with the starch to produce a deep-blue color. The time taken, \(t\), for the blue color to appear is recorded. The rate of reaction is proportional to \(\frac{1}{t}\).

The student plans an experiment to determine the order of reaction with respect to iodide ions, \(\text{I}^-\), by varying the concentration of \(\text{I}^-\), while keeping the concentration of \(\text{S}_2\text{O}_8^{2-}\) and the total volume constant.

The student is provided with:
- \(0.200\text{ mol dm}^{-3}\) aqueous potassium iodide, \(\text{KI}(\text{aq})\)
- \(0.200\text{ mol dm}^{-3}\) aqueous potassium chloride, \(\text{KCl}(\text{aq})\)
- \(0.100\text{ mol dm}^{-3}\) aqueous ammonium peroxodisulfate, \((\text{NH}_4)_2\text{S}_2\text{O}_8(\text{aq})\)
- \(0.0050\text{ mol dm}^{-3}\) aqueous sodium thiosulfate, \(\text{Na}_2\text{S}_2\text{O}_3(\text{aq})\)
- \(1\%\) starch indicator solution
- Distilled water

(a) Explain why potassium chloride, \(\text{KCl}(\text{aq})\), is added to the mixtures where the volume of \(\text{KI}(\text{aq})\) is reduced. (1 mark)

(b) Design a table to show the volumes of each solution that the student should mix to carry out five different trials to determine the order of reaction with respect to \(\text{I}^-\).
The total volume of each reaction mixture must be exactly \(50.0\text{ cm}^3\).
In each trial, the volume of \(0.100\text{ mol dm}^{-3}\) \((\text{NH}_4)_2\text{S}_2\text{O}_8\) must be \(10.0\text{ cm}^3\), the volume of \(0.0050\text{ mol dm}^{-3}\) \(\text{Na}_2\text{S}_2\text{O}_3\) must be \(5.0\text{ cm}^3\), and the volume of starch indicator must be \(2.0\text{ cm}^3\).
Your table must show the volumes of \(\text{KI}(\text{aq})\), \(\text{KCl}(\text{aq})\), and distilled water (if any) used for each trial. (4 marks)

(c) The results of the experiment are shown below. The initial concentration of iodide ions, \([\text{I}^-]\), is calculated for each of the five trials.

| Trial | \([\text{I}^-]\) / \(\text{mol dm}^{-3}\) | Time, \(t\) / s | \(\frac{1}{t}\) / \(\text{s}^{-1}\) |
|:---:|:---:|:---:|:---:|
| 1 | 0.080 | 25 | 0.040 |
| 2 | 0.060 | 33 | 0.030 |
| 3 | 0.040 | 50 | 0.020 |
| 4 | 0.030 | 91 | 0.011 |
| 5 | 0.020 | 100 | 0.010 |

(i) Plot a graph of \(\frac{1}{t}\) on the y-axis against \([\text{I}^-]\) on the x-axis.
Describe the relationship between \(\frac{1}{t}\) and \([\text{I}^-]\), and identify the anomalous trial. (3 marks)

(ii) Suggest a practical reason why Trial 4 might be anomalous. (1 mark)

(iii) Deduce the order of reaction with respect to iodide ions, \(\text{I}^-\). Explain your reasoning. (2 marks)

(d) In a separate experiment, the student wants to determine the activation energy, \(E_a\), of this reaction.
State the additional variable that must be measured and varied, and describe how the data obtained can be used to determine \(E_a\) graphically. (4 marks)