2026 Cambridge IAS-Level Chemistry (9701) 模擬試題連答案詳解

A sample containing \(0.120\text{ g}\) of a volatile liquid hydrocarbon, \(\text{Y}\), was vaporised at \(373\text{ K}\) and \(1.00 \times 10^5\text{ Pa}\).
The vapour occupied a volume of \(44.5\text{ cm}^3\).

What is the relative molecular mass, \(M_r\), of \(\text{Y}\)?
[The molar gas constant, \(R = 8.31\text{ J}\,\text{K}^{-1}\,\text{mol}^{-1}\)]

Standard enthalpy changes of combustion, \(\Delta H^\ominus_c\), are given in the table below.

\[\begin{array}{|c|c|} \hline \text{Substance} & \Delta H^\ominus_c / \text{kJ}\,\text{mol}^{-1} \\ \hline \text{C(graphite)} & -393.5 \\ \text{H}_2\text{(g)} & -285.8 \\ \text{CH}_3\text{CH}_2\text{COOH(l)} & -1527.0 \\ \hline \end{array}\]

What is the standard enthalpy change of formation, \(\Delta H^\ominus_f\), of propanoic acid, \(\text{CH}_3\text{CH}_2\text{COOH(l)}\), in \(\text{kJ}\,\text{mol}^{-1}\)?

Two solid Period 3 chlorides, \(\text{E}\) and \(\text{F}\), are each added separately to excess water.

- When \(\text{E}\) is added to water, it dissolves without reaction to give a solution with a pH of 7.
- When \(\text{F}\) is added to water, vigorous hydrolytic fuming occurs, giving an acidic solution with a pH of 2.

Which row correctly identifies \(\text{E}\) and \(\text{F}\)?

Solid sodium iodide is treated with concentrated sulfuric acid.

Which products are formed by the redox reactions that take place?

The first six successive ionisation energies of an element \(\text{Q}\), in \(\text{kJ}\,\text{mol}^{-1}\), are:
\[578, \quad 1817, \quad 2745, \quad 11578, \quad 14842, \quad 18379\]

What is the formula of the chloride formed when element \(\text{Q}\) reacts completely with excess chlorine gas?

An alkene \(\text{W}\) has the molecular formula \(\text{C}_6\text{H}_{12}\).
When \(\text{W}\) is heated under reflux with acidified potassium manganate(VII), the only organic product obtained is propanone, \(\text{CH}_3\text{COCH}_3\).

What is the structure of \(\text{W}\)?

An organic compound \(\text{Z}\), \(\text{C}_4\text{H}_{10}\text{O}\), gives a yellow precipitate when warmed with alkaline aqueous iodine.

Which statement about \(\text{Z}\) is correct?

The mass spectrum of an unknown organic compound shows a molecular ion peak, \(\text{M}^+\), at \(m/e = 72\) with a relative abundance of \(28.4\%\), and an \([\text{M}+1]^+\) peak at \(m/e = 73\) with a relative abundance of \(1.25\%\).

How many carbon atoms are present in one molecule of this compound?

A \(20.0\text{ cm}^3\) sample of a gaseous hydrocarbon was mixed with \(150\text{ cm}^3\) of oxygen (an excess) and completely combusted.

After cooling to room temperature, the volume of the remaining gaseous mixture was \(110\text{ cm}^3\).

When this mixture was shaken with excess aqueous sodium hydroxide, the volume decreased to \(30.0\text{ cm}^3\).

All gas volumes were measured at the same temperature and pressure.

What is the molecular formula of the hydrocarbon?

The standard enthalpy changes of combustion are given:
- \(\Delta H^\circ_{\text{c}}[\text{C(s, graphite)}] = -393.5\text{ kJ mol}^{-1}\)
- \(\Delta H^\circ_{\text{c}}[\text{H}_2(\text{g})] = -285.8\text{ kJ mol}^{-1}\)
- \(\Delta H^\circ_{\text{c}}[\text{CH}_3\text{CH}_2\text{OH(l)}] = -1367.0\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of formation, \(\Delta H^\circ_{\text{f}}\), of liquid ethanol, \(\text{CH}_3\text{CH}_2\text{OH(l)}\)?

The table shows the first six successive ionisation energies of an element \(X\).

$$\begin{array}{|c|c|c|c|c|c|c|} \hline \text{Ionisation number} & 1\text{st} & 2\text{nd} & 3\text{rd} & 4\text{th} & 5\text{th} & 6\text{th} \\ \hline \text{Ionisation energy / kJ mol}^{-1} & 578 & 1817 & 2745 & 11578 & 14842 & 18379 \\ \hline \end{array}$$

Which formula represents the chloride formed when element \(X\) reacts with excess chlorine?

Which species has a trigonal pyramidal molecular geometry and a bond angle of approximately \(107^\circ\)?

Separate samples of four Period 3 chlorides are added to equal volumes of cold water at \(298\text{ K}\).

Which row correctly shows the approximate pH of the resulting solutions or mixtures?

When separate solid samples of sodium halides, \(\text{Na}X\), react with concentrated sulfuric acid:
- \(\text{NaCl}\) gives steamy white fumes only;
- \(\text{NaBr}\) gives steamy white fumes, a brown vapour, and a colourless gas that turns acidified potassium dichromate(VI) from orange to green;
- \(\text{NaI}\) gives a purple vapour, a yellow solid, and a gas that turns moist lead(II) ethanoate paper black.

Which statement is correct?

An unbranched alkene with molecular formula \(\text{C}_6\text{H}_{12}\) is heated under reflux with acidified potassium manganate(VII).

The reaction produces only one organic compound, \(Y\).

Compound \(Y\) reacts with aqueous sodium carbonate to produce carbon dioxide gas.

What is the identity of the original alkene?

Compound \(Z\) is an alcohol with molecular formula \(\text{C}_4\text{H}_{10}\text{O}\).

- \(Z\) produces a yellow precipitate when warmed with alkaline aqueous iodine.
- When \(Z\) is heated with an excess of concentrated sulfuric acid, a mixture of three isomeric alkenes of formula \(\text{C}_4\text{H}_8\) is formed, including a pair of stereoisomers.

What is the structural formula of compound \(Z\)?

A gaseous hydrocarbon, \(\text{C}_x\text{H}_y\), with a volume of \(15.0\text{ cm}^3\) was completely combusted in \(100.0\text{ cm}^3\) of oxygen gas (an excess).

After cooling to room temperature and pressure, the total volume of gas remaining was \(77.5\text{ cm}^3\).
Passing this remaining gas through aqueous potassium hydroxide reduced the volume to \(17.5\text{ cm}^3\).

What is the molecular formula of the hydrocarbon?

The standard enthalpy changes of combustion, \(\Delta H^\circ_{\text{c}}\), of carbon (graphite), hydrogen, and propanoic acid are given in the table.

\[\begin{array}{|l|c|}\hline\text{Substance} & \Delta H^\circ_{\text{c}} / \text{kJ mol}^{-1} \\hline\text{C(graphite)} & -394 \\text{H}_2(\text{g}) & -286 \\text{CH}_3\text{CH}_2\text{COOH}(\text{l}) & -1527 \\hline\end{array}\]

What is the standard enthalpy change of formation, \(\Delta H^\circ_{\text{f}}\), of propanoic acid, \(\text{CH}_3\text{CH}_2\text{COOH}(\text{l})\)?

The first eight successive ionisation energies of an element \(X\) are given in the table.

\[\begin{array}{|l|c|c|c|c|c|c|c|c|}\hline\text{Ionisation number} & 1\text{st} & 2\text{nd} & 3\text{rd} & 4\text{th} & 5\text{th} & 6\text{th} & 7\text{th} & 8\text{th} \\hline\text{Ionisation energy} / \text{kJ mol}^{-1} & 738 & 1450 & 7730 & 10540 & 13630 & 18020 & 21710 & 25660 \\hline\end{array}\]

What is the formula of the chloride formed when element \(X\) reacts completely with chlorine?

Which species has the smallest bond angle?

Which row correctly describes the reactions of silicon(IV) chloride, \(\text{SiCl}_4\), and phosphorus(V) oxide, \(\text{P}_4\text{O}_{10}\), when each is added to water at room temperature?

Solid sodium iodide reacts with concentrated sulfuric acid to produce a mixture of products because iodide ions act as a strong reducing agent.

Which sulfur-containing product is formed when iodide ions reduce sulfur from oxidation state \(+6\) to oxidation state \(-2\)?

An alkene, \(Y\), is heated under reflux with hot, concentrated, acidified potassium manganate(VII).

The only organic compound detected in the reaction product mixture is propanone, \(\text{CH}_3\text{COCH}_3\).

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

An alcohol \(Z\) has the molecular formula \(\text{C}_4\text{H}_{10}\text{O}\).

When \(Z\) is warmed with alkaline aqueous iodine, a pale yellow precipitate is observed.
When \(Z\) is heated in the presence of an aluminium oxide catalyst, it dehydrates to form a mixture containing three isomeric alkenes of formula \(\text{C}_4\text{H}_8\) (including stereoisomers).

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

A gaseous hydrocarbon, \(\text{C}_x\text{H}_y\), has a volume of \(20\text{ cm}^3\). It requires \(130\text{ cm}^3\) of oxygen gas for complete combustion. Complete combustion produces \(80\text{ cm}^3\) of carbon dioxide.

All gas volumes are measured at the same temperature and pressure.

What is the formula of the hydrocarbon?

The standard enthalpy changes of combustion, \(\Delta H^\circ_{\text{c}}\), of three substances are given.

- \(\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} \quad \Delta H^\circ_{\text{c}} = -394\text{ kJ mol}^{-1}\)
- \(\text{H}_2\text{(g)} + \frac{1}{2}\text{O}_2\text{(g)} \rightarrow \text{H}_2\text{O(l)} \quad \Delta H^\circ_{\text{c}} = -286\text{ kJ mol}^{-1}\)
- \(\text{CH}_3\text{COOH(l)} + 2\text{O}_2\text{(g)} \rightarrow 2\text{CO}_2\text{(g)} + 2\text{H}_2\text{O(l)} \quad \Delta H^\circ_{\text{c}} = -874\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of formation of liquid ethanoic acid, \(\Delta H^\circ_{\text{f}}[\text{CH}_3\text{COOH(l)}]\)?

An anhydrous chloride of a Period 3 element is a white solid that reacts vigorously with water to produce an acidic solution and white steamy fumes.

When aqueous sodium hydroxide is added dropwise to the resulting solution, a white precipitate forms that dissolves when excess aqueous sodium hydroxide is added.

Which element forms this chloride?

An alkene \(\text{X}\) with the molecular formula \(\text{C}_6\text{H}_{12}\) is heated under reflux with hot concentrated acidified potassium manganate(VII).

Propanone is the only organic product obtained.

What is the identity of alkene \(\text{X}\)?

The first six successive ionisation energies, in \(\text{kJ mol}^{-1}\), of an element \(\text{E}\) are shown.

\[578, \quad 1817, \quad 2745, \quad 11578, \quad 14842, \quad 18379\]

Which formula represents a stable compound of element \(\text{E}\)?

When solid potassium halide \(\text{KX}\) is treated with concentrated sulfuric acid, steamy fumes, a purple vapour, and a yellow solid are observed.

Which row correctly identifies the halide ion \(\text{X}^-\) and the yellow solid?

Which species has a trigonal planar shape with bond angles of \(120^\circ\)?

An alcohol \(\text{Y}\) has the molecular formula \(\text{C}_4\text{H}_{10}\text{O}\). When \(\text{Y}\) is warmed with alkaline aqueous iodine, a yellow precipitate is observed.

When \(\text{Y}\) is heated under reflux with acidified potassium dichromate(VI), compound \(\text{Z}\) is formed. Compound \(\text{Z}\) gives no reaction with Tollens' reagent.

What is the identity of compound \(\text{Z}\)?

A \(10.0\text{ cm}^3\) sample of a gaseous hydrocarbon \(\text{C}_x\text{H}_y\) is completely burned in \(70.0\text{ cm}^3\) of oxygen (an excess). After cooling to room temperature, the residual gas volume is \(50.0\text{ cm}^3\). On passing this residual gas through excess aqueous sodium hydroxide, the volume decreases by \(30.0\text{ cm}^3\). All gas volumes are measured at room temperature and pressure.

What is the formula of the hydrocarbon?

The standard enthalpy changes of combustion, \(\Delta H_\text{c}^\ominus\), of carbon, hydrogen, and ethanol are given below:

\(\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} \quad \Delta H_\text{c}^\ominus = -394\text{ kJ mol}^{-1}\)
\(\text{H}_2\text{(g)} + \frac{1}{2}\text{O}_2\text{(g)} \rightarrow \text{H}_2\text{O(l)} \quad \Delta H_\text{c}^\ominus = -286\text{ kJ mol}^{-1}\)
\(\text{CH}_3\text{CH}_2\text{OH(l)} + 3\text{O}_2\text{(g)} \rightarrow 2\text{CO}_2\text{(g)} + 3\text{H}_2\text{O(l)} \quad \Delta H_\text{c}^\ominus = -1367\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of formation of ethanol, \(\Delta H_\text{f}^\ominus [\text{CH}_3\text{CH}_2\text{OH(l)}]\)?

The first six successive ionisation energies of an element \(X\) in Period 3 of the Periodic Table are shown below.

\(789, \; 1577, \; 3232, \; 4356, \; 16091, \; 19785\text{ kJ mol}^{-1}\)

What is the formula of the chloride of element \(X\) and the approximate pH of the solution formed when this chloride is added to excess water?

Which pair contains two species that both have a non-linear (bent) molecular shape?

Solid samples of sodium halides are added separately to concentrated sulfuric acid at room temperature.

Which statement is correct?

An alkene \(Y\) is heated under reflux with hot concentrated acidified potassium manganate(VII). The only organic products obtained are propanone, \(\text{CH}_3\text{COCH}_3\), and propanoic acid, \(\text{CH}_3\text{CH}_2\text{COOH}\).

What is the structural formula of alkene \(Y\)?

The temperature of a gaseous reaction mixture is increased from \(T_1\) to \(T_2\) in the absence of a catalyst.

Which row correctly describes the changes to the Maxwell–Boltzmann distribution curve and the activation energy, \(E_\text{a}\)?

Compound \(Z\) is an organic liquid with the molecular formula \(\text{C}_4\text{H}_{10}\text{O}\).

- When \(Z\) is heated with acidified potassium dichromate(VI), the solution turns from orange to green.
- When \(Z\) is warmed with alkaline aqueous iodine, a yellow precipitate is formed.

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

Calculate the total number of chloride ions present in \(0.0250\text{ mol}\) of aluminium chloride, \(\text{AlCl}_3\). Give your answer to 3 significant figures. [\(L = 6.022 \times 10^{23}\text{ mol}^{-1}\)]

Calculate the volume, in \(\text{cm}^3\), of \(0.0250\text{ mol}\,\text{dm}^{-3}\text{ Ba(OH)}_2\text{(aq)}\) required to neutralise completely \(20.0\text{ cm}^3\) of \(0.0400\text{ mol}\,\text{dm}^{-3}\text{ HNO}_3\text{(aq)}\).

Calculate the enthalpy change of reaction, \(\Delta H_{\text{r}}\,\), in \(\text{kJ}\,\text{mol}^{-1}\), for the hydrogenation of ethene:

\[\text{C}_2\text{H}_4\text{(g)} + \text{H}_2\text{(g)} \rightarrow \text{C}_2\text{H}_6\text{(g)}\]

Use the following average bond energy values:
- \(E(\text{C}=\text{C}) = 612\text{ kJ}\,\text{mol}^{-1}\)
- \(E(\text{C}-\text{C}) = 347\text{ kJ}\,\text{mol}^{-1}\)
- \(E(\text{C}-\text{H}) = 413\text{ kJ}\,\text{mol}^{-1}\)
- \(E(\text{H}-\text{H}) = 436\text{ kJ}\,\text{mol}^{-1}\)

Construct a balanced chemical equation for the reaction of solid phosphorus(V) oxide, \(\text{P}_4\text{O}_{10}\), with water.

An alkene, \(\mathbf{W}\), with molecular formula \(\text{C}_5\text{H}_{10}\) is oxidised by heating under reflux with hot, concentrated acidified \(\text{KMnO}_4\). The only organic products formed are propanone, \(\text{CH}_3\text{COCH}_3\), and ethanoic acid, \(\text{CH}_3\text{COOH}\).

State the systematic IUPAC name of alkene \(\mathbf{W}\).

Hydroxylamine has the molecular formula \(\text{NH}_2\text{OH}\).

(i) Draw a dot-and-cross diagram to show the bonding in a molecule of hydroxylamine. Show outer-shell electrons only. [1]
(ii) State the total number of lone pairs of electrons in one molecule of \(\text{NH}_2\text{OH}\). [1]

Phosphorus(V) oxide reacts vigorously with water in an exothermic reaction.

(i) Construct the balanced chemical equation for the reaction of solid tetraphosphorus decaoxide, \(\text{P}_4\text{O}_{10}\), with water. [1]
(ii) Suggest the approximate pH of the resulting solution. [1]

In the vapour phase at moderate temperatures, aluminium chloride exists as a dimer, \(\text{Al}_2\text{Cl}_6\).

(i) Draw a dot-and-cross diagram to represent the bonding in \(\text{Al}_2\text{Cl}_6\). Show outer-shell electrons only. [1]
(ii) Identify the type of bond that holds the two monomer units together in the dimer. [1]

When chlorine gas is bubbled into hot concentrated aqueous sodium hydroxide, a disproportionation reaction occurs.

(i) Construct the balanced chemical equation for this reaction. [1]
(ii) State the initial and two final oxidation states of chlorine in this reaction. [1]

Hydrogen cyanide, \(\text{HCN}\), is a volatile liquid used in organic synthesis.

(i) Draw a dot-and-cross diagram of a molecule of \(\text{HCN}\). Show outer-shell electrons only. [1]
(ii) Predict the \(\text{H}-\text{C}-\text{N}\) bond angle in \(\text{HCN}\). [1]

Group 2 nitrates undergo thermal decomposition when heated strongly.

(i) Construct the balanced chemical equation for the thermal decomposition of anhydrous barium nitrate, \(\text{Ba(NO}_3)_2\). [1]
(ii) Identify the brown gas evolved during this reaction. [1]

Magnesium reacts with nitrogen gas at elevated temperatures to form magnesium nitride, \(\text{Mg}_3\text{N}_2\).

(i) Draw a dot-and-cross diagram to show the arrangement of outer-shell electrons and charges in magnesium nitride. [1]
(ii) State the electronic configuration of the nitride ion, \(\text{N}^{3-}\). [1]

Silicon tetrachloride, \(\text{SiCl}_4\), reacts vigorously with water in a hydrolysis reaction.

(i) Construct the balanced chemical equation for the reaction between liquid silicon tetrachloride and water. [1]
(ii) Describe one observation that can be made during this reaction. [1]

When 2-methylbut-2-ene, \(\text{CH}_3\text{C}(\text{CH}_3)=\text{CHCH}_3\), reacts with gaseous hydrogen bromide, \(\text{HBr}\), 2-bromo-2-methylbutane is obtained as the major organic product and 2-bromo-3-methylbutane is obtained as the minor product.

Explain why 2-bromo-2-methylbutane is the major product in this reaction.

Ethane reacts with chlorine in the presence of ultraviolet light via a free-radical substitution mechanism.

(i) Construct equations for the two propagation steps leading to the formation of chloroethane.
(ii) Suggest how a small amount of butane is formed during this reaction.

2-bromo-2-methylpropane reacts with aqueous sodium hydroxide predominantly via an \(\text{S}_\text{N}1\) mechanism, whereas 1-bromobutane reacts predominantly via an \(\text{S}_\text{N}2\) mechanism.

Describe the initial step of the \(\text{S}_\text{N}1\) mechanism for 2-bromo-2-methylpropane and explain why 2-bromo-2-methylpropane reacts via \(\text{S}_\text{N}1\) rather than \(\text{S}_\text{N}2\).

Propanone reacts with hydrogen cyanide, \(\text{HCN}\), in the presence of a small amount of sodium cyanide, \(\text{NaCN}\), to form 2-hydroxy-2-methylpropanenitrile.

Describe the role of the cyanide ion, \(\text{CN}^-\), and the two mechanistic steps involved in this reaction.

Separate samples of 1-chlorobutane and 1-iodobutane are heated with aqueous silver nitrate in ethanol under identical conditions.

State which halogenoalkane produces a precipitate more rapidly. Explain your answer in terms of bond strength and reaction kinetics.

When butan-2-ol is heated with concentrated sulfuric acid, an elimination reaction occurs yielding a mixture of three isomeric alkenes of molecular formula \(\text{C}_4\text{H}_8\).

(i) Name the three isomeric alkenes formed.
(ii) Explain why two of these isomers exhibit stereoisomerism.

Propene reacts with aqueous bromine, \(\text{Br}_2(\text{aq})\), via an electrophilic addition mechanism.

Describe the stages of this mechanism for the reaction between propene and \(\text{Br}_2\), explaining how the dipole in the bromine molecule is induced and how the final product, 1,2-dibromopropane, is formed.

1-bromopropane reacts with warm aqueous sodium hydroxide to form propan-1-ol via an \(\text{S}_\text{N}2\) mechanism.

Describe the key features of this \(\text{S}_\text{N}2\) mechanism, including the direction of nucleophilic attack, the structure of the transition state, and the stereochemical outcome at the reacting carbon atom.

An unknown carbonyl compound J with the molecular formula \(\text{C}_n\text{H}_{2n}\text{O}\) gives a mass spectrum with a molecular ion peak, \(\text{M}^+\), at \(m/e = 58\) (relative abundance \(28.4\)) and an \([\text{M}+1]^+\) peak at \(m/e = 59\) (relative abundance \(0.94\)).

(a) Show by calculation that compound J contains 3 carbon atoms.

(b) Compound J does not react when warmed with Tollens' reagent. Draw the displayed formula of compound J.

Compound K has the molecular formula \(\text{C}_3\text{H}_6\text{O}_2\). The infrared spectrum of K shows strong absorptions at \(1735\text{ cm}^{-1}\) and \(1240\text{ cm}^{-1}\), but shows no absorption in the region \(2500\text{--}3600\text{ cm}^{-1}\).

(a) Identify the functional group present in K.

(b) Suggest the structural formula of an isomer of K that exhibits a very broad absorption band in the region \(2500\text{--}3000\text{ cm}^{-1}\).

Compound L is a mono-halogenated alkane. In the mass spectrum of L, two molecular ion peaks are observed at \(m/e = 122\) and \(m/e = 124\) with an intensity ratio of approximately \(1:1\). A major fragment ion peak is recorded at \(m/e = 43\).

(a) Deduce the identity of the halogen atom present in L. Explain your answer using the peak data provided.

(b) Give the formula of the fragment ion responsible for the peak at \(m/e = 43\), including its charge.

An organic compound W containing carbon, hydrogen, and oxygen gives a molecular ion peak at \(m/e = 74\) in its mass spectrum. The infrared spectrum of W shows a broad absorption at \(3200\text{--}3650\text{ cm}^{-1}\) but no absorption between \(1650\text{ cm}^{-1}\) and \(1750\text{ cm}^{-1}\). When W is heated under reflux with acidified potassium dichromate(VI), no reaction occurs and the solution remains orange.

(a) Identify the bond responsible for the absorption at \(3200\text{--}3650\text{ cm}^{-1}\) and state the classification of alcohol (primary, secondary, or tertiary) that compound W represents.

(b) Deduce the structural formula of W.

In this experiment, you will determine the enthalpy change of neutralisation, \(\Delta H_{\text{neut}}\), for the reaction between aqueous sodium hydroxide and aqueous hydrochloric acid.

$$\text{NaOH(aq)} + \text{HCl(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)}$$

FA 1 is \(2.00\text{ mol dm}^{-3}\text{ NaOH(aq)}\).
FA 2 is \(2.20\text{ mol dm}^{-3}\text{ HCl(aq)}\).

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### Method

1. Support an expanded polystyrene cup inside a \(250\text{ cm}^3\) glass beaker.
2. Using a measuring cylinder, transfer \(30.0\text{ cm}^3\) of FA 1 into the polystyrene cup.
3. Place the thermometer in the solution and start the stopwatch. Record the temperature of the solution in the cup every \(30\text{ s}\) for \(2.5\text{ min}\).
4. At \(t = 3.0\text{ min}\), use a second measuring cylinder to rapidly add \(30.0\text{ cm}^3\) of FA 2 to the cup. Do not record the temperature at \(t = 3.0\text{ min}\).
5. Stir the mixture thoroughly using the thermometer and continue to record the temperature every \(30\text{ s}\) from \(t = 3.5\text{ min}\) to \(t = 8.0\text{ min}\).

---

(a) In the space below, prepare a single table to record all your temperature and time readings. Record all raw temperature measurements to the nearest \(0.5\,^\circ\text{C}\).

[4 marks]

(b) On the grid provided in the examination, plot a graph of temperature (\(y\)-axis) against time (\(x\)-axis).

1. Choose suitable scales so that your plotted points occupy at least half the grid in both directions.
2. Draw two straight lines of best fit:
- one line through the points from \(t = 0\text{ min}\) to \(t = 2.5\text{ min}\);
- one line through the cooling points from \(t = 4.5\text{ min}\) to \(t = 8.0\text{ min}\).
3. Extrapolate both lines of best fit to \(t = 3.0\text{ min}\).
4. Determine the theoretical temperature change, \(\Delta T\), at \(t = 3.0\text{ min}\).

$$\Delta T = \dots\dots\dots\dots\dots\,^\circ\text{C}$$

[4 marks]

(c) Calculations

Assume that the specific heat capacity of the final reaction mixture is \(c = 4.18\text{ J g}^{-1}\,^\circ\text{C}^{-1}\) and that the density of the solution is \(1.00\text{ g cm}^{-3}\).

(i) Calculate the heat energy released, \(q\), in \(\text{J}\), during this neutralisation reaction. Show your working.

$$q = \dots\dots\dots\dots\dots\text{ J}$$

[2 marks]

(ii) Calculate the amount, in \(\text{mol}\), of FA 1 (\(\text{NaOH}\)) and of FA 2 (\(\text{HCl}\)) mixed together. Hence, state the amount, in \(\text{mol}\), of water formed in this reaction.

$$\text{amount of FA 1} = \dots\dots\dots\dots\dots\text{ mol}$$
$$\text{amount of FA 2} = \dots\dots\dots\dots\dots\text{ mol}$$
$$\text{amount of H}_2\text{O}\text{ formed} = \dots\dots\dots\dots\dots\text{ mol}$$

[2 marks]

(iii) Calculate the molar enthalpy change of neutralisation, \(\Delta H_{\text{neut}}\), in \(\text{kJ mol}^{-1}\), for the reaction between \(\text{NaOH(aq)}\) and \(\text{HCl(aq)}\).

Include a sign with your answer.

$$\Delta H_{\text{neut}} = \text{sign}\dots\dots\dots\dots\dots \quad \text{value}\dots\dots\dots\dots\dots\text{ kJ mol}^{-1}$$

[2 marks]

(d) Evaluation and Extension

(i) The thermometer used has graduations of \(1\,^\circ\text{C}\), and the maximum uncertainty for each reading is \(\pm 0.5\,^\circ\text{C}\). Calculate the maximum percentage uncertainty in your value of \(\Delta T\) (assume a temperature rise of \(13.5\,^\circ\text{C}\)).

$$\text{percentage uncertainty} = \dots\dots\dots\dots\dots\,\%$$

[1 mark]

(ii) A student repeats the experiment using \(30.0\text{ cm}^3\) of \(2.00\text{ mol dm}^{-3}\text{ CH}_3\text{COOH(aq)}\) (ethanoic acid) instead of \(30.0\text{ cm}^3\) of FA 2.

Predict and explain whether the magnitude of \(\Delta H_{\text{neut}}\) obtained for ethanoic acid will be greater than, less than, or the same as that for \(\text{HCl(aq)}\).

[1 mark]

Read the entire question and plan your method before starting.

FB 1 is hydrated magnesium sulfate, \(\text{MgSO}_4 \cdot x\text{H}_2\text{O}\).

You will determine the value of \(x\) by heating FB 1 in a crucible to remove all water of crystallisation.

\[\text{MgSO}_4 \cdot x\text{H}_2\text{O}\text{(s)} \xrightarrow{\Delta} \text{MgSO}_4\text{(s)} + x\text{H}_2\text{O(g)}\]

Method

1. Weigh an empty, clean and dry crucible with its lid.
2. Add between 2.50\text{ g} and 3.00\text{ g} of FB 1 into the crucible.
3. Reweigh the crucible, lid and FB 1.
4. Place the crucible containing FB 1 with its lid on a pipe-clay triangle supported by a tripod.
5. Leave the lid slightly displaced to allow steam to escape.
6. Heat the crucible gently for 2 minutes, then heat strongly for 5 minutes.
7. Cover the crucible completely with the lid, place it on a heatproof mat and allow it to cool for at least 5 minutes.
8. Reweigh the crucible, lid and anhydrous residue.
9. Reheat strongly for a further 2 minutes, cool with the lid on, and reweigh.
10. Repeat heating, cooling and reweighing until constant mass is attained.

(a) In an appropriate format in the space below, record all mass measurements, including the final heating to constant mass, with appropriate headings and units.

(b) Calculations
Show your working and appropriate units in all parts of your calculations. Give your answers to 3 significant figures.
[\(A_{\text{r}}\): \(\text{H}, 1.0\); \(\text{O}, 16.0\); \(\text{Mg}, 24.3\); \(\text{S}, 32.1\)]

(i) Calculate the mass of FB 1 used, the mass of anhydrous \(\text{MgSO}_4\) residue formed, and the mass of \(\text{H}_2\text{O}\) lost.

(ii) Calculate the percentage by mass of water of crystallisation in FB 1.

(iii) Calculate the amount, in \(\text{mol}\), of anhydrous \(\text{MgSO}_4\) residue obtained.

(iv) Calculate the amount, in \(\text{mol}\), of \(\text{H}_2\text{O}\) driven off during heating.

(v) Calculate the experimental value of \(x\) in \(\text{MgSO}_4 \cdot x\text{H}_2\text{O}\) to the nearest integer.

(c) Explain why it is necessary to reheat the crucible and residue until two successive masses are constant to within 0.02\text{ g}.

(d) The balance used has an uncertainty of \(\pm 0.01\text{ g}\) for each individual reading. Calculate the percentage uncertainty in the mass of FB 1 measured.

(e) A student performing this experiment heated the crucible with an intense roaring flame for 15 minutes without a lid. The value of \(x\) calculated by the student was significantly greater than 7.

Suggest one procedural reason for this higher value of \(x\) and explain how this error led to the overestimated value.

Qualitative Analysis

Read through the whole question before starting and prepare a table for your observations where indicated.

(a) $\text{FA 6}$ is an aqueous solution containing two cations and one anion, all of which are listed in the Qualitative Analysis Notes.

Carry out the following tests on $\text{FA 6}$ and record your observations in a single table.

• Test 1: To a $1\text{ cm}$ depth of $\text{FA 6}$ in a test-tube, add aqueous sodium hydroxide dropwise until in excess. Then, warm the mixture gently and test any gas evolved with damp red litmus paper.
• Test 2: To a $1\text{ cm}$ depth of $\text{FA 6}$ in a test-tube, add aqueous ammonia dropwise until in excess.
• Test 3: To a $1\text{ cm}$ depth of $\text{FA 6}$ in a test-tube, add a few drops of aqueous barium nitrate followed by dilute nitric acid.
• Test 4: To a $1\text{ cm}$ depth of $\text{FA 6}$ in a test-tube, add an equal volume of dilute sulfuric acid, then add a few drops of aqueous potassium manganate(VII).

(i) Record all your observations for Tests 1–4 in a suitable table.

(ii) Identify the ions present in $\text{FA 6}$.
Cations: ....................................... and .......................................
Anion: .......................................

(iii) Construct an ionic equation, including state symbols, for the reaction occurring when aqueous sodium hydroxide is first added to $\text{FA 6}$.

(b) $\text{FA 7}$ is an aqueous solution containing one cation and one anion.

(i) Carry out the following tests on $\text{FA 7}$ and record your observations.

• Test 1: To a $1\text{ cm}$ depth of $\text{FA 7}$ in a test-tube, add aqueous sodium hydroxide dropwise until in excess.
Observations: .........................................................................................................................

• Test 2: To a $1\text{ cm}$ depth of $\text{FA 7}$ in a test-tube, add a few drops of dilute nitric acid followed by aqueous silver nitrate. Then add aqueous ammonia (both dilute and concentrated) to the mixture.
Observations: .........................................................................................................................

(ii) Identify the cation and anion present in $\text{FA 7}$.
Cation: .......................................
Anion: .......................................

(iii) Suggest the type of reaction that occurs when excess aqueous sodium hydroxide is added to the precipitate formed in Test 1 on $\text{FA 7}$.