2022 Edexcel A-Level Chemistry (9CH0) Practice Paper with Answers

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 \(25.0\text{ cm}^3\) of \(0.120\text{ mol dm}^{-3}\) sodium hydroxide. What is the pH of the resulting buffer solution at \(298\text{ K}\)?

An element \(X\) in Period 3 of the Periodic Table has the following successive ionization energies in \(\text{kJ mol}^{-1}\): \(IE_1 = 1000\), \(IE_2 = 2250\), \(IE_3 = 3360\), \(IE_4 = 4560\), \(IE_5 = 7010\), \(IE_6 = 8500\), \(IE_7 = 27100\), \(IE_8 = 31700\). In which group of the Periodic Table is element \(X\)?

How many stereoisomers exist for the octahedral complex ion \([\text{Co}(\text{en})_2\text{Cl}_2]^+\) (where \(\text{en}\) represents the bidentate ligand ethane-1,2-diamine)?

Use the following data to calculate the experimental lattice energy, \(\Delta_{\text{latt}}H^\ominus\), of calcium chloride, \(\text{CaCl}_2(\text{s})\) in \(\text{kJ mol}^{-1}\): \(\Delta_fH^\ominus(\text{CaCl}_2(\text{s})) = -796\text{ kJ mol}^{-1}\), \(\Delta_{\text{at}}H^\ominus(\text{Ca}(\text{s})) = +178\text{ kJ mol}^{-1}\), \(1^{\text{st}}\text{ IE}(\text{Ca}) = +590\text{ kJ mol}^{-1}\), \(2^{\text{nd}}\text{ IE}(\text{Ca}) = +1145\text{ kJ mol}^{-1}\), \(\Delta_{\text{at}}H^\ominus(\text{Cl}_2(\text{g})) = +122\text{ kJ mol}^{-1}\) (enthalpy of atomization per mole of \(\text{Cl}(\text{g})\)), \(1^{\text{st}}\text{ EA}(\text{Cl}) = -349\text{ kJ mol}^{-1}\).

A vessel is filled with \(1.00\text{ mol}\) of \(\text{PCl}_5(\text{g})\) and allowed to reach equilibrium at a constant temperature and a total pressure of \(2.00\text{ atm}\). \(\text{PCl}_5(\text{g}) \rightleftharpoons \text{PCl}_3(\text{g}) + \text{Cl}_2(\text{g})\). At equilibrium, the mixture contains \(0.40\text{ mol}\) of \(\text{Cl}_2(\text{g})\). What is the value of the equilibrium constant \(K_p\) in \(\text{atm}\)?

Which of the following statements correctly explains the trend in thermal stability of the Group 2 nitrates down the group?

Chlorine reacts with hot, concentrated aqueous sodium hydroxide to form sodium chloride, sodium chlorate(V), and water. What are the oxidation states of chlorine in the products of this disproportionation reaction?

Which of the following molecules or ions has a non-linear shape with a bond angle of approximately \(104.5^\circ\)?

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 \(25.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) sodium hydroxide.

What is the pH of this buffer solution at \(298\text{ K}\)?

Which of the following gaseous ions has the same number of unpaired d-electrons as a gaseous \(\text{Co}^{2+}\) ion?

A buffer solution is prepared by mixing \(20.0\text{ cm}^3\) of \(0.150\text{ mol dm}^{-3}\) methanoic acid, \(\text{HCOOH}\), with \(10.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) sodium hydroxide, \(\text{NaOH}\). Calculate the pH of the resulting buffer solution at 298 K. [\(K_a\text{ for HCOOH} = 1.6 \times 10^{-4}\text{ mol dm}^{-3}\text{ at 298 K}\)]

An anhydrous chloride of chromium, \(\text{CrCl}_x\), has a mass of \(0.125\text{ g}\). It was dissolved in water and reacted with an excess of silver nitrate solution, producing \(0.339\text{ g}\) of dry silver chloride precipitate, \(\text{AgCl}\). Deduce the value of \(x\) to find the formula of the chromium chloride. [Molar masses: \(\text{Cr} = 52.0\text{ g mol}^{-1}\), \(\text{Ag} = 107.9\text{ g mol}^{-1}\), \(\text{Cl} = 35.5\text{ g mol}^{-1}\)]

Use the following data to calculate the first electron affinity of fluorine, in \(\text{kJ mol}^{-1}\):
- Standard enthalpy of formation of \(\text{NaF(s)}\) = \(-574\text{ kJ mol}^{-1}\)
- Enthalpy of atomisation of sodium, \(\text{Na(s)} \rightarrow \text{Na(g)}\) = \(+107\text{ kJ mol}^{-1}\)
- First ionisation energy of sodium = \(+496\text{ kJ mol}^{-1}\)
- Enthalpy of atomisation of fluorine, \(\frac{1}{2}\text{F}_2\text{(g)} \rightarrow \text{F(g)}\) = \(+79\text{ kJ mol}^{-1}\)
- Lattice energy of \(\text{NaF(s)}\) = \(-930\text{ kJ mol}^{-1}\)

A \(2.97\text{ g}\) sample of anhydrous magnesium nitrate, \(\text{Mg(NO}_3)_2\), is heated until it completely decomposes according to the following equation:

\(2\text{Mg(NO}_3)_2\text{(s)} \rightarrow 2\text{MgO(s)} + 4\text{NO}_2\text{(g)} + \text{O}_2\text{(g)}\)

Calculate the total volume of gas, in \(\text{dm}^3\), produced at room temperature and pressure (RTP). [Molar volume of gas at RTP = \(24.0\text{ dm}^3\text{ mol}^{-1}\); Molar mass of \(\text{Mg(NO}_3)_2 = 148.3\text{ g mol}^{-1}\)]

Explain the differences in the bond angles of ammonia (\(\text{NH}_3\)) and the amide ion (\(\text{NH}_2^-\)), stating the shape and approximate bond angle in each species.

In a closed vessel, the following equilibrium is established at a specific temperature:

\(\text{PCl}_5\text{(g)} \rightleftharpoons \text{PCl}_3\text{(g)} + \text{Cl}_2\text{(g)}\)

At equilibrium, the partial pressure of \(\text{PCl}_5\) is \(0.240\text{ atm}\), and the partial pressure of \(\text{Cl}_2\) is \(0.360\text{ atm}\). Assuming the mixture was initially formed from pure \(\text{PCl}_5\), calculate the equilibrium constant, \(K_p\), for this reaction, including its units.

A student titrates \(25.0\text{ cm}^3\) of an acidified solution containing \(\text{Fe}^{2+}\) ions with \(0.0200\text{ mol dm}^{-3}\) potassium manganate(VII), \(\text{KMnO}_4\). The end-point is reached when \(18.50\text{ cm}^3\) of the \(\text{KMnO}_4\) solution has been added. Calculate the concentration of the \(\text{Fe}^{2+}\) ions in the original solution, to 3 significant figures.

The table below shows the successive ionisation energies, in \(\text{kJ mol}^{-1}\), for a Period 3 element, \(X\):
- 1st: \(578\)
- 2nd: \(1817\)
- 3rd: \(2745\)
- 4th: \(11578\)
- 5th: \(14831\)

Identify element \(X\) and explain your choice by referring to the data.

A buffer solution is prepared by mixing \(50.0\text{ cm}^3\) of \(0.150\text{ mol dm}^{-3}\) propanoic acid (\(K_a = 1.35 \times 10^{-5}\text{ mol dm}^{-3}\)) and \(25.0\text{ cm}^3\) of \(0.200\text{ mol dm}^{-3}\) sodium propanoate at \(298\text{ K}\). Calculate the pH of this buffer solution, giving your answer to two decimal places.

Explain, in terms of the size and charge of the cations, why magnesium carbonate decomposes at a lower temperature than barium carbonate.

A transition metal complex ion has the formula \([\text{Co}(\text{NH}_3)_4(\text{H}_2\text{O})\text{Cl}]^{n+}\). The cobalt ion has an oxidation state of \(+3\). State: (i) the coordination number of the cobalt ion, (ii) the value of \(n\), and (iii) the shape of this complex ion.

Calculate the standard entropy change of system (\(\Delta S^\ominus_{\text{sys}}\)) at \(298\text{ K}\) for the following reaction:
\(\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightarrow 2\text{NH}_3\text{(g)}\)

Given the standard entropies (\(S^\ominus\)) at \(298\text{ K}\):
\(\text{N}_2\text{(g)} = 191.6\text{ J K}^{-1}\text{ mol}^{-1}\)
\(\text{H}_2\text{(g)} = 130.6\text{ J K}^{-1}\text{ mol}^{-1}\)
\(\text{NH}_3\text{(g)} = 192.3\text{ J K}^{-1}\text{ mol}^{-1}\)

Sulfur tetrafluoride, \(\text{SF}_4\), is a highly reactive species. Determine the number of bonding pairs and lone pairs of electrons surrounding the central sulfur atom. Use this information to predict the shape and the approximate equatorial \(\text{F-S-F}\) bond angle in \(\text{SF}_4\).

A sample of an unknown volatile liquid with a mass of \(0.231\text{ g}\) was vaporised completely in a gas syringe at a temperature of \(97^\circ\text{C}\) and a pressure of \(1.00 \times 10^5\text{ Pa}\). The volume of the gas produced was \(74.0\text{ cm}^3\). Calculate the molar mass of the liquid. [Gas constant, \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\)]

A standard electrochemical cell is constructed from two standard half-cells:

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

(i) Write the conventional cell representation for this operating cell under standard conditions.
(ii) Calculate the standard cell potential, \(E^\ominus_{\text{cell}}\), and state which electrode is positive.

A buffer solution is prepared by mixing 50.0 cm3 of 0.200 mol dm-3 lactic acid (CH3CH(OH)COOH, Ka = 1.38 x 10^-4 mol dm-3) and 50.0 cm3 of 0.300 mol dm-3 sodium lactate. Calculate the pH of this buffer solution after the addition of 2.00 cm3 of 0.100 mol dm-3 hydrochloric acid. Show your working to 3 significant figures.

A sample of hydrated ammonium iron(II) sulfate, (NH4)2Fe(SO4)2 . xH2O, with a mass of 1.48 g was dissolved in excess dilute sulfuric acid and made up to 250.0 cm3 in a volumetric flask. A 25.0 cm3 portion of this solution required 15.10 cm3 of 0.00500 mol dm-3 potassium manganate(VII) solution for complete oxidation. Calculate the value of x in the formula of the hydrated salt. [Molar masses in g mol-1: N = 14.0, H = 1.0, Fe = 55.8, S = 32.1, O = 16.0]

Using the following data, calculate the standard lattice energy (lattice enthalpy of formation) of calcium chloride, CaCl2(s). Show all working. Data: Standard enthalpy change of formation of CaCl2(s) = -795.8 kJ mol-1; Standard enthalpy change of atomisation of calcium = +178.2 kJ mol-1; First ionisation energy of calcium = +590.0 kJ mol-1; Second ionisation energy of calcium = +1145.0 kJ mol-1; Standard enthalpy change of atomisation of chlorine = +121.7 kJ mol-1; First electron affinity of chlorine = -349.0 kJ mol-1. Then, explain why the experimental lattice energy of calcium iodide is less exothermic than expected from a theoretical purely ionic model.

Explain the trend in the thermal stability of Group 2 carbonates down the group, from magnesium carbonate to barium carbonate, in terms of cation size, charge density, and polarization.

Predict and compare the shapes and bond angles of the phosphorus trichloride molecule (PCl3) and the tetrachlorophosphate(V) ion (PCl4+). Additionally, explain why the boiling temperature of phosphorus trichloride (PCl3) is higher than that of nitrogen trichloride (NCl3) despite nitrogen being more electronegative than phosphorus.

An oxide of nitrogen is found to contain 30.43% nitrogen and 69.57% oxygen by mass. (a) Determine the empirical formula of this oxide. (b) Under conditions of 101 kPa and 298 K, a 1.15 g sample of this gaseous oxide occupies a volume of 306 cm3. Using the ideal gas equation (PV = nRT), calculate the molar mass of the oxide to 3 significant figures and deduce its molecular formula. [R = 8.31 J K-1 mol-1, molar masses: N = 14.0 g mol-1, O = 16.0 g mol-1]

When chlorine gas is reacted with hot concentrated sodium hydroxide solution, a disproportionation reaction occurs, forming sodium chloride, sodium chlorate(V), and water. (a) Define the term 'disproportionation'. (b) Write the half-equations for the oxidation and reduction processes, and use them to construct the overall balanced ionic equation for this reaction.

A mixture containing 2.00 mol of SO2(g) and 1.00 mol of O2(g) is allowed to reach equilibrium in a sealed container at a constant temperature: 2SO2(g) + O2(g) <=> 2SO3(g). At equilibrium, the total pressure of the system is 3.00 atm and the mixture is found to contain 0.400 mol of SO2. Calculate the equilibrium constant, Kp, for this reaction at this temperature. Include units in your answer.

For a reaction between reactants P and Q, the rate equation is: \(\text{rate} = k[\text{P}]^2[\text{Q}]\). In a series of experiments, the initial concentration of P is doubled, and the initial concentration of Q is halved. What is the overall effect on the initial rate of the reaction?

Which carbonyl compound reacts with hydrogen cyanide, \(\text{HCN}\), in the presence of potassium cyanide, \(\text{KCN}\), to form a product that exists as a racemic mixture?

In the electrophilic substitution reaction of benzene to form nitrobenzene, what is the role of the concentrated sulfuric acid?

How many peaks are observed in the carbon-13 (\(^{13}\text{C}\)) NMR spectrum of methylbenzene?

When propene is reacted with bromine water, \(\text{Br}_2\text{(aq)}\), the major product obtained is 1-bromopropan-2-ol. Which statement correctly explains why this is the major product?

Which of the following isomeric organic compounds has the highest boiling point?

A student reacts 9.20 g of ethanol (\(M_r = 46.0\)) with excess ethanoic acid to produce ethyl ethanoate (\(M_r = 88.0\)) in a condensation reaction. If the percentage yield of the reaction is 60.0%, what mass of ethyl ethanoate is obtained?

An organic compound X is known to be either propanone, propan-1-ol, or propanoic acid. The infrared spectrum of X shows a broad absorption band at \(3300\text{ cm}^{-1}\) but does not show any absorption at \(1700\text{ cm}^{-1}\). Identify X.

The rate constant, \(k\), of a reaction was determined at several different temperatures. A graph of \(\ln k\) against \(\frac{1}{T}\) (where \(T\) is measured in \(\text{K}\)) was plotted and found to be a straight line with a gradient of \(-9.50 \times 10^3\text{ K}\). What is the activation energy, \(E_a\), of this reaction? [Gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\)]

Which of the following describes the reaction that occurs when phenol is treated with excess bromine water at room temperature?

A reaction has rate constants \(k_1 = 3.40 \times 10^{-4} \text{ s}^{-1}\) at \(298 \text{ K}\) and \(k_2 = 1.25 \times 10^{-2} \text{ s}^{-1}\) at \(348 \text{ K}\). Calculate the activation energy (\(E_a\)) for this reaction in \( \text{kJ mol}^{-1} \). (Gas constant \(R = 8.31 \text{ J K}^{-1} \text{ mol}^{-1}\)). Give your answer to 3 significant figures.

Identify the organic product formed when propanoyl chloride reacts with ethylamine. Write the IUPAC name of the organic product and name the mechanism of this reaction.

A Grignard reagent, ethylmagnesium bromide, reacts with a carbonyl compound followed by hydrolysis to form 3-methylpentan-3-ol. Deduce the IUPAC name and the structural formula of this carbonyl compound.

An organic compound has the molecular formula \(\text{C}_5\text{H}_{10}\text{O}_2\) and exhibits only three peaks in its \(^{13}\text{C}\) NMR spectrum. One of these peaks is in the region \(\delta = 160\text{--}185\text{ ppm}\). Identify the functional group responsible for this peak, and deduce the IUPAC name of the compound.

When a single enantiomer of 2-bromobutane reacts with warm aqueous sodium hydroxide, the organic product, butan-2-ol, is formed as a single enantiomer with inversion of configuration. State the mechanism of this reaction and explain why the configuration of the chiral centre is inverted.

Ethyl benzoate (\(\text{C}_9\text{H}_{10}\text{O}_2\), molar mass \(= 150.2 \text{ g mol}^{-1}\)) is hydrolysed using excess sodium hydroxide to form benzoic acid (\(\text{C}_7\text{H}_6\text{O}_2\), molar mass \(= 122.1 \text{ g mol}^{-1}\)) after acidification. Starting with \(4.51 \text{ g}\) of ethyl benzoate, a student obtains \(2.75 \text{ g}\) of pure benzoic acid. Calculate the percentage yield of benzoic acid. Give your answer to 3 significant figures.

In the mass spectrum of 2-chloropropane, two major molecular ion peaks are observed at \(m/z = 78\) and \(m/z = 80\). State the isotope of chlorine responsible for each of these peaks, and give the theoretical ratio of the abundance of the \(m/z = 78\) peak to the \(m/z = 80\) peak.

Explain, in terms of intermolecular forces, why propan-1-ol (boiling point \(97^\circ\text{C}\)) has a significantly higher boiling point than propanal (boiling point \(49^\circ\text{C}\)), despite both compounds having similar molar masses.

The rate constant, \(k\), for a certain organic decomposition reaction was measured at two different temperatures. At \(300\text{ K}\), \(k_1 = 3.20 \times 10^{-4}\text{ s}^{-1}\), and at \(340\text{ K}\), \(k_2 = 1.50 \times 10^{-2}\text{ s}^{-1}\). Calculate the activation energy, \(E_a\), for this reaction in \\text{kJ mol}^{-1}\). The gas constant, \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\).

Explain why the nucleophilic substitution of optically active 2-bromobutane with aqueous sodium hydroxide proceeds via an \(S_N1\) mechanism to form a racemic mixture, whereas an \(S_N2\) mechanism would produce a single optical isomer.

State the reagents and reaction conditions required to convert nitrobenzene to phenylamine in a laboratory synthesis.

State the number of peaks observed in the \(^{13}\text{C}\) NMR spectrum of isopropyl methanoate, \(\text{HCOOCH(CH}_3)_2\), and explain your answer by identifying the different carbon environments.

A student synthesises 1-bromobutane by reacting \(15.0\text{ g}\) of butan-1-ol with an excess of sodium bromide and sulfuric acid. After purification, \(19.5\text{ g}\) of 1-bromobutane is obtained. Calculate the percentage yield of 1-bromobutane. Give your answer to 3 significant figures. [Molar masses: butan-1-ol = \(74.0\text{ g mol}^{-1}\); 1-bromobutane = \(136.9\text{ g mol}^{-1}\)]

The reaction \(A + B \rightarrow C\) was studied at \(298\text{ K}\). The following initial rates data were obtained:

- Run 1: \([A] = 0.10\text{ mol dm}^{-3}\), \([B] = 0.10\text{ mol dm}^{-3}\), Initial Rate = \(2.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\)
- Run 2: \([A] = 0.20\text{ mol dm}^{-3}\), \([B] = 0.10\text{ mol dm}^{-3}\), Initial Rate = \(8.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\)
- Run 3: \([A] = 0.20\text{ mol dm}^{-3}\), \([B] = 0.20\text{ mol dm}^{-3}\), Initial Rate = \(8.0 \times 10^{-4}\text{ mol dm}^{-3}\text{ s}^{-1}\)

Deduce the rate equation and calculate the rate constant, \(k\), including its units.

Arrange the following compounds in order of increasing boiling point: propan-1-ol, propanal, butane. Explain the trend in boiling points based on the intermolecular forces present.

An unknown organic compound, \(X\), containing carbon, hydrogen, and oxygen, has a molecular ion peak at \(m/z = 58\) in its mass spectrum. The infrared spectrum of \(X\) shows a strong absorption peak at \(1715\text{ cm}^{-1}\) but no absorption peak between \(3200\text{ and } 3600\text{ cm}^{-1}\). Identify the functional group present, determine the molecular formula of \(X\), and draw or state a possible structural formula for \(X\).

A student investigates the rate of the dehydrochlorination of a chloroalkane at different temperatures. The rate constant, \(k\), was determined at two different temperatures:
- At \(350\text{ K}\), \(k_1 = 3.20 \times 10^{-4}\text{ s}^{-1}\)
- At \(410\text{ K}\), \(k_2 = 2.45 \times 10^{-2}\text{ s}^{-1}\)

Calculate the activation energy, \(E_a\), for this reaction in \\text{kJ mol}^{-1}\). The gas constant, \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\). Show all your working.

The reaction of both butanal and butanone with HCN in the presence of KCN produces mixtures of optical isomers.

Explain, in terms of the structure of the carbonyl group, why both reactions produce a racemic mixture. Compare the relative reactivity of butanal and butanone towards this nucleophilic addition, justifying your answer.

An unknown organic compound Y has the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\).
In its \(^1\text{H}\) NMR spectrum, the following signals are recorded:
- Singlet at \(\delta = 2.05\text{ ppm}\) (relative peak area = 3)
- Triplet at \(\delta = 1.25\text{ ppm}\) (relative peak area = 3)
- Quartet at \(\delta = 4.12\text{ ppm}\) (relative peak area = 2)

In its mass spectrum, a major fragment peak appears at \(m/z = 43\).

Deduce the structural formula of Y. Show how all the NMR signals and the mass spectrum peak support your proposed structure.

Outline a multi-step synthesis to prepare 4-(dimethylamino)azobenzene starting from phenylamine (aniline). State the reagents, necessary reaction conditions, and the structure of the intermediate compound.

Explain how you would use Infrared (IR) spectroscopy and Mass Spectrometry (MS) to distinguish between three structural isomers with the molecular formula \(\text{C}_3\text{H}_6\text{O}\): propanal, propanone, and prop-2-en-1-ol. Give characteristic absorption values and structural fragments where appropriate.

A organic ester contains only carbon, hydrogen, and oxygen. A \(1.50\text{ g}\) sample of this liquid ester was burned completely in excess oxygen.

The combustion products were \(3.00\text{ g}\) of carbon dioxide and \(1.23\text{ g}\) of water.

Calculate the empirical formula of the ester. Show all steps in your working.

A student compared the relative rates of hydrolysis of 1-chlorobutane, 1-bromobutane, and 1-iodobutane by reacting each compound with aqueous silver nitrate in ethanol solvent at \(50^\circ\text{C}\).

State the relative order of rates of hydrolysis of these three halogenoalkanes. Explain this order, writing relevant ionic equations, and state whether bond enthalpy or bond polarity is the deciding factor in determining the rate of reaction. Explain the role of the ethanol.

Ethanol (\(\text{CH}_3\text{CH}_2\text{OH}\)) has a boiling point of \(78^\circ\text{C}\), whereas its structural isomer dimethyl ether (\(\text{CH}_3\text{OCH}_3\)) has a boiling point of \(-24^\circ\text{C}\).

Explain this difference in boiling points in terms of intermolecular forces. In addition, discuss the solubility of both isomers in water, explaining how each is able to interact with water molecules.

A student heats a sample of hydrated calcium sulfate, \(\text{CaSO}_4 \cdot x\text{H}_2\text{O}\), in a crucible to determine the value of \(x\).

Experimental data:
- Mass of empty crucible = \(18.20\text{ g}\)
- Mass of crucible + hydrated salt = \(21.64\text{ g}\)
- Mass of crucible + anhydrous salt after heating to constant mass = \(20.92\text{ g}\)

What is the value of \(x\) based on this experimental data? (Molar masses: \(\text{CaSO}_4 = 136.1\text{ g mol}^{-1}\), \(\text{H}_2\text{O} = 18.0\text{ g mol}^{-1}\))

During the purification of crude cyclohexene prepared from cyclohexanol, the crude liquid is shaken with saturated sodium chloride solution (brine) in a separating funnel. What is the primary purpose of this step?

A student investigates the kinetics of a clock reaction at different temperatures. A plot of \(\ln(\text{rate})\) against \(\frac{1}{T}\) (where temperature \(T\) is in Kelvin) yields a straight line with a gradient of \(-6120\text{ K}\).

What is the activation energy, \(E_a\), for this reaction?
\((R = 8.31\text{ J K}^{-1}\text{ mol}^{-1})\)

A student wants to measure the standard electrode potential of the \(\text{Fe}^{3+}(\text{aq}) / \text{Fe}^{2+}(\text{aq})\) half-cell. Which of the following describes the correct experimental setup for this half-cell?

In an experiment to determine the molar volume of a gas, a student reacts a known mass of magnesium ribbon with excess hydrochloric acid and collects the hydrogen gas in a gas syringe.

If a small amount of hydrogen gas escapes from the delivery tube before the stopper is fully inserted, how will this affect the calculated molar volume of the gas?

An unknown transition metal compound \(\text{Y}\) is dissolved in water to form a pale blue solution. When aqueous ammonia is added dropwise, a pale blue precipitate is formed. Upon adding excess aqueous ammonia, this precipitate dissolves to form a deep blue solution.

Identify the formula of the complex ion present in the final deep blue solution.

In a calorimetry experiment, \(50.0\text{ cm}^3\) of \(1.00\text{ mol dm}^{-3}\text{ HCl}\) is mixed with \(50.0\text{ cm}^3\) of \(1.00\text{ mol dm}^{-3}\text{ NaOH}\) in a polystyrene cup. The temperature of the mixture rises by \(6.5\text{ }^\circ\text{C}\).

What is the enthalpy change of neutralisation, \(\Delta H_{\text{neut}}\), in \(\text{kJ mol}^{-1}\)?
(Assume the density of the solution is \(1.00\text{ g cm}^{-3}\) and its specific heat capacity is \(4.18\text{ J g}^{-1}\text{ K}^{-1}\).)

A student tests an aqueous solution containing halide ions. On adding dilute nitric acid followed by silver nitrate solution, a cream precipitate is formed.

Which reagent should the student add next, and what observation would confirm the identity of the halide ion?

A student carries out a titration using a Class B burette which has an uncertainty of \(\pm 0.05 \text{ cm}^3\) per reading. The initial burette reading is \(0.15 \text{ cm}^3\) and the final reading is \(24.35 \text{ cm}^3\). What is the percentage uncertainty in the calculated titre volume?

During the preparation and purification of a liquid organic product, cyclohexene, a student uses anhydrous calcium chloride to dry the organic layer. Which of the following is the correct observation when the organic liquid is fully dry, and what is the correct subsequent step?

In an iodine clock reaction used to study chemical kinetics, which of the following describes the role of sodium thiosulfate (\(\text{Na}_2\text{S}_2\text{O}_3\)) and starch indicator?

A student heated a \(2.50\text{ g}\) sample of an anhydrous Group 2 metal carbonate, \(\text{MCO}_3\), until constant mass to determine the identity of \(\text{M}\). The final mass of the Group 2 metal oxide (\(\text{MO}\)) obtained was \(1.40\text{ g}\). Identify the metal \(\text{M}\). (Atomic masses: \(\text{C} = 12.0\), \(\text{O} = 16.0\), \(\text{Mg} = 24.3\), \(\text{Ca} = 40.1\), \(\text{Sr} = 87.6\), \(\text{Ba} = 137.3\))

A student uses a colorimeter to determine the concentration of copper(II) ions in an aqueous solution. Which filter color should be selected for the colorimeter, and what is the chemical justification?

A student runs a thin-layer chromatography (TLC) experiment to separate a mixture of amino acids. The solvent front travels \(8.0\text{ cm}\) and one of the amino acid spots (X) travels \(3.6\text{ cm\). Which of the following shows the correct \(R_f\) value for spot X and the correct method for locating the spots?

A bomb calorimeter is calibrated by burning \(0.500\text{ g}\) of benzoic acid (molar mass = \(122.1\text{ g mol}^{-1}\); enthalpy of combustion \(\Delta_c H = -3227\text{ kJ mol}^{-1}\)). The temperature of the calorimeter increases by \(2.45\text{ K}\). What is the heat capacity of the calorimeter in \(\text{kJ K}^{-1}\)?

A student weighs out \(1.624\text{ g}\) of hydrated copper(II) malonate, \(\text{Cu}(C_3H_2O_4) \cdot xH_2O\). The salt is dissolved in deionised water and made up to \(250.0\text{ cm}^3\) in a volumetric flask. A \(25.0\text{ cm}^3\) aliquot of this solution is transferred to a conical flask, and an excess of potassium iodide, \(\text{KI}\), is added. The liberated iodine is titrated with \(0.0400\text{ mol dm}^{-3}\) sodium thiosulfate solution, \(\text{Na}_2\text{S}_2\text{O}_3\), using starch indicator. The mean titre is \(18.50\text{ cm}^3\). The equations for the reactions are: \(2\text{Cu}^{2+}(aq) + 4\text{I}^{-}(aq) \rightarrow 2\text{CuI}(s) + \text{I}_2(aq)\) and \(\text{I}_2(aq) + 2\text{S}_2\text{O}_3^{2-}(aq) \rightarrow 2\text{I}^{-}(aq) + \text{S}_4\text{O}_6^{2-}(aq)\). (a) Describe the colour change at the end-point of this titration when starch is used. (b) Explain why starch is only added near the end-point, rather than at the start. (c) Calculate the moles of \(\text{Cu}^{2+}\) in the \(25.0\text{ cm}^3\) aliquot and hence the concentration of \(\text{Cu}^{2+}\) in the original volumetric flask. (d) Calculate the value of \(x\) in \(\text{Cu}(C_3H_2O_4) \cdot xH_2O\) to the nearest whole number. [Molar masses: \(\text{Cu} = 63.5\), \(\text{C} = 12.0\), \(\text{H} = 1.0\), \(\text{O} = 16.0\)]

A student synthesises cyclohexene by the dehydration of cyclohexanol using concentrated phosphoric acid. The procedure is: 1. Place \(10.0\text{ cm}^3\) of cyclohexanol (density = \(0.962\text{ g cm}^{-3}\)) and \(4\text{ cm}^3\) of concentrated phosphoric(V) acid into a round-bottomed flask. Add anti-bumping granules. 2. Heat the mixture and distil off the liquid boiling below \(100^\circ\text{C}\). 3. Transfer the distillate to a separating funnel, wash with saturated sodium chloride solution, and discard the aqueous layer. 4. Transfer the organic layer to a conical flask, add an anhydrous inorganic salt to dry it, then decant the liquid. 5. Distil the dry liquid and collect the fraction boiling between \(81\text{--}83^\circ\text{C}\) to obtain \(4.12\text{ g}\) of pure cyclohexene. (a) Explain the purpose of the anti-bumping granules. (b) Explain why sodium hydrogencarbonate solution is preferred over sodium chloride solution by some students if traces of acid carried over, and write an ionic equation for this reaction. (c) State the name of a suitable anhydrous inorganic salt that could be used as a drying agent in step 4, and describe how the student would know the cyclohexene is dry. (d) Calculate the percentage yield of cyclohexene achieved in this synthesis. [Molar masses: Cyclohexanol, \(C_6H_{11}OH = 100.0\text{ g mol}^{-1}\); Cyclohexene, \(C_6H_{10} = 82.0\text{ g mol}^{-1}\)]

A student wants to prepare a buffer solution with a pH of 4.85. They have access to \(0.200\text{ mol dm}^{-3}\) propanoic acid (\(CH_3CH_2COOH\), \(K_a = 1.35 \times 10^{-5}\text{ mol dm}^{-3}\)) and solid sodium propanoate (\(CH_3CH_2COONa\), \(M_r = 96.0\)). (a) Define the term 'buffer solution'. (b) Calculate the mass of sodium propanoate that must be dissolved in \(500\text{ cm}^3\) of the \(0.200\text{ mol dm}^{-3}\) propanoic acid to obtain a buffer solution of pH 4.85. Assume that the addition of solid sodium propanoate does not change the volume of the solution. (c) Write an ionic equation to show how this buffer solution minimises pH changes when a small amount of aqueous nitric acid is added.

A student investigates the kinetics of the reaction between peroxodisulfate(VIII) ions, \(S_2O_8^{2-}\), and iodide ions, \(I^-\), by a clock reaction. They determine the rate constant, \(k\), at several different absolute temperatures, \(T\). The student plots a graph of \(\ln(k)\) against \(\frac{1}{T}\). The gradient of the line of best fit is determined to be \(-6450\text{ K}\). (a) Write the Arrhenius equation in logarithmic form, explaining the meaning of all terms. (b) Calculate the activation energy, \(E_a\), for this reaction in \(\text{kJ mol}^{-1}\) to 3 significant figures. (Gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\)) (c) The rate-determining step for this reaction is: \(S_2O_8^{2-}(aq) + I^-(aq) \rightarrow \text{intermediate products}\). Explain why this step is slow, referring to collision theory and the charges of the reacting ions.

An organic compound X has the molecular formula \(C_4H_8O_2\). A student is given the following spectroscopic data: - The IR spectrum of X shows a strong, sharp absorption at \(1740\text{ cm}^{-1}\), but no broad absorption in the region \(2500\text{--}3300\text{ cm}^{-1}\) or \(3200\text{--}3600\text{ cm}^{-1}\). - The \(^1\text{H}\) NMR spectrum of X displays three environments: a triplet at \(\delta = 1.25\text{ ppm}\) (relative area 3), a singlet at \(\delta = 2.05\text{ ppm}\) (relative area 3), and a quartet at \(\delta = 4.12\text{ ppm}\) (relative area 2). - In the mass spectrum, there is a prominent peak at \(m/z = 43\). (a) Identify the functional group present in X using the IR data. State which bonds are responsible for this and the one that is clearly absent. (b) Explain the splitting patterns and relative areas of the three peaks in the \(^1\text{H}\) NMR spectrum, including the structural fragments they represent. (c) Deduce the structural formula of X and identify the fragment responsible for the peak at \(m/z = 43\).

A student uses a colorimeter to determine the concentration of copper(II) ions in an unknown solution. To make the colour more intense, they add excess ammonia to form the deep-blue complex \([\text{Cu}(\text{H}_2\text{O})_2(\text{NH}_3)_4]^{2+}\). (a) Write the balanced equation for the reaction of \([\text{Cu}(\text{H}_2\text{O})_6]^{2+}\) with excess aqueous ammonia, and state the type of reaction. (b) Describe how a student would use a colorimeter and standard solutions of copper(II) ions to find the concentration of an unknown copper(II) solution. (c) Suggest, with a reason, a suitable colour of filter that should be used in the colorimeter for this analysis. (d) State why colorimetry is a more suitable method for determining low concentrations of copper(II) ions than gravimetric analysis.

A student prepares methyl 3-nitrobenzoate by nitrating methyl benzoate using a mixture of concentrated nitric acid and concentrated sulfuric acid. (a) Write the equations showing how the active electrophile, \(\text{NO}_2^+\), is generated in the nitrating mixture. (b) Explain why the temperature must be kept below \(15^\circ\text{C}\) during the addition of the nitrating mixture. (c) Describe the practical steps required to carry out the recrystallisation of the crude methyl 3-nitrobenzoate.

A student is asked to determine the experimental lattice energy of calcium chloride, \(\text{CaCl}_2\), using a Born-Haber cycle and the following thermodynamic data: Enthalpy of atomisation of calcium, \(\Delta H_{\text{at}}^\ominus[\text{Ca}(s)] = +178\text{ kJ mol}^{-1}\); First ionisation energy of calcium, \(\text{IE}_1[\text{Ca}] = +590\text{ kJ mol}^{-1}\); Second ionisation energy of calcium, \(\text{IE}_2[\text{Ca}] = +1145\text{ kJ mol}^{-1}\); Enthalpy of atomisation of chlorine, \(\Delta H_{\text{at}}^\ominus[\text{Cl}_2(g)] = +122\text{ kJ mol}^{-1}\); Electron affinity of chlorine, \(\text{EA}[\text{Cl}] = -349\text{ kJ mol}^{-1}\); Enthalpy of formation of calcium chloride, \(\Delta H_f^\ominus[\text{CaCl}_2(s)] = -796\text{ kJ mol}^{-1}\). (a) Define the term 'lattice energy'. (b) Calculate the experimental lattice energy, \(\Delta H_{\text{latt}}^\ominus\), of \(\text{CaCl}_2(s)\) (defined as the formation of the solid lattice from gaseous ions). (c) The theoretical lattice energy of \(\text{CaCl}_2\) calculated using an ionic model is \(-2223\text{ kJ mol}^{-1}\). Explain why the experimental value differs from this theoretical value, and what this tells us about the bonding in calcium chloride.

A student carried out an experiment to determine the percentage by mass of copper in a sample of brass.

The student used the following procedure:
1. Weigh out exactly \(2.00\text{ g}\) of brass into a beaker.
2. Dissolve the brass sample in a minimum volume of concentrated nitric acid.
3. Transfer the resulting solution and washings to a volumetric flask and make up to the mark with deionised water so that the total volume is \(250.0\text{ cm}^3\).
4. Pipette \(25.0\text{ cm}^3\) of this solution into a conical flask and neutralize excess acid by adding sodium carbonate solution dropwise until a faint precipitate forms, then dissolve it with a few drops of ethanoic acid.
5. Add an excess of potassium iodide solution to the flask.
6. Titrate the liberated iodine with \(0.100\text{ mol dm}^{-3}\) sodium thiosulfate solution.

(a) State **one** safety precaution, other than wearing safety goggles and a lab coat, that must be taken in Step 2, and explain why it is necessary. (2 marks)

(b) Write the ionic equation for the reaction occurring in Step 5. State symbols are not required. (1 mark)

(c) Describe how the student should use starch indicator in the titration in Step 6 to determine the end-point accurately. Include the stage at which the indicator is added and the colour change observed at the end-point. (3 marks)

(d) The student repeated the titration and obtained a mean titre of \(22.00\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) sodium thiosulfate solution.
Calculate the percentage by mass of copper in the brass sample. Give your answer to three significant figures.
The relative atomic mass of copper, \(A_r(Cu) = 63.5\). (3 marks)

The reaction between propanone and iodine in acidic conditions is represented by the equation:
\(CH_3COCH_3(aq) + I_2(aq) \xrightarrow{H^+(aq)} CH_3COCH_2I(aq) + H^+(aq) + I^-(aq)\)

A student investigated the kinetics of this reaction.

(a) (i) Explain why the samples withdrawn at regular intervals must be 'quenched' immediately. (1 mark)
(ii) Suggest a reagent that could be added to quench the reaction. Explain how this reagent stops the reaction, writing an ionic equation for the process. (3 marks)

(b) In an alternative method, the student used a colorimeter to monitor the concentration of iodine continuously. Explain how a colorimeter can be used to monitor the concentration of iodine over time, including how the absorbance data is converted into concentration. (2 marks)

(c) The initial concentration of acid was held constant at \([H^+] = 0.0500\text{ mol dm}^{-3}\). The following initial rates were obtained:

| Experiment | Initial \([CH_3COCH_3]\) / \(\text{mol dm}^{-3}\) | Initial \([I_2]\) / \(\text{mol dm}^{-3}\) | Initial rate / \(\text{mol dm}^{-3}\text{ s}^{-1}\) |
| :--- | :--- | :--- | :--- |
| 1 | \(0.400\) | \(0.00200\) | \(1.20 \times 10^{-5}\) |
| 2 | \(0.800\) | \(0.00200\) | \(2.40 \times 10^{-5}\) |
| 3 | \(0.800\) | \(0.00400\) | \(2.40 \times 10^{-5}\) |

Using these data:
- Deduce the order of reaction with respect to propanone and with respect to iodine.
- Given that the reaction is first-order with respect to \(H^+\), write the overall rate equation.
- Calculate the rate constant, \(k\), using the data from Experiment 1, and state its units. (3 marks)