2022 HKDSE Chemistry Practice Paper | DSE Mock

Consider the polymer formed by the condensation polymerisation of 2-hydroxybutanoic acid: (1) It contains ester linkages. (2) It is biodegradable via hydrolysis. (3) Its empirical formula is the same as that of 2-hydroxybutanoic acid. Which of the above statements are correct?

Given the standard enthalpies of combustion: \(\Delta H_c^\theta [\text{C(graphite)}] = -394\text{ kJ mol}^{-1}\), \(\Delta H_c^\theta [\text{H}_2\text{(g)}] = -286\text{ kJ mol}^{-1}\), \(\Delta H_c^\theta [\text{CH}_3\text{CH(OH)CH}_3\text{(l)}] = -2006\text{ kJ mol}^{-1}\). What is the standard enthalpy of formation of propan-2-ol(l)?

Which of the following reaction pathways is most suitable for preparing ethyl propanoate starting from propan-1-ol?

Which of the following lists the species in order of decreasing bond angle?

Which of the following statements concerning the electrolysis of concentrated sodium chloride solution using inert carbon electrodes is correct?

The rate constant, \(k\), of a reaction is measured at different temperatures. A plot of \(\ln k\) against \(\frac{1}{T}\) (where \(T\) is the absolute temperature in Kelvin) yields a straight line with a slope of \(-1.20 \times 10^4\text{ K}\). What is the activation energy (\(E_a\)) of this reaction? (Given: Gas constant, \(R = 8.31\text{ J mol}^{-1}\text{ K}^{-1}\))

Which of the following statements about transition metals and their compounds is/are correct? (1) Aqueous \(\text{Cu}^{2+}\) ions are blue because they absorb orange-red light during d-d electron transition. (2) Zinc is classified as a transition metal because it is in the d-block of the Periodic Table. (3) Transition metals often exhibit variable oxidation states because the energy difference between the 4s and 3d subshells is relatively small.

Which of the following substances has the highest boiling point?

Consider a hydrogen-oxygen fuel cell using a hot aqueous potassium hydroxide (\(\text{KOH(aq)}\)) electrolyte. Which of the following statements is correct?

A \(1.00\text{ g}\) sample of impure calcium carbonate was reacted with \(50.0\text{ cm}^3\) of \(0.500\text{ mol dm}^{-3}\text{ HCl(aq)}\). The excess acid required \(40.0\text{ cm}^3\) of \(0.250\text{ mol dm}^{-3}\text{ NaOH(aq)}\) for complete neutralization. What is the percentage by mass of calcium carbonate (\(\text{CaCO}_3\)) in the sample? (Molar mass of \(\text{CaCO}_3 = 100.1\text{ g mol}^{-1}\))

Given the standard enthalpy changes of combustion of carbon, hydrogen, and propene are \(-394\text{ kJ mol}^{-1}\), \(-286\text{ kJ mol}^{-1}\), and \(-2058\text{ kJ mol}^{-1}\) respectively. What is the standard enthalpy change of formation of propene (\(\text{C}_3\text{H}_6(g)\))?

A section of a polymer is shown below:\n\text{—CO—(CH}_2)_4\text{—CONH—(CH}_2)_6\text{—NH—}\nWhich of the following statements is/are correct?\n(1) It is a polyamide.\n(2) It is formed by addition polymerisation.\n(3) Its monomers are hexanedioic acid and hexane-1,6-diamine.

Consider the following reaction sequence:\n\text{Propene} \rightarrow \text{X} \rightarrow \text{Propan-2-ol} \rightarrow \text{Y}\nwhere X is formed by reacting propene with \text{HBr}(g) under dark conditions, and Y is formed by heating propan-2-ol with acidified potassium dichromate solution.\nWhat are the structural formulae of X and Y?

Which of the following lists the species in order of decreasing bond angle?

During the electrolysis of concentrated sodium chloride solution using carbon electrodes, which of the following statements are correct?\n(1) A pale green gas with a choking smell is evolved at the anode.\n(2) The pH of the electrolyte increases overall.\n(3) Oxygen gas is evolved at the cathode.

The rate constant \(k\) of a certain first-order reaction is measured at different temperatures. A plot of \(\ln k\) against \(\frac{1}{T}\) (where \(T\) is in Kelvin) yields a straight line with a slope of \(-1.20 \times 10^4\text{ K}\). What is the activation energy (\(E_a\)) of this reaction?\n(Given: Gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\))

Which of the following compounds has the highest boiling point?

Metal X reacts with cold water to liberate hydrogen. Metal Y does not react with steam, but its oxide can be reduced by heating with carbon. Metal Z does not react with dilute hydrochloric acid, but can be obtained by heating its oxide alone. What is the order of reactivity of these metals in decreasing order?

In which of the following reactions does the underlined substance act as a reducing agent?

Consider the following gaseous equilibrium system in a closed container of fixed volume at temperature \(T\):\n2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g) \quad \Delta H < 0\nIf the temperature of the system is increased while keeping the volume constant, which of the following statements is correct?

An organic compound \(X\) has the molecular formula \(C_4H_8O\). \(X\) does not react with acidified \(K_2Cr_2O_7\)(aq), nor does it react with \(NaHCO_3\)(aq). However, \(X\) rapidly decolourises bromine in \(CH_2Cl_2\) in the dark. Which of the following is the most likely structure of \(X\)?

Given the following standard enthalpy changes of combustion (\(\Delta H^{\theta}_c\)) at \(298 \text{ K}\):\n\(C(s, \text{graphite}) = -393.5 \text{ kJ mol}^{-1}\)\n\(H_2(g) = -285.8 \text{ kJ mol}^{-1}\)\n\(C_3H_6(g) = -2058.0 \text{ kJ mol}^{-1}\)\nWhat is the standard enthalpy change of formation of propene (\(C_3H_6(g)\))?

Polylactide (PLA) is a synthetic polymer with the following repeating unit:\n\(-[O-CH(CH_3)-CO]_n-\)\nWhich of the following statements about PLA are correct?\n(1) It is biodegradable because its ester linkages can be hydrolysed.\n(2) It is a thermoplastic polymer.\n(3) The monomer used to prepare PLA contains a chiral carbon atom.

An oxide of chlorine contains 42.5% chlorine by mass. Which of the following is the empirical formula of this oxide?\n(Relative atomic masses: O = 16.0, Cl = 35.5)

During the electrolysis of concentrated sodium chloride solution (brine) using carbon electrodes, which of the following combinations correctly describes the product at the anode, the product at the cathode, and the change in pH of the solution around the cathode?

The rate constant \(k\) of a first-order reaction was measured at several temperatures. A plot of \(\ln k\) against \(\frac{1}{T}\) (where \(T\) is the absolute temperature in \(\text{K}\)) yields a straight line with a slope of \(-1.20 \times 10^4 \text{ K}\). What is the activation energy (\(E_a\)) of this reaction?\n(Universal gas constant \(R = 8.31 \text{ J mol}^{-1} \text{ K}^{-1}\))

Which of the following statements concerning transition metals and their compounds are correct?\n(1) They can exhibit variable oxidation states in their compounds.\n(2) Most of their aqueous ions are coloured.\n(3) They can act as catalysts in various chemical reactions.

Consider the following compounds:\n(1) Propan-1-ol\n(2) Propanal\n(3) Butane\nWhich of the following outlines the correct order of decreasing boiling points of these compounds?

A mixture of \(NO_2(g)\) (brown) and \(N_2O_4(g)\) (colourless) is at equilibrium in a gas syringe:\n\(2NO_2(g) \rightleftharpoons N_2O_4(g) \quad \Delta H < 0\)\nIf the piston of the syringe is suddenly pushed in to halve the volume of the gas mixture at constant temperature, what is the change in the appearance of the mixture?

In the industrial purification of copper using electrolysis, an impure copper block containing zinc, silver, and gold impurities is used as the anode, and a pure copper sheet is used as the cathode in a copper(II) sulphate electrolyte.\nWhich of the following statements about this process are correct?\n(1) Zinc is oxidized at the anode and remains in the solution as \(Zn^{2+}(aq)\).\n(2) Silver and gold are not oxidized and settle at the bottom as anode slime.\n(3) The concentration of \(Cu^{2+}(aq)\) in the electrolyte decreases gradually.

An organic compound \(W\) has the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\). Upon heating under reflux with dilute sodium hydroxide, it forms two products, \(P\) and \(Q\). Product \(P\) can be oxidized by acidified \(\text{K}_2\text{Cr}_2\text{O}_7\text{(aq)}\) to form a ketone. What is the IUPAC name of compound \(W\)?

Consider the following thermochemical equations: (1) \(\text{C(graphite)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} \quad \Delta H_1 = -393.5\text{ kJ mol}^{-1}\) (2) \(\text{H}_2\text{(g)} + \frac{1}{2}\text{O}_2\text{(g)} \rightarrow \text{H}_2\text{O(l)} \quad \Delta H_2 = -285.8\text{ kJ mol}^{-1}\) (3) \(2\text{C}_2\text{H}_2\text{(g)} + 5\text{O}_2\text{(g)} \rightarrow 4\text{CO}_2\text{(g)} + 2\text{H}_2\text{O(l)} \quad \Delta H_3 = -2598.8\text{ kJ mol}^{-1}\) What is the standard enthalpy change of formation of ethyne, \(\text{C}_2\text{H}_2\text{(g)}\)?

A segment of a synthetic addition polymer has the following structure: \(-\text{CH}_2-\text{CH(Cl)}-\text{CH}_2-\text{CH(Cl)}-\text{CH}_2-\text{CH(Cl)}-\) Which of the following statements about this polymer and its monomer is/are correct? (1) The monomer of this polymer is chloroethene. (2) The polymer can be softened by heating. (3) The monomer contains a carbon-carbon double bond with cis-trans isomerism.

Which of the following chemical species has a trigonal pyramidal molecular shape?

An aqueous solution of concentrated sodium chloride (brine) is electrolyzed using carbon electrodes. Which of the following combinations correctly describes the observations/products at the electrodes and the change in pH of the solution around the cathode? (Format: Cathode product / Anode product / pH around the cathode)

The rate constant, \(k\), of a certain reaction was measured at different temperatures, \(T\). A plot of \(\ln k\) against \(\frac{1}{T}\) yields a straight line with a slope of \(-1.20 \times 10^4\text{ K}\). What is the activation energy (\(E_{\text{a}}\)) of the reaction? (Given: gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\))

A student set up an experiment to determine the enthalpy change of combustion of propan-1-ol (\( \text{CH}_3\text{CH}_2\text{CH}_2\text{OH} \)). Inside a copper calorimeter, \( 150.0\text{ g} \) of water was heated. Burning \( 0.90\text{ g} \) of propan-1-ol caused the water temperature to rise by \( 32.5 ^\circ\text{C} \).\n(a) Calculate the experimental enthalpy change of combustion of propan-1-ol. (Specific heat capacity of water = \( 4.2\text{ J g}^{-1}\text{ K}^{-1} \); molar mass of propan-1-ol = \( 60.0\text{ g mol}^{-1} \))\n(b) Suggest TWO reasons why the experimental value is less exothermic than the literature value.\n(c) Suggest one modification to the experimental setup to improve accuracy.

A student proposed a synthesis of 1,2-dibromocyclohexane from cyclohexanone via cyclohexene.\n(a) Suggest reagents and reaction conditions to convert cyclohexanone to cyclohexanol, and then cyclohexanol to cyclohexene.\n(b) State the type of reaction involved in the conversion of cyclohexanol to cyclohexene.\n(c) Suggest reagents and conditions to convert cyclohexene to 1,2-dibromocyclohexane. Describe the expected color change during this reaction.

Polylactic acid (PLA) is a biodegradable polymer synthesized from lactic acid (\( \text{CH}_3\text{CH(OH)COOH} \)).\n(a) Draw the repeating unit of PLA.\n(b) Explain why PLA is biodegradable whereas polyethene is non-biodegradable in terms of structure and chemical properties.\n(c) State one environmental advantage of using PLA over traditional plastics like polyethene, other than decreasing landfill accumulation.

Consider nitrogen trifluoride (\( \text{NF}_3 \)) and boron trifluoride (\( \text{BF}_3 \)).\n(a) Draw the electron diagram (showing octet electrons where appropriate) for both molecules.\n(b) State the shape and bond angle of each molecule. Explain the difference in their shapes in terms of the Valence Shell Electron Pair Repulsion (VSEPR) theory.\n(c) Determine whether each molecule is polar or non-polar. Explain.

Electrolysis of concentrated sodium chloride solution (brine) is an important industrial process.\n(a) Draw a labelled diagram of a laboratory setup for the electrolysis of concentrated sodium chloride solution using carbon electrodes.\n(b) Write the half-equations for the reactions occurring at the anode and the cathode respectively.\n(c) Explain the change in pH of the electrolyte in the vicinity of the cathode as the electrolysis proceeds.\n(d) Give one industrial use of the gas produced at the anode.

The decomposition of nitrogen dioxide has rate constants of \( 1.3 \times 10^{-3}\text{ dm}^3\text{ mol}^{-1}\text{ s}^{-1} \) at \( 600\text{ K} \) and \( 2.3 \times 10^{-2}\text{ dm}^3\text{ mol}^{-1}\text{ s}^{-1} \) at \( 650\text{ K} \).\n(a) Using the Arrhenius equation \( \ln\left(\frac{k_2}{k_1}\right) = -\frac{E_a}{R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right) \), calculate the activation energy (\( E_a \)) of the reaction in \( \text{kJ mol}^{-1} \).\n(Gas constant \( R = 8.31\text{ J K}^{-1}\text{ mol}^{-1} \))\n(b) Briefly explain how a catalyst increases the rate of this reaction with reference to the activation energy.

Hydrazine (\( \text{N}_2\text{H}_4 \)) is a liquid used as a rocket propellant.\nUsing the following standard enthalpy changes of combustion (\( \Delta H_c^
ormal_standard \)):\n\( \text{H}_2(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{H}_2\text{O}(\text{l}) \quad \Delta H_c^
ormal_standard = -286\text{ kJ mol}^{-1} \)\n\( \text{N}_2\text{H}_4(\text{l}) + \text{O}_2(\text{g}) \rightarrow \text{N}_2(\text{g}) + 2\text{H}_2\text{O}(\text{l}) \quad \Delta H_c^
ormal_standard = -622\text{ kJ mol}^{-1} \)\n(a) Write the chemical equation for the standard enthalpy change of formation (\( \Delta H_f^
ormal_standard \)) of liquid hydrazine.\n(b) Construct an enthalpy change cycle (Hess's Law cycle) linking the formation of hydrazine with the combustion reactions.\n(c) Calculate the standard enthalpy change of formation of liquid hydrazine.

There are three isomeric organic compounds: propanone, propanal, and prop-2-en-1-ol.\n(a) Draw the structural formula for each compound.\n(b) Describe one chemical test (reagent and observation) that can distinguish propanal from propanone.\n(c) Describe one chemical test (reagent and observation) that can distinguish prop-2-en-1-ol from both propanone and propanal.

Silicon dioxide (\( \text{SiO}_2 \)) and carbon dioxide (\( \text{CO}_2 \)) are both oxides of Group IV elements, but they exhibit very different physical properties.\n(a) Compare the melting point of silicon dioxide and carbon dioxide, and explain the difference in terms of structure and bonding.\n(b) State and explain whether silicon dioxide can conduct electricity in the molten state.

Kevlar is a high-strength synthetic polyamide used in bulletproof vests.\n(a) Draw the structures of the TWO monomers used to synthesize Kevlar.\n(b) State the type of polymerisation involved in the synthesis of Kevlar.\n(c) Explain how intermolecular forces between adjacent polymer chains contribute to the exceptionally high tensile strength of Kevlar.

An experiment was conducted to determine the enthalpy change of the decomposition of lithium hydrogencarbonate:
\(2LiHCO_3(s) \rightarrow Li_2CO_3(s) + CO_2(g) + H_2O(l)\)

(a) Describe how to measure the temperature change when solid \(LiHCO_3(s)\) is added to excess hydrochloric acid in a polystyrene cup, and state one precaution to minimize heat loss. (3 marks)

(b) In an experiment, \(3.40\text{ g}\) of \(LiHCO_3(s)\) (molar mass = \(68.0\text{ g mol}^{-1}\)) was added to \(50.0\text{ cm}^3\) of \(1.0\text{ M } HCl(aq)\) in a polystyrene cup. The temperature of the mixture decreased from \(21.5\ ^\circ\text{C}\) to \(17.2\ ^\circ\text{C}\). Calculate the enthalpy change of this reaction, \(\Delta H_2\), in \(\text{kJ mol}^{-1}\).
\(\quad LiHCO_3(s) + HCl(aq) \rightarrow LiCl(aq) + CO_2(g) + H_2O(l) \quad \Delta H_2\)
(Assume the mass of the final mixture is \(50.0\text{ g}\), and its specific heat capacity is \(4.2\text{ J g}^{-1}\ \text{K}^{-1}\).) (2.46 marks)

(c) Given that the enthalpy change for the reaction of solid \(Li_2CO_3\) with hydrochloric acid is \(\Delta H_1 = -25.0\text{ kJ mol}^{-1}\):
\(\quad Li_2CO_3(s) + 2HCl(aq) \rightarrow 2LiCl(aq) + CO_2(g) + H_2O(l) \quad \Delta H_1\)
Calculate the enthalpy change of the decomposition of lithium hydrogencarbonate. (1 mark)

PLGA is a synthetic copolymer used in medical applications, such as biodegradable surgical sutures. It is synthesized from glycolic acid (\(HO-CH_2-COOH\)) and lactic acid (\(HO-CH(CH_3)-COOH\)).

(a) State the type of polymerisation involved in the formation of PLGA. Draw the structure of the repeating unit of PLGA containing one unit of glycolic acid and one unit of lactic acid. (2.46 marks)

(b) Explain, in terms of structure, why PLGA is biodegradable, whereas polyethene is non-biodegradable. (2 marks)

(c) The degradation rate of PLGA can be adjusted by changing the ratio of the two monomers. Explain why a copolymer with a higher proportion of lactic acid degrades more slowly. (2 marks)

The thermal decomposition of dinitrogen pentoxide is a first-order reaction:
\(2N_2O_5(g) \rightarrow 4NO_2(g) + O_2(g)\)

(a) State the meaning of the term "activation energy". (1 mark)

(b) The rate constants (\(k\)) of this reaction at two different temperatures are measured:
- At \(298\text{ K}\), \(k_1 = 3.46 \times 10^{-5}\text{ s}^{-1}\)
- At \(328\text{ K}\), \(k_2 = 1.50 \times 10^{-3}\text{ s}^{-1}\)

Calculate the activation energy (\(E_a\)) for this reaction in \(\text{kJ mol}^{-1}\).
(Given: Gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\)) (3.46 marks)

(c) The enthalpy change (\(\Delta H\)) for this reaction is \(-110\text{ kJ mol}^{-1}\). Sketch a labelled energy profile for this reaction. Label the activation energy (\(E_a\)) and the enthalpy change (\(\Delta H\)) on your diagram. (2 marks)

This question consists of three parts: (a), (b), and (c).

**Part (a)**
The rate constant \(k\) for the catalytic dehydration of methanol to dimethyl ether (\(2\text{CH}_3\text{OH}(g) \rightarrow \text{CH}_3\text{OCH}_3(g) + \text{H}_2\text{O}(g)\)) over an acidic alumina catalyst was measured at two different temperatures:
- At \(523\text{ K}\), \(k_1 = 1.45 \times 10^{-3}\text{ s}^{-1}\)
- At \(573\text{ K}\), \(k_2 = 1.12 \times 10^{-2}\text{ s}^{-1}\)
Calculate the activation energy (\(E_a\)) for this reaction in \(\text{kJ mol}^{-1}\).
(Given: Gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\)) (6 marks)

**Part (b)**
The dehydration of methanol to dimethyl ether is a reversible exothermic reaction:
\[2\text{CH}_3\text{OH}(g) \rightleftharpoons \text{CH}_3\text{OCH}_3(g) + \text{H}_2\text{O}(g) \quad \Delta H < 0\]
(i) Predict and explain the effect of increasing the pressure on the equilibrium yield of dimethyl ether. (3 marks)
(ii) In industry, the reaction is typically operated at a temperature of around \(250 - 300^\circ\text{C}\) (\(523 - 573\text{K}\)) rather than at room temperature. Explain why from both kinetic and thermodynamic viewpoints. (3 marks)

**Part (c)**
(i) State the function of the acidic alumina catalyst in terms of the reaction pathway and activation energy. (2 marks)
(ii) Calculate the atom economy of this synthesis of dimethyl ether, assuming dimethyl ether is the only desired product.
(Relative atomic masses: \(\text{H} = 1.0\), \(\text{C} = 12.0\), \(\text{O} = 16.0\)) (3 marks)
(iii) Discuss TWO green chemistry principles (other than atom economy) that are illustrated by or can be applied to this industrial production of dimethyl ether from methanol. (3 marks)

This question consists of two parts: (a) and (b).

**Part (a)**
An organic liquid compound \(W\) with molecular formula \(\text{C}_4\text{H}_8\text{O}_2\) was isolated from a fruit extract.
(i) The infrared (IR) spectrum of \(W\) shows a strong, sharp absorption peak at \(1735\text{ cm}^{-1}\), but does not show any broad absorption in the region \(2500 - 3300\text{ cm}^{-1}\) or \(3230 - 3670\text{ cm}^{-1}\). Deduce the functional group present in \(W\). (2 marks)
(ii) The mass spectrum of \(W\) shows a molecular ion peak at \(m/z = 88\) and a significant fragment peak at \(m/z = 57\). Explain how this fragment peak helps deduce the structure of \(W\), and suggest the structural formula of \(W\). (5 marks)

**Part (b)**
A student determined the mass of iron in a dietary supplement tablet by colorimetry.
(i) Briefly explain the principle of colorimetry in quantitative analysis. (2 marks)
(ii) The iron in the tablet exists as iron(II) ions (\(\text{Fe}^{2+}\)). Suggest why an excess of 1,10-phenanthroline (which forms an intensely red-orange complex with \(\text{Fe}^{2+}\)) is added to the sample solution before measuring absorbance. (2 marks)
(iii) Outline how the student can prepare a set of standard solutions and use them to construct a calibration curve. (3 marks)
(iv) A tablet weighing \(0.520\text{ g}\) was dissolved in acid, filtered, and made up to \(250.0\text{ cm}^3\) in a volumetric flask (Solution A). Then, \(10.0\text{ cm}^3\) of Solution A was pipetted into a \(100.0\text{ cm}^3\) volumetric flask, treated with excess 1,10-phenanthroline and buffer, and diluted to the mark with deionized water (Solution B).
Using the calibration curve, the concentration of iron in Solution B was found to be \(3.15\text{ mg dm}^{-3}\).
Calculate:
(1) the mass (in mg) of iron in the tablet. (4 marks)
(2) the percentage by mass of iron in the tablet. (2 marks)