2023 HKDSE Chemistry Practice Paper | DSE Mock

Which of the following species has a molecular shape that is NOT planar?

Consider two monobasic acids at \(25^\circ\text{C}\): Acid X has a pH of 2.0 and Acid Y has a pH of 4.0. Which of the following statements MUST be correct?
(1) Acid X is a stronger acid than Acid Y.
(2) The concentration of \( \text{H}^+(\text{aq}) \) in Acid X is 100 times that in Acid Y.
(3) To completely neutralize the same volume of both acids, a larger volume of \(0.1 \text{ mol dm}^{-3} \text{ NaOH(aq)}\) is required for Acid X than Acid Y.

In which of the following compounds does chlorine have the highest oxidation number?

What is the IUPAC name of the compound \( \text{CH}_3\text{CH(Cl)CH}_2\text{CH(CH}_3\text{)}_2 \)?

Some information about three metals, X, Y and Z, is given below:
- Metal X does not react with dilute hydrochloric acid.
- Metal Y can displace Metal X from its nitrate solution.
- The oxide of metal Z cannot be reduced by heating with carbon, but the oxide of metal Y can.
Which of the following represents the increasing order of reactivity of the three metals?

At a certain temperature, the equilibrium constant \( K_c \) for the reaction \( 2\text{SO}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons 2\text{SO}_3(\text{g}) \) is \( 4.0 \times 10^2 \text{ mol}^{-1}\text{dm}^3 \). What is the equilibrium constant \( K_c \) for the following reaction at the same temperature?
\( \text{SO}_3(\text{g}) \rightleftharpoons \text{SO}_2(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \)

Which of the following statements about catalysts is/are correct?
(1) A catalyst increases the rate of reaction by increasing the average kinetic energy of the reactant molecules.
(2) A catalyst does not alter the enthalpy change (\( \Delta H \)) of the reaction.
(3) A catalyst increases the yield of the products in a reversible reaction.

Consider the following thermochemical equations:
\( \text{C(graphite)} + \text{O}_2(\text{g}) \rightarrow \text{CO}_2(\text{g}) \quad \Delta H = -393.5 \text{ kJ mol}^{-1} \)
\( \text{CO}(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{CO}_2(\text{g}) \quad \Delta H = -283.0 \text{ kJ mol}^{-1} \)
What is the standard enthalpy change of formation of \( \text{CO(g)} \)?

Which of the following statements concerning the elements in the second period of the Periodic Table (from Li to Ne) is correct?

How many structural isomers (excluding stereoisomers) are there for the compound with molecular formula \( \text{C}_4\text{H}_9\text{Br} \)?

Which of the following species has/have a trigonal pyramidal shape?

(1) \(\text{H}_3\text{O}^+\)
(2) \(\text{BF}_3\)
(3) \(\text{NH}_3\)

Metal \(X\) can be extracted from its oxide by heating with carbon. Metal \(Y\) reacts with cold water to give a colorless gas. Metal \(Z\) does not react with dilute hydrochloric acid but reacts with heating in oxygen. Which of the following shows the descending order of reactivity of the three metals?

Consider the following enthalpy changes of formation at \(298\text{ K}\):

\(\Delta H_f^\theta[\text{CO}_2(g)] = -393.5\text{ kJ mol}^{-1}\)
\(\Delta H_f^\theta[\text{H}_2\text{O}(l)] = -285.8\text{ kJ mol}^{-1}\)
\(\Delta H_c^\theta[\text{C}_3\text{H}_8(g)] = -2220.0\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of formation of propane, \(\text{C}_3\text{H}_8(g)\), at \(298\text{ K}\)?

In which of the following reactions does nitrogen undergo both oxidation and reduction (disproportionation)?

Consider the following equilibrium system in a closed container at constant temperature:

\(\text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g) + \text{Cl}_2(g) \quad \Delta H > 0\)

Which of the following changes would increase the value of the equilibrium constant \(K_c\) for this reaction?

An organic compound \(X\) has the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\). It reacts with sodium hydrogencarbonate solution to produce a colorless gas which turns limewater milky. Which of the following is the IUPAC name of \(X\)?

\(25.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) of a weak diprotic acid \(H_2A\) requires \(20.0\text{ cm}^3\) of a sodium hydroxide solution for complete neutralization. What is the concentration of the sodium hydroxide solution?

At \(298\text{ K}\), which of the following aqueous solutions has the lowest pH value?

Which of the following statements concerning transition metals is/are correct?

(1) They have high melting points and high densities compared to Group I metals.
(2) They can form colored compounds.
(3) They can exhibit variable oxidation states in their compounds.

Which of the following compounds can exhibit enantiomerism (optical isomerism)?

Which of the following molecules has/have a net dipole moment of zero?

(1) \( \text{SF}_4 \)
(2) \( \text{BF}_3 \)
(3) \( \text{trans-1,2-dichloroethene} \)

Consider the following experimental results of four metals, W, X, Y and Z:

(1) X can displace Y from \( \text{Y(NO}_3\text{)}_2(\text{aq}) \).
(2) Heating the oxide of X with carbon powder produces no change, whereas heating the oxide of W with carbon powder produces metal W.
(3) Both W and Y react with dilute \( \text{HCl}(\text{aq}) \) to produce hydrogen gas, but W reacts more vigorously.
(4) Metal Z is obtained by heating its oxide alone.

Which of the following shows the descending order of reactivity of the four metals?

When chlorine gas is bubbled into a hot concentrated sodium hydroxide solution, chlorine undergoes disproportionation. What are the oxidation numbers of chlorine in the products formed?

Consider \( 100\text{ cm}^3 \) of \( 0.10\text{ mol dm}^{-3}\ \text{HCl(aq)} \) and \( 100\text{ cm}^3 \) of \( 0.10\text{ mol dm}^{-3}\ \text{CH}_3\text{COOH(aq)} \) at room temperature. Which of the following statements are correct?

(1) Both solutions require the same volume of \( 0.10\text{ mol dm}^{-3}\ \text{NaOH(aq)} \) for complete neutralisation.
(2) Both solutions have the same electrical conductivity.
(3) Both solutions produce the same volume of hydrogen gas when reacted with excess zinc granules.

A \( 1.25\text{ g} \) sample of eggshell was reacted with \( 50.0\text{ cm}^3 \) of \( 0.500\text{ mol dm}^{-3}\ \text{HCl(aq)} \). The excess acid required \( 28.50\text{ cm}^3 \) of \( 0.100\text{ mol dm}^{-3}\ \text{NaOH(aq)} \) for complete neutralisation. What is the percentage by mass of calcium carbonate in the eggshell?

(Molar mass of \( \text{CaCO}_3 = 100.1\text{ g mol}^{-1} \))

Consider the following synthetic route:

\( \text{Propene} \xrightarrow{\text{Step 1}} \text{2-bromopropane} \xrightarrow{\text{Step 2}} \text{Propan-2-ol} \xrightarrow{\text{Step 3}} \text{Propanone} \)

Which of the following combinations of reagents is most suitable?

How many structural isomers (including cyclic compounds) have the molecular formula \( \text{C}_4\text{H}_8 \)?

Given the following standard enthalpy changes of combustion:

\( \Delta H_c^\theta[\text{C(graphite)}] = -393.5\text{ kJ mol}^{-1} \)
\( \Delta H_c^\theta[\text{H}_2(\text{g})] = -285.8\text{ kJ mol}^{-1} \)
\( \Delta H_c^\theta[\text{C}_2\text{H}_2(\text{g})] = -1299.6\text{ kJ mol}^{-1} \)

What is the standard enthalpy change of formation of ethyne (\( \text{C}_2\text{H}_2(\text{g}) \))?

In a closed container of volume \( 2.0\text{ dm}^3 \), \( 1.0\text{ mol} \) of \( \text{PCl}_5(\text{g}) \) is heated to a constant temperature. When the system reaches equilibrium, \( 0.60\text{ mol} \) of \( \text{PCl}_3(\text{g}) \) is found in the container.

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

What is the value of the equilibrium constant \( K_c \) at this temperature?

Which of the following methods is/are suitable for monitoring the rate of the alkaline hydrolysis of ethyl ethanoate?

\( \text{CH}_3\text{COOCH}_2\text{CH}_3(\text{l}) + \text{NaOH}(\text{aq}) \rightarrow \text{CH}_3\text{COONa}(\text{aq}) + \text{CH}_3\text{CH}_2\text{OH}(\text{aq}) \)

(1) Measuring the change in electrical conductivity of the mixture.
(2) Measuring the change in pH of the mixture.
(3) Measuring the change in volume of the mixture.

Consider the following chemical processes:

I. \(\underline{\text{Cr}}_2\text{O}_7^{2-} \rightarrow \text{Cr}^{3+}\)
II. \(\text{H}_2\underline{\text{O}}_2 \rightarrow \text{O}_2\)
III. \(\underline{\text{N}}\text{O}_2 \rightarrow \text{N}_2\text{O}_4\)

Which of the processes involves reduction of the underlined element?

Which of the following species has a trigonal pyramidal shape?

Consider the following reversible reaction at equilibrium in a closed container:

\(2\text{SO}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons 2\text{SO}_3(\text{g})\) \(\Delta H < 0\)

Which of the following changes would increase the value of the equilibrium constant (\(K_c\))?

An organic compound \(X\) has the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\). It reacts with hot sodium hydroxide solution under reflux to give sodium ethanoate and ethanol. What is the structure of \(X\)?

Consider the following thermochemical equations:

\(2\text{C(s)} + 2\text{H}_2\text{(g)} + \text{O}_2\text{(g)} \rightarrow \text{CH}_3\text{COOH(l)}\) \(\Delta H_1\)
\(\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)}\) \(\Delta H_2\)
\(\text{H}_2\text{(g)} + \frac{1}{2}\text{O}_2\text{(g)} \rightarrow \text{H}_2\text{O(l)}\) \(\Delta H_3\)

What is the enthalpy change of combustion of ethanoic acid (\(\text{CH}_3\text{COOH(l)}\))?

A solution is prepared by dissolving \(1.38\text{ g}\) of a metal carbonate (\(\text{M}_2\text{CO}_3\)) in water and making it up to \(250.0\text{ cm}^3\). \(25.0\text{ cm}^3\) of this solution requires \(20.0\text{ cm}^3\) of \(0.100\text{ mol dm}^{-3}\) hydrochloric acid (\(\text{HCl}\)) for complete neutralisation. What is the metal \(\text{M}\)?

(Relative atomic masses: \(\text{Li} = 6.9\), \(\text{Na} = 23.0\), \(\text{K} = 39.1\), \(\text{Rb} = 85.5\), \(\text{C} = 12.0\), \(\text{O} = 16.0\))

Carbonyl chloride (\(\text{COCl}_2\)) is a highly toxic gas. (a) Draw a 3-dimensional representation of a \(\text{COCl}_2\) molecule and state its shape. (b) Explain whether \(\text{COCl}_2\) is a polar molecule with reference to its shape and electronegativity.

A student performs experiments with three metals: Mg, Zn, and Cu. (a) State the expected observations when magnesium ribbon is added to aqueous copper(II) sulfate. (b) Write an ionic equation for the reaction that occurs when zinc is added to copper(II) sulfate solution, and explain why this is a redox reaction in terms of electron transfer.

A 25.00 mL sample of a commercial vinegar brand was diluted to 250.0 mL with deionized water in a volumetric flask. A 25.00 mL aliquot of this diluted solution was titrated against \(0.120\text{ mol dm}^{-3}\) \(\text{NaOH}(aq)\), requiring exactly 18.50 mL of the alkali for complete neutralization. (a) Suggest a suitable indicator for this titration and state the color change at the end point. (b) Calculate the concentration of ethanoic acid in the original commercial vinegar in \(\text{mol dm}^{-3}\).

Consider the carboxylic acid and ester isomers with the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\). (a) Draw the structures of the TWO possible carboxylic acid isomers of this formula and give their systematic names. (b) Draw the structure of an ester isomer with this formula that, upon alkaline hydrolysis followed by acidification, yields methanol as one of the products. State its systematic name.

The following equilibrium exists in an aqueous solution of chromate and dichromate ions: \(2\text{CrO}_4^{2-}(aq) [\text{yellow}] + 2\text{H}^+(aq) \rightleftharpoons \text{Cr}_2\text{O}_7^{2-}(aq) [\text{orange}] + \text{H}_2\text{O}(l)\). (a) Describe and explain the color change of the solution when a few drops of concentrated \(\text{NaOH}(aq)\) are added. (b) State and explain how the equilibrium position shifts when concentrated \(\text{HCl}(aq)\) is added to the mixture.

Given the following standard enthalpy changes of combustion (\(\Delta H_c^\ominus\)): \(\Delta H_c^\ominus[\text{C}(graphite)] = -393.5\text{ kJ mol}^{-1}\), \(\Delta H_c^\ominus[\text{H}_2(g)] = -285.8\text{ kJ mol}^{-1}\), and \(\Delta H_c^\ominus[\text{C}_3\text{H}_7\text{OH}(l)] = -2021.0\text{ kJ mol}^{-1}\). (a) Write the chemical equation representing the standard enthalpy change of formation of propan-1-ol (\(\text{C}_3\text{H}_7\text{OH}(l)\)). (b) Calculate the standard enthalpy change of formation of propan-1-ol.

An aqueous solution of concentrated sodium chloride (brine) is electrolyzed using inert carbon electrodes. (a) State the product formed at the anode and write the half-equation for its formation. (b) Explain why the solution around the cathode becomes alkaline as the electrolysis proceeds.

A student investigates the reaction: \(\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)\). She compares the rate using 5.0 g of large calcium carbonate chips versus 5.0 g of finely powdered calcium carbonate under identical conditions. (a) Sketch a graph to show the volume of \(\text{CO}_2(g)\) collected over time for both reactions on the same axes. Label the curves clearly. (b) Explain the difference in the initial rate of reaction in terms of collision theory.

Silicon and carbon are both Group IV elements in the Periodic Table. However, silicon dioxide (\(\text{SiO}_2\)) has a melting point of over \(1700^\circ\text{C}\) while carbon dioxide (\(\text{CO}_2\)) sublimes at \(-78^\circ\text{C}\). (a) Describe the structure and bonding of silicon dioxide and explain why it has such a high melting point. (b) Describe the structure and bonding of carbon dioxide and explain why it sublimes at a very low temperature.

Poly(phenylethene), commonly known as polystyrene, is produced by the addition polymerisation of phenylethene. (a) Draw the structure of the monomer, phenylethene. (b) Draw the repeating unit of poly(phenylethene). (c) Suggest ONE environmental problem associated with the disposal of polystyrene products, and propose a green solution to mitigate this problem.

A student wanted to determine the percentage by mass of \(\text{CaCO}_3\) in a sample of eggshell. A sample of dried eggshell weighing \(1.50\text{ g}\) was crushed and treated with \(50.0\text{ cm}^3\) of \(1.00\text{ mol dm}^{-3}\) \(\text{HCl(aq)}\). The mixture was boiled and filtered. The filtrate and washings were transferred to a \(250.0\text{ cm}^3\) volumetric flask and made up to the mark with deionised water. \(25.0\text{ cm}^3\) of this diluted solution required \(22.40\text{ cm}^3\) of \(0.125\text{ mol dm}^{-3}\) \(\text{NaOH(aq)}\) for complete neutralisation using phenolphthalein as indicator.

(a) Write the chemical equation for the reaction between \(\text{CaCO}_3\) and \(\text{HCl}\). (1 mark)
(b) State the color change of the indicator at the end point of the titration. (1 mark)
(c) Explain why the mixture was boiled after adding \(\text{HCl(aq)}\) but before filtration and titration. (2 marks)
(d) Calculate the percentage by mass of \(\text{CaCO}_3\) in the eggshell sample. (5 marks)
(e) Suggest one potential source of error in this analysis (other than transfer losses) and how it would affect the calculated percentage by mass. (2 marks)

An organic compound A is a liquid ester with molecular formula \(\text{C}_5\text{H}_{10}\text{O}_2\). Acid hydrolysis of A yields a carboxylic acid B and an alcohol C. Oxidation of C with acidified potassium dichromate solution yields a ketone D.

(a) Deduce the structures of A, B, C, and D. Explain your reasoning. (5 marks)
(b) Describe a chemical test to distinguish between B and D. (2 marks)
(c) Compound B can react with alcohol C in the presence of concentrated sulfuric acid to regenerate ester A.
(i) Name this reaction type. (1 mark)
(ii) State two roles of concentrated sulfuric acid in this reaction. (2 marks)
(iii) Suggest why a boiling water bath is used to heat the reaction mixture instead of direct heating with a Bunsen burner. (1 mark)

Consider the following reversible gas-phase reaction:
\[2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)} \quad \Delta H < 0\]
A mixture of \(0.60\text{ mol}\) of \(\text{SO}_2\text{(g)}\) and \(0.40\text{ mol}\) of \(\text{O}_2\text{(g)}\) was placed in a \(2.0\text{ dm}^3\) sealed vessel at a constant temperature \(T\). When the system reached equilibrium, \(0.16\text{ mol}\) of \(\text{O}_2\text{(g)}\) remained in the vessel.

(a) Write the expression for the equilibrium constant \(K_c\) for this reaction, and state its units. (2 marks)
(b) Calculate the value of \(K_c\) at temperature \(T\). (4 marks)
(c) Predict and explain the effect on the position of equilibrium and the value of \(K_c\) if:
(i) the volume of the vessel is decreased to \(1.0\text{ dm}^3\) at constant temperature \(T\). (3 marks)
(ii) the temperature of the system is increased at constant volume. (2 marks)

Direct methanol fuel cells (DMFCs) are promising power sources for portable electronic devices. A DMFC uses a proton exchange membrane (acidic) as the electrolyte. In this cell, methanol (\(\text{CH}_3\text{OH}\)) and water are supplied to the anode, where carbon dioxide is produced, and oxygen gas is supplied to the cathode, where water is produced.

(a) Write the chemical half-equation for the reaction occurring at the anode. (2 marks)
(b) Write the chemical half-equation for the reaction occurring at the cathode. (2 marks)
(c) Write the overall equation for the reaction occurring in the cell. (1 mark)
(d) State the direction of electron flow in the external circuit, and explain your answer in terms of redox processes. (2 marks)
(e) State one advantage and one disadvantage of a DMFC compared to a hydrogen-oxygen fuel cell. (2 marks)
(f) A portable electronic device requires a constant current of \(0.50\text{ A}\) for \(3.0\text{ hours}\). Calculate the minimum mass of methanol required to power the device for this duration. (Faraday constant \(F = 96500\text{ C mol}^{-1}\), molar mass of methanol = \(32.0\text{ g mol}^{-1}\)) (2 marks)

**Section A: Industrial Chemistry**

1. (a) The kinetics of the gas-phase reaction \(2A(g) + B(g) \rightarrow C(g)\) was studied at 298 K. The initial rates of reaction under different initial concentrations of reactants were measured and shown below:

| Experiment | \([A]_0\) (mol dm\(^{-3}\)) | \([B]_0\) (mol dm\(^{-3}\)) | Initial Rate (mol dm\(^{-3}\) s\(^{-1}\)) |
|---|---|---|---|
| 1 | 0.10 | 0.10 | \(1.2 \times 10^{-3}\) |
| 2 | 0.20 | 0.10 | \(4.8 \times 10^{-3}\) |
| 3 | 0.20 | 0.20 | \(9.6 \times 10^{-3}\) |

(i) Determine the rate equation for the reaction. Show your working. (3 marks)
(ii) Calculate the rate constant \(k\) at 298 K with appropriate units. (2 marks)
(iii) The rate constant for this reaction at 318 K is \(11.8 \text{ dm}^6\text{ mol}^{-2}\text{ s}^{-1}\). Calculate the activation energy \(E_a\) of the reaction. (Gas constant \(R = 8.31 \text{ J K}^{-1}\text{ mol}^{-1}\)) (4 marks)

(b) Dimethyl carbonate (DMC, \(\text{C}_3\text{H}_6\text{O}_3\)) is an environmentally friendly solvent. It can be synthesized via two different routes:

Route 1: \(2\text{CH}_3\text{OH} + \text{COCl}_2 \rightarrow \text{C}_3\text{H}_6\text{O}_3 + 2\text{HCl}\)
Route 2: \(2\text{CH}_3\text{OH} + \text{CO}_2 \rightarrow \text{C}_3\text{H}_6\text{O}_3 + \text{H}_2\text{O}\)

(i) Calculate the atom economy for the production of DMC using Route 1 and Route 2 respectively. (Relative atomic masses: H = 1.0, C = 12.0, O = 16.0, Cl = 35.5) (4 marks)
(ii) Discuss TWO advantages of Route 2 over Route 1 from the perspective of safety and environmental friendliness, other than atom economy. (3 marks)
(iii) The reaction in Route 2 is highly reversible and endothermic. It is carried out in the presence of a solid \(\text{CeO}_2\) catalyst.
(1) State the term used to describe this type of catalyst and explain why it is preferred over homogeneous catalysts in industrial separation. (2 marks)
(2) Suggest how Le Chatelier's principle can be applied to shift the position of equilibrium of Route 2 to increase the yield of DMC. (2 marks)

**Section C: Analytical Chemistry**

2. (a) A student determined the percentage by mass of iron in a dietary supplement tablet using redox titration.

5.00 g of the iron tablets were crushed and dissolved in excess dilute sulfuric acid to form a 250.0 cm\(^3\) solution. A 25.00 cm\(^3\) portion of this solution was titrated against \(0.0200 \text{ mol dm}^{-3}\) acidified potassium permanganate (\(\text{KMnO}_4\)) solution. The average titre of \(\text{KMnO}_4\) was 22.50 cm\(^3\).

(i) Write the ionic equation for the redox reaction during the titration. (2 marks)
(ii) State the color change at the end point of the titration. (1 mark)
(iii) Calculate the percentage by mass of iron (as \(\text{Fe}^{2+}\)) in the tablet. (Relative atomic mass: Fe = 55.8) (4 marks)
(iv) Explain why hydrochloric acid cannot be used instead of sulfuric acid to acidify the potassium permanganate. (2 marks)

(b) An organic compound \(X\) with molecular formula \(\text{C}_4\text{H}_8\text{O}_2\) was analyzed.

(i) When \(X\) was added to sodium hydrogencarbonate solution, no effervescence was observed. Deduce what functional group is absent in \(X\). (1 mark)
(ii) The infrared (IR) spectrum of \(X\) shows a strong absorption peak at around 1735 cm\(^{-1}\), but lacks any broad absorption peak in the region of 3230–3670 cm\(^{-1}\). Identify the functional group present in \(X\). (2 marks)
(iii) The mass spectrum of \(X\) shows prominent peaks at \(m/z = 43\) and \(m/z = 59\). Propose TWO possible structures for \(X\), and identify the species responsible for the peaks at \(m/z = 43\) and \(m/z = 59\) respectively. (4 marks)
(iv) A student suggested using \(^1\text{H}\) NMR spectroscopy to distinguish between the two proposed structures in (b)(iii). State the number of signals, integration ratio, and splitting pattern for each signal in the \(^1\text{H}\) NMR spectrum for BOTH compounds. Explain how this information can distinguish them. (4 marks)