2024 HKDSE Chemistry Practice Paper | DSE Mock

An organic compound X has the molecular formula \(C_3H_6O_2\). Its infrared (IR) spectrum shows a strong absorption at \(1740 \text{ cm}^{-1}\) but no absorption in the region of \(2500 - 3300 \text{ cm}^{-1}\) or \(3230 - 3670 \text{ cm}^{-1}\). Which of the following statements about X is/are correct?

(1) It can undergo alkaline hydrolysis.
(2) It gives a prominent peak at m/z = 59 in its mass spectrum.
(3) It can react with sodium hydrogencarbonate solution to release carbon dioxide gas.

The rate constant \(k\) of a reaction was measured at different absolute temperatures \(T\). A plot of \(\ln k\) against \(1/T\) gives a straight line with a slope of \(-6015 \text{ K}\). What is the activation energy of the reaction?
(Given: gas constant \(R = 8.31 \text{ J K}^{-1} \text{ mol}^{-1}\))

Consider the following reaction pathway:

But-2-ene \(\rightarrow\) 2-chlorobutane \(\rightarrow\) Butan-2-ol \(\rightarrow\) Butanone

Which of the following reagents is/are suitable for carrying out the corresponding conversions?

(1) But-2-ene \(\rightarrow\) 2-chlorobutane: \(HCl(g)\)
(2) 2-chlorobutane \(\rightarrow\) Butan-2-ol: \(NaOH(aq)\), heat
(3) Butan-2-ol \(\rightarrow\) Butanone: acidified \(K_2Cr_2O_7(aq)\), heat under reflux

In a closed vessel of volume \(2.0 \text{ dm}^3\) at a certain temperature, \(2.0 \text{ mol}\) of \(X(g)\) and \(1.0 \text{ mol}\) of \(Y(g)\) are mixed. The following equilibrium is established:

\(2X(g) + Y(g) \rightleftharpoons 2Z(g)\)

At equilibrium, the concentration of \(Z(g)\) is found to be \(0.40 \text{ mol dm}^{-3}\). What is the equilibrium constant \(K_c\) for the reaction at this temperature?

Which of the following elements has an oxide that is insoluble in water but can dissolve in both dilute hydrochloric acid and dilute sodium hydroxide solution?

When \(SO_2(g)\) is bubbled into an acidified solution of \(K_2Cr_2O_7(aq)\), the solution changes from orange to green. Which of the following statements about this reaction is/are correct?

(1) \(SO_2(g)\) acts as a reducing agent and is oxidized to \(SO_4^{2-}(aq)\).
(2) The oxidation number of chromium changes from \(+6\) to \(+3\).
(3) The pH of the solution increases during the reaction.

Given the following standard enthalpy changes of formation (\(\Delta H_f^\theta\)):

\(\Delta H_f^\theta [CO_2(g)] = -394 \text{ kJ mol}^{-1}\)
\(\Delta H_f^\theta [H_2O(l)] = -286 \text{ kJ mol}^{-1}\)
\(\Delta H_f^\theta [C_3H_8(g)] = -104 \text{ kJ mol}^{-1}\)

What is the standard enthalpy change of combustion of propane (\(C_3H_8(g)\))?

Which of the following molecules has polar covalent bonds but is a non-polar molecule?

To monitor the rate of reaction between calcium carbonate and dilute hydrochloric acid:

\(CaCO_3(s) + 2HCl(aq) \rightarrow CaCl_2(aq) + H_2O(l) + CO_2(g)\)

Which of the following methods is/are suitable?

(1) Measuring the volume of carbon dioxide gas released over time.
(2) Measuring the mass of the reaction mixture over time.
(3) Measuring the pH of the reaction mixture over time.

\(25.0 \text{ cm}^3\) of \(0.050 \text{ M}\) ethanedioic acid (\(H_2C_2O_4\)) solution is titrated against a sodium hydroxide solution of unknown concentration. It requires \(20.0 \text{ cm}^3\) of the sodium hydroxide solution to reach the end point. What is the concentration of the sodium hydroxide solution?

An organic compound \(X\) has the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\). It does not react with acidified potassium dichromate solution. The IR spectrum of \(X\) shows a strong absorption peak around \(1735\text{ cm}^{-1}\) but no broad absorption peak around \(2500 - 3300\text{ cm}^{-1}\) or \(3230 - 3670\text{ cm}^{-1}\). Which of the following is/are the possible structure(s) of \(X\)?

(1) Ethyl ethanoate
(2) Methyl propanoate
(3) Butanoic acid

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

An organic compound \(P\) with molecular formula \(\text{C}_5\text{H}_{10}\text{O}\) undergoes the following reactions:
1. It forms a yellow precipitate with 2,4-dinitrophenylhydrazine.
2. It does not form a silver mirror with Tollens' reagent.
3. Upon reduction with \(\text{NaBH}_4\), it yields an achiral alcohol \(Q\).

Which of the following is the IUPAC name of \(P\)?

At temperature \(T\), the equilibrium constant \(K_c\) for the reaction:
\(\text{CO}(g) + \text{H}_2\text{O}(g) \rightleftharpoons \text{CO}_2(g) + \text{H}_2(g)\)
is \(4.0\).

In a closed vessel of \(2.0\text{ dm}^3\) at temperature \(T\), \(1.0\text{ mol}\) of \(\text{CO}(g)\), \(1.0\text{ mol}\) of \(\text{H}_2\text{O}(g)\), \(2.0\text{ mol}\) of \(\text{CO}_2(g)\), and \(2.0\text{ mol}\) of \(\text{H}_2(g)\) are mixed.
Which of the following statements is correct?

A student titration experiment is performed to determine the concentration of a commercial vinegar. A \(25.00\text{ cm}^3\) sample of vinegar is diluted to \(250.0\text{ cm}^3\) with distilled water in a volumetric flask. \(25.00\text{ cm}^3\) of this diluted vinegar is then titrated with \(0.100\text{ M}\) sodium hydroxide solution using phenolphthalein as indicator. The average titre is \(18.50\text{ cm}^3\).

What is the concentration of ethanoic acid in the original vinegar in \(\text{g dm}^{-3}\)?
(Molar mass of \(\text{CH}_3\text{COOH} = 60.05\text{ g mol}^{-1}\))

Consider the following chemical cell:
\(\text{Pt}(s) | \text{Fe}^{2+}(aq), \text{Fe}^{3+}(aq) || \text{MnO}_4^-(aq), \text{Mn}^{2+}(aq), \text{H}^+(aq) | \text{Pt}(s)\)

Which of the following statements about this cell is/are correct?
(1) The left-hand electrode is the anode.
(2) Oxidation occurs at the left-hand electrode.
(3) The pH of the solution in the right-hand half-cell increases during discharge.

Kevlar is a high-strength synthetic polyamide. It can be prepared by the condensation polymerisation between benzene-1,4-dicarboxylic acid and benzene-1,4-diamine. Which of the following represents the repeating unit of Kevlar?

Which of the following statements about catalysts in industrial chemical processes is INCORRECT?

For the reaction between calcium carbonate and dilute hydrochloric acid:
\(\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)\)

Which of the following experimental modifications would increase the initial rate of production of carbon dioxide gas?

(1) Using the same mass of calcium carbonate in the form of powder instead of large chips.
(2) Doubling the concentration of hydrochloric acid while keeping its volume constant.
(3) Increasing the temperature of the reaction mixture from \(25^\circ\text{C}\) to \(35^\circ\text{C}\).

Consider the following dynamic equilibrium system in a sealed syringe:
\(2\text{NO}_2(g) \rightleftharpoons \text{N}_2\text{O}_4(g) \quad \Delta H < 0\)
(brown) (colourless)

If the piston of the syringe is suddenly pushed inwards to halve the volume of the gas mixture at a constant temperature, which of the following describes the changes in the color of the gas mixture?

Consider the following dynamic equilibrium system in a closed container of volume \(V\) at temperature \(T\):
\[\text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g) + \text{Cl}_2(g)\]
At equilibrium, the concentration of \(\text{Cl}_2(g)\) is \(0.40\text{ mol dm}^{-3}\). If the volume of the container is suddenly halved to \(\frac{1}{2}V\) while keeping the temperature constant, which of the following statements about the new equilibrium concentration of \(\text{Cl}_2(g)\) is correct?

Which of the following organic compounds does NOT change the color of acidified \(\text{K}_2\text{Cr}_2\text{O}_7\) solution, but reacts with sodium metal to produce a colorless gas?

Phenol (\(\text{C}_6\text{H}_5\text{OH}\)) can be manufactured from benzene (\(\text{C}_6\text{H}_6\)) and propene (\(\text{C}_3\text{H}_6\)) via the cumene process. The overall equation of the process is shown below:
\[\text{C}_6\text{H}_6 + \text{C}_3\text{H}_6 + \text{O}_2 \rightarrow \text{C}_6\text{H}_5\text{OH} + \text{CH}_3\text{COCH}_3\]
What is the atom economy of this process for the manufacture of phenol?
(Relative atomic masses: \(\text{H} = 1.0\), \(\text{C} = 12.0\), \(\text{O} = 16.0\))

An organic compound \(Y\) with molecular formula \(\text{C}_3\text{H}_6\text{O}_2\) shows a strong absorption peak at \(1715\text{ cm}^{-1}\) and a very broad absorption band in the region of \(2500 - 3300\text{ cm}^{-1}\) in its infrared spectrum. Which of the following statements about \(Y\) is correct?

In which of the following reactions does hydrogen peroxide (\(\text{H}_2\text{O}_2\)) act as a reducing agent?
(1) Reaction with acidified \(\text{KMnO}_4(aq)\)
(2) Reaction with acidified \(\text{FeSO}_4(aq)\)
(3) Reaction with acidified \(\text{KI}(aq)\)

For which of the following gaseous equilibrium systems does the equilibrium constant \(K_c\) have the unit \(\text{mol}^{-1}\text{ dm}^3\)?

Which of the following reaction mixtures, when heated under reflux in the presence of a few drops of concentrated sulfuric acid, will produce ethyl propanoate as the major organic product?

The rate constant \(k\) of a certain chemical reaction was measured at different 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 of this reaction?}
(Universal gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\))

The mass spectrum of an ester with the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\) shows a prominent peak at \(m/z = 57\), but no significant peak at \(m/z = 43\). Which of the following is the most likely structure of the ester?

Which of the following sequences correctly lists the compounds in order of increasing boiling point?

An organic compound X has the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\). The IR spectrum of X shows a strong absorption peak at around \(1740\text{ cm}^{-1}\), but no absorption in the region of \(2500-3300\text{ cm}^{-1}\) or \(3230-3670\text{ cm}^{-1}\). In the mass spectrum of X, a strong signal at \(m/z = 57\) is observed, but the signal at \(m/z = 43\) is very weak. Which of the following is the IUPAC name of X?

For a certain chemical reaction, the rate constant \(k\) increases by a factor of 4.00 when the temperature is increased from \(300\text{ K}\) to \(320\text{ K}\). What is the activation energy of this reaction? (Given: \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\))

Consider the following reaction pathway: A straight-chain compound A (\(\text{C}_4\text{H}_{10}\text{O}\)) reacting with acidified \(\text{K}_2\text{Cr}_2\text{O}_7\) under reflux gives compound B (\(\text{C}_4\text{H}_8\text{O}_2\)). When compound A is heated with concentrated \(\text{H}_2\text{SO}_4\), compound C is formed as the major product. When C reacts with hydrogen bromide (\(\text{HBr}\)), compound D is formed as the major product. Which of the following statements about compounds A, B, C, and D is/are correct? (1) Compound A is a secondary alcohol. (2) Compound C can exhibit cis-trans isomerism. (3) Compound D contains a chiral carbon.

At a certain temperature, the equilibrium constant \(K_c\) for the following reaction is \(0.25\text{ mol}^{-1}\text{ dm}^3\): \(2\text{SO}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons 2\text{SO}_3(\text{g})\). In a closed vessel of volume \(2.0\text{ dm}^3\), an equilibrium mixture contains \(0.40\text{ mol}\) of \(SO_2(\text{g})\) and \(0.80\text{ mol}\) of \(SO_3(\text{g})\). What is the number of moles of \(O_2(\text{g})\) in this equilibrium mixture?

Which of the following combinations of species and its molecular shape is correct?

When sulfur dioxide gas (\(\text{SO}_2\)) is bubbled into an acidified solution of potassium dichromate (\(\text{K}_2\text{Cr}_2\text{O}_7\)), the solution changes color from orange to green. Which of the following statements concerning this reaction is/are correct? (1) The oxidation number of sulfur increases from +4 to +6. (2) Chromium(VI) is reduced to chromium(III). (3) \(\text{SO}_2\) acts as an oxidizing agent.

A first-order reaction has rate constants \(k_1 = 2.10 \times 10^{-3} \text{ s}^{-1}\) at \(300 \text{ K}\) and \(k_2 = 1.05 \times 10^{-2} \text{ s}^{-1}\) at \(320 \text{ K}\).

(a) State the Arrhenius equation and define all terms except \(R\). (2 marks)
(b) Calculate the activation energy \(E_a\) of this reaction in \( \text{kJ mol}^{-1} \). (Given: \(R = 8.31 \text{ J mol}^{-1} \text{ K}^{-1}\)) (3 marks)
(c) State the effect of adding a catalyst on the value of \(E_a\). (1 mark)

Consider the equilibrium: \(\text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g) + \text{Cl}_2(g)\)
At a certain temperature, \(1.00 \text{ mol}\) of \(\text{PCl}_5(g)\) is placed in a closed \(2.0 \text{ dm}^3\) container. When equilibrium is reached, \(0.40 \text{ mol}\) of \(\text{PCl}_5(g)\) remains.

(a) Calculate the equilibrium constant \(K_c\) at this temperature, with units. (4 marks)
(b) Explain how the equilibrium position shifts if the volume of the container is suddenly decreased to \(1.0 \text{ dm}^3\) at constant temperature. (2 marks)

One industrial route for the synthesis of butanoic acid (\(\text{C}_4\text{H}_8\text{O}_2\), molar mass \(= 88.0 \text{ g mol}^{-1}\)) involves the direct catalytic oxidation of butan-1-ol (\(\text{C}_4\text{H}_{10}\text{O}\), molar mass \(= 74.0 \text{ g mol}^{-1}\)) with oxygen gas:
\(\text{C}_4\text{H}_{10}\text{O} + \text{O}_2 \rightarrow \text{C}_4\text{H}_8\text{O}_2 + \text{H}_2\text{O}\)

(a) Calculate the atom economy of this reaction. (3 marks)
(b) An alternative route uses acidified potassium dichromate (\(\text{K}_2\text{Cr}_2\text{O}_7\)) to oxidize butan-1-ol. Apart from atom economy, state two advantages of using oxygen gas with a catalyst over acidified dichromate from a green chemistry perspective. (2 marks)
(c) Suggest one reason why a high atom economy is desirable in industrial chemical processes. (1 mark)

An organic compound Y with molecular formula \(\text{C}_3\text{H}_6\text{O}\) is analyzed.

(a) In the mass spectrum of Y, a prominent peak is observed at \(m/z = 29\). Suggest the formula of the species responsible for this peak. (1 mark)
(b) The infrared spectrum of Y shows a strong absorption peak at around \(1715\text{ cm}^{-1}\), but no broad absorption peak around \(3200-3600\text{ cm}^{-1}\).
(i) Identify the functional group present in Y. (1 mark)
(ii) Deduce the structural formula of Y. Explain your reasoning based on both the IR and mass spectrum. (3 marks)
(c) State one safety precaution when handling volatile organic compounds like Y in a school laboratory. (1 mark)

Consider but-2-ene.

(a) Draw the structural formulae of the two stereoisomers of but-2-ene and label them as *cis* and *trans*. (2 marks)
(b) Explain why but-2-ene exhibits stereoisomerism while but-1-ene does not. (2 marks)
(c) But-2-ene can be converted to butane-2,3-diol.
(i) State the reagent and conditions required for this conversion. (1 mark)
(ii) Does the product butane-2,3-diol exhibit enantiomerism? Explain briefly. (1 mark)

A student wanted to determine the percentage by mass of calcium carbonate (\(\text{CaCO}_3\)) in an eggshell sample. \(1.50\text{ g}\) of the dried eggshell was treated with \(50.0\text{ cm}^3\) of \(1.00\text{ M HCl(aq)}\) (an excess).
The resulting mixture was filtered and the filtrate was made up to \(100.0\text{ cm}^3\) with distilled water.
\(25.0\text{ cm}^3\) of this diluted solution required \(28.80\text{ cm}^3\) of \(0.200\text{ M NaOH(aq)}\) for complete neutralization.

(a) Write a chemical equation for the reaction between \(\text{CaCO}_3\) and \(\text{HCl}\). (1 mark)
(b) Calculate the number of moles of \(\text{HCl}\) that reacted with \(\text{CaCO}_3\) in the eggshell sample. (4 marks)
(c) Calculate the percentage by mass of \(\text{CaCO}_3\) in the eggshell sample. (Molar mass of \(\text{CaCO}_3 = 100.1\text{ g mol}^{-1}\)) (1 mark)

A student sets up a chemical cell consisting of a \(\text{Zn(s)}|\text{Zn}^{2+}\text{(aq)}\) half-cell and a \(\text{Cu(s)}|\text{Cu}^{2+}\text{(aq)}\) half-cell connected by a salt bridge.

(a) Write the half-equations for the reactions occurring at the anode and the cathode. (2 marks)
(b) State the function of the salt bridge and suggest a suitable electrolyte to prepare the salt bridge. (2 marks)
(c) Explain what would happen to the cell voltage if the \(\text{Zn(s)}|\text{Zn}^{2+}\text{(aq)}\) half-cell is replaced by a \(\text{Mg(s)}|\text{Mg}^{2+}\text{(aq)}\) half-cell. (2 marks)

Calculate the standard enthalpy change of formation of liquid ethanol (\(\text{C}_2\text{H}_5\text{OH(l)}\)) given the following standard enthalpy changes of combustion (\(\Delta H_c^\theta\)):
\(\Delta H_c^\theta [\text{C(graphite)}] = -393.5\text{ kJ mol}^{-1}\)
\(\Delta H_c^\theta [\text{H}_2(g)] = -285.8\text{ kJ mol}^{-1}\)
\(\Delta H_c^\theta [\text{C}_2\text{H}_5\text{OH(l)}] = -1367.3\text{ kJ mol}^{-1}\)

(a) Define the term "standard enthalpy change of combustion". (2 marks)
(b) Construct an enthalpy cycle (or use Hess's Law equations) to calculate the standard enthalpy change of formation of \(\text{C}_2\text{H}_5\text{OH(l)}\). (4 marks)

An organic compound P with molecular formula \(\text{C}_3\text{H}_7\text{Br}\) can be converted into compound Q (\(\text{C}_3\text{H}_8\text{O}\)), which can then be oxidized to compound R (\(\text{C}_3\text{H}_6\text{O}_2\)).

(a) Deduce the structure of P, Q, and R. Assume P is a primary haloalkane. (3 marks)
(b) State the reagent and conditions required for the conversion of P to Q. (1 mark)
(c) Write the chemical equation for the reaction of R with methanol in the presence of concentrated sulphuric acid, and state the type of reaction. (2 marks)

Ethanol (\(\text{CH}_3\text{CH}_2\text{OH}\)), dimethyl ether (\(\text{CH}_3\text{OCH}_3\)), and propane (\(\text{CH}_3\text{CH}_2\text{CH}_3\)) have similar relative molecular masses but very different boiling points.

(a) Arrange these three compounds in order of increasing boiling point. (1 mark)
(b) Explain the difference in boiling points between ethanol and dimethyl ether in terms of intermolecular forces. (3 marks)
(c) Explain why ethanol is highly soluble in water while propane is virtually insoluble. (2 marks)

At \(500\text{ K}\), \(1.0\text{ mol}\) of \(\text{CO}(g)\) and \(2.0\text{ mol}\) of \(\text{H}_2(g)\) are placed in a \(2.0\text{ dm}^3\) sealed container. The system reaches equilibrium according to the following equation:

\(\text{CO}(g) + 2\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g)\)

When equilibrium is reached, \(0.4\text{ mol}\) of \(\text{CH}_3\text{OH}(g)\) is formed.

(a) Calculate the equilibrium constant \(K_c\) for the reaction at \(500\text{ K}\), including its unit. (4 marks)

(b) If the volume of the container is suddenly halved at constant temperature, state and explain the effect on the equilibrium yield of \(\text{CH}_3\text{OH}(g)\). (2 marks)

The thermal decomposition of dinitrogen pentoxide, \(2\text{N}_2\text{O}_5(g) \rightarrow 4\text{NO}_2(g) + \text{O}_2(g)\), is a first-order reaction.
At \(298\text{ K}\), the rate constant \(k_1\) is \(3.4 \times 10^{-5}\text{ s}^{-1}\).
At \(318\text{ K}\), the rate constant \(k_2\) is \(5.0 \times 10^{-4}\text{ s}^{-1}\).

(a) Calculate the activation energy (\(E_a\)) of this reaction in \(\text{kJ mol}^{-1}\).
(Given: Gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\)) (4 marks)

(b) Sketch a Maxwell-Boltzmann distribution curve for the system at the two different temperatures (\(298\text{ K}\) and \(318\text{ K}\)) on the same axes. Clearly label the curves, the axes, and the activation energy (\(E_a\)). (2 marks)

Consider the following reaction sequence starting from propan-1-ol:

\(\text{Propan-1-ol} \xrightarrow{\text{Reagent X}} \text{Propene} \xrightarrow{\text{HBr}(g)} \text{Compound Y} \xrightarrow{\text{NaOH}(aq)} \text{Propan-2-ol}\)

(a) Identify Reagent X and state the required reaction conditions for Step 1. (2 marks)

(b) Draw the structural formula of Compound Y. (1 mark)

(c) State the type of structural isomerism shown between propan-1-ol and propan-2-ol. (1 mark)

(d) Suggest a chemical test to distinguish between propan-1-ol and propan-2-ol. State the expected observation for each compound. (2 marks)

To determine the percentage by mass of calcium carbonate (\(\text{CaCO}_3\)) in a dried eggshell sample, a student performed a back titration.

A \(2.00\text{ g}\) sample of the eggshell was treated with \(50.00\text{ cm}^3\) of \(1.00\text{ M HCl}(aq)\). The mixture was heated gently to ensure complete reaction, filtered, and then the filtrate and washings were transferred to a volumetric flask and made up to \(250.0\text{ cm}^3\) with distilled water.

Then, \(25.00\text{ cm}^3\) of this diluted solution required \(22.40\text{ cm}^3\) of \(0.100\text{ M NaOH}(aq)\) for complete neutralization.

(a) Write a balanced chemical equation for the reaction between eggshell (\(\text{CaCO}_3\)) and \(HCl(aq)\). (1 mark)

(b) Calculate the number of moles of excess \(HCl(aq)\) present in the \(250.0\text{ cm}^3\) volumetric flask. (2 marks)

(c) Calculate the percentage by mass of \(\text{CaCO}_3\) in the eggshell sample. (3 marks)
(Molar mass: \(\text{CaCO}_3 = 100.1\text{ g mol}^{-1}\))

Part (a) [8 marks]
(i) The rate constant \(k\) of the gas-phase reaction \(2\text{N}_2\text{O}_5(g) \rightarrow 4\text{NO}_2(g) + \text{O}_2(g)\) was measured at different temperatures in the presence of a catalyst:
At \(500\text{ K}\), \(k_1 = 2.45 \times 10^{-4}\text{ s}^{-1}\).
At \(600\text{ K}\), \(k_2 = 3.82 \times 10^{-3}\text{ s}^{-1}\).
Calculate the activation energy (\(E_a\)) for this catalysed reaction in \(\text{kJ mol}^{-1}\). (Gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\)) (4 marks)
(ii) In the absence of a catalyst, the activation energy of the reaction is \(180\text{ kJ mol}^{-1}\). Explain, using a Maxwell-Boltzmann distribution curve, why the presence of a catalyst increases the rate of reaction. (4 marks)

Part (b) [8 marks]
(i) Ethylene oxide (\(\text{C}_2\text{H}_4\text{O}\)) reacts with carbon dioxide (\(\text{CO}_2\)) to produce ethylene carbonate (\(\text{C}_3\text{H}_4\text{O}_3\)):
\(\text{C}_2\text{H}_4\text{O} + \text{CO}_2 \rightarrow \text{C}_3\text{H}_4\text{O}_3\)
State the atom economy of this reaction for producing ethylene carbonate. Explain your answer. (2 marks)
(ii) Ethylene glycol (\(\text{CH}_2(\text{OH})\text{CH}_2(\text{OH})\)) can be produced via two different industrial methods:
Method A (Hydrolysis of ethylene oxide):
\(\text{C}_2\text{H}_4\text{O} + \text{H}_2\text{O} \rightarrow \text{CH}_2(\text{OH})\text{CH}_2(\text{OH})\)
Method B (Reaction of 1,2-dichloroethane with sodium hydroxide):
\(\text{CH}_2\text{ClCH}_2\text{Cl} + 2\text{NaOH} \rightarrow \text{CH}_2(\text{OH})\text{CH}_2(\text{OH}) + 2\text{NaCl}\)
Calculate the atom economy for both methods for the production of ethylene glycol. (Relative atomic masses: \(\text{H} = 1.0\), \(\text{C} = 12.0\), \(\text{O} = 16.0\), \(\text{Na} = 23.0\), \(\text{Cl} = 35.5\)) (4 marks)
(iii) Suggest why Method A is greener than Method B in terms of waste management and hazard prevention. (2 marks)

Part (c) [4 marks]
(i) Methanol can be produced by the following reversible reaction:
\(\text{CO}(g) + 2\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g) \quad \Delta H = -91\text{ kJ mol}^{-1}\)
Predict and explain the effect of increasing the pressure on the equilibrium yield of methanol. (2 marks)
(ii) The industrial synthesis of methanol is carried out at around \(250^\circ\text{C}\) and \(50\text{ atm}\) in the presence of a catalyst. Explain why \(250^\circ\text{C}\) is described as a "compromise temperature". (2 marks)

Part (a) [9 marks]
An unknown organic compound X with the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\) was analyzed using different methods:
- The infra-red (IR) spectrum of X shows a strong absorption peak at \(1735\text{ cm}^{-1}\), but no broad absorption peak around \(3200 - 3600\text{ cm}^{-1}\) or \(2500 - 3300\text{ cm}^{-1}\).
- The mass spectrum of X shows a molecular ion peak at \(m/z = 88\), and prominent fragment peaks at \(m/z = 59\) and \(m/z = 29\).
(i) Identify the functional group present in X and explain how you ruled out other oxygen-containing functional groups based on the IR spectrum. (3 marks)
(ii) Deduce the structure of X by analyzing the mass spectrum fragments at \(m/z = 59\) and \(m/z = 29\). Write the chemical formulas of the species responsible for these two peaks. (3 marks)
(iii) Write the IUPAC name of X. (1 mark)
(iv) Suggest a chemical test to distinguish X from its isomer butanoic acid. State the expected observations for both compounds. (2 marks)

Part (b) [6 marks]
A mixture containing ethyl ethanoate, methyl propanoate, and butanoic acid is separated by Gas Chromatography (GC).
(i) State the working principle of Gas Chromatography. (2 marks)
(ii) Compare the retention times of ethyl ethanoate (boiling point \(77^\circ\text{C}\)) and butanoic acid (boiling point \(164^\circ\text{C}\)) if a non-polar stationary phase is used. Explain your answer. (2 marks)
(iii) State how Gas Chromatography can be coupled with another instrumental method to both separate and identify the components of the mixture. Name this combined technique. (2 marks)

Part (c) [5 marks]
A \(2.50\text{ g}\) sample of a mixture containing anhydrous sodium carbonate (\(\text{Na}_2\text{CO}_3\)) and sodium chloride (\(\text{NaCl}\)) was dissolved in distilled water to make a \(250.0\text{ cm}^3\) solution. A \(25.00\text{ cm}^3\) portion of this solution required \(22.40\text{ cm}^3\) of \(0.0950\text{ M}\) hydrochloric acid (\(\text{HCl}\)) for complete neutralization.
(i) Write a balanced chemical equation for the reaction between sodium carbonate and hydrochloric acid. (1 mark)
(ii) Calculate the percentage by mass of sodium carbonate in the original mixture. (4 marks)