2025 HKDSE Chemistry Practice Paper | DSE Mock

Which of the following reaction pathways can be used to convert propan-1-ol into propan-2-ol?

(1) Heat propan-1-ol with concentrated \(\text{H}_2\text{SO}_4\) at \(170^\circ\text{C}\), then react the product with \(\text{H}_2\text{O(g)}\) in the presence of \(\text{H}_3\text{PO}_4\) catalyst at high temperature and pressure.
(2) Warm propan-1-ol with acidified \(\text{K}_2\text{Cr}_2\text{O}_7\text{(aq)}\), then react the product with \(\text{NaBH}_4\).
(3) Heat propan-1-ol with concentrated \(\text{H}_2\text{SO}_4\) at \(170^\circ\text{C}\), react the product with \(\text{HBr(g)}\), and then heat the resulting compound with \(\text{NaOH(aq)}\).

Standard enthalpies of combustion (\(\Delta H_c^\theta\)) of \(\text{C}_2\text{H}_4\text{(g)}\) and \(\text{C}_2\text{H}_5\text{OH(l)}\) are \(-1411 \text{ kJ mol}^{-1}\) and \(-1367 \text{ kJ mol}^{-1}\) respectively. What is the standard enthalpy change of the following reaction?

\(\text{C}_2\text{H}_4\text{(g)} + \text{H}_2\text{O(l)} \rightarrow \text{C}_2\text{H}_5\text{OH(l)}\)

Xenon difluoride (\(\text{XeF}_2\)) reacts with water to produce xenon gas, oxygen gas, and hydrofluoric acid. In the balanced chemical equation for this reaction, what is the mole ratio of \(\text{XeF}_2\) reacted to \(\text{O}_2\) produced?

Which of the following statements about the activation energy (\(E_a\)) and rate constant (\(k\)) of a chemical reaction is/are correct?

(1) A reaction with a higher activation energy must have a smaller rate constant at any given temperature than a reaction with a lower activation energy.
(2) The activation energy of a reaction decreases when the temperature is raised.
(3) A plot of \(\ln k\) against \(\frac{1}{T}\) (where \(T\) is in Kelvin) yields a straight line with a slope equal to \(-\frac{E_a}{R}\).

An organic compound \(X\) has the molecular formula \(\text{C}_3\text{H}_6\text{O}\). The infrared (IR) spectrum of \(X\) shows a strong and broad absorption band at around \(3300\text{ cm}^{-1}\), and a sharp absorption band at around \(1640\text{ cm}^{-1}\). Which of the following is most likely the structure of \(X\)?

At a certain temperature \(T\), \(1.00\text{ mol}\) of \(\text{PCl}_5\text{(g)}\) is introduced into a \(2.00\text{ dm}^3\) evacuated sealed container. The gas decomposes according to the equation:

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

When the system reaches chemical equilibrium, the container contains \(0.40\text{ mol}\) of \(\text{Cl}_2\text{(g)}\). What is the equilibrium constant \(K_c\) of the reaction at temperature \(T\)?

Which of the following statements about transition metals and d-block elements are correct?

(1) Zinc is not classified as a transition metal because neither its atom nor its stable ion has an incomplete d-subshell.
(2) Transition metal complexes are often coloured because of electronic transitions between split d-orbitals.
(3) Fe(II) ions can act as a catalyst in the redox reaction between \(\text{S}_2\text{O}_8^{2-}\) and \(\text{I}^-\) because iron can readily switch between +2 and +3 oxidation states.

Which of the following compounds can exhibit enantiomerism?

Which of the following pairs of species have the same molecular shape?

Which of the following compounds has the highest boiling point?

Given the following standard enthalpy changes of combustion:
\(\Delta H_c^\theta [C_2H_2(g)] = -1300\text{ kJ mol}^{-1}\)
\(\Delta H_c^\theta [C_6H_6(l)] = -3268\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of the following reaction?
\(3C_2H_2(g) \rightarrow C_6H_6(l)\)

An organic compound \(X\) has the molecular formula \(C_4H_8O\). It does not react with Tollens' reagent, but can be reduced by \(LiAlH_4\) to form an alcohol \(Y\). Which of the following statements about \(Y\) is/are correct?

(1) \(Y\) can be dehydrated to form a mixture of but-1-ene and but-2-ene.
(2) \(Y\) contains a chiral carbon atom.
(3) \(Y\) can be oxidized by acidified \(K_2Cr_2O_7(aq)\) to form a carboxylic acid.

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

\(N_2O_4(g) \rightleftharpoons 2NO_2(g) \quad \Delta H > 0\)

If the volume of the container is suddenly halved at constant temperature, which of the following describes the subsequent change in the concentration of \(NO_2(g)\)?

In which of the following reactions does sulfur undergo BOTH oxidation and reduction (disproportionation)?

(1) \(3S + 6KOH \rightarrow 2K_2S + K_2SO_3 + 3H_2O\)
(2) \(SO_2 + 2H_2S \rightarrow 3S + 2H_2O\)
(3) \(S_2O_3^{2-} + 2H^+ \rightarrow S + SO_2 + H_2O\)

For a certain reaction, the rate constant \(k\) is measured at different temperatures. A plot of \(\ln k\) against \(\frac{1}{T}\) (where \(T\) is in Kelvin) gives 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 \(R = 8.314\text{ J mol}^{-1}\text{ K}^{-1}\))

Which of the following pairs of species have the same molecular shape?

An organic compound has the molecular formula \(C_3H_6O_2\). Its infrared (IR) spectrum shows a strong absorption peak around \(1740\text{ cm}^{-1}\), but no broad absorption peak in the region \(2500 - 3300\text{ cm}^{-1}\). Which of the following compounds could this be?

(1) Propanoic acid
(2) Methyl ethanoate
(3) Ethyl methanoate

In an industrial electrolysis cell used for purifying copper, a crude copper anode is refined to produce pure copper at the cathode. Which of the following statements regarding this process is correct?

At \(25^\circ\text{C}\), two beakers contain \(0.10\text{ mol dm}^{-3}\) of hydrochloric acid (HCl) and \(0.10\text{ mol dm}^{-3}\) of ethanoic acid (\(CH_3COOH\)) respectively. Which of the following properties is/are the SAME for both solutions?

(1) The volume of \(0.10\text{ mol dm}^{-3}\text{ NaOH}(aq)\) required to completely neutralize \(25.0\text{ cm}^3\) of each acid.
(2) The electrical conductivity of the solutions.
(3) The initial rate of reaction when excess magnesium ribbon is added.

How many structural isomers (excluding stereoisomers) exist for the acyclic compound with the molecular formula \(C_4H_7Br\)?

Consider the following standard enthalpy changes of combustion (\(\Delta H_c^\theta\)) at \(298\text{ K}\):
\(\Delta H_c^\theta [C_2H_4(g)] = -1411\text{ kJ mol}^{-1}\)
\(\Delta H_c^\theta [H_2(g)] = -286\text{ kJ mol}^{-1}\)
\(\Delta H_c^\theta [C_2H_6(g)] = -1560\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of the following reaction?
\(C_2H_4(g) + H_2(g) \rightarrow C_2H_6(g)\)

An organic compound \(X\) with molecular formula \(C_8H_{16}O_2\) undergoes acid-catalyzed hydrolysis to form two organic products, \(Y\) and \(Z\). Under suitable conditions, \(Y\) can be oxidized by acidified potassium dichromate(VI) solution to form a carboxylic acid which is a structural isomer of \(Z\). Which of the following is a possible identity of \(X\)?

Consider the following equilibrium system established in a closed container of volume \(V\) at temperature \(T\):
\(2NO_2(g) \rightleftharpoons N_2O_4(g) \quad \Delta H < 0\)
(
\(NO_2\) is a brown gas; \(N_2O_4\) is a colorless gas)

Which of the following statements is/are correct?
(1) If the volume of the container is decreased to \(0.5V\) at temperature \(T\), the brown color of the mixture first intensifies, then fades slightly, but remains darker than before the change.
(2) If helium gas is injected into the container at constant volume and temperature, the equilibrium shifts to the left.
(3) If the temperature of the system is increased at constant volume, the equilibrium constant \(K_c\) increases.

When the following chemical equation is balanced using the simplest whole numbers, what is the value of \(z\)?
\(x I^-(aq) + y NO_2^-(aq) + z H^+(aq) \rightarrow a I_2(aq) + b NO(g) + c H_2O(l)\)

Which of the following pairs of chemical species has/have the same molecular shape?
(1) \(NH_4^+\) and \(CH_4\)
(2) \(H_3O^+\) and \(NH_3\)
(3) \(BF_3\) and \(NF_3\)

A polymer \(P\) has the repeating unit shown below:
\(-[ \text{NH}-\text{CH}_2-\text{CH}_2-\text{NH}-\text{CO}-\text{CH}_2-\text{CH}_2-\text{CO} ]_n-\)

Which of the following statements about \(P\) are correct?
(1) It is a polyamide.
(2) Its monomers are ethane-1,2-diamine and butanedioic acid.
(3) It can be hydrolyzed by heating with aqueous sodium hydroxide.

In a closed container of volume \(5.0\text{ dm}^3\), \(1.0\text{ mol}\) of gas \(P\) and \(1.0\text{ mol}\) of gas \(Q\) are mixed and allowed to reach equilibrium at temperature \(T\):
\(P(g) + Q(g) \rightleftharpoons 2R(g)\)
At equilibrium, there are \(1.2\text{ mol}\) of gas \(R\) in the container. What is the equilibrium constant \(K_c\) of the reaction at this temperature?

For a certain chemical reaction, the rate constant doubles when the temperature is increased from \(300\text{ K}\) to \(310\text{ K}\). What is the activation energy (\(E_a\)) of this reaction?
(Given: gas constant \(R = 8.31\text{ J K}^{-1}\text{ mol}^{-1}\))

Which of the following methods can be used to distinguish between propanoic acid and methyl ethanoate?
(1) Comparing their infrared (IR) spectra.
(2) Adding sodium hydrogencarbonate solution to each.
(3) Heating each with acidified potassium dichromate(VI) solution.

Consider the following two electrolysis setups operating under the same constant current for 10 minutes:
Setup X: Electrolysis of \(1.0\text{ M } CuSO_4(aq)\) using carbon electrodes.
Setup Y: Electrolysis of \(1.0\text{ M } CuSO_4(aq)\) using copper electrodes.

Which of the following statements is/are correct?
(1) The mass of copper deposited at the cathode in Setup X is the same as that in Setup Y.
(2) The pH of the electrolyte in Setup X decreases, while the pH of the electrolyte in Setup Y remains unchanged.
(3) Gas bubbles are observed at the anode in Setup Y, but not in Setup X.

Consider the following chemical equation: \(2\text{N}_2\text{O}(g) + \text{N}_2\text{H}_4(l) \rightarrow 3\text{N}_2(g) + 2\text{H}_2\text{O}(l)\). Given the standard enthalpy changes of formation (\(\Delta H_f^\theta\)) below: \(\Delta H_f^\theta[\text{N}_2\text{O}(g)] = +82\text{ kJ mol}^{-1}\), \(\Delta H_f^\theta[\text{N}_2\text{H}_4(l)] = +51\text{ kJ mol}^{-1}\), \(\Delta H_f^\theta[\text{H}_2\text{O}(l)] = -286\text{ kJ mol}^{-1}\). What is the standard enthalpy change of the reaction?

How many moles of potassium permanganate (\(\text{KMnO}_4\)) are required to completely oxidize 1.0 mole of iron(II) oxalate (\(\text{FeC}_2\text{O}_4\)) in an acidic medium?

Which of the following reaction sequences can be used to convert propan-1-ol to propan-2-ol?

For a certain reaction, when the temperature is increased from 300 K to 310 K, the rate constant \(k\) doubles. Which of the following statements are correct? (Given: \(R = 8.314\text{ J mol}^{-1}\text{ K}^{-1}\))
(1) The activation energy of the reaction is approximately \(54\text{ kJ mol}^{-1}\).
(2) If a catalyst is added at 300 K, the activation energy decreases and the rate constant increases.
(3) A plot of \(\ln k\) against \(\frac{1}{T}\) for this reaction has a positive slope.

An organic compound \(X\) has the molecular formula \(\text{C}_4\text{H}_8\text{O}_2\). The infrared spectrum of \(X\) shows a very broad absorption band in the region \(2500 - 3300\text{ cm}^{-1}\) and a strong absorption peak at \(1715\text{ cm}^{-1}\). The mass spectrum of \(X\) shows a prominent peak at \(m/z = 45\). Which of the following is the most likely structural formula of \(X\)?

2.0 mol of \(\text{A}(g)\) and 3.0 mol of \(\text{B}(g)\) are mixed in a closed \(2.0\text{ dm}^3\) container to undergo the following reaction: \(\text{A}(g) + 2\text{B}(g) \rightleftharpoons 2\text{C}(g)\). When equilibrium is reached, the concentration of \(\text{C}(g)\) is found to be \(1.0\text{ mol dm}^{-3}\). What is the equilibrium constant \(K_c\) of the reaction at this temperature?

An experiment was conducted to determine the standard enthalpy change of formation of propan-2-ol (\(\text{CH}_3\text{CH(OH)CH}_3\)).\nGiven the standard enthalpy changes of combustion (\(\Delta H_c^\ominus\)) at \(298\text{ K}\):\n\(\text{C(graphite)} = -393.5 \text{ kJ mol}^{-1}\)\n\(\text{H}_2\text{(g)} = -285.8 \text{ kJ mol}^{-1}\)\n\(\text{CH}_3\text{CH(OH)CH}_3\text{(l)} = -2006.0 \text{ kJ mol}^{-1}\)\n\n(a) Write a balanced chemical equation for the reaction representing the standard enthalpy change of formation of propan-2-ol. (1 mark)\n(b) Construct a Hess's law cycle and calculate the standard enthalpy change of formation of propan-2-ol. (3 marks)\n(c) Suggest why the standard enthalpy change of formation of propan-2-ol cannot be determined directly by a simple calorimetric experiment. (2.14 marks)

Outline a synthetic route to prepare propan-2-yl ethanoate starting from propene and ethanol. You may use any inorganic reagents required. (6.14 marks)

Consider the following reversible reaction at a temperature \(T\):\n\(\text{CO(g)} + 2\text{H}_2\text{(g)} \rightleftharpoons \text{CH}_3\text{OH(g)} \quad \Delta H < 0\)\n\nAt this temperature, \(1.00\text{ mol}\) of \(CO\text{(g)}\) and \(2.00\text{ mol}\) of \(H_2\text{(g)}\) were introduced into a \(5.0\text{ dm}^3\) sealed container. When the system reached equilibrium, the container was found to contain \(0.40\text{ mol}\) of \(\text{CH}_3\text{OH(g)}\).\n\n(a) Calculate the equilibrium constant \(K_c\) for the reaction at temperature \(T\), including its units. (4 marks)\n(b) Predict and explain the effect on the position of equilibrium if the volume of the container is decreased to \(2.5\text{ dm}^3\) at constant temperature. (2.14 marks)

For the aqueous reaction: \(\text{A(aq)} + \text{B(aq)} \rightarrow \text{C(aq)}\), the rate equation is found to be:\n\n\(\text{Rate} = k[\text{A(aq)}][\text{B(aq)}]^2\)\n\n(a) Deduce the overall order of the reaction. (1 mark)\n(b) In a series of experiments, when \([\text{A(aq)}] = 0.10 \text{ mol dm}^{-3}\) and \([\text{B(aq)}] = 0.20 \text{ mol dm}^{-3}\), the initial rate of reaction was measured to be \(4.0 \times 10^{-4} \text{ mol dm}^{-3} \text{s}^{-1}\). Calculate the rate constant \(k\) for this reaction and state its units. (2.14 marks)\n(c) State and explain how the value of the rate constant \(k\) changes when the temperature of the reaction mixture is increased. (3 marks)

An unknown organic compound \(X\) has the molecular formula \(\text{C}_3\text{H}_6\text{O}\).\n\n(a) The infrared (IR) spectrum of \(X\) shows a strong, sharp absorption peak at around \(1715\text{ cm}^{-1}\), but lacks any broad absorption peak in the region of \(3230 - 3670\text{ cm}^{-1}\).\n(i) Identify the functional group present in \(X\) based on this IR data. (1 mark)\n(ii) Deduce the structural formula and systematic name of \(X\) if it does not react with Tollens' reagent. (2 marks)\n\n(b) Compound \(Y\) is an isomer of \(X\). The IR spectrum of \(Y\) shows a broad peak in the region of \(3230 - 3670\text{ cm}^{-1}\) and a sharp peak at around \(1640\text{ cm}^{-1}\).\n(i) Deduce the TWO functional groups present in \(Y\). (2 marks)\n(ii) Suggest a chemical test to distinguish between \(X\) and \(Y\), stating the expected observation for each compound. (1.14 marks)

An electrolytic cell is set up using two copper electrodes immersed in a \(1.0 \text{ M } \text{CuSO}_4\text{(aq)}\) solution. A constant current of \(1.50 \text{ A}\) is passed through the cell for \(40.0 \text{ minutes}\).\n\n(a) State the observation at the anode and write the half-equation for the reaction occurring at the anode. (2 marks)\n(b) Calculate the theoretical change in mass of the anode during this electrolysis. (3 marks)\n(Given: Faraday constant, \(F = 96500 \text{ C mol}^{-1}\); relative atomic mass: \(\text{Cu} = 63.5\))\n(c) Explain why the blue color of the \(\text{CuSO}_4\text{(aq)}\) solution remains unchanged throughout the electrolysis. (1.14 marks)

But-2-ene-1,4-dioic acid exhibits stereoisomerism.\n\n(a) Draw the structures of the *cis*- and *trans*-isomers of but-2-ene-1,4-dioic acid. (2 marks)\n(b) State the type of stereoisomerism shown by these two isomers, and explain why this type of isomerism can exist in this compound. (2.14 marks)\n(c) One of the isomers can undergo intramolecular dehydration when heated to form a cyclic anhydride, while the other does not. Identify which isomer undergoes this reaction and explain why. (2 marks)

Transition metals and their compounds are widely used as catalysts in industrial processes.\n\n(a) State TWO characteristic chemical properties of transition metals other than catalytic activity. (2 marks)\n(b) In the Contact Process for the manufacture of sulfuric acid, sulfur dioxide is oxidized to sulfur trioxide:\n\n\(2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)}\)\n\n(i) Identify the catalyst used in this process. (1 mark)\n(ii) Explain, in terms of activation energy, how the catalyst increases the rate of this reaction. (1.14 marks)\n(iii) State whether this catalyst is a homogeneous or heterogeneous catalyst, and explain your answer. (2 marks)

A student determined the calcium carbonate (\(\text{CaCO}_3\)) content in a sample of eggshell.\n\nA \(1.50 \text{ g}\) sample of crushed eggshell was treated with \(50.0 \text{ cm}^3\) of \(1.00 \text{ M } \text{HCl(aq)}\). After the reaction was complete, the mixture was filtered, and the filtrate was made up to \(250.0 \text{ cm}^3\) with deionised water in a volumetric flask.\n\nThen, a \(25.0 \text{ cm}^3\) portion of this diluted solution was titrated and required \(26.00 \text{ cm}^3\) of \(0.100 \text{ M } \text{NaOH(aq)}\) for complete neutralisation.\n\n(a) Write the chemical equation for the reaction between \(\text{CaCO}_3\) and \(\text{HCl}\). (1 mark)\n(b) Calculate the number of moles of \(\text{HCl}\) that reacted with the \(\text{CaCO}_3\) in the eggshell sample. (3.14 marks)\n(c) Calculate the percentage by mass of \(\text{CaCO}_3\) in the eggshell sample. (2 marks)\n(Relative atomic masses: \(\text{C} = 12.0\), \(\text{O} = 16.0\), \(\text{Ca} = 40.1\))

Consider two molecules: boron trifluoride (\(\text{BF}_3\)) and nitrogen trifluoride (\(\text{NF}_3\)).\n\n(a) Draw the electron-dot structures (Lewis structures) of \(\text{BF}_3\) and \(\text{NF}_3\), showing valence electrons only. (2 marks)\n(b) Predict the shape of each molecule and state the bond angle in each. (2.14 marks)\n(c) Explain why \(\text{BF}_3\) is a non-polar molecule, whereas \(\text{NF}_3\) is a polar molecule, even though both contain highly polar bonds. (2 marks)

Ethene is an important feedstock in chemical industry.\n\n(a) Name the industrial process used to obtain ethene from heavy fractions of petroleum. (1 mark)\n(b) Ethene can undergo polymerization to form polyethene.\n(i) State the type of polymerization involved. (1 mark)\n(ii) Draw the structural formula of the repeating unit of polyethene. (1 mark)\n(c) Account for the difference in physical properties (density and flexibility) between Low-Density Polyethene (LDPE) and High-Density Polyethene (HDPE) in terms of their molecular structures. (3.14 marks)

Acid rain is a severe environmental problem caused by pollutants released from burning fossil fuels.\n\n(a) Identify the primary gaseous pollutant responsible for the formation of acid rain, and write a balanced chemical equation to show how it forms an acidic solution in the atmosphere. (2 marks)\n(b) Describe ONE harmful effect of acid rain on the environment. (1 mark)\n(c) To reduce the emission of this pollutant from coal-fired power stations, a process called "flue gas desulfurization" is used. In this process, the flue gas is reacted with calcium carbonate (\(\text{CaCO}_3\)) and oxygen to form calcium sulfate (\(\text{CaSO}_4\)).\n(i) Write a balanced chemical equation for this desulfurization reaction. (1.14 marks)\n(ii) Suggest why the calcium sulfate produced is considered a useful byproduct. (2 marks)

The standard enthalpy changes of combustion can be used to determine enthalpy changes that are difficult to measure directly.

(a) Define the term 'standard enthalpy change of combustion'.

(b) Given the following standard enthalpy changes of combustion at \(298\text{ K}\) and \(1\text{ atm}\):
- \(\Delta H_c^\theta [\text{C(graphite)}] = -394\text{ kJ mol}^{-1}\)
- \(\Delta H_c^\theta [\text{H}_2(g)] = -286\text{ kJ mol}^{-1}\)
- \(\Delta H_c^\theta [\text{CH}_3\text{COOH}(l)] = -874\text{ kJ mol}^{-1}\)

Calculate the standard enthalpy change of formation of liquid ethanoic acid (\(\text{CH}_3\text{COOH}(l)\)).

(c) Explain why the standard enthalpy change of formation of ethanoic acid cannot be determined directly by a simple calorimetric experiment.

Consider the following dynamic equilibrium established in a sealed container of volume \(2.0\text{ dm}^3\) at \(350\text{ K}\):

\(\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)\)

Initially, \(0.80\text{ mol}\) of \(\text{N}_2\text{O}_4(g)\) was introduced into the container. At equilibrium, the concentration of \(\text{NO}_2(g)\) was found to be \(0.30\text{ mol dm}^{-3}\).

(a) Write the expression for the equilibrium constant \(K_c\) for this reaction and state its units.

(b) Calculate the equilibrium concentration of \(\text{N}_2\text{O}_4(g)\) and hence determine the value of \(K_c\) at \(350\text{ K}\).

(c) Explain how the position of equilibrium would shift if the volume of the container is decreased to \(1.0\text{ dm}^3\) at constant temperature.

A direct methanol fuel cell (DMFC) is an electrochemical cell that uses liquid methanol (\(\text{CH}_3\text{OH}\)) as fuel and oxygen as oxidant under acidic conditions. The overall reaction equation is as follows:

\(\text{CH}_3\text{OH}(l) + \frac{3}{2}\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)\)

(a) Determine the oxidation number of carbon in \(\text{CH}_3\text{OH}\) and \(\text{CO}_2\), and state the change in the oxidation number of carbon.

(b) Write the half-equation for the reaction occurring at the anode (negative electrode) of this fuel cell under acidic conditions.

(c) State one advantage and one disadvantage of using a direct methanol fuel cell instead of a hydrogen-oxygen fuel cell.

Consider the following synthetic route of an organic compound:

\(\text{CH}_3\text{CH}=\text{CHCH}_3 \xrightarrow{\text{Step 1}} \text{CH}_3\text{CH(Cl)CH}_2\text{CH}_3 \xrightarrow{\text{Step 2}} \text{CH}_3\text{CH(OH)CH}_2\text{CH}_3 \xrightarrow{\text{Step 3}} \text{Compound X}\)

(a) Name the type of reaction in Step 1.

(b) State the reagents and reaction conditions required for Step 2.

(c) Draw the structural formula of Compound X, and state the expected colour change of the reaction mixture in Step 3 when acidified potassium dichromate solution is used.

(d) Suggest a physical method to isolate Compound X from the reaction mixture after Step 3.

(a) Methanol (\(\text{CH}_3\text{OH}\)) is an important industrial chemical and solvent. The rate constant \(k\) of the reaction:
\[ \text{CO(g)} + 2\text{H}_2\text{(g)} \rightarrow \text{CH}_3\text{OH(g)} \]
was measured at two different temperatures:
At \( 500 \text{ K} \), \( k_1 = 2.5 \times 10^{-3} \text{ dm}^6\text{ mol}^{-2}\text{ s}^{-1} \).
At \( 550 \text{ K} \), \( k_2 = 1.2 \times 10^{-2} \text{ dm}^6\text{ mol}^{-2}\text{ s}^{-1} \).

(i) Calculate the activation energy (\(E_a\)) for this reaction in \(\text{kJ mol}^{-1}\).
(ii) Deduce the overall order of this reaction. Explain your answer.
(iii) Sketch a Maxwell-Boltzmann distribution curve for the reactant molecules at \( 500 \text{ K} \) and \( 550 \text{ K} \). Label the activation energy \(E_a\), and explain how the curves illustrate the effect of temperature on the rate of reaction.


(b) In industry, the synthesis of methanol from syngas is carried out as a reversible reaction:
\[ \text{CO(g)} + 2\text{H}_2\text{(g)} \rightleftharpoons \text{CH}_3\text{OH(g)} \quad \Delta H = -90.8 \text{ kJ mol}^{-1} \]
The reaction is typically performed at \( 250^\circ\text{C} \) and a pressure of \( 50-100 \text{ atm} \) in the presence of a copper-zinc oxide catalyst.

(i) Explain why a high pressure of \( 50-100 \text{ atm} \), rather than atmospheric pressure, is used in this process in terms of reaction rate and equilibrium yield.
(ii) Explain why \( 250^\circ\text{C} \) is considered a compromise temperature for this reaction.
(iii) Contrast the effect of the copper-zinc oxide catalyst on the rate of reaction and the equilibrium position.


(c) Methanol can also be synthesized via the direct hydrogenation of carbon dioxide captured from industrial exhaust:
Reaction A: \[ \text{CO}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightarrow \text{CH}_3\text{OH(g)} + \text{H}_2\text{O(l)} \]
Compare this with the standard syngas reaction:
Reaction B: \[ \text{CO(g)} + 2\text{H}_2\text{(g)} \rightarrow \text{CH}_3\text{OH(g)} \]

(i) Calculate the atom economy of both Reaction A and Reaction B for the production of methanol. (Relative atomic masses: \(\text{H} = 1.0, \text{C} = 12.0, \text{O} = 16.0\))
(ii) Discuss which of these two reaction pathways is greener, taking into account both atom economy and environmental sustainability.

(a) An organic compound $X$ (molecular formula $\text{C}_3\text{H}_6\text{O}$) is known to be either propan-1-ol, propanal, or propanone.

(i) The infrared (IR) spectrum of $X$ shows a strong absorption peak at around $1715\text{ cm}^{-1}$ but no broad absorption peak in the region of $3200 - 3600\text{ cm}^{-1}$. Explain how these IR features can be used to rule out one of the three possibilities.
(2 marks)

(ii) Describe a chemical test to distinguish between the remaining two possibilities. State the reagents, conditions, and expected observations for both.
(3 marks)

(iii) In the mass spectrum of $X$, a prominent peak is observed at $m/z = 43$. Give the formula of the ionic species corresponding to this peak.
(1 mark)




(b) Chromatography is widely used to separate and identify components in mixtures.

(i) State the general principle of separation in Thin-Layer Chromatography (TLC).
(2 marks)

(ii) A student used TLC with a silica gel plate (stationary phase) and a mixture of ethyl acetate and hexane (mobile phase) to separate aspirin and salicylic acid. Salicylic acid is more polar than aspirin.

(1) Predict which compound will have a larger $R_f$ value. Explain your answer in terms of intermolecular forces and phase affinity.
(3 marks)

(2) State how the spots on the TLC plate can be visualized if both compounds are colorless.
(1 mark)




(c) The concentration of sodium hypochlorite ($\text{NaClO}$) in a brand of household bleach can be determined using an iodometric titration.

A $10.0\text{ cm}^3$ sample of the bleach was diluted to $250.0\text{ cm}^3$ with deionized water in a volumetric flask. A $25.0\text{ cm}^3$ portion of this diluted solution was transferred into a conical flask, and excess potassium iodide solution ($\text{KI(aq)}$) and dilute sulfuric acid ($\text{H}_2\text{SO}_4\text{(aq)}$) were added. The liberated iodine ($\text{I}_2$) was then titrated against $0.100\text{ M}$ sodium thiosulfate solution ($\text{Na}_2\text{S}_2\text{O}_3\text{(aq)}$).

(i) Write the ionic equation for the reaction of hypochlorite ions ($\text{ClO}^-$) with iodide ions ($\text{I}^-$) in acidic medium.
(1 mark)

(ii) Write the ionic equation for the reaction between iodine ($\text{I}_2$) and thiosulfate ions ($\text{S}_2\text{O}_3^{2-}$).
(1 mark)

(iii) State the indicator used in this titration, and describe the color change at the end point.
(2 marks)

(iv) The titration required an average of $24.20\text{ cm}^3$ of $0.100\text{ M}$ $\text{Na}_2\text{S}_2\text{O}_3\text{(aq)}$ to reach the end point. Calculate the concentration of $\text{NaClO}$ in the original bleach sample in $\text{g dm}^{-3}$.
(Molar mass of $\text{NaClO} = 74.5\text{ g mol}^{-1}$)
(4 marks)