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Chemistry HSC practice questions

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Question 1Equilibrium and acid reactions2 marks
At $25 \text{ } ^\circ C$, the $K_w$ for water is $1.0 \times 10^{-14}$. Calculate the $pH$ of a neutral solution at this temperature.
What a full answer covers
A complete answer will recognise that in a neutral solution, the concentrations of hydrogen ions and hydroxide ions are equal. It will then use the $K_w$ expression to calculate the hydrogen ion concentration and subsequently the $pH$.
Question 2Organic chemistry7 marks
Polyethylene terephthalate (PET) is a common polymer used in drink bottles and clothing. Explain the formation of PET, including the monomers involved and the type of polymerisation reaction. Discuss two properties of PET that make it suitable for its common uses.
What a full answer covers
A comprehensive response will identify the two monomers of PET (ethylene glycol and terephthalic acid) and describe their structures. It will then explain that PET is formed via condensation polymerisation, where water is eliminated. Finally, it will discuss two specific properties of PET, such as its strength, transparency, or chemical resistance, and clearly link these properties to its suitability for use in drink bottles and clothing.
Question 3Organic chemistry2 marks
Draw the structural formula for 2,2-dimethylpropan-1-ol.
What a full answer covers
A full-mark answer will show a three-carbon chain with a hydroxyl group attached to the first carbon, and two methyl groups attached to the second carbon, with all valencies satisfied by hydrogen atoms.
Question 4Applying chemical ideas4 marks
A student is given an unknown organic liquid and performs a series of tests. They observe the following: * It turns moist blue litmus paper red. * It reacts with sodium carbonate to produce gas bubbles. * It has a boiling point of $118 \text{ } ^\circ C$. Identify the functional group present in the unknown liquid and justify your answer based on the observations.
What a full answer covers
A full-mark response will identify the functional group as a carboxylic acid. It will justify this by explaining that both turning blue litmus red and reacting with sodium carbonate to produce gas are characteristic properties of carboxylic acids. Additionally, it will note that the given boiling point is consistent with the strong intermolecular forces (hydrogen bonding) present in carboxylic acids.
Question 5Equilibrium and acid reactions6 marks
Compare and contrast the properties of a strong acid and a weak acid, providing a specific example for each. Include their behaviour in aqueous solution and their relative $pH$ values for solutions of the same concentration.
What a full answer covers
A comprehensive answer will define strong acids as those that completely dissociate in water and weak acids as those that partially dissociate, providing an example for each. It will then compare their behaviour in aqueous solution, noting the presence of an equilibrium for weak acids. Finally, it will contrast their $pH$ values for solutions of the same concentration, explaining that strong acids will have a lower $pH$ due to a higher concentration of $H^+$ ions.
Question 6Acid and base reactions8 marks
Sulfuric acid is a highly important industrial chemical. Discuss the environmental impacts of the industrial production and use of sulfuric acid. In your answer, consider both its manufacture and its applications, and suggest strategies to mitigate these impacts.
What a full answer covers
A full-mark answer will discuss the environmental impacts of both the production (e.g., acid rain from sulfur oxide emissions, energy consumption) and the use (e.g., release of acidic wastewater) of sulfuric acid. It will then suggest specific mitigation strategies for each identified impact, such as using catalytic converters and scrubbers for emissions, neutralising or recycling waste acid, and optimising industrial processes for energy efficiency.
Question 7Equilibrium and acid reactions3 marks
Consider the following reversible reaction at equilibrium in a closed system: $$2SO_{2(g)} + O_{2(g)} \rightleftharpoons 2SO_{3(g)} \quad \Delta H = -198 \text{ kJ mol}^{-1}$$ Explain how increasing the temperature would affect the concentration of $SO_3$ and provide a reason for this change.
What a full answer covers
A full-mark answer will state that increasing the temperature decreases the concentration of $SO_3$. It will then explain that because the forward reaction is exothermic, the system will shift the equilibrium in the endothermic (reverse) direction to absorb the added heat, leading to the consumption of $SO_3$.
Question 8Acid and base reactions4 marks
A student performs a titration to determine the concentration of an unknown sulfuric acid solution. They use $25.00 \text{ mL}$ aliquots of the acid and titrate with a standard $0.100 \text{ mol L}^{-1}$ sodium hydroxide solution. The average titre volume is $22.50 \text{ mL}$. Calculate the concentration of the sulfuric acid solution.
What a full answer covers
A complete answer will begin by writing the balanced chemical equation for the neutralisation reaction. It will then calculate the moles of sodium hydroxide used, apply the correct stoichiometric ratio to determine the moles of sulfuric acid, and finally calculate the concentration of the sulfuric acid in mol L$^{-1}$.
Question 9Organic chemistry3 marks
Describe the type of reaction and conditions required to convert an alkene to an alkane.
What a full answer covers
A complete answer will identify the reaction as hydrogenation or an addition reaction. It will then state that hydrogen gas ($H_2$) is required as a reactant, along with a catalyst such as nickel, platinum, or palladium, and potentially heat.
Question 10Organic chemistry5 marks
An unknown alcohol, compound X, has the molecular formula $C_3H_8O$. When compound X is oxidised, it forms a product that gives a positive result with Benedict's solution. Identify compound X, draw its structural formula, and write a balanced chemical equation for its oxidation reaction.
What a full answer covers
A complete answer will identify compound X as propan-1-ol and provide its structural formula. It will explain that primary alcohols oxidise to aldehydes, which can then be further oxidised to carboxylic acids, and that aldehydes give a positive result with Benedict's solution. Finally, it will provide a balanced chemical equation for the oxidation of propan-1-ol to propanal.

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Chemistry HSC practice questions

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