IB DP Chemistry Mock Exam SL Paper 2 Set 2 - 2025 Syllabus

IB DP Chemistry Mock Exam SL Paper 2 Set 2

Prepare for the IB DP Chemistry Exam with our comprehensive IB DP Chemistry Exam Mock Exam SL Paper 2 Set 2. Test your knowledge and understanding of key concepts with challenging questions covering all essential topics. Identify areas for improvement and boost your confidence for the real exam

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Question

An unidentified organic substance is composed only of carbon, hydrogen and oxygen.

(a) A sample of mass \(4.32 \text{ g}\) was completely burned in excess oxygen, producing \(9.49 \text{ g}\) of \(\text{CO}_2\) and \(5.18 \text{ g}\) of \(\text{H}_2\text{O}\). Determine the empirical formula of the compound, using sections 1 and 7 of the data booklet.

(b) The same organic compound was fully vaporized under controlled conditions of temperature and pressure.
(i) A mass of \(0.108 \text{ g}\) of the gaseous compound occupied a volume of \(55.7 \text{ cm}^3\) at \(100^{\circ}\text{C}\) and a pressure of \(1.00 \times 10^5 \text{ Pa}\). Calculate the amount of the compound, in moles.
(ii) Hence, determine the molar mass of the organic compound.

▶️ Answer/Explanation

Detailed solution

(a)
• \(C\): \(9.49 / 44.01 = 0.216 \text{ mol}\). Mass \(C = 2.59 \text{ g}\).
• \(H\): \(2 \times (5.18 / 18.02) = 0.575 \text{ mol}\). Mass \(H = 0.581 \text{ g}\).
• \(O\): \(4.32 – (2.59 + 0.581) = 1.15 \text{ g}\). Moles \(O = 1.15 / 16.00 = 0.0719 \text{ mol}\).
• Ratio \(C:H:O = 0.216 : 0.575 : 0.0719\). Divide by \(0.0719\) \(\rightarrow\) \(3 : 8 : 1\).
• Empirical formula: \(\text{C}_3\text{H}_8\text{O}\).

(b)
(i) \(n = \frac{PV}{RT} = \frac{1.00 \times 10^5 \times 55.7 \times 10^{-6}}{8.31 \times 373} = \mathbf{0.00180 \text{ mol}}\).
(ii) \(M = \frac{m}{n} = \frac{0.108}{0.00180} = \mathbf{60.0 \text{ g mol}^{-1}}\).

Question

A mass of \(3.162 \text{ g}\) of calcium carbonate, \(\text{CaCO}_3(s)\), reacts with \(20.0 \text{ cm}^3\) of \(4.00 \text{ mol dm}^{-3}\) hydrochloric acid, \(\text{HCl}(aq)\).

(a) Write the balanced chemical equation for this reaction, including state symbols.

(b) Determine which reactant is the limiting reagent. Use sections 1, 4 and 7 of the data booklet.

(d) The progress of this reaction can be investigated by measuring the volume of gas formed over time. Sketch an additional curve for the reaction when the acid is at a higher temperature, with all other conditions kept constant.

▶️ Answer/Explanation

Detailed solution

(a)
\[ \text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l) \]

(b)
• \(n(\text{HCl}) = 4.00 \times 0.020 = 0.0800 \text{ mol}\)
• \(n(\text{CaCO}_3) = \frac{3.162}{100.09} = 0.0316 \text{ mol}\)
• Stoichiometric ratio is \(1:2\). The amount of \(\text{HCl}\) required for \(0.0316 \text{ mol}\) of \(\text{CaCO}_3\) is \(0.0632 \text{ mol}\).
• Since \(0.0800 > 0.0632\), \(\text{HCl}\) is in excess and \(\text{CaCO}_3\) is the limiting reactant.

(c)
\(n(\text{CO}_2) = n(\text{CaCO}_3) = 0.0316 \text{ mol}\)
\(V = n \times 22.7 \text{ dm}^3 \text{ mol}^{-1} = 0.0316 \times 22.7 = \mathbf{0.717 \text{ dm}^3}\).

(d)
The curve should begin at the origin, show a steeper initial gradient (indicating a faster rate), and level off at the same final volume since the amount of limiting reactant is unchanged.

IB DP Chemistry Mock Exam SL Paper 2 Set 2 - 2025 Syllabus