IB DP Chemistry Mock Exam SL Paper 1B Set 4 - 2025 Syllabus

IB DP Chemistry Mock Exam SL Paper 1B Set 4

Prepare for the IB DP Chemistry Exam with our comprehensive IB DP Chemistry Exam Mock Exam SL Paper 1B Set 4. 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

Nitrogen dioxide, NO₂, is a brown, toxic, and corrosive gas. It can be prepared in a school laboratory by heating a group 2 metal nitrate or by reacting copper, Cu, with concentrated nitric acid, HNO₃.

(a) (i) Suggest two distinct safety precautions that should be implemented when carrying out either of these experiments, and provide a reason for each.

(a) (ii) Deduce the coefficients to balance the chemical equation for the reaction between Cu and concentrated HNO₃.
___Cu (s) + ___HNO₃ (aq) → ___Cu(NO₃)₂ (aq) + ___NO₂ (g) + ___H₂O (l)

(a) (iii) Calculate the mass, in grams, of Cu needed to produce 0.0100 moles of NO₂. (Refer to Section 7 of the data booklet.)

(b) The NO₂ produced was sealed in a glass container, establishing the equilibrium:
2NO₂ (g) ⇌ N₂O₄ (g) ∆\(H^⦵\) = –55.3 kJ mol⁻¹
Propose two different measurements, excluding colour observation, that could be used to follow the progress of this reaction over time, and describe the expected trend for each.

(c) A sample of 0.0100 moles of NO₂ was placed in a sealed 1 dm³ container held at a constant 40 °C.
(i) Suggest a straightforward method to maintain this constant temperature in a school laboratory.
(ii) The equilibrium concentration of NO₂ was tracked using a colorimeter. A student took an absorbance reading immediately after starting. Explain why this reading might be unreliable.
(iii) Suggest how the issue identified in part (c)(ii) could be resolved.

(d) The experiment from part (c) was repeated at 0 °C. The equilibrium mixture contained 0.00732 mol of NO₂(g) and 0.00134 mol of N₂O₄(g).
Given that \( K = \frac{[\text{N}_2\text{O}_4]}{[\text{NO}_2]^2} \), calculate the equilibrium constant, K, at 0 °C. Express your answer to two significant figures.

(e) The initial quantity of NO₂ was found by titration. The gas was first dissolved in water according to the reaction:
2NO₂(g) + H₂O(l) → HNO₃(aq) + HNO₂(aq)
The resulting solution was diluted to 250.0 cm³. Then, 25.0 cm³ portions of this solution were titrated against a 0.0500 mol dm⁻³ standard solution of sodium hydroxide, NaOH.
(i) Identify the most precise piece of equipment for:
• Transferring 25.0 cm³ of the solution for titration.
• Adding the NaOH solution during the titration.
(ii) Design a table suitable for recording the titration results. Include headers for variables, units, and other relevant information, but leave the data cells empty.
(iii) The burette used for the NaOH titration had an uncertainty of ±0.05 cm³. The average titre volume was 20.05 cm³. Determine the percentage uncertainty in this volume.

(f) The equilibrium experiment from part (b) was repeated at three other temperatures. The determined equilibrium constant (K) values are shown below. The value from part (d) should be included.
2NO₂(g) ⇌ N₂O₄(g) ∆\(H^⦵\) = –55.3 kJ mol⁻¹

T (°C)	T (K)	K
0.0		Value from (d)
20.0		4.74
50.0		5.76 × 10⁻¹
100.0		3.64 × 10⁻²

(iv) Calculate the corresponding temperatures in Kelvin and complete the table.
(v) Using the completed table, determine whether the results are consistent with the given standard enthalpy change, ∆\(H^⦵\).

▶️ Answer/Explanation

(a) (i)
Precaution 1: Use a fume cupboard.
Reason: To prevent inhalation of toxic NO₂ gas.
Precaution 2: Wear safety goggles.
Reason: To protect eyes from corrosive acid splashes or glass fragments.
\(\boxed{\text{Fume cupboard}}\) & \(\boxed{\text{Safety goggles}}\)

(a) (ii)
The balanced equation is:
Cu (s) + 4HNO₃ (aq) → Cu(NO₃)₂ (aq) + 2NO₂ (g) + 2H₂O (l)
\(\boxed{1, 4, 1, 2, 2}\)

(a) (iii)
From the equation, 1 mol Cu → 2 mol NO₂.
Moles of Cu needed = \( \frac{0.0100}{2} = 0.00500 \) mol.
Molar mass of Cu = 63.55 g mol⁻¹.
Mass = \( 0.00500 \times 63.55 = 0.318 \) g.
\(\boxed{0.318}\)

(b)
Measurement 1: Temperature.
Expected result: Increases initially (exothermic forward reaction).
Measurement 2: Total pressure (at constant volume).
Expected result: Decreases (fewer gas moles in forward direction).
\(\boxed{\text{Temperature}}\) & \(\boxed{\text{Pressure}}\)

(c) (i)
Use a thermostatically controlled water bath.
\(\boxed{\text{Water bath}}\)

(c) (ii)
The system has not reached equilibrium; concentrations are still changing.
\(\boxed{\text{Equilibrium not reached}}\)

(c) (iii)
Wait until the absorbance reading becomes constant before recording.
\(\boxed{\text{Wait for constant absorbance}}\)

(d)
\( [\text{N}_2\text{O}_4] = \frac{0.00134}{1} = 0.00134 \) mol dm⁻³
\( [\text{NO}_2] = \frac{0.00732}{1} = 0.00732 \) mol dm⁻³
\( K = \frac{0.00134}{(0.00732)^2} = \frac{0.00134}{0.0000536} \approx 25 \)
\(\boxed{25}\)

(e) (i)
• Transferring 25.0 cm³: Volumetric pipette.
• Adding NaOH: Burette.
\(\boxed{\text{Pipette}}\) & \(\boxed{\text{Burette}}\)

(e) (ii)
Example table:

Titration	Initial Burette Reading / cm³	Final Burette Reading / cm³	Volume of NaOH / cm³
1
2
3

\(\boxed{\text{Table with headers}}\)

(e) (iii)
% uncertainty = \( \frac{0.05}{20.05} \times 100 \approx 0.25\% \)
\(\boxed{0.25}\)

(f) (iv)
T(K) = T(°C) + 273.15
0.0 °C → 273.2 K
20.0 °C → 293.2 K
50.0 °C → 323.2 K
100.0 °C → 373.2 K
\(\boxed{273.2, 293.2, 323.2, 373.2}\)

(f) (v)
Yes, the results are consistent. As temperature increases, K decreases, confirming the reaction is exothermic (∆H⦵ < 0).
\(\boxed{\text{Yes}}\)

IB DP Chemistry Mock Exam SL Paper 1B Set 4 - 2025 Syllabus

IB DP Chemistry Mock Exam SL Paper 1B Set 4

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