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The reaction between aluminium and EXCESS sulphuric acid is used to investigate factors affecting rates of reactions - NSC Physical Sciences - Question 5 - 2024 - Paper 2
Question 5
The reaction between aluminium and EXCESS sulphuric acid is used to investigate factors affecting rates of reactions. 2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g) ... show full transcript
Worked Solution & Example Answer:The reaction between aluminium and EXCESS sulphuric acid is used to investigate factors affecting rates of reactions - NSC Physical Sciences - Question 5 - 2024 - Paper 2
Step 1
5.1.1 Is the reaction between Al(s) and dilute H2SO4(aq) ENDOTHERMIC or EXOTHERMIC? Give a reason for the answer by referring to the above diagrams.
Answer
The reaction between Al(s) and dilute H2SO4(aq) is EXOTHERMIC. This is indicated by the lower potential energy of the products compared to the reactants in Diagram A. The enthalpy change (ΔH) is negative, which signifies that more energy is released than absorbed during the reaction.
Step 2
5.1.2 What does the shaded area to the right of line P represent?
Answer
The shaded area to the right of line P represents the number of particles with sufficient kinetic energy to overcome the activation energy barrier and effectively collide to result in a reaction. This area indicates the proportion of reacting particles.
Step 3
5.1.3 Determine the numerical value represented by the letter X on diagram B.
Answer
The numerical value represented by the letter X on diagram B corresponds to the activation energy required for the reaction to occur with a catalyst. By approximation, it is generally observed that this value is around 55 kJ.
Step 7
Step 8
5.3.2 Use the collision theory to explain how the average rate of the reaction is affected in this investigation.
Answer
According to the collision theory, the average rate of reaction increases with higher concentrations of reactants, as there are more particles available per unit volume to collide with each other. Therefore, in this investigation, as the concentration of H2SO4 increases, the collision frequency between reactant particles also increases, resulting in a higher average rate of reaction.
Step 9
5.3.3 Calculate the percentage purity of the aluminium.
Answer
To calculate the percentage purity of the aluminium, we first find the total volume of hydrogen produced in RUN 3:
- Total volume = 40 cm³·s⁻¹ × 2.6 min × 60 s/min = 6240 cm³
Now using the molar gas volume at 60 °C, we convert this volume:
- Moles of H₂ = Volume / Molar gas volume = 6240 cm³ / 207 cm³·mol⁻¹ ≈ 30.1 mol
From the stoichiometry of the reaction, 2 moles of Al produce 3 moles of H₂. Thus, moles of Al that reacted = (2/3) × moles of H₂ ≈ 20.1 mol.
Now calculate the mass of Al (using molar mass of Al, 27 g/mol):
- Mass = Moles × Molar Mass = 20.1 mol × 27 g/mol ≈ 542.7 g.
Percentage Purity = (mass of pure Al / initial mass) × 100 = (542.7 g / 5 g) × 100 ≈ 81.2%.