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CIE iGCSE Co-Ordinated Science C7.1 The characteristic properties of acids and bases Exam Style Questions Paper 4

CIE iGCSE Co-Ordinated Science Paper 4 - All Chapters

Question

(a) A student tests three different solutions to identify the ion in each solution.
Draw lines to match each test to the observation and the ion in each solution.
(b) Dilute sulfuric acid, H₂SO₄, reacts with solid copper oxide, CuO. Copper sulfate solution and water are made.
(i) Construct the balanced symbol equation for this reaction. Include state symbols.
(……) + (……) → (……) + (……)
(ii) Tick \((\checkmark)\) the correct box to identify the type of reaction that takes place.
(iii) The reaction between dilute sulfuric acid and copper oxide is faster when more concentrated acid is used.
Explain why, using collision theory.
(iv) The enthalpy change, \(\Delta H\), for the reaction is negative.
Fig. 7.1 shows two reaction pathway diagrams, A and B.
State which of these reaction pathway diagrams, A or B, represents the energy change for this reaction. Explain your answer.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C12.5 — Qualitative analysis
• Topic C7.1 — Characteristic properties of acids and bases
• Topic C6.2 — Rate of reaction
• Topic C5.1 — Exothermic and endothermic reactions

▶️ Answer/Explanation

(a)

These tests are standard qualitative analysis techniques used to identify ions in solution. The colour of precipitates formed with specific reagents helps identify the ions present.

(b)(i) H₂SO₄(aq) + CuO(s) → CuSO₄(aq) + H₂O(l)
Sulfuric acid reacts with copper oxide to form copper sulfate and water. Copper sulfate is a soluble salt, so it is in aqueous solution.

(b)(ii) neutralisation
This is an acid-base reaction where an acid (H₂SO₄) reacts with a base (CuO) to form a salt (CuSO₄) and water.

(b)(iii) more particles per unit volume ; frequency of collision (of particles) is higher
Higher concentration means more acid particles in the same volume, increasing the frequency of successful collisions with copper oxide particles and speeding up the reaction.

(b)(iv) diagram A ; any two from:

• exothermic
• products have lower energy than reactants
• energy is released to the surroundings

A negative ΔH indicates an exothermic reaction, where the products have lower energy than the reactants and energy is released to the surroundings. Diagram A shows this energy profile.

Question

A student investigates the reaction between dilute hydrochloric acid and solid pieces of calcium carbonate.
(a) The balanced symbol equation for the reaction is shown. Complete the state symbols in the equation.
2HCl( ) + CaCO₃( ) → CaCl₂(aq) + CO₂( ) + H₂O(l)
(b) The student measures the total volume of carbon dioxide made every minute for 7 minutes. Fig. 8.1 shows a graph of the student’s results.
(i) State when the reaction finished.
(ii) The student repeats the experiment with larger pieces of calcium carbonate.
The student uses the same volume and concentration of hydrochloric acid and the same mass of calcium carbonate.
Draw on Fig. 8.1 the line for the student’s results.
(c) The student predicts the reaction will be faster with a higher concentration of hydrochloric acid. Explain why the student is correct.
(d) Calculate the mass of calcium chloride, CaCl₂, made when 0.2 moles of hydrochloric acid react with excess calcium carbonate.
2HCl + CaCO₃ → CaCl₂ + CO₂ + H₂O
[Aᵣ: Ca = 40; Cl = 35.5; H = 1]

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C7.1 — Characteristic properties of acids and bases (Part (a))
• Topic C6.2 — Rate of reaction (Part (b), (c))
• Topic C3.2 — Relative masses of atoms and molecules (Part (d))

▶️ Answer/Explanation

(a) State symbols:
2HCl(aq) + CaCO₃(s) → CaCl₂(aq) + CO₂(g) + H₂O(l)

(b)(i) Reaction finished at 4.8 minutes.
The graph reaches a plateau (no further increase in CO₂ volume) at approximately 4.8 minutes.

(b)(ii) Line for larger pieces:
The line would be less steep (slower initial rate) but reach the same final volume. This is because larger pieces have a smaller total surface area, reducing the frequency of collisions between acid particles and the calcium carbonate.

(c) Why higher concentration increases rate:
• Higher concentration means more HCl molecules per unit volume.
• This increases the frequency of collisions between reactant particles.
• More successful collisions occur per unit time, increasing the rate of reaction.

(d) Calculation:
Moles of CaCl₂ produced = 0.2 ÷ 2 = 0.1 mol (from equation: 2 mol HCl → 1 mol CaCl₂)
Mᵣ of CaCl₂ = 40 + (2 × 35.5) = 111
Mass = 0.1 × 111 = 11.1 g

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