These nine questions mix the skills in acids, bases and salts. Write a full answer before you open the explanation.
Questions
Q1. 0.10 mol dm⁻³ hydrochloric acid and 0.10 mol dm⁻³ ethanoic acid are compared. Which has the lower pH, and why?
Answer
Hydrochloric acid has the lower pH. It is a strong acid that ionises completely in water, so the hydrogen ion concentration is 0.10 mol dm⁻³. Ethanoic acid is a weak acid that ionises partially, so its hydrogen ion concentration is much lower at the same concentration.
Q2. Write a balanced equation for sulfuric acid reacting with sodium hydroxide.
Answer
The salt is Na₂SO₄. The equation is H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O.
Check hydrogen: 2 + 2 = 4 on the left and 4 on the right.
Q3. 20.0 cm³ of 0.10 mol dm⁻³ sulfuric acid is neutralised by 0.25 mol dm⁻³ sodium hydroxide. Find the volume of sodium hydroxide needed.
Answer
Moles of H₂SO₄ = 0.0200 × 0.10 = 0.0020 mol. From the equation, 1 mol H₂SO₄ needs 2 mol NaOH, so NaOH = 0.0040 mol.
Volume = 0.0040 ÷ 0.25 = 0.016 dm³, which is 16.0 cm³.
Q4. What mass of copper(II) oxide reacts fully with 50.0 cm³ of 1.0 mol dm⁻³ sulfuric acid? (Cu = 64, O = 16)
Answer
Moles of H₂SO₄ = 0.0500 × 1.0 = 0.050 mol. The equation CuO + H₂SO₄ → CuSO₄ + H₂O is 1 : 1, so CuO = 0.050 mol.
Mr of CuO = 64 + 16 = 80, so mass = 0.050 × 80 = 4.0 g. In the preparation, use more than this so that all the acid reacts.
Q5. Name the method for preparing (a) potassium nitrate, (b) zinc sulfate, (c) lead(II) chloride.
Answer
(a) Potassium nitrate: titration of nitric acid with potassium hydroxide, because it is a potassium salt.
(b) Zinc sulfate: sulfuric acid with excess zinc, zinc oxide or zinc carbonate, filter, then crystallise.
(c) Lead(II) chloride: it is insoluble, so mix lead(II) nitrate solution with sodium chloride solution, then filter and rinse.
Q6. Why can copper not be used with dilute sulfuric acid to make copper(II) sulfate?
Answer
Copper is below hydrogen in the reactivity series, so it does not displace hydrogen from dilute acid. No reaction occurs. Use copper(II) oxide or copper(II) carbonate instead.
Q7. Solution W gives a blue precipitate with sodium hydroxide that stays in excess. Ammonia solution gives a blue precipitate that dissolves in excess to a deep blue solution. Name the cation.
Answer
The cation is Cu²⁺. The blue precipitate rules out ions that give white or green precipitates. The deep blue solution in excess ammonia is the feature of Cu²⁺.
Q8. Write the ionic equation for silver nitrate solution reacting with sodium chloride solution.
Answer
Full equation: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq). Na⁺ and NO₃⁻ are spectators.
Ionic equation: Ag⁺(aq) + Cl⁻(aq) → AgCl(s). The charge is 0 on both sides.
Q9. Write the ionic equation for zinc with dilute hydrochloric acid and check the charges.
Answer
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g). Cancel Cl⁻, which appears on both sides.
Ionic equation: Zn(s) + 2H⁺(aq) → Zn²⁺(aq) + H₂(g). The charge is +2 on both sides.
If you got these wrong
Return to the lesson that matches the slip.
- Q1: distinguishing strength from concentration.
- Q2: writing neutralisation equations.
- Q3 and Q4: calculating acid-base quantities.
- Q5 and Q6: planning salt preparation.
- Q7: interpreting qualitative analysis observations.
- Q8 and Q9: writing ionic equations.
Use the concentration and dilution tutor for more calculation practice, and record slips in the mistake log. For a teacher to go through new questions with you, see online one-to-one Chemistry tuition.