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A Level H2 Chemistry Acids Bases Salts Quiz
Free A Level H2 Chemistry Acids Bases Salts quiz, Exam version, with questions, answers, and A Level-style practice for Singapore students.
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A-Level Chemistry H2 Quiz - Acids Bases Salts - Answer Key
Total Marks: 35
Section A: Short Answer Questions [15 marks]
1. Complete the following table for gas identification tests. [4 marks]
| Gas | Test and Result |
|---|---|
| Ammonia, NH₃ | Turns damp red litmus paper blue [1] |
| Hydrogen, H₂ | Burns with a pop sound / rekindles a glowing splint [1] |
| Chlorine, Cl₂ | Bleaches damp litmus paper (turns white) [1] |
| Sulfur dioxide, SO₂ | Bleaches damp litmus paper but does not rekindle splint [1] |
2. Write the ionic equation for the reaction between aluminum oxide and hot aqueous sodium hydroxide. [2 marks]
Al₂O₃(s) + 2OH⁻(aq) + 3H₂O(l) → 2[Al(OH)₄]⁻(aq) [2] Award 1 mark for correct reactants and products, 1 mark for balancing and state symbols
3. State what is observed when aqueous ammonia is added dropwise to a solution containing Cu²⁺ ions until the ammonia is in excess. [2 marks]
Initial observation: Blue precipitate forms [1] In excess ammonia: Blue precipitate dissolves to form deep blue solution [1]
4. A student performs a titration and records the following volumes... [3 marks]
Working:
- Exclude Trial 1 (rough titration) [1]
- Concordant results: 24.25, 24.20, 24.30 cm³ (within 0.1 cm³)
- Mean = (24.25 + 24.20 + 24.30) ÷ 3 = 24.25 cm³ [1]
Suitable volume: 24.25 cm³ or 24.3 cm³ [1]
5. Explain why BrF₃ exhibits electrical conductivity... [4 marks]
Explanation: BrF₃ undergoes autoionization/self-dissociation [1] to produce ions [1] which can carry electric current [1]
Equation: 2BrF₃ ⇌ BrF₂⁺ + BrF₄⁻ [1]
Section B: Structured Questions [20 marks]
6. A student investigates the reaction between magnesium carbonate and hydrochloric acid.
(a) Write a balanced equation for this reaction, including state symbols. [2 marks]
MgCO₃(s) + 2HCl(aq) → MgCl₂(aq) + H₂O(l) + CO₂(g) [2] 1 mark for correct formula and products, 1 mark for balancing and state symbols
(b)(i) Calculate the number of moles of MgCO₃ added. [1 mark]
n = m/M = 2.50/(24.3 + 12.0 + 48.0) = 2.50/84.3 = 0.0297 mol [1]
(b)(ii) Calculate the number of moles of HCl added. [1 mark]
n = c × V = 2.00 × (50.0/1000) = 0.100 mol [1]
(b)(iii) Determine which reagent is in excess and by how many moles. [2 marks]
From equation: 1 mol MgCO₃ reacts with 2 mol HCl Moles HCl needed = 0.0297 × 2 = 0.0594 mol [1] HCl is in excess by 0.100 - 0.0594 = 0.0406 mol [1]
(c) Calculate the volume of CO₂ gas produced... [2 marks]
Moles CO₂ = moles MgCO₃ = 0.0297 mol [1] Volume = 0.0297 × 24.0 = 0.713 dm³ [1]
7. The following table shows the reactions of some aqueous cations...
(a) Complete the table below. [6 marks]
| Cation | Reaction with NaOH(aq) | Reaction with NH₃(aq) |
|---|---|---|
| Al³⁺(aq) | White ppt., soluble in excess [1] | White ppt., insoluble in excess |
| Fe²⁺(aq) | Green [1] ppt., insoluble in excess | White ppt., oxidizes to brown [1] |
| Zn²⁺(aq) | White ppt., soluble in excess | White ppt., soluble in excess [3] |
(b) Write the formula of the complex ion formed... [1 mark]
[Cu(NH₃)₄]²⁺ [1]
(c) Explain why Al³⁺ forms a precipitate that dissolves in excess NaOH but not in excess NH₃. [3 marks]
Al³⁺ forms Al(OH)₃ precipitate initially [1] Al(OH)₃ is amphoteric and dissolves in excess NaOH to form [Al(OH)₄]⁻ [1] NH₃ is a weaker base and cannot deprotonate Al(OH)₃ / NH₃ does not form a stable complex with Al³⁺ [1]