Key Concepts: Acids produce H⁺ ions and alkalis produce OH⁻ ions. Indicators show pH. Solubility rules help predict salts. Gas and ion tests identify substances.
Section A: pH and Indicators
1. Describe the pH scale and classify solutions as strong/weak acids or alkalis. [4]
2. State the colour changes for litmus, phenolphthalein and methyl orange in acids and alkalis. [6]
Section B: Acids, Bases and Salts
3. Define acids and alkalis in terms of H⁺ and OH⁻ ions. [2]
4. Write equations for acids reacting with: metals, bases, and carbonates. [3]
5. Use solubility rules to predict whether these salts are soluble: AgCl, Na₂SO₄, BaSO₄, KNO₃. [4]
6. Describe how to prepare a pure, dry sample of copper(II) sulfate crystals from copper(II) oxide and sulfuric acid. [4]
Section C: Tests for Gases, Cations and Anions
7. State the test and positive result for hydrogen, oxygen, carbon dioxide, ammonia and chlorine. [5]
8. Describe flame tests and give the flame colours for Li⁺, Na⁺, K⁺, Ca²⁺ and Cu²⁺. [5]
9. Describe the tests for NH₄⁺, Cu²⁺, Fe²⁺ and Fe³⁺ using sodium hydroxide. [4]
10. Describe tests for Cl⁻/Br⁻/I⁻, SO₄²⁻ and CO₃²⁻. [5]
11. Describe tests for water and for purity of water. [2]
Total marks: 44
Mark Scheme
1. pH 0–3 strong acid, 4–6 weak acid, 7 neutral, 8–10 weak alkali, 11–14 strong alkali [4]
2. Litmus: red in acid, blue in alkali; phenolphthalein: colourless in acid, pink in alkali; methyl orange: red in acid, yellow in alkali [6]
3. Acids are sources of H⁺ ions; alkalis are sources of OH⁻ ions [2]
4. Metal + acid → salt + H₂; base + acid → salt + water; carbonate + acid → salt + water + CO₂ [3]
5. AgCl insoluble; Na₂SO₄ soluble; BaSO₄ insoluble; KNO₃ soluble [4]
6. Add excess CuO to warm H₂SO₄; filter; crystallise; wash and dry crystals [4]
7. H₂: squeaky pop with lit splint; O₂: relights glowing splint; CO₂: turns limewater milky; NH₃: turns damp red litmus blue; Cl₂: bleaches damp litmus [5]
8. Flame tests: Li red, Na yellow, K lilac, Ca orange-red, Cu blue-green [5]
9. NH₄⁺: warm with NaOH gives ammonia; Cu²⁺ blue precipitate; Fe²⁺ green; Fe³⁺ brown [4]
10. Halides: acidified AgNO₃ gives AgCl white/AgBr cream/AgI yellow; SO₄²⁻: acidified BaCl₂ gives white BaSO₄; CO₃²⁻: acid gives CO₂ [5]
11. Water: anhydrous CuSO₄ turns blue; purity: sharp boiling point 100°C [2]