The questions are on the group 2 and halogens test. Take it under real conditions before reading the mark scheme.
Quick answer: Group 2 metals are reactive metals that lose two outer electrons to form 2+ ions, and their reactivity rises down the group. This mark scheme gives the model answers and the marks for the 8 questions of the Chemistry 11-12 test on group 2 and halogens, from calcium and water to limewater concentration, with the equivalent answers to accept.
Use these model answers and the marking points to check your work. Award marks for correct method even when the final number is wrong, and note which trend or equation you need to revise.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.2.2-3.2.3
Question 1 Calcium and water (2 marks)
- Any two: bubbles of gas (hydrogen); the metal dissolves/disappears; the solution turns cloudy white as sparingly soluble Ca(OH)₂ forms; the test tube warms.
Marking: 1 mark each observation.
Question 2 Ionisation energy trend (2 marks)
- Barium’s first ionisation energy (503 kJ mol⁻¹) is lower than magnesium’s (738), so its outer electrons are lost more easily; the outer electrons are further from the nucleus and better shielded.
Marking: 1 mark for lower ionisation energy, 1 for distance or shielding.
Question 3 Testing for sulfate (3 marks)
- Add dilute hydrochloric acid, then barium chloride solution; a white precipitate forms.
- Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
Marking: 1 for acid then BaCl₂, 1 for white precipitate, 1 for equation with state symbols.
Question 4 Magnesium and acid (2 marks)
- n(Mg) = 2.43 ÷ 24.3 = 0.100 mol = n(H₂); V = 0.100 × 24.0 = 2.40 dm³.
Marking: 1 for the amount, 1 for the volume.
Question 5 Halogen displacement (2 marks)
- The solution turns brown (iodine forms): Br₂ + 2I⁻ → 2Br⁻ + I₂.
Marking: 1 for the colour, 1 for the balanced equation.
Question 6 Trend in boiling points (2 marks)
- Br₂ molecules have more electrons, so the London forces are stronger and more energy is needed to overcome them.
Marking: 1 for more electrons, 1 for stronger London forces.
Question 7 Making bleach (3 marks)
- 0, −1 and +1.
- Chlorine is reduced (0 → −1) and oxidised (0 → +1) in the same reaction.
Marking: 1 for oxidation states, 1 for reduced and oxidised named, 1 for the same element.
Question 8 Limewater concentration (4 marks)
- Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O.
- n(HCl) = 0.02000 × 0.0500 = 1.00 × 10⁻³ mol; n(Ca(OH)₂) = 5.00 × 10⁻⁴ mol; c = 5.00 × 10⁻⁴ ÷ 0.0250 = 0.0200 mol dm⁻³.
- 0.0200 × 74.1 = 1.48 g dm⁻³.
Marking: 1 equation, 1 amount of HCl and ratio, 1 concentration, 1 solubility.
