The questions are on the chemical analysis test. Take it under real conditions before reading the mark scheme.
Quick answer: Chemical analysis identifies what a sample contains. This mark scheme gives the model answers and the marks for the 8 questions of the Chemistry 9-10 test on chemical analysis, from chromatogram to unknown white solid, with the equivalent answers to accept.
Use this guide to mark the paper out of 20. Each mark is for one clear point, a correct formula or a correct equation. Accept any other equivalent wording, and do not penalise British or American spelling.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE C8
Question 1 Chromatogram (3 marks)
a. 4.2 ÷ 6.0 = 0.70.b. Yes: the spot is at the same distance as dye 1.
c. No: X has two spots, so it is a mixture.
Marking: 1 mark each.
Question 2 Flame tests (2 marks)
a. Potassium (K⁺).b. Calcium (Ca²⁺).
Marking: 1 mark each.
Question 3 Sodium hydroxide tests (3 marks)
a. Fe³⁺.b. Al³⁺.
c. Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(s).
Marking: 1 mark each.
Question 4 Gas tests (2 marks)
a. Hold a lit splint at the gas: it gives a squeaky pop.b. Use a glowing splint: it relights.
Marking: 1 mark each.
Question 5 Testing for sulfate (3 marks)
a. Dilute hydrochloric acid, then barium chloride solution.b. A white precipitate.
c. The acid removes carbonate ions, which would also give a white precipitate with barium.
Marking: 1 mark each.
Question 6 Purity (2 marks)
A pure substance melts at one sharp temperature. A mixture melts over a range and usually begins to melt at a lower temperature.Marking: 1 mark for sharp fixed melting point, 1 mark for mixture range or lower.
Question 7 Testing for bromide (2 marks)
Add dilute nitric acid, then silver nitrate solution: a cream precipitate forms. Ag⁺(aq) + Br⁻(aq) → AgBr(s).Marking: 1 mark for correct test and cream result, 1 mark for equation.
Question 8 Unknown white solid (3 marks)
The yellow flame shows sodium and the white precipitate shows chloride, so the solid is sodium chloride. Ag⁺(aq) + Cl⁻(aq) → AgCl(s).Marking: 1 mark for sodium, 1 mark for chloride, 1 mark for the equation.
