Topic 12 Practice Paper: Experimental techniques and chemical analysis — mark scheme
IGCSE · Cambridge IGCSE Chemistry (Extended (Core + Supplement))
Mark scheme
Experimental techniques and chemical analysis
Topic 12 Practice Paper · Maximum mark: 30
Notes for markers
- Award one mark for each point marked [1], up to the marks shown for the part.
- Accept answers worded differently that show the same understanding.
- Units are required where the answer line shows one. ecf: allow an error carried forward.
Section A: Multiple-choice questions[10 marks]
| Question | Answer | |
|---|---|---|
| 1 | AThe burette’s tap gives drop-by-drop control and its scale records the delivered volume to 0.05 cm³. | 1 |
| 2 | DThe insoluble chalk is the residue; the water that passes through is the filtrate. | 1 |
| 3 | BCarbon dioxide turns limewater milky. The relighting splint is oxygen, the bleach is chlorine and the pop is hydrogen. | 1 |
| 4 | CRelighting a glowing splint is the defining test for oxygen. | 1 |
| 5 | ADistillation evaporates and condenses the solvent, collecting it pure; crystallisation instead recovers the solid solute. | 1 |
| 6 | DTwo miscible liquids with different boiling points separate on a fractionating column; a separating funnel only works for immiscible liquids. | 1 |
| 7 | BA white precipitate soluble in excess NaOH but insoluble in excess ammonia points to aluminium ions; zinc ions dissolve in both. | 1 |
| 8 | CAll three halides are tested with silver nitrate after acidifying with nitric acid; iodide gives a yellow precipitate. | 1 |
| 9 | BRf = distance by dye ÷ distance by solvent = 3.0 ÷ 12.0 = 0.25. | 1 |
| 10 | DChromium(III) gives a grey-green precipitate that redissolves in excess sodium hydroxide, forming a green solution. | 1 |
Section B: Structured questions[20 marks]
| Question | Answer and marking points | Marks |
|---|---|---|
| 11(a) | Rinse a volumetric pipette with the potassium hydroxide solution, then fill it to the graduation mark and run exactly 25.0 cm³ into the conical flask.
| 2 |
| 11(b) | A burette is used; the final burette reading is taken at the first permanent colour change, and the difference from the initial reading gives the volume of acid added.
| 2 |
| 11(c) | Its colour changes gradually over a range of pH, so the exact end point cannot be judged; a single-change indicator is needed.
| 1 |
| Total for Question 11 | 5 | |
| 12(a) | The amino acids are colourless, so a locating agent is needed to make their spots visible.
| 1 |
| 12(b) | Q is a mixture of at least two substances.
| 1 |
| 12(c) | Rf = 5.4 ÷ 9.0 = 0.6. [1] | 1 |
| 12(d) | Pencil is insoluble in the solvent, so the line stays fixed; ink would dissolve and travel up the paper.
| 1 |
| 12(e) | Run the known amino acid on the same chromatogram and compare the heights of the spots (or Rf values) in the same solvent.
| 1 |
| Total for Question 12 | 5 | |
| 13(a) | filtration [1] | 1 |
| 13(b) | The solid product left on the filter paper is the residue; the solution passing through is the filtrate.
| 2 |
| 13(c) | Heat the filtrate to evaporate some water until crystals just form on a glass rod, then leave the concentrated solution to cool so crystals grow, and dry them between filter papers.
| 2 |
| Total for Question 13 | 5 | |
| 14(a) | T contains water. [1] | 1 |
| 14(b) | T is not pure: a pure liquid boils at one fixed temperature, and boiling over a range shows a mixture (ethanol with water).
| 2 |
| 14(c) | Fractional distillation; it relies on the different boiling points of ethanol (78 °C) and water (100 °C).
| 2 |
| Total for Question 14 | 5 |
— End of mark scheme —