Paper 4 Experimental Techniques Structured Practice
5 structured exam questions on experimental techniques for IGCSE Chemistry Paper 4. Covers separation methods, chromatography, tests for ions and gases, and practical skills. Total: 26 marks.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Five structured questions in the style of IGCSE Chemistry Paper 4, totalling 26 marks. Write your answers in full before checking the mark scheme.
Question 1 (5 marks)
A mixture contains sand, salt, and iron filings.
Describe a method to separate this mixture into its three components. [5]
Mark scheme
Step 1: Use a magnet to attract and remove the iron filings from the mixture [1].
Step 2: Add water to the remaining mixture (sand and salt) and stir to dissolve the salt [1].
Step 3: Filter the mixture. The sand remains as the residue on the filter paper. The salt solution passes through as the filtrate [1].
Step 4: Dry the sand (e.g. in an oven or leave in air) [1].
Step 5: Heat the filtrate gently to evaporate the water and obtain the salt as crystals/solid [1].
Total: 5 marks
Question 2 (6 marks)
A student carries out paper chromatography on a food colouring. The chromatogram shows that the food colouring separates into three spots.
| Distance from start line (cm) | |
|---|---|
| Solvent front | 12.0 |
| Spot A | 9.6 |
| Spot B | 6.0 |
| Spot C | 3.6 |
(a) Calculate the Rf value of spot B. [1]
(b) A known dye has an Rf value of 0.80 under the same conditions. Which spot could be this dye? [1]
(c) State why the start line should be drawn in pencil, not ink. [1]
(d) State why the level of the solvent must be below the start line when the chromatography paper is placed in the beaker. [1]
(e) Explain how chromatography can distinguish between a pure substance and a mixture. [2]
Mark scheme
(a) Rf = 6.0 / 12.0 = 0.50 [1]
(b) Spot A (Rf = 9.6 / 12.0 = 0.80) [1]
(c) Pencil does not dissolve in the solvent / ink would dissolve and move with the solvent, interfering with the results [1].
(d) If the solvent level is above the start line, the spots would dissolve directly into the solvent instead of being carried up the paper by the solvent [1].
(e) A pure substance produces only one spot on the chromatogram [1]. A mixture produces two or more spots, showing it contains more than one component [1].
Total: 6 marks
Question 3 (5 marks)
An unknown solution could contain one of the following cations: Cu²⁺, Fe²⁺, Fe³⁺, or Zn²⁺.
The student adds sodium hydroxide solution to a sample of the unknown solution. A white precipitate forms that dissolves in excess sodium hydroxide.
(a) Identify the cation present. Explain your reasoning. [2]
(b) State the colour of the precipitate that would form if the solution contained Fe³⁺ ions. [1]
(c) Write the ionic equation for the reaction of Cu²⁺ ions with sodium hydroxide solution. [1]
(d) State the colour of the precipitate formed when NaOH is added to a solution containing Cu²⁺ ions. [1]
Mark scheme
(a) Zn²⁺ [1]. Zinc hydroxide forms a white precipitate with NaOH, and zinc hydroxide is amphoteric so it dissolves in excess NaOH to form a colourless solution / zincate [1].
(b) Red-brown / rust-brown precipitate [1].
(c) Cu²⁺(aq) + 2OH⁻(aq) → Cu(OH)₂(s) [1]
(d) Blue precipitate [1].
Total: 5 marks
Question 4 (5 marks)
A student collects four test tubes of gas from different reactions. Describe the test and the expected result for each gas.
(a) Hydrogen [1]
(b) Oxygen [1]
(c) Carbon dioxide [1]
(d) Chlorine [1]
(e) Ammonia [1]
Mark scheme
(a) Place a burning/lit splint at the mouth of the test tube. Hydrogen burns with a squeaky pop [1].
(b) Place a glowing splint into the test tube. Oxygen relights the glowing splint [1].
(c) Bubble the gas through limewater (calcium hydroxide solution). Carbon dioxide turns limewater milky/cloudy [1].
(d) Hold damp litmus paper (or damp universal indicator paper) near the mouth of the test tube. Chlorine bleaches the damp litmus paper / turns it white [1].
(e) Hold damp red litmus paper near the mouth of the test tube. Ammonia turns damp red litmus paper blue [1].
Total: 5 marks
Question 5 (5 marks)
A student wants to determine the purity of a sample of barium chloride. She dissolves the sample in water and adds excess sodium sulfate solution.
(a) State the observation when the solutions are mixed. [1]
(b) Write the ionic equation for this reaction. [1]
(c) Describe how the student obtains and weighs the barium sulfate precipitate. [3]
Mark scheme
(a) A white precipitate forms [1].
(b) Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s) [1]
(c) Filter the mixture to collect the barium sulfate precipitate on the filter paper [1]. Wash the precipitate with distilled water to remove any soluble impurities [1]. Dry the precipitate in a warm oven (or between filter papers) and weigh it [1].
Total: 5 marks
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