Home / iGCSE Chemistry 0620 Extended – 12.3 Chromatography- Exam Style Questions Paper 2

iGCSE Chemistry 0620 Extended - 12.3 Chromatography- Exam Style Questions Paper 2- New Syllabus

iGCSE Chemistry MCQ (Extended) Paper 2 - All Chapters

Question

Chromatography is used to separate and analyse mixtures of soluble substances.

The first steps are:

  • apply sample to baseline
  • develop chromatogram in solvent

What is the next step to detect soluble colourless substances?

A. calculate the \(R_f\) values
B. compare the results with known substances
C. count the number of spots
D. use a suitable locating agent

▶️ Answer/Explanation
If the substances are colourless, they are not visible on the chromatogram. A locating agent (e.g., ninhydrin for amino acids, or viewing under UV light) must be used to make the spots visible before any measurements or analysis like calculating \(R_f\) values can be done.
✅ Answer: (D)

Question

A colourless mixture is separated by paper chromatography.

The steps below describe the method. These steps are not in the correct order.

  1. Remove the chromatography paper from the solvent when the solvent front is near the top of the paper.
  2. Place the chromatography paper in the solvent.
  3. Spray the chromatography paper with a locating agent.
  4. Place a spot of the mixture on the pencil line.
  5. Draw a pencil line at the bottom of the chromatography paper.
  6. Draw a pencil line to mark the position of the solvent front.

What is the correct order for these steps?

A. 3 → 5 → 6 → 4 → 2 → 1
B. 5 → 4 → 3 → 2 → 1 → 6
C. 3 → 5 → 4 → 1 → 2 → 6
D. 5 → 4 → 2 → 1 → 6 → 3

▶️ Answer/Explanation
The correct sequence for paper chromatography is:
Step 5: Draw a pencil line at the bottom of the chromatography paper (baseline).
Step 4: Place a spot of the mixture on the pencil line.
Step 2: Place the chromatography paper in the solvent (solvent level below the baseline).
Step 1: Remove the paper when the solvent front is near the top.
Step 6: Draw a pencil line to mark the position of the solvent front immediately.
Step 3: Spray with a locating agent to make colourless spots visible.
Order: 5 → 4 → 2 → 1 → 6 → 3.
✅ Answer: (D)

Question

In paper chromatography, what is the equation for the \(R_{\mathrm{f}}\) value?

A. \(R_{\mathrm{f}} = \dfrac{\text{distance travelled by solvent}}{\text{distance travelled by substance}}\)
B. \(R_{\mathrm{f}} = \dfrac{\text{distance travelled by locating agent}}{\text{distance travelled by substance}}\)
C. \(R_{\mathrm{f}} = \dfrac{\text{distance travelled by substance}}{\text{distance travelled by locating agent}}\)
D. \(R_{\mathrm{f}} = \dfrac{\text{distance travelled by substance}}{\text{distance travelled by solvent}}\)

▶️ Answer/Explanation
The Rf (retention factor) is calculated by dividing the distance moved by the substance (the spot) from the baseline by the distance moved by the solvent front from the baseline. Option D gives this correct formula. The solvent always travels further, so Rf is a fraction less than 1.
✅ Answer: D
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