Purity and separating mixtures

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Question 19
Medium

A scientist uses thin-layer chromatography (TLC) and melting point analysis to investigate the purity of three samples of caffeine extracted from different sources, labeled X, Y, and Z.

The scientist compares the three samples with a sample of pure caffeine. Look at the chromatogram and the melting point data below.

A chromatogram profile of four lanes: X, Y, Z, and Pure caffeine. The pencil baseline is at the bottom, and the solvent front is at the top. Lane 'Pure caffeine' contains a single spot at Rf = 0.60. Lane Z contains a single spot at Rf = 0.60. Lane X contains two spots: one at Rf = 0.60 and one at Rf = 0.35. Lane Y contains two spots: one at Rf = 0.20 and one at Rf = 0.45. Only lanes X, Z, and Pure caffeine have a spot at Rf = 0.60.

Melting Point Data Table:

  • Sample X: 230∘C−233∘C230^\circ\text{C} - 233^\circ\text{C}230∘C−233∘C
  • Sample Y: 195∘C−200∘C195^\circ\text{C} - 200^\circ\text{C}195∘C−200∘C
  • Sample Z: 235∘C235^\circ\text{C}235∘C
  • Pure caffeine: 235∘C235^\circ\text{C}235∘C

Determine which samples (X, Y, and Z) are pure, and which samples contain caffeine. Explain your answer using both the chromatogram and melting point data.

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Purity and separating mixtures Questions

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