Q75 · Practice questionComplex familiar4 marks
QUESTION 75 (4 marks)
A TLC plate compares amino-acid standards G and A with a mixture. The solvent front travels 8.0 cm. The lower and upper spots travel 2.4 cm and 4.8 cm respectively. Standards and mixture are run under identical conditions.
a) Calculate the two retention factors. [2 marks]
b) Infer the mixture components and state one limitation of this inference. [2 marks]
WORKED SOLUTION
4 marksPractice marking scheme
Rf values 0.30 and 0.60; the mixture is consistent with containing G and A, but identical Rf does not prove identity.
Divide each spot distance by 8.0 cm. The mixture spots align with the standards. Other amino acids may share the same retention factor in this solvent, so an additional solvent or analytical method could be needed.
- Calculates 0.30. [1 marks]
- Calculates 0.60. [1 marks]
- Infers G and A consistently with the standards. [1 marks]
- States co-migration does not uniquely identify a compound. [1 marks]
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