Paper chromatography
2 marks · EasyExplain why two different dyes can have the same colour but different R_f values in paper chromatography.
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Dyes may have similar colours but different chemical structures. These differences affect how strongly they stick to the paper and how soluble they are in the solvent, so they move different distances up the paper and have different R_f values.
Also accept: Different dyes may appear the same colour but have different solubility in the solvent or different affinity to the paper.
Common mistakes: Stating it is only due to colour; Not mentioning chemical properties or solubility
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Marking points
B1 · 1 mark · States that dyes can have the same colour but different chemical properties/solubility/affinity for paper.
B2 · 1 mark · Explains that different solubility or affinity for paper causes different R_f values.
Worked solution
Two dyes might be the same colour but have different chemical structures. These differences mean they may not dissolve equally well in the solvent or may stick to the paper with different strength. This results in the dyes moving different distances (different R_f values), even if their colours look the same.