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Hidden colours in a chromatogram
A student used chromatography to investigate the colours in a printer ink.
There were four colours in the printer ink.
Suggest one reason why only three colours were visible on the chromatogram.
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Study the marking See what earns credit and compare it with a full-mark answer.
Marking points
- 1 Suggests that two dyes have the same Rf value.
- 2 Suggests that two dye spots are in the same place.
- 3 Suggests that two colours are insoluble.
- 4 Suggests that the fourth colour is white.
Full-mark answer
Two of the dyes may have had the same Rf value, so their spots overlapped and appeared as one colour.
Why this answer loses marks
The missing dye was colourless.
The official scheme ignores “colourless”; use a supported chromatogram-based or visible-colour reason.