The question
Name: ______________________ Date: ____________ Separating two food dyes (4 points)
Experimental setup
A paper chromatogram
A student spots a green candy coating on chromatography paper (cellulose, which is covered in –OH groups) and develops it in a 1% salt-water solvent. The solvent front ends 9.6 cm above the start line. Two spots appear: a yellow spot 7.2 cm and a blue spot 3.6 cm above the start line.
(a) Calculate the Rf value of the blue spot. [1 point]
(b) Which dye interacts more strongly with the paper? Justify your answer. [1 point]
(c) The student repeats the experiment with a less polar solvent. Predict how the Rf of the blue dye will change, and justify your prediction in terms of intermolecular forces. [1 point]
(d) Explain why the start line must be drawn in pencil and placed above the level of the solvent in the beaker. [1 point]