Paper chromatography
3 marks · EasyA student is testing three samples using paper chromatography. The chromatogram below shows the positions of the spots after the experiment was completed. The solvent front moved 9.0 cm from the pencil line.
(a) Which sample travelled furthest from the pencil line? [1]
(b) Calculate the R_f value for sample Y. [1]
(c) Explain what a high R_f value tells you about a dye's solubility in the solvent. [1]
Which sample travelled furthest from the pencil line?
Calculate the R_f value for sample Y.
Explain what a high R_f value tells you about a dye's solubility in the solvent.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Sample Z
(b) 0.60
(c) A high R_f value shows the dye is very soluble in the solvent (moves easily up the paper).
Common mistakes: Dividing the wrong way round for Rf; Not stating relation to solubility
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies correct sample: Z
M1 (b) · 1 mark · Calculates R_f for sample Y as 5.4/9.0 = 0.60
B2 (c) · 1 mark · States that a high R_f value means the dye is highly soluble/moves easily in the solvent
Worked solution
a) Sample Z travelled furthest from the pencil line. b) R_f for Y = distance travelled by Y / distance travelled by solvent front = 5.4 cm / 9.0 cm = 0.60 c) A high R_f value indicates the dye is very soluble in the solvent and does not stick much to the paper.