Paper chromatography
4 marks · NormalYou want to check whether a green dye in a drink is a single substance or a mixture of dyes. You will use paper chromatography to investigate.
Describe how you would set up and carry out this experiment, naming all key steps.
Explain how you would use the chromatogram to decide if the green dye is pure or a mixture.
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.
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(a) Draw a pencil line about 1 cm from the bottom of chromatography paper. Place a spot of the green dye on the line. Suspend the paper in a beaker with a small amount of suitable solvent, making sure the solvent is below the spot. Cover the beaker and let the solvent rise up the paper until near the top. Remove paper and mark the solvent front.
(b) If there is one spot above the start line, the dye is pure; if there are two or more spots, the dye is a mixture.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Mentions setting up paper with pencil line and placing green dye spot on the line.
M2 (a) · 1 mark · Mentions suspending paper in solvent, solvent below the spot, and covering beaker or allowing solvent to rise.
B1 (b) · 1 mark · Explains that one spot means pure dye, more than one spot means a mixture.
B2 (b) · 1 mark · Correctly links the appearance on chromatogram to purity or mixture.
Worked solution
a) Draw a pencil line 1 cm from the bottom of the chromatography paper. Place a small spot of green dye on the pencil line. Suspend the paper in a beaker with solvent, ensuring the solvent is below the spot. Cover the beaker, allow the solvent to rise, remove the paper before it reaches the top, and mark the solvent front.
b) If only one green spot appears above the pencil line, the dye is pure. If two or more spots appear with different colours or distances, the dye is a mixture.