Separation of Solutions and Mixtures

AP Chemistry· difficulty 1/5

A student spots a black ink sample 1.5 cm from the bottom of a strip of chromatography paper and develops it in 70/30 isopropanol/water. The solvent front travels 8.0 cm from the spot. Three components are observed: blue (3.2 cm), red (5.6 cm), yellow (7.2 cm), all measured from the original spot.

origin front blue 3.2 red 5.6 yellow 7.2

What is the Rf value of the red component?

  • A

    1.43

  • B

    0.40

  • C

    5.6

  • D

    0.70

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Explanation

Rf = distance solute / distance solvent front = 5.6 / 8.0 = 0.70.

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