Interpreting Chromatograms Flashcards

All 7 cards in this deck

In paper chromatography, what are the mobile phase and the stationary phase?

The mobile phase is the solvent that moves through the paper; the stationary phase is the paper.

Why do substances end up in different places on a chromatogram?

They are carried by the solvent at different rates over the paper.

What is the formula for the $R_f$ value?

$R_f = \dfrac{\text{distance moved by the dye}}{\text{distance moved by solvent front}}$

True or false? An $R_f$ value can be greater than 1.

False. A substance cannot travel further than the solvent front, so $R_f$ is never more than 1.

On a chromatogram, what does the number of spots produced by an ink tell you?

The number of different dyes (coloured substances) in that ink.
e.g. an ink giving 5 spots contains 5 dyes.

How does a chromatogram show whether a substance is pure or impure?

A pure substance gives only one spot. An impure substance (a mixture) gives more than one spot.

How can paper chromatography be used to identify a substance in a mixture?

Run samples of known pure substances on the same paper next to the mixture. If a spot from the mixture moves the same distance (same $R_f$ value) as a known substance, it may be that substance.