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How does a solvent affect rf value?

The better something dissolves in the solvent, the higher its Rf value will be.

The retention factor ##r_f## of something in chromatography is basically a measure of how well something can be carried in the as it moves. For example, things that spend a lot of time in the mobile phase (dissolved in the solvent) and a little time in the stationary phase (stuck to the silica gel or other medium) will have a higher ##r_f## value than something that spends most of its time stuck to the stationary phase.

As a result, the polarity of the solvent is very important. As I'm sure you've already seen, are very good at dissolving in solvents with similar polarities ("like dissolves like.") As a result, a polar will have a much higher ##r_f## value if the solvent is also polar.

In practice, this requires some tinkering in the lab. You may find that using acetone isn't good at separating the solutes because both have similar polarities. As a result, you may want to go with a less polar solvent such as hexane, or a combination of polar and nonpolar solvents (ethyl acetate/hexane).

Here is a video which shows a paper chromatography experiment which was conducted to separate the pigments found in a black overhead marker. Video from: Noel Pauller


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