TLC: Solvent Effects Question

[justadream]

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1) Do polar solvents or nonpolar solvents travel up a silica gel TLC plate faster?

2) For a polar solvent traveling up a SUPER polar plate, as you increase the polarity of your solvent, what happens to the speed?

 

[The Brown Knight]

The silica gel is made of SiO2 polymers, where some of the oxygen atoms are negatively charged (or could be bound to a proton). This means polar solvents (as well as polar solutes) will be attracted to the gel and won't move up as quickly. Hence, you need non polar solvents like hexane to develop a TLC.

Increasing the polarity of solvent will increase its intermolecular interactions with the stationary phase and slow the solvent down.