\"Explain why a particular solvent system gives a different set of Rf values whe
ID: 915781 • Letter: #
Question
"Explain why a particular solvent system gives a different set of Rf values when compared to a different solvent system."
We did TLC and Column Chromatography in order to determine the suitable solvent for the separation of an unkown mixture of organic chemistry. For TLC, we did the procedure with multiple different solvents, (i.e. 2:1 EtOAc:Hexane and 4:1 Hexane:EtOAc) and then determined which solvent was best at separating our compound and determined the Rf values.
I'm just a little bit confused about what this question is asking, and am pretty confused about it.
Explanation / Answer
Different solvents have different polarity. The organic compounds move on a TLC plate depending upon its polarity and interaction with the stationary phase. Going with the principle of like dissolves like. Say we have a less polar compound like bromoalkane and a more polar compound say an alcohol. Now in hexane only the less polar compound will move up on the tlc plate. When we add some amount of ethylacetate to the hexane and use the combination as a mobile phase. The less polar compound will be pushed further up on the tlc plate, along with that now the more polar compound the alcohol will also partition in the organic component of the mobile phase and move up. So as we increase the polarity of solvent mixture the compounds move at different rates on a tlc plate.
It is always a must that we do a tlc prior to running a separation column chromatography. This ensures that we use the right solvent for our elution on the column. Saves time and solvent.
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