For a TLC lab,the stationary phase is the mixture of isopropanol and ammonia or the mixture of hexane,ethyl acetate and ethanol, the stationary phase is silica gel. text some dyes and drugs.
what is the relationship between the polarity of molecules and the Rf values?
Read your first paragraph. It makes no sense.
The second paragraph containing the question does. The Rf value increases with decreasing polarity. That is, increased polarity of the molecule means it is attracted more to the polar stationary phase; therefore, it moves less and the Rf value is less.
Also, for the same situation, which one of the two mobile phases is the more polar? Actualy I need two pieces of evidence... I think the polar one should be the isopropanol and ammonia because it moves slower. Can you help me come up another reason? Thank you~
The polarity of molecules and the Rf (retention factor) values in TLC (thin-layer chromatography) are related. Rf value represents the ratio between the distance traveled by a compound relative to the distance traveled by the solvent front. It helps determine the relative polarities of different compounds in a mixture.
In TLC, the stationary phase is the silica gel, and the mobile phase is either the mixture of isopropanol and ammonia or the mixture of hexane, ethyl acetate, and ethanol. The stationary phase consists of polar molecules, such as silica gel, while the mobile phase consists of nonpolar or less polar solvents.
Polar compounds have stronger interactions with the polar stationary phase, thereby moving slower and having smaller Rf values. On the other hand, nonpolar compounds have weaker interactions with the stationary phase, allowing them to travel faster and have higher Rf values.
Therefore, in general, the more polar a compound is, the lower its Rf value will be, as it will tend to "stick" to the stationary phase more strongly. Conversely, less polar compounds will have higher Rf values, indicating that they move more freely through the mobile phase.
Keep in mind that the exact relationship between polarity and Rf values can be influenced by various factors, including the composition of the mobile phase, the composition of the stationary phase, and the specific interactions between the compounds and the phases used in the TLC experiment.