Question: What would happen to the Rf values of the pigments if you were to increase the relative concntration of acetone in the developing solvent?
Note: The development solvent used was 70% hexane - 30% acetone.
My answer: Acetone is more polar than hexane so the increase in its concentration would move the spots more rapidly up the plate and therefore would increase all Rf values.
Please check this.
Sheryl
That sounds ok to me but I'm a novice at TLC.
The Rf values would increase since you are increasing the polarity of the mobile phase. Normally the more polar the substance the slower it moves, however you are changing the relative polarity in the developing chamber.
Your explanation is correct. When you increase the relative concentration of acetone in the developing solvent (70% hexane - 30% acetone), the solvent becomes more polar. Since acetone is more polar than hexane, the increased concentration of acetone would make the solvent more polar overall.
A more polar solvent would have a stronger affinity for the polar components of the pigments, causing them to move more rapidly up the plate during TLC (thin-layer chromatography). As a result, all Rf (retention factor) values would increase because the distance traveled by the spots divided by the distance traveled by the solvent front would be greater.
So, in summary, increasing the relative concentration of acetone in the developing solvent would lead to an increase in the Rf values of the pigments.
You're actually on the right track with your answer! The Rf value in thin layer chromatography (TLC) is calculated by dividing the distance traveled by the pigment spot by the distance traveled by the solvent front.
In TLC, the development solvent is composed of a nonpolar component, such as hexane, and a polar component, such as acetone. The nonpolar component carries the nonpolar substances, like hydrocarbons, while the polar component carries the polar substances, like polar pigments.
When you increase the relative concentration of acetone in the developing solvent, it means you are increasing the polarity of the solvent mixture. Since acetone is more polar than hexane, this increase in polarity can affect how quickly the pigments move up the TLC plate.
As a result, increasing the concentration of acetone in the developing solvent would make the solvent front move faster up the plate. The pigments, being polar, will also move faster along with the solvent front. This increased speed of the pigments' movement will lead to higher Rf values since the distance traveled by the pigments is increased relative to the distance traveled by the solvent front.
So, to summarize, increasing the relative concentration of acetone in the developing solvent would increase the Rf values of the pigments in TLC due to the increased polarity of the solvent mixture, which causes the pigments to move more rapidly up the plate.