Question

Please help

2. Consider the TLC plate shown below that was done on silica gel using a solvent mixture of 4:1 hexane/EtoAc as the eluent. 4:1 Hexane:EtOAC marked solvent front Spot B Spot A A origin (a) Which of the two organic compounds labeled A and B is less polar? (b) Calculate the Rf value of compound B. (c) How would the following changes affect the Rf values of A and B? i. Change to a more polar solvent mixture - Draw the resulting TLC chromatogram using the blank plate provided on the left above. Also, write in your eluent on the line provided above the chromatogram. ii. Change to a less polar solvent mixture. iii. Add more sample to the TLC slide before it is eluted. iv. Allow more time for the solvent front to move further.

Answer 1

2 (a) compound B is less polar than compound B it is because the Rf value of the less polar compound will be more in comparison with the polar compound of the same eluent.

(b) Since the distance travelled by the solvent front and the compounds is not provided therefore Rf can not be calculated.

Rf = distance travelled by the compound / distance travelled by the solvent front

the expect Rf of the compound B is in the range of 0.25-0.30.

(c)

4:1 Hexane:EtOAC 3:2 hexane:EtOAC 4.5:0.5 hexane: EtoAc marked solvent front Spot B Spot A origin more polar less polar

III Addition of the more sample before elution will lead to form the drag in place of the clear spots.

IV More time will lead to cross the solvent front from the top of the TLC plate that is not a good way for TLC analysis.