Question

1. When separating mixtures using TLC, why is it important to choose a solvent (mobile phase) that has a different polarity than the TLC plate (stationary phase)? 2. Why will some substances in a mixture travel farther up the TLC plate than others?

Answer 1

ANSWER:-

1)-it is very important to choose a different polarity solvent than the stationary phase because we know that stationary phase is made up of silica(most commonly) .

in TLC the analyte exists in an equilibrium between the stationary and mobile phases. If there exists a greater polar attraction between the solvent and the analyte than the silica and the anaylte, then the analyte will spend more time traveling in the mobile phase along the plate than it will being attached to the stationary phase. Thus, the greater the polarity of a solvent, the greater the elution. However, this is all relative to the polarity of the analyte itself. If the analyte has a greater polarity than the solvent, it will remain more easily attached to the silica. Thus, different analytes will behave differently to the polarity of a solvent, depending on their own polarities. By experimenting with solvent mixtures and keeping in mind this idea of polarity, you can achieve a desirable separation that;s why it is important to choose different polarity solvent.

2)-

How fast(farther up) the compounds travel up the plate depends on two things:

• If the compound is soluble in the solvent, it will travel further up the TLC plate
• How well the compound likes the stationary phase. If the compound likes the stationary phase, it will stick to it, which will cause it to not move very far on the chromatogram.

this is the main reason why one compound travel farther than other. all things depends upon polarity.