Question

Why does the TLC tank need to be covered?

Answer 1

it is extremely important that the solvent in the developing chamber be lower than the spotos on the plate, because the solvent must be drawn upward through the sample in order to draw the sample along with it. ... Finally it is important to cover the chamber to be sure that the solvent does not evaporate.

Step-by-step explanation:

Answer 2

The reason for covering the container is to make sure that the atmosphere in the beaker is saturated with solvent vapour. Saturating the atmosphere in the beaker with vapour stops the solvent from evaporating as it rises up the paper.