Terms & Definitions Lab 5

Question 1

CAPILLARY ACTION

Answer 1

Phenomena of elevation or depression and of adhesion and cohesion of a liquid observed in a thin tube which is placed in a liquid. This is due to surface tension.

Question 2

R_f. Is this value a physical constant for a solute?

Answer 2

The distance traveled by a solute on a TLC plate divided by the distance traveled by the solvent on the same plate. This value is not a physical constant for a solute since it will vary with (1) the solvent used, (2) the thickness of the plate and (3) even the relative amount of substance spotted on the plate.

Question 3

STREAKING. Why does this occur? How do we fix this problem?

Answer 3

“Streaking” of a substance along a TLC plate; usually occurs if too much of the initial material is spotted on the plate (or if the material is very polar, then it is more attracted to the plate then to the developing solvent and consequently is very difficult to move up the plate.) This latter case can usually be minimized by the addition of a few drops of acetic acid (or some polar liquid) to the developing solvent to increate its polarity.