Question

to know if a solid substance is pure, which of the following criteria would be the most appropriate?
a. solubility
b. lambda absortion in the U.V.
c.absence of coloration in the compound
d.the presence of only one stain when running it in chromatography TLC
e. that it presents well formed crystals in the microscope

Answer 1

good question.

a. From solubility, we can't predict its purity if the same solubility of impurities are present. most of the impurities are similar solubility.

b. UV absorption will give you idea because every molecule has differnt wavelengths in UV. but again if solid has non-UV active impurites present agin we will fail to tell about purity

c. Impurities also colorless as the compound or the same color as the compound. hence it is not useful

d. Again TLC stain will not tell the purity. Stains are useful to find the compound many compound/impurities are not stained in particular stain

e. Crystallization is a perfect/appropriate technique. we can find solid compound purity.

most of the well-formed crystals are pure because of the similar type of interactions between them.

Answer is e