posted by J on .
A sample of naphthalene, which should be pure white, was found to have a grayish color after the usual purification procedure. The melting point was correct, and the
melting point range was small. Explain the gray color.
There are only two explanations for this: One, the compound that your purified contains soluble impurities that have the same melting point or range; or two, the compound isn't naphthalene.
The first explanation is impossible, since any purity would change the melting point, even if the impurity has the same melting point as naphthalene.
If the procedure involves the removal of colored impurities via charcoal, then it is likely that the color is caused by residual charcoal. Keep in mind, charcoal doesn't form a solution with naphthalene, so the melting point wouldn't be affected, even with the charcoal present as an impurity.