Question

A student measures the melting point of a sample of salicylic acid and records 140-150 degrees C. The known value of salicylic acid is 158-161 degrees C. What does this information tell you about the sample of salicylic acid?

a. The sample is impure and may or may not be salicylic acid.
b. The sample is pure and is not salicylic acid.
c. The sample is impure and is not salicylic acid.
d. The sample is pure and is salicylic acid

Answer 1

Answer: Option (a) is the correct answer.

Explanation:

As the actual melting point of solid salicylic acid is from $158^{o}C to 161^{o}C$.

Any impurity present in salicylic acid will lead to a decrease in its melting point because of the presence of impurity that actually disrupts the energies of solid crystal lattice.

This is known as freezing point depression.

The difference between generally observed melting point and actual melting point is ±5.

Thus, we can conclude that according to the given information the sample is impure and may or may not be salicylic acid.