Question

Glacial acetic acid is obtained by:
(a) chemically separating acetic acid
(b) treating vinegar with dehydrating agents
(c) crystallising, separating and melting acetic acid
(d) distilling vinegar

Answer 1

Hint: Vinegar is the diluted form of acetic acid. We can separate the vinegar and the acetic acid. This can be done by knowing the difference in properties of vinegar and acetic acid.

Complete step by step solution:
- Vinegar contains a very dilute solution of acetic acid. It is used for flavourings. It contains around 5-8% of acetic and acid and the rest is water. Acetic acid in its pure form is called glacial acetic acid. Acetic acid has a sour taste and a pungent smell.
- In olden times, around in eighteen century, glacial acetic acid was concentrated from vinegar through a distillation process So, by distillation process we can extract acetic acid from vinegar.
- Another method of obtaining glacial acetic acid from vinegar is by crystallising. Acetic acid and water have different melting points. The melting point of acetic acid is ${{16.6}^{o}}C$ and melting point of water is at ${{0}^{{}^\circ }}C$. So if we freeze vinegar, first acetic acid would freeze at ${{16.6}^{o}}C$. Its crystals would form which can be separated from the solution of water. This crystallised acetic acid is in its pure form. It is then melted to give a liquid form of glacial acetic acid. This process is also called crystallisation. Thus, by crystallisation also we can obtain glacial acetic acid that is acetic acid in its pure form, from vinegar.
So, we can conclude that glacial acetic acid can be obtained by distilling vinegar and by crystallising, separating and melting acetic acid. The option (c) is correct.

Note: We can get confused with option (b). Because, we know that in vinegar it is water and acetic acid. But we cannot separate acetic acid in this manner; there is a chance of formation of other products.