(a) What is glacial acid and why is it called so ?
(b) What is vinegar and how is it prepared ?
( c) The experimentally determined (by colligative properties method) molecular weight of acetic acid in the vapour state is `120`. Explain why.

Explanation

Hundred percent acetic acid free of water is called glacial acetic acid. Water is removed from acetic acid by freezing the bottle containing acetic acid in a refrigerator. The melting point of anhydrous acetic acid is `17^@ C` (more than the melting point of `H_2 O`). So it is soldified first and water in the liquid form is removed by inverting the bottle. Water falls down drop by drop leaving pure `100 %` acetic acid. Solid anhydrous acetic looks 'icy'. So the word glacial is used, since water is removed by making it in 'glacier' form, Acetic acid is abbreviated as `AcOH`, where `Ac` refers to acetyl, `(Me-overset(O)overset(||)(C)-)` group.
(b) Five precent aqueous solution of `AcOH` is called vinegar. It is prepared by the fermentation of sugars and starch. Ethanol is an intermediate fermentation product.
( c) Acetic acid exists as a dimer through intermolecular `H-`bonding. So the experimentally determined molecular weight is twice the calculated molecular weight of acetic acid.