Question

What is an acid according to Arrhenius?

Answer 1

According the Arrhenius, an acid is such a compound which in an aquous solution releases proton (or `H^+`).

Such compounds must fulfill two criteria -

1) First, it must be soluble in water (even if it is partly soluble, that'll do but, total insolubility of a compound disqualifies it to be regarded as an Arrhenius acid).

2) Second, it must be able to donate `H^+` in the solution.

Such acids may be classified as -

(a) Strong acids with a degree of dissociation `alpha = 1` which are almost completely dissociated.

Example - `H_2SO_4, HNO_3, HCl`

(b) Weak acids with a degree of dissociation `0 < alpha < 1` which are only partially dissociated but still donate `H^+` to some extent in aquous solution.

Example - `CH_3COOH, HCN, HCOOH`