Tue December 20, 2011 By: Sruti S

What is the definition of acid dissociation constant i.e, Pl. state the difference between pka and ka value & Why is ka2 of sulphuric acid less than ka1?

Expert Reply
Wed December 21, 2011

An acid dissociation constant, Ka, (also known as acidity constant, or acid-ionization constant) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions. The equilibrium can be written symbolically as:

HA A? + H+,
            where HA is a generic acid that dissociates by splitting into A?, known as the conjugate base of the acid, and the hydrogen ion or proton, H+ .

The logarithmic constant, pKa, which is equal to ?log10 Ka, is sometimes also (but incorrectly) referred to as an acid dissociation constant:
sulphuric acid is a diacid.Ka1 is the dissociation constant when it dissociates and one proton is released.HSO4- is formed which again dissociates but because of one negative charge now present on the molecule removal of proton is a bit difficult hence the dissociation constant for the abstraction of second proton from sulphuric acid is less .

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