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CBSE - XII Science - Chemistry - The p-Block Elements.

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?

Asked by Sruti S 20th December 2011, 2:47 PM
Answered by Expert


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 .

Answered by Expert 21st December 2011, 10:46 AM

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