Question

The first and second dissociation constants of an acid H${}_2$A are 1.0 x 10${}^{-5}$ & 5.0 x 10${}^{-10}$ respectively. The overall dissociation constant of the acid will be:

• A. 5.0 x 10${}^{-5}$
• B. 5.0 x 10${}^{15}$
• C. 5.0 x 10${}^{-15}$
• D. 0.2 x 10${}^5$

Answer 1

The correct option is C 5.0 x 10${}^{-15}$

The overall dissociation constant is equal to the product of first and second dissociation constant. It is $K_a=K_{a1}\times K_{a2}=1.0\times {10}^{-5}\times 5.0\times {10}^{-10}=5.0\times {10}^{-15}$