Question

The first and second dissociation constants of an acid $H_{2}A$ are $1.0\times {10}^{-5}$ and $5.0\times {10}^{-10}$ respectively. The overall dissociation constant of the acid will be:

• A. $5.0\times {10}^{-5}$
• B. $5.0\times {10}^{15}$
• C. $5.0\times {10}^{-15}$
• D. $2.0\times {10}^5$

Answer 1

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

For the dissociation of a dibasic acid, the overall dissociation constant is equal to the product of the first and second dissociation constants.
Therefore, $K=K_1\times K_2=1.0\times {10}^{-5}\times 5.0\times {10}^{-10}=5.0\times {10}^{-15}$

Hence, the overall dissociation constant is $5.0\times {10}^{-15}$.