Question

100 mL of 1.0 M solution of a monobasic acid $(p{K}_a=5)$ is titrated against $Ca(OH{)}_2$ solution. At equivalence point the pH of solution is ?

• A. 7
• B. 6
• C. 4.5
• D. 9.5

Answer 1

The correct option is D

9.5

The $\left[A^{-}\right]$ of the salt $Ca{A}_2$ fromed by the reaction between $Ca(OH{)}_2$ and HA (monobasic acid). $\left[A^{-}\right]=0.52\times 2$ at equivalence point $\left[Ca{A}_2\right]=0.5M$
$\therefore pH=\frac{1}{2}[p{K}_w+p{K}_a+logC]$
$=\frac{1}{2}[4+5+0]=9.5(C=[A^{-}]=0.1M)$