Question

Given for $HA$ acid, $K_a={10}^{-6}$ and for $MOH$ base, $K_b={10}^{-6}.$ The $pH$ of $0.1MMA$ salt solution will be

• A. 5
• B. 7
• C. 9
• D. 2

Answer 1

Answer: (B)

As $MA$ is a salt of weak acid $(HA)$ and weak base $(MOH)$ , $\therefore$ $pH=7+\frac{1}{2}\times [p{K}_a-p{K}_b]$ ... (i) $\because$ $p{K}_a=-\log K_a$ $=-\log {10}^{-6}=6$ Similarly $p{K}_b=-\log K_b$ $=-\log {10}^{-6}=6$ By putting these values in equation (i) $pH=7+\frac{1}{2}\times (6-6)$ or $pH=7$