Question

In a buffer solution containing equal concentration of $B^-$ and HB, the $K_b$ for $B^-$ is $10^{-10}$ . The pH of buffer solution is

• A. 10
• B. 7
• C. 6
• D. 4

Answer 1

Answer: (D)

4

Answer 2

(i) For basic buffer,
$\, \, \, \, \, \, \, \, pOH = pK_b + log \frac{[salt]}{[base]}$
(ii) $pH + pOH = 14$
Given, $K_b = 1 \times 10^{-10} , [salt] = [base]$
$\, \, \, \, \, \, \, \, pOH = - log K_b + log \frac{[salt]}{[base]}$
$\therefore \, \, \, \, \, pOH = - log (1 \times 10^{-10} ) + log1 = 10$
$pH + pOH = 14 [\because$ concentration of $[B^-] = [HB]$
$\, \, \, \, \, \, \, \, pH = 14 - 10 = 4$