Question

What is the pH of 0.2 M aqueous solution of sodium butyrate $(K_a=2.0\times {10}^{-5})$?

• A. 9
• B. 7
• C. 8
• D. 5

Answer 1

The correct option is A 9

$NaBu+H_{2}O\rightleftharpoons NaOH+BuH$
Conc before hydrolysis 1 0 0
Conc after hydrolysis 1 - h h h

$\therefore \left[O{H}^{⊝}\right]=C\cdot h=\sqrt{\left(\frac{K_h}{C}\right)}$

$=\sqrt{(K_h\cdot C)}=\sqrt{(\frac{K_w}{K_a}\cdot C)}$

$\left[O{H}^{⊝}\right]=\frac{{10}^{-14}\times 0.2}{2\times {10}^{-5}}=\sqrt{{10}^{-10}}={10}^{-5}$

$pOH=5,pH=9$