Question

$pH$ of a strong diprotic acid ($H_{2}A$) at concentration, are respectively:
(i) ${10}^{-4}$M, (ii) ${10}^{-4}$ N

• A. 3.7 and 4.0
• B. 4 and 3.7
• C. 4 and 4
• D. 3.7 and 3.7

Answer 1

Answer: (A)

3.7 and 4.0

$pH$ of strong diprotic acid

$\left(i\right){10}^{-4}M$

diprotic cone=${10}^{-4}M$

$\left[H_{2}A\right]={10}^{-4}M$

$\left[H^{+}\right]=2\times {10}^{-4}M$

$pH=-\log [2\times {10}^{-4}]$

$=-\log 2+4\log 10$

$=-0.301+4$

$=3.699\sim 3.7$

$\left(ii\right){10}^{-4}N$

for diprotic acid,

$[H^+]=Normality.

So,$pH=-\log \left[H^{+}\right]$

$=-log{10}^{-4}$

$=4$