Question

The pH of a 2 M solution of a weak monobasic acid (HA) is 4. What is the value of the Van't Hoff factor?

• A. 0.00005
• B. 1.005
• C. 1.00005
• D. None of the above

Answer 1

The correct option is C 1.00005

pH = 4 means $\left[H^{+}\right]={10}^{-4}M$
Total = C (1+ $\alpha$)
Thus, $\left[H^{+}\right]=C\alpha ,i.e.,{10}^{-4}=2\times \alpha$ or $\alpha =5\times {10}^{-5}=0.00005$
For dissociation of HA
$\alpha =\frac{i-1}{n-1}$
$\alpha =\frac{i-1}{2-1}$
$i=\alpha +1$
$i=1+\alpha =1+0.00005=\mathrm{1.00005.}$