Question

$pH$ of $0.1M$ monobasic solution is found to be 2. Thus its osmotic pressure at $T\left(K\right)$ is:

• A. $1.11RT$
• B. $0.11RT$
• C. $0.011RT$
• D. $11.11RT$

Answer 1

The correct option is B $0.11RT$

We know,
$pH=-log\left[H^{+}\right]$
$pH=2$
$\left[H^{+}\right]={10}^{-2}$
$HA\rightleftharpoons H^{+}+A^{-}$
$\text{Initially}C00$

At equilibrium,
$(1-\alpha )C\alpha C\alpha$

$\left[H^{+}\right]=C\alpha$

$\alpha =\frac{\left[H^{+}\right]}{C}=\frac{{10}^{-2}}{0.1}=0.1$
Here, $n=2$
$i=1+\alpha (n-1)i=1+0.1i=1.1$

Now
$\text{Osmotic pressure}\pi =iCRT$

$i=1.1\times 0.1\times RT=0.11RT$