Question

If the $pH$ of $NaOH$ solution is $12$, then what is the amount in grams of $NaOH$ present in one litre of this solution?

• A. $40.0$
• B. $4.0$
• C. $0.4$
• D. $20.0$

Answer 1

The correct option is C $0.4$

It is given that the pH of $NaOH$ solution is $12$.

We know, $pH+pOH=14$

Hence, $pOH=14-12=2$

But $pOH=-log\left[O{H}^{-}\right]$

Hence, $\left[O{H}^{-}\right]={10}^{-2}$ M

Thus, $1$ L of $NaOH$ solution having $pH$ $=12$ contains $0.01$ moles of it.

Molecular weight of $NaOH$ is $40$ g/mol.

Thus, weight of $NaOH$ present $=0.01\times 40=0.4$ g $NaOH$ in $1$ L of the solution.

Option C is correct.