Question

Rashi prepared an aqueous solution of caustic soda. If concentration of the solution is 0.001 M, then the pH of the solution will be

• A. 10
• B. 11
• C. 3
• D. 14

Answer 1

The correct option is B 11

Concentration of the caustic soda (NaOH) solution = 0.001 M

So, concentration of $O{H}^{-}$ ions = 0.001 M = ${10}^{-3}$ M

Now, $\left[O{H}^{-}\right]\left[H^{+}\right]={10}^{-14}$

∴ ${10}^{-3}\left[H^{+}\right]={10}^{-14}$

$\left[H^{+}\right]={10}^{-14}+3={10}^{–11}M$

The pH of a solution is calculated as:

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

$pH=-\log \left[{10}^{–11}\right]=11$

Hence, the correct answer is option (b).