The volume of water that must be added to `100 ml` of `NaOH` solution to change its pH value from `12.6990` to `12` is

Options

A. `500 mL`
B. `400 mL`
C. `100 mL`
D. `200 mL`

Answer

B

Explanation

(i) `pH = 12.699, [OH^(-)] = 5 xx 10^(-2)`
`pOH = 1.3010`
(ii) `pH = 12, pOH = 2, [OH^(-)] = 10^(-2)`
`100 xx 5 xx 10^(-2) = 10^(-2) xx V`
`V = 500`
Volume of water acid
`= 500 - 100`
`= 400 ml`