When 200 ml of aqueous solution of HCl (pH = 2) is mixed with 300 ml of of an aqueous solution of NaOH (pH = 12), the pH of the resulting mixture is :

Options

A. 10
B. `2.7`
C. `4.0`
D. `11.2`

Answer

D

Explanation

`underset(pH = 2)underset(200 ml)(HCl)+underset(pH=12)underset(300 ml)(NaOH)rarr NaCl+H_(2)O`
For HCl solution
`pH=-log[H^(+)]=2`
`therefore [H^(+)]=10^(-2)M`
Moles of `H^(+)` in 200 ml
`=(10^(-2))/(1000)xx200`
`=2xx10^(-3)` moles
For NaOH solution, `pH=14-pOH=12`
`therefore pOH = 2`
`[OH^(-)]=10^(-2)M`
Moles of `[OH^(-)]` in 300 ml solution
`=(10^(-2))/(1000)xx300`
`=3xx10^(-3)` moles
`therefore` Moles of `OH^(-)` left
`=3xx10^(-3)-2xx10^(-3)=10^(-3)` moles
Total volume = 500 ml
`therefore [OH^(-)]=(10^(-3))/(500)xx1000=2xx10^(-3)M`
`pOH=-log[OH^(-)]=-log(2xx10^(-3))=2.699`
`therefore pH=14-2.699=11.30`