`10 mL` of `10^(-6) M HCl` solution is mixed with `90mL H_(2)O`. `pH` will change approximately:

Options

A. by one unit
B. by `0.3` unit
C. by `0.7` unit
D. by `0.1` unit

Answer

C

Explanation

`pH of 10^(-6)MHCI = 6`, on dilution
`[HCI]= (10^(-6)xx10)/(100)=10^(-7)`
Thus new pH of HCI is not 7 because it is acid. For new solution pH:
`[H^(+)]=10^(-7)+10^(-7) (f rom H_(2)O)=2xx10^(-7)`
`:. pH=6.7`