Question

1)Calculate the pH of a 0.1M solution of NaOH ,knowing that the volume of the solution is 300mL. 2)Calculate the pH of a 0.3M solution of HCl , knowing that the volume of the solution is 250mL (?)

Answer 1

We use the relationship.........`pH+pOH=14`............in aqueous solution under standard conditions............

Explanation:

`(i)`.........`pH+pOH=14`............ and by definition, `pH=-log_10[H_3O^+]`, and `pOH=-log_10[HO^-]`.

For a `0.1*mol*L^-1` solution of `NaOH`, we KNOW (do we?) that `HO^(-)-=0.1*mol*L^-1`, and thus `pOH=-log_10(0.1)=-(-1)=1`.

And given `pH+pOH=14`, `pH=14-pOH=14-1=13`. The volume of the solution is irrelevant here.

`(ii)`.........`pH=-log_10[H_3O^+]=-log_10(0.300)=0.523`. Again the volume of the solution is a distractor............