Question

Calculate the PH of a 0.00001 M solution of HCL what is the hydroxide ion concentration?

Answer 1

Well, `pH=+5`..and `pOH=9`, thus `[HO^-]=10^-9*mol*L^-1`.

Explanation:

We address the equilibrium...

`2H_2O(l) rightleftharpoonsH_3O^+ + HO^-`

And under standard conditions, `K_w=[H_3O^+][HO^-]=10^-14`..

We take `log_10` of both sides...

`log_10K_w=log_10{[H_3O^+][HO^-]}=underbrace(log_(10)10^-14)_-14`

And so....

`underbrace(-log_10[H_3O^+])_(pH)underbrace(-log_10[HO^-])_(pOH)=14`

...we gots our working relationship...

`pH+pOH=14`

And so we got `[H_3O^+]=10^-5*mol*L^-1`.

And so `pH=-log_(10)10^-5=-(-5)=5`

And `[HO^-]=10^-(14-5)=10^-9*mol*L^-1`