What is the pH of a solution which is 1x10^-4 in [OH]? 1x10^-5 in [H3O+]?

Question

What is the pH of a solution which is 1x10^-4 in [OH]?
What is the pH of a solution which is 1x10^-5 in [H3O+]?

Please explain your answer, I totally don't understand this concept!
Thanks!

Answer 1

pH of 10^-4 in [OH-] ?

you have like as pH ---> pOH = log [1/[OH]
here pOH = log 1/10^-4 = log 10^4 = 4
And pH +pOH =14

Hence pH = 10


pH solution 10^-5 in [H3O+]

pH = log 1/[H3O+] = log 1/10^-5 = log 10^-5 =5

the pH =5