PH solution Homework--please show step by step !! it would really help me!!?

Question

Calculate

a)pH of a soultion in which [H3O+]=1.5e-3 M.

b)pH of a solution in whihc [OH-] =3.1e-4 M

c) [H3O+] when pH of 8.42

d) [H3O+] wehn pOH =5.58

Answer 1

Using the equations

pH= - log([H30+])  conversely: 10^(-pH)=[H3O+]

pOH = -log( [OH-] )  conversely: 10^(-pOH)=[OH-]

and pH+pOH=14

you should be able to do this without help.