How do i do this? (concentrations)

1. This one is simple, just put 10^-pOH. This gives you OH- concentration
Example: pOH=5, the OH- conc. = 10^-5 which equals 1x10^-5 mol/L

2. You can't use pH to find OH concentration, so you need to find the pOH using pH. To find pOH if you have pH, the equation is pH + pOH = 14.00. Manipulate it to find pOH, so you get pOH = 14.00 - pH. Then do the same steps as above. 

3. First you need to find the pH, so just enter -log(H3O+ conc.) into your calculator. This gives you pH, then just do all of the steps above.