1. The problem statement, all variables and given/known data NaOH is an example of a strong base. if 0.45g of NaOH is mixed with 500ml of water what is the [OH] [H3O+] pH 2. Relevant equations 3. The attempt at a solution so, i calculating moles thru molar mass and divided by 0.5 to get mol/l. put that as the concentration of the hydroxyl. (0.0225) What i dont understand is how to get the hydronium ion concentration. I know that its going to involve doing the -log of 0.025 to get the pH. Which is 1.4. But why do i do 14-1.4 then do the antilog of that to get the concentration of the hydronium ion? I know how its solved, My real question is... why do i do 14- (ph of hydroxl) to find the concentration of the hydronium?