Calculate [H+], [OH -], and the pH for this solution...?

Question

A solution is prepared by mixing 74.0 mL of 5.00 M HCl and 36.0 mL of 8.00 M HNO3. Water is then added until the final volume is 1.00 L. Okay, I didn't quite get my first question and something strange is up with my scientific calculator, so I changed the numbers a bit just to confirm that I'm doing my calculations correctly...Please include the step by step calculations, thanks!

Answer 1

We can assume that both acids disassociate totally in the final solution, so the H+ from the acids is that in the original additions.
From HCL: moles H+ = Vol x Molarity = 0.074 x 5 = .370 moles
From HNO3: moles H+ = 0.036 x 8 = 0.288 moles
Total [H+] = 0.658 mole/liter
In an aqueous solution [H+]x[OH-]= 1x10-14
Thus, [OH-]= (1/.658)x10-14
about 1.6x10-14 mol/L
For pH: pH=Log 1/[H+] (if I remember right)
pH = Log (1.6) or about 0.2