CHEMISTRYURGENT
posted by Maggie .
HNO3 with pH 3 is mixed with 2 L KOH with pH 12. assuming volumes are additive what is the pH of the final solution?
I have absolutely no idea how to do this. I do know the answer, though. I have a test tomorrow and I would really appreciate it if someone could help!!!!

Why didn't you share the answer? Then we would know if I did it right or not?
However, I don't think you copied all of the problem. HOW MUCH HNO3 with a pH of 3. It makes a huge difference.
Here is how you do it.
mL HNO3 x M = millimoles HNO3. (pH 3 makes M = 1 x 10^3) = millimoles H^+..
mL KOH x M = millimoles KOH = 2000 x 1 x 10^2 (pH = 12, pOH = 2; therefore, OH^ = 1 x 10^2 M).
So which millimoles is the greater, the H^+ or the OH^.
Subtract the smaller from the larger divide the difference by TOTAL mL and that will be either the H^+ or the OH^ and you can get pH or pOH from that. 
oh, sorry!
its 2 liters HNO3 and the answer is 11.65
so it would be:
log [(20  2e8) / 4000] = 2.3 = [OH]
14  2.3 = 11.65 (without the rounding of the 2.3)
why, though, would you subtract it from the other? 
HNO3 + KOH ==> KNO3 + H2O
moles HNO3 = 2000 x 1 x 10^3 = 2 mmoles.
moles KOH = 2ooo x 1 x 10^2 = 20 mmoles.
Why subtract. This is an acid/base reaction, they neutralize each other. ALL of the HNO3 is GONE and you are left with an excess of 202 =18 mmoles KOH.
So (OH^) = 18 mmoles/4000 mL = 0.00450 M.
pOH = 2.35 and pH = 11.65. :).
Isn't chemistry FUN?!