Calculating pH when given volume and concentration of solution?

[Violagirl]

I'm stuck on these two problems:

 

A) IF you make a 50 mL of a 0.1 M Tris solution (in acid form), what will be the pH?

B) If you add 2 mL of 1 M NaOH to the above solution, what will be the pH?

I'm not sure how to go about solving this. I know HH equation is typically used when is a concentration is given but how do you account then for the volume given? Any help is great.

[chamz]

first fin how many H+ ions come out of tris soln
multiply by the concentration of tris soln and get the H+ concentration

then find ph

when NaOH is added
calculate moles of H+ (concentration and volume found)

calculate moles of OH-(concentration and volume given)

if H+ is more then devide by total vol(50+2) and find H+ conc
then find ph

if OH- is more

use equation 1* 10^-14 = [H+]*[OH-]

to find H+ conc

then find ph