Find the pH of a Buffer after Adding HCl

You use the Henderson-Hasselbalch equation to calculate the pH of a buffer, and you can use MOLES of conjugate base and MOLES of weak acid in the "base over acid" section. Adding HCl will increase the amount of weak acid there is, and decrease the amount of conjugate base by the same amount. These affect the ratio that is logged, so adding a little bit of HCl doesn't change the pH significantly. Check me out: http://www.chemistnate.com