We did a lab in class a while ago involving weak acid and base equilibria where we had to make up some .10 M solutions, measure pH and the later on calculate the pH and compare.
Here's the set of calculations I'm stuck on:
Solution 8: 25ml 0.10 M NH3 + 25ml 0.10 M NH4NO3
pH obtained in Lab - 9.17
Solution 9: 10ml soln 8 + 6 ml H2O
pH obtained in Lab - 9.24
Solution 10: 10ml soln 8 + 5 ml H2O +1ml 0.10 M HCl
pH obtained in Lab - 8.82
Solution 11: 10ml soln 8 + 6 ml 0.10 M HCl
pH obtained in Lab - 2.13
Solution 8 is a buffer solution, I know that... I'm having trouble going back to dilutions and calculating molarity. I need the concentrations of the solutions so I can calculate the pH of each on with the Henderson-Hasselbalch equation:
pH = -log(Ka) + log([base]/[acid])
How can I go about getting the concentrations for the HH equation?? I just can't seem to get started; I may be thinking too hard about it.
Any help is appreciated! Thanks.
Kris
Ka for NH4+ = 5.6 x 10-10
Kb for NH3 = 1.8 x 10-5