Question

Calculate the change in pH when 9.00 mL of 0.100 M HCl(aq) is added to 100.0 mL of a buffer solution that is 0.100 M in NH3(aq) and 0.100 M in NH4Cl(aq).

Answer 1

This is a bit of a long problem to type out the whole procedure. Did you have a specific part of it that you are stuck on?

Answer 2

Write down the reaction that is taking place and work out the new amounts in reaction.
This will allow you to find the new pH.
It should change by about one tenth of a unit.