A 50 ml sample fo 0.240M NH3(aq) is titrated with aqueous hydrochloric acid. What is the pH after the addition fo 15.0 ml of 0.0600M HCl(aq)? (kb of NH3 = 1.8 x 10^5)

Question

A 50 ml sample fo 0.240M NH3(aq) is titrated with aqueous hydrochloric acid.  What is the pH after the addition fo 15.0 ml of 0.0600M HCl(aq)?  (kb of NH3 = 1.8 x 10^5)

DrBob222 · Answer

I believe this is a buffer solution problem so you should use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/(acid)]
NH3 + HCl ==> NH4Cl
How much NH3 do you have to start with?
M x L = ??
How much HCl has reacted with it.
M x L = ??
Subtract to see how much and what is in excess and substitute into the HH equation.
Remember that Ka = Kw/Kb