Finding the pH of a buffer solution when a strong acid is added

TheSwede

1. The problem statement, all variables and given/known data

Three milliliters of a 2.0 M solution of HCL are added to 1 liter of buffer solution containing 0.40 moles of the weak acid, propanoic acid (Ka = 1.4 x 10^-5) and .50 moles of its conjugate base, sodium propanate.

1) find the ph of the buffer solution

2) find the ph when the strong acid is added to the buffer solution

2. Relevant equations

Henderson Hasselbach equation: pH = Pka + log( A- / HA)

3. The attempt at a solution

1) to find the pKa -log(1.4 x 10^-5) = 4.85
pH = 4.85 + log(.4/.5) = 4.75
is this correct?

2) clueless

Borek

What happens when you add a strong acid? Is there any reaction taking place? How does it change concentrations of propanate and its conjugate acid?