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

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To find the pH of the buffer solution, the pKa of propanoic acid is calculated as 4.85, leading to an initial pH of 4.75 using the Henderson-Hasselbalch equation. When a strong acid like HCl is added, it reacts with the conjugate base, sodium propanate, decreasing its concentration and increasing the concentration of the weak acid, propanoic acid. This shift in concentrations will lower the pH of the buffer solution. The exact new pH after the addition of HCl requires recalculating the concentrations of the acid and base. Understanding these changes is crucial for accurately determining the buffer's new pH.
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Homework Statement



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

Homework Equations



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

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
 
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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?
 

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