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

In summary, a 2.0 M solution of HCL is added to a 1 liter buffer solution containing 0.40 moles of propanoic acid and 0.50 moles of sodium propanate. To find the pH of the buffer solution, the Henderson Hasselbach equation is used to calculate a pH of 4.75. When the strong acid is added, there is a change in concentrations of propanate and its conjugate acid, leading to a change in pH.
  • #1
TheSwede
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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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  • #2
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?
 

1. What is a buffer solution?

A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. It consists of a weak acid and its conjugate base, or a weak base and its conjugate acid.

2. How do you find the pH of a buffer solution when a strong acid is added?

To find the pH of a buffer solution when a strong acid is added, you can use the Henderson-Hasselbalch equation: pH = pKa + log([conjugate base]/[weak acid]).

3. What is the role of a strong acid in a buffer solution?

A strong acid is used to change the pH of a buffer solution. When a strong acid is added, it reacts with the weak base in the buffer solution, shifting the equilibrium and causing the pH to decrease.

4. How does the concentration of the strong acid affect the pH of a buffer solution?

The concentration of the strong acid will affect the pH of the buffer solution. A higher concentration of strong acid will result in a larger decrease in pH, while a lower concentration will result in a smaller decrease.

5. Can a buffer solution be made using only a strong acid?

No, a buffer solution must contain a weak acid or base in addition to a strong acid or base. This is because the weak acid or base is needed to resist changes in pH when a strong acid or base is added.

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