I'm new to chemistry and I need help with this

Question

A chemist starts with a 50.0 mL sample of 0.265 M propanoic acid, HC3H5O2, then adds 0.496 g of sodium propanoate, NaC3H5O2.

1.Explain how this creates an effective buffer.

2.Propanoic acid has an acid dissociation constant of 1.34 x 10-5. Assuming that no change in the volume of the solution occurs, calculate the pH of the buffer solution.

Answer 1

Hello Cole!

1. This system creates an effective buffer because of the presence of the acid (HC3H5O2) "HA" and its conjugate base (C3H5O2^-) "A-".
2. Because we need to calculate the pH of a buffer solution, we need to use Henderson-Hasselbalch equation: pH = pKa + log( [A-]/[HA]). The concentration of HA is 0.265M as given in the problem, and the concentration of A- is [0.00516 mol A-]/ [0.05 L] = 0.103 M. Plugging everything in, making sure that we convert Ka to pKa we have pH = -log(1.34 x 10^-5) + log(0.103/0.265) = 4.46.