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

1) The buffer consists of C3H5O2- as a weak base and HC3H5O2 as a weak acid. A weak acid and its conjugate base is present to buffer addition of added base or acid, respectively.

2)

Molar concentrations of both buffer components are needed. [HC3H5O2] is given as 0.265. Determine [C3H5O2-].

use molar mass of NaC3H5O2

0.496g/96.0604=0.0051629mol NaC3H5O2

1 mol NaC3H5O2=1 mol C3H5O2-

0.0051629mol C3H5O2- present

50mL=0.050 L

[C3H5O2-]=0.0051629mol/0.050L

[C3H5O2-]=0.10326

[HC3H5O2]=0.265

Use Henderson equation:

pH=pKa+log([conj. base]/[weak acid])

pH=-log(1.34·10^-5)+log(0.10326/0.265)

pH=4.4636