Source
r/chemhelp•
-Ghostface-

Buffer question

General/High School

Describe the preparation of 500 mL of a 0.100 M propanoate buffer that has a pH of 4.90. Assume you have solid sodium propanoate (NaC3H5O2) and 0.250 M propanoic acid (HC3H5O2).

answer: 2.42 g of NaC3H5O2 and 98.8 mL of 0.250 M HC3H5O2 diluted to 500 mL

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Despite having the answer, I still am incapable of understanding how to go about this

Posted May 24, 2023, 12:33 AM UTC

22
chemprof4real•

The Henderson hasselbalch equation will help you calculate the concentrations of acid and base needed to achieve a specific pH in a buffer solution. Dilution doesn’t effect the pay of a buffer solution because both the acid and base are diluted by the same factor, so the ratio of their concentrations in said equation won’t change upon dilution. The dilution here is just to get it to the required 500 mL.

3
chem44•

There are various ways to do these things. That is why we really want you to get us started, so we can build on what you have.

One way here, the Henderson... gives you the ratio of acid and base forms, and you are told the sum. Two equations, two unknowns.

2