July 02, 2022, 02:03:09 PM
Forum Rules: Read This Before Posting

### Topic: Buffer Problem - am I approaching this right?  (Read 489 times)

0 Members and 1 Guest are viewing this topic.

#### helplessnerd0402

• New Member
• Posts: 6
• Mole Snacks: +0/-0
##### Buffer Problem - am I approaching this right?
« on: September 17, 2021, 05:01:43 PM »
I am being asked to produce 1 liter of 50 mM buffered solution of pH 8. I am given 1M buffer at pH 7, HCl,  and NaOH. The pKa of my buffer is also 8. To solve this problem, I just added 50 mL of buffer solution to a 1 liter volumetric flask (as this would give a 50 mM final concentration). Then, I added 9 x 10^-7 moles of NaOH to raise the pH to 8. Is this wrong? Should I be using the Henderson Hasselbach equation for this somehow?

#### VP_JQ

• Regular Member
• Posts: 10
• Mole Snacks: +0/-0
##### Re: Buffer Problem - am I approaching this right?
« Reply #1 on: September 17, 2021, 06:06:50 PM »
Hi,

I'm not understanding something...
You are writing about a pKa of a buffer, but the pKa is a parameter of a weak acid...

#### helplessnerd0402

• New Member
• Posts: 6
• Mole Snacks: +0/-0
##### Re: Buffer Problem - am I approaching this right?
« Reply #2 on: September 17, 2021, 06:57:07 PM »
Right- we are given a buffer, "Buffer A" with a pKa of 8. I'm not sure if this information is given to confuse, or if it's actually needed to create the buffered solution.

#### Borek

• Mr. pH
• Administrator
• Deity Member
• Posts: 27121
• Mole Snacks: +1761/-405
• Gender:
• I am known to be occasionally wrong.
##### Re: Buffer Problem - am I approaching this right?
« Reply #3 on: September 18, 2021, 02:56:44 AM »
"Buffer with pKa" means "buffer made of a weak acid with pKa".

You need HH equation, no doubt about it. Assume added base (after all you want pH to go up) reacts with the acid stoichiometrically.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info