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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: helplessnerd0402 on September 17, 2021, 05:01:43 PM

Title: Buffer Problem - am I approaching this right?
Post by: helplessnerd0402 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?

Title: Re: Buffer Problem - am I approaching this right?
Post by: VP_JQ 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...

Title: Re: Buffer Problem - am I approaching this right?
Post by: helplessnerd0402 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.

Title: Re: Buffer Problem - am I approaching this right?
Post by: Borek 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.