Did I Prepare My Phosphate Buffer Solution Correctly?

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Discussion Overview

The discussion revolves around the preparation of a phosphate buffer solution, specifically addressing the calculations involved in achieving a desired pH of 7.0 using the Henderson-Hasselbalch equation. Participants are examining the correctness of the mole calculations for the components of the buffer solution.

Discussion Character

  • Technical explanation, Debate/contested, Homework-related

Main Points Raised

  • One participant describes their approach using the Henderson-Hasselbalch equation to calculate the required moles of H2PO4- and HPO42- for a phosphate buffer solution.
  • Another participant requests clarification on the specific pKa used and the definitions of [salt] and [acid] in the context of the equation.
  • A participant confirms their calculations and the pKa value they used, identifying H2PO4- as the acid and HPO42- as the salt.
  • One participant agrees with the calculations presented, suggesting consistency in the approach taken.

Areas of Agreement / Disagreement

While some participants express agreement with the calculations, there is no explicit consensus on the correctness of the initial participant's approach, as further clarification and verification are sought.

Contextual Notes

Participants have not fully resolved the assumptions regarding the choice of pKa or the definitions of the species involved in the buffer preparation.

Who May Find This Useful

Individuals interested in buffer preparation, particularly in a laboratory or educational context, may find this discussion relevant.

brendw2005
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Hi everybody!
I want to prepare 1000 ml of 0.1M phosphate buffer solution, pH = 7.0. I used Henderson Hasselbach's equation: pH = pka + log [salt]/[acid]. I obtained 0.062 moles of H2PO4- and 0.038 moles of HPO42-. Where I am wrong? Thanks a lot!
B
 
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Show your work. Which pKa did you use? What species did you use for [salt] and [acid]?
 
Thanks for replying!

I used (H2PO4)- ↔H+ + (HPO4)2-
Ka for this equation is 6.2*10-8, deci pKa = 7.21.
Salt = (HPO4)2-
Acid = (H2PO4)-
 
I get the same...
 
So, I did it right! Thanks!
 

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