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Finding the pH of a buffered System

  • Thread starter Glitche
  • Start date
  • #1
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1. A buffer system commonly used in the biochemistry lab uses a substance abbreviated TRIS, and it's conjugate acid TRISH+. A Buffer is prepared with [TRIS] = 0.60M and
[TRISH+]= 0.30M. What is the pH of this buffered System? The Ka for TRISH+ is 1.20 x 10^-6




[H+]=Ka [HA]/[A-] (Equation Attached)



3. I know the answer because I am studying off of a practice exam our professor gave to us, but I'd like to know how to solve it. The method I tried was [(1.20x10^-6)*(0.60/0.30)].

Thank you in advance!
 

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Answers and Replies

  • #2
Borek
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Equation you listed is just a rearranged version of the dissociation constant. It can be modified even further, yielding so called Henderson-Hasselbalch equation:

[tex]pH = pK_a + \log \frac {[A^-]}{[HA]}[/tex]

Once you have it it is just a plug and chug. You just have to understand what is the acid and what is the conjugate base in the case of TRIS.
 

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