Henderson Hassalbach equation problem

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Discussion Overview

The discussion revolves around the preparation of a Tris-HCl buffer solution at pH 7, specifically focusing on the calculation of the required molarity of HCl to achieve this buffer. Participants explore the underlying chemical reactions and concepts related to buffer solutions, including the role of acids and bases.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant presents a calculation using the Henderson-Hasselbalch equation to determine the molarity of HCl needed, arriving at two potential values: 0.92M and 0.08M.
  • Another participant questions the chemical reaction that occurs when HCl is added, suggesting a possible reaction involving TRIS and HCl.
  • Further clarification is sought regarding the nature of the products formed when HCl is added, with a participant asserting that TRIS hydrochloride is produced and emphasizing the distinction between acids and their conjugate bases.
  • There is a discussion about the definitions of Brønsted acids and bases, with a focus on their roles in the buffer system.
  • Speculative reactions involving TRIS and HCl are proposed, but there is uncertainty about their correctness and the formation of TRIS hydrochloride.

Areas of Agreement / Disagreement

Participants express differing views on the chemical reactions involved in the buffer preparation and the correct interpretation of the products formed. There is no consensus on the exact nature of the reactions or the correct molarity of HCl to be used.

Contextual Notes

Participants have not fully resolved the assumptions regarding the chemical behavior of TRIS in the presence of HCl, nor have they clarified the definitions and roles of acids and bases in this context.

hianghao
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Homework Statement


I am trying to prepare a 1L Tris-HCl buffer 1M pH7. The pKa value is 8.06. The question is, how many molar of HCl should be added to produce this buffer?


Homework Equations


pH = pKa + log [base/acid]


The Attempt at a Solution


7=8.06 + lg (a/b)
-1.06=lg (a/b)
a/b = 0.0871 -----1
a+b= 1M
a=1-b --------2
Hence,
(1-b)/b = 0.0871
b = 0.92M
a = 0.08M
So, the molarity of HCl to be added is 0.92M or 0.08M. Why?
 
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What reaction takes place when you add HCl?

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hianghao said:
C4H11NO3 + HCl <-> C4H10NO2Cl + H2O?

No. HCl is neutralized, but there is no water between products. TRIS hydrochloride is produced.

Because b=salts conc while a=acid/base conc?

Buffer is a mixture of salt & acid/base, but acid and conjugate base.

You need to identify an acid and its conjugate base in the case of TRIS.

What is a Broensted acid? What is a Broensted base? How are they related?

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methods
 
Borek said:
No. HCl is neutralized, but there is no water between products. TRIS hydrochloride is produced.
Buffer is a mixture of salt & acid/base, but acid and conjugate base.

You need to identify an acid and its conjugate base in the case of TRIS.

What is a Broensted acid? What is a Broensted base? How are they related?

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chemical calculators - buffer calculator, concentration calculator
www.titrations.info - all about titration methods


So buffer should be acid+conjugate base or base + conjugate acid.
Bronsted Acid donate proton while base receive proton.
HCl is suppose to be the acid because it has H+ to be donated.

If no water product, could it be
(CH2OH)3CNH2 + HCl <> (CH2OH)3CCl + NH3?
but still it doesn't become TRIS hydrochloride..
Or it becomes (CH2OH)2CClNH2+ CH3OH? I can't hink of other possiblity..
 
Last edited:

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