Explaining Resistance in pH of Buffer: Strong vs Weak Acids

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Discussion Overview

The discussion centers on the application of the Henderson-Hasselbalch equation to strong and weak acids in the context of buffer solutions and their resistance to pH changes. Participants explore the theoretical implications of using this equation for strong acids and the differences in buffer capacity between strong and weak acids.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that the Henderson-Hasselbalch equation can be applied to strong acids, but caution that it cannot be used for pH calculations in the same manner as for weak acids.
  • There is a discussion about buffer capacity, with some arguing that strong acids resist pH changes differently than weak acids due to their high dissociation rates.
  • One participant notes that strong acids can maintain a relatively stable pH in concentrated solutions, even with significant neutralization.
  • Others point out that weak acids are less dissociated and thus allow for more significant changes in the concentrations of [A-] and [HA], leading to better pH resistance.
  • Concerns are raised about the practicality of using strong acids in standard buffer preparations, with some participants asserting that they are not typically used for this purpose.
  • A question is posed regarding the preparation of a buffer solution at pH = 1, highlighting the challenges associated with strong acids.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of the Henderson-Hasselbalch equation for strong acids and the nature of buffer capacity. There is no consensus on the best approach to explaining the resistance to pH changes in buffers made from strong versus weak acids.

Contextual Notes

Participants note limitations in using the Henderson-Hasselbalch equation for strong acids, and there are unresolved questions regarding the specific conditions under which strong acids can be considered in buffer solutions.

Samurai33
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could the equation - pH=pKa+log([A]/[HA]) - be applied for the case of strong acid? Although the percentage of dissociation of strong acid/base is very high, there still exists a equilibrium, right?

secondly, if i tried to explain the resistance in pH of buffer *in terms of* the above equation, then the pH of a buffer will depend only on the ratio of [A]/[HA]; then for both strong/weak acid with its salt, if i add H+ to each solution, the result will be: [A] decrease; [HA] increase (both cases). then how can i explain the difference that weak acid buffer has the ability to resist change in pH?

Please help me to solve this query, thanks a lot!
 
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First question - Henderson-Hasselbalch equation works for strong acids too, although it can't be used for pH calculation, at least not in the same way as in the case of weak acids.

Second question is in fact about buffer capacity. Strong acids resist pH changes as well, although in slightly different way. In the case of strong acid pH changes only slightly in the case of relatively concentrated solutions, as neutralizing even 10% of acid doesn't change pH much. In the case of weak acids pH changes only slightly because weak acids are in a way inert - they almost don't dissociate on their own. Thus concentration of A- and HA can be easily forced on the solution, and as long as they don't change much, pH doesn't change as well.
 
Borek said:
First question - Henderson-Hasselbalch equation works for strong acids too, although it can't be used for pH calculation, at least not in the same way as in the case of weak acids.
To be more specific, it cannot be used for calculating pH of buffer with strong acid and its salt??
 
See the page mentioned (part about dichloroacetic acid).
 
Samurai33 said:
To be more specific, it cannot be used for calculating pH of buffer with strong acid and its salt??

You don't need to use the H-H equation, also, strong acids/bases are not employed for making standard buffers.
 
GCT said:
Ystrong acids/bases are not employed for making standard buffers.

How are you going to prepare pH = 1 buffer solution?
 

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