Buffer Solution question (mult. choice).

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Discussion Overview

The discussion revolves around identifying which mixtures can act as buffer solutions when dissolved in water. Participants explore the characteristics of buffer solutions, particularly focusing on the roles of weak acids and bases, as well as the implications of strong acids and bases in buffer systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the correct answer is D, which involves acetic acid and NaOH, but expresses confusion about the nature of weak acids and bases.
  • Another participant confirms that D is indeed the correct answer, explaining the reaction between acetic acid and NaOH produces sodium ethanoate and retains some acetic acid, thus forming a buffer.
  • A different participant questions whether option E could also be a buffer, noting its similar concentrations of acid and base.
  • It is pointed out that HBr is a strong acid that fully dissociates, which negates its ability to form a buffer in option E.
  • One participant clarifies that for a buffer, the acid must be weak while the salt acts as a strong electrolyte, providing an example with acetic acid and its conjugate base.
  • Another participant elaborates on the buffer mechanism, explaining how the equilibrium shifts in response to added acids or bases, using acetic acid and its salt as an example.
  • A participant proposes a similar analysis for the NH3/NH4Cl system, prompting further exploration of its buffering behavior.
  • Another participant attempts to write the equilibrium equations for NH3 and NH4Cl to clarify the buffering process.

Areas of Agreement / Disagreement

Participants generally agree that option D is a buffer solution, but there is disagreement regarding the potential of option E to also serve as a buffer. The discussion remains unresolved regarding the specifics of buffering mechanisms and the conditions required for different mixtures.

Contextual Notes

Participants express uncertainty about the definitions and characteristics of weak versus strong acids and bases, as well as the implications for buffer solutions. There are also unresolved mathematical steps in the analysis of the buffering behavior of the discussed mixtures.

Who May Find This Useful

This discussion may be useful for students and individuals interested in chemistry, particularly those studying buffer solutions and acid-base equilibria.

RESmonkey
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New here, hello :)

Which of following mixtures will be a buffer when dissolved in a liter of water?

a. .1 mole of Ba(OH)2 and .2 mole of HBr
b. .3 mole of KCl and .3 mole of HCl
c. .4 mole of NH3 and .4 mole of HCl
d. .2 mole of CH3COOH and .1 mole of NaOH
e. .2 mole of HBr and .1 mole of NaOH

My guess is that it has something to do with being a weak acid/base. Unfortunately, this doesn't make sense, because the answer is D, and D has acetic acid and NaOH, which aren't weak?

Thanks in advance :)
 
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it is D

0.1 mol from the 0.2 mole ethanoic acid reacts with 0.1 mol NaOH to give 0.1 mol sodium ethanoate.

0.1 mol ethanoic acid also remains.

the buffer is CH3COOH/CH3COONa
 
hmmm

Using that, couldn't e also be an answer? It has similar concentrations of an acid and base.
 
but HBr is a strong acid. it fully dissociates in solution. it is stronger than HCl. there is no equilibirum between H+ and HBr.
 
Gotcha. So the two compounds have to be weak, and one of them has to be left over in the end?
 
errmm not really. the acid has to be weak but the salt is a strong electrolyte.

e.g. CH3COOH/CH3COO-Na+

CH3COOH <------> CH3COO- + H+

CH3COO-Na+ ------> CH3COO- + Na+

when you add a small amount of acid, the H+ added will combine with the conjugate base CH3COO- from the fully ionised salt to give CH3COOH. there is no drastic change in pH.

when you add a small amount of alkali, the OH- will combine with H+ from the partially ionised acid to minimise the chnage in pH. now, H+ concentration will also decrease, but since the dissociation of the acid is an equilibrium, according to LCP, the equilibrium will shift to the right, and the H+ will be restored.

this also applies to alkaline buffers. try to guess what happens with NH3/NH4Cl?
 
Nh3 + H30+ <------> Nh4 + H20 ?
 
you have to write an equation for each species, you will get a clearer overview...

NH3 + H2O <-----> NH4+ + OH-

NH4Cl -----> NH4+ + Cl-

remeber that NH3 dissociates only partially, but the salt ionises fully.

what happens when you add some acid? or some alkali?
 

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