Is NaHCO3 a versatile compound in aqueous solutions?

  • Thread starter Thread starter synergix
  • Start date Start date
  • Tags Tags
    Acid Base
Click For Summary

Discussion Overview

The discussion revolves around the behavior of sodium bicarbonate (NaHCO3) in aqueous solutions, specifically its ability to act as both an acid and a base. Participants explore the relevant chemical equations and the equilibrium constants associated with these reactions, as well as the implications for the predominant reaction in pure water.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents the equations for NaHCO3 acting as an acid and as a base, suggesting that the acid dissociation constant (Ka1) is greater than the base dissociation constant (Kb1), indicating that NaHCO3 will predominantly act as an acid.
  • Another participant agrees with the initial assessment that Ka1 being greater than Kb1 supports the claim that the acid reaction predominates.
  • A different participant suggests checking the hydrolysis steps of Na2CO3 and the dissociation steps of H2CO3 to evaluate which dissociation of bicarbonate is more favorable.
  • One participant expresses confusion about the process of NaHCO3 becoming Na2CO3 and seeks clarification on the hydrolysis steps mentioned.
  • Another participant acknowledges potential terminology issues and encourages a comparison of the acidic dissociation constant for bicarbonate with the equilibrium constant for the reaction involving H2CO3 and OH-.
  • A later reply questions the ability to definitively state which reaction dominates, noting that the ratio of [H2CO3] to [CO32-] is close to 1, suggesting that both reactions may proceed to a similar extent.

Areas of Agreement / Disagreement

Participants express differing views on whether one reaction predominates over the other, with some supporting the idea that the acid reaction is favored while others argue that both reactions may occur to a similar degree. The discussion remains unresolved regarding the dominance of the reactions.

Contextual Notes

Participants reference specific equilibrium constants (Ka1 and Kb1) and their relationships, but there are uncertainties regarding the implications of these constants and the hydrolysis steps involved. The discussion does not reach a consensus on the predominant reaction.

synergix
Messages
177
Reaction score
0

Homework Statement



Write two equations that illustrate that an aqeous solution of NaHCO3 can act either as an acid or a base. In pure water show quantitatively which of the two reactions predominate. ka1= 4.2x10-7, Ka2=4.8x10-11


The Attempt at a Solution


as an acid:

NaHCO3(aq) + H2O(l)---> H3O+(aq) + NaCO3-(aq)

Base:

NaHCO3(aq) + H2O(l) ------> OH-(aq) + NaH2CO3+(aq)

The second part is where I am having some trouble. I am not sure if I am doing this correctly so i will try to show and explain what I think will happen as best I can. I think Ka1 will predominate the reason being that kb1= (1x10^-14)/(4.2x10^-7)=2.38x10^-8
so Ka1>Kb1 therefore this reaction will proceed. Meaning most of the sodium bicarbonate will act as an acid and release protons. whereas Kb2=(1x10^-14)/(4.8x10^11)=2.08x10^-4.
so Kb2>>Ka2 so releasing a 2nd proton is not very favorable the species is much more likely to pick up another proton then it is to release another proton.
 
Last edited:
Physics news on Phys.org
I guess if I am correct then the fact that Ka1 is quantitatively greater then kb1 is the proof that ka1 will predominate.
 
Your written reactions are good. For which dissocation of bicarbonate is more favorable, check the Na2CO3 hydrolysis steps on the way towards H2CO3, or check the dissocation steps of H2CO3 toward Na2CO3. You know how to find Ka from corresponding Kb, right?
 
How does NaHCO3 become Na2CO3? I am not sure exactly what you mean by checking the Na2CO3 hydrolysis steps on the way towards H2CO3.
 
Synergix, maybe I was sloppy with my terminology or notation. You were on a good track with your idea of comparing the acidic dissociation constant for bicarbonate to the equilibrium constant for HCO3- + H20 <===> H2CO3 + OH-
Are you studying weak acid-base equilibria right now? If so, you will soon know how to evaluate those constants.
 
Ya we have covered that already as part of the last section. I will look at it again maybe I can figure it out thanks.
 
pH of amphiprotic salt

I am not sure you can say which of the reactions dominate. If you will read through the lecture you will find that ratio [H2CO3]/[CO32-] is close to 1, that means both reactions proceed to the same degree.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 3 ·
Replies
3
Views
9K
  • · Replies 3 ·
Replies
3
Views
4K
Replies
2
Views
18K
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
6K
  • · Replies 1 ·
Replies
1
Views
22K
Replies
7
Views
38K