Why Use a Weak Base to Neutralize a Strong Acid?

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Discussion Overview

The discussion revolves around the use of weak bases, specifically TRIS and calcium carbonate, to neutralize strong acids like HCl. Participants explore the calculations involved in determining pH when a weak base reacts with a strong acid, as well as the practical implications of choosing weak versus strong bases for neutralization in various applications.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant computes the pH of a solution containing TRIS and HCl, but arrives at a different answer than expected, prompting a request for assistance in identifying errors.
  • Another participant questions the identification of the conjugate acid and base, suggesting that RNH3 is the conjugate acid of RNH2 and providing a reaction equation for clarity.
  • A participant provides a detailed calculation of pOH and pH based on the reaction between RNH2 and HCl, concluding with a pH of 8.26.
  • Questions are raised about the advantages of using weak bases like calcium carbonate for neutralizing strong acids, with one participant suggesting that the choice depends on the specific application.
  • Concerns are expressed regarding the potential for bubbling or foaming when using calcium carbonate, along with considerations about producing a buffer solution.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the advantages of using weak bases over strong bases for neutralization, indicating multiple competing views on the topic. The mathematical calculations regarding the pH of the TRIS solution also show some uncertainty and differing interpretations.

Contextual Notes

Participants express uncertainty regarding the proper identification of conjugate acids and bases, as well as the implications of using different bases for neutralization. There are unresolved aspects concerning the calculations of pH and pOH, particularly in relation to the initial concentrations and the resulting equilibrium states.

Who May Find This Useful

This discussion may be useful for students and professionals interested in acid-base chemistry, particularly those exploring the practical applications of weak and strong bases in neutralization reactions.

enigmatic
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Question: TRIS is a weak base. Compute pH of a solution containing .050 moles of TRIS and .020 moles of HCl in a total volume of 2L. pKb for TRIS is 5.92. Use RNH2 to represent TRIS.

Equation: pH = pKa+ log ([conjugate base]/[acid])

Work:
change equation for pOH:
pH = 14-pOH
pOH = pKb + log ([conjugate acid]/[base])
pOH = 5.02 + log (.010/.025) <---- I converted to mol/L for these values
pOH = 5.52
pH = 8.48

Real Answer: 8.26

Can someone show me where I went wrong? Thanks!
 
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What are your conjugated acid and base? What is your base concentration? (Hint: write reaction equation).

Borek
 
Last edited by a moderator:
They don't say what the conjugate acid and base is, except that the base is RNH2, so then its conjugate acid would be RNH3, right?

The base concentration would be .05/2 = .025 M.

The reaction equation would be
RNH2 + HCl <--> H2O + RNH3
Initial:
.25M .1M 0
Change:
-.1M -.1M .1M
Final:
.15M 0M .1M

pOH = pKb + log (.1/.15)
pOH = 5.92 + log (.1/.15)
pOH = 5.74
pH = 8.26

...

That's it! Thank you! :D :D
 
Why is it better to use a weak base(such as calcium carbonate) to neutralise strong acid (such as hcl) rather than strong base?

Thank you so much
 
Booo said:
Why is it better to use a weak base(such as calcium carbonate) to neutralise strong acid (such as hcl) rather than strong base?

Thank you so much

Generally, a weak base is not better and not worse. The choice depends on the application. Why do you ask?

If you use calcium carbonate to neutralize a strong acid, you hopefully are not worried about the presence of calcium, and the resulting carbon dioxide may be mostly insoluble, but beware of bubbling or foaming. Depending on quantities involved of the base(calcium carbonate) and the acid, you might be choosing to produce a buffer; is that what you wanted? Did you want some bicarbonate present?
 

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