How can the titration curve be used to determine the strength of an acid?

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Discussion Overview

The discussion revolves around how to determine if an acid is strong or weak using a titration curve. Participants explore various characteristics of titration curves, particularly in relation to the pH changes observed during the titration process, and the implications for acid strength.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that a weak acid can be identified if the equivalence point occurs at a pH above 7 when titrated with a strong base.
  • Another participant proposes comparing two titration curves to analyze differences in acid strength.
  • A participant mentions calculating the concentration of an unknown monoprotic acid during titration, noting uncertainty in the result.
  • It is noted that a weak acid will show a gradual change in pH over a longer range of titrant addition until approaching the equivalence point, which should occur at a pH of about 8 or greater.
  • One participant calculates the concentration of hydrogen ions at the equivalence point and questions whether this can indicate the degree of dissociation of the acid.
  • Another participant states that at the equivalence point, the solution contains mostly the salt of the acid rather than the acid itself.
  • There is a request for additional methods to demonstrate that an acid is weak, indicating ongoing exploration of the topic.
  • A response highlights that the characteristics of the titration curve can help determine acid strength, emphasizing that strong acids do not exhibit pH buffering near the endpoint.

Areas of Agreement / Disagreement

Participants express various viewpoints on how to identify weak acids through titration curves, with no consensus reached on a definitive method or conclusion. Multiple competing ideas and calculations are presented, indicating an ongoing exploration of the topic.

Contextual Notes

Some participants express uncertainty about specific calculations and the implications of pH measurements, suggesting that assumptions about acid purity and dissociation may affect conclusions drawn from the titration data.

Physics197
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Homework Statement



How can you determine if an acid is strong or weak given the titration curve? I need two reasons.

Homework Equations





The Attempt at a Solution



1 Reason that it is weak is that its being titrated by a strong base and the equivalence point is above pH of 7.

Need a 2nd
 
Last edited:
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Take two titration curves and compare them.

You may try (there is a free trial).
 
Not sure what the acid is, but through a tritaion calculation I found the concentration of the acid to be 0.2083M.

That may not be correct..

Heres the data:
NaOH: 0.125M
25mL
acid: 15mL
unknown concentration

But it is a monoprotic acid
 
Depending on concentrations used, pH will change at a very high rate through pH 7 through the equivalence point. A weak acid will further show fairly small change in pH as the titrant is added over a "long" range of titrant addition until close to the equivalence point. Equivalence point should happen at about pH 8 or greater for a weak acid.
 
Yes, it happens at pH = 8.7

It just occurred to me that weak acids do not 100% dissociate

So could I use the pH of 8.7 to determine the concentration of H+ and compare that number to the concentration of the acid, and if they are different, that means it wasnt 100% dissociated?

HX ---------> H+ + X-
0.2M -------> 2x10^-9M

[H+] = 10^-pH = 2x10^-9
 
At equivalence point there is (almost) no acid, there is (almost) only its salt.
 
Well what's another way I could show that this acid is weak?
 
Physics197 said:
Well what's another way I could show that this acid is weak?

You just did, according to some of your description in post #5.

Was the original acid available in relatively pure, dry form? Even a pH measurement before titrating might not be strong enough information compared to performing a titration. As long as you can refer to your titration curve, you can easily enough judge whether the acid is weak or strong. Note, that a strong acid will not present pH buffering as you begin and continue to approach the endpoint with titrant additions; and the equivalence point pH should be sudden and extremely close to 7.
 

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