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Why is Sodium acetate called a salt of weak acid and strong base, when Acetic acid behaves as a strong acid (i.e. it shows almost cent percent dissociation) in Sodium hydroxide solution ?

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  • $\begingroup$ Strength and weakness are relative terms, of course when we compare acetic acid and sodium hydroxide in terms of acidity it is considered as strong acid, but this is not the case when this compare acetic acid and sulfuric acid in the same terms. In other words sodium hydroxide is very much weak acid to a degree that is considered as a strong base. $\endgroup$ – M.ghorab Jan 16 '16 at 17:22
  • $\begingroup$ @M.Ibrahim Please add that as an answer. Thanks! :) $\endgroup$ – jonsca Jan 17 '16 at 2:54
  • $\begingroup$ @M.Ibrahim you got my question wrong. Acetic acid acts as a strong acid in sodium hydroxide soln., doesn't it ? and sodium acetate is formed when acetic acid reacts with sodium hydroxide, so doesn't it behave as strong acid then ? $\endgroup$ – Abhirikshma Jan 17 '16 at 5:14
  • $\begingroup$ do you mean the strength of sodium acetate salt ? It is for sure a weaker acid than the parent acetic acid. $\endgroup$ – M.ghorab Jan 17 '16 at 6:19
  • $\begingroup$ @M.Ibrahim I did not mean the acidic strength of sodium acetate salt. $\endgroup$ – Abhirikshma Jan 21 '16 at 15:20
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Your definition of strong acid is wrong.

Simplistically speaking, it is defined with respect to dissociation in water, not in NaOH.

Acetic acid only dissociates partially in water, so it is a weak acid. It doesn't matter whether it dissociates completely in NaOH or not. That's irrelevant.

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  • $\begingroup$ The dissociation is affected by the PH of the medium, water is more acidic than NaOH. It is not necessary to use the standard definition to compare these characteristics especially qualitatively as here. $\endgroup$ – M.ghorab Jan 21 '16 at 21:32
  • $\begingroup$ No, sorry to be blunt, you don't understand the question at all. $\endgroup$ – orthocresol Jan 21 '16 at 22:07
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Good question.

You are right. In sodium hydroxide solution, you should not call sodium acetate a salt of strong base and weak acid. If so then the pH should be even more greater than what we expect. However, the pH should be less than expected, though not appreciable. It is because the ionization of NaOH will compete with the ionization of sodium acetate as well as with the hydrolysis of acetate ion.

However, defining of strong or weak acids or bases is done in water not in sodium hydroxide solution.

Ref: www.adichemistry.com

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  • $\begingroup$ Yeah, that's exactly what I meant to say, but unfortunately very few people understood that, and what is more surprising is that the ones who understood the least spoke out the most !! $\endgroup$ – Abhirikshma Feb 8 '16 at 5:05

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