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In $\ce{CH3COOH/CH3COONa}$ buffer, the reserve acidity of the solution is due to the $\ce{CH3COO-}$ ions.

What is the meaning of the term of 'reserve acidity' in the above statement?

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  • $\begingroup$ One would expect buffers to maintain constant pH. Thus, in that context, reserve acidity of CH3COO- ions could mean that the CH3COO- ions help neutralize the base that has been added to the buffer solution. Though, I've been reading the mech here, and apparently my intuition doesn't seem to be correct. Will wait for someone to post a proper answer. $\endgroup$ – Gaurang Tandon Feb 17 '18 at 2:57
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Reserve acidity, more commonly known as Buffer capacity, is the amount of acid/base (in gram equivalents) that must be added to a buffer solution to change it's pH by one unit.

In your question, the $\ce{CH3COO-}$ is able to react with any Hydrogen ions that are added to the solution, decreasing the $[\ce{CH3COO-}]$ while increasing the $[\ce{CH3COOH}]$. It takes care of any excess acidity, hence, it is called as the reserve acidity. Similarly, the $\ce{CH3COOH}$ should be called the reserve basicity, as it can reach with any base to prevent much pH change.

For a mathematical approach, we use the Henderson-Hasselbach equation for calculating the final pH.

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  • $\begingroup$ Hi, thanks for your answer! You seem to suggest, by your statement - "Reserve acidity, more commonly known as Buffer capacity", that reserve acidity is the same as buffer capacity. I've been searching the literature but couldn't find any statement regarding this equivalence of buffer capacity and reserve acidity. Can you please cite one source that would affirm that statement of yours? Thanks! $\endgroup$ – Gaurang Tandon Feb 21 '18 at 16:17

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