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I'm trying to replace vinegar with sodium diacetate in a recipe, and I would like to understand better what is happening from a chemical point of view.

What I imagine happens when I add sodium diacetate to the pot:

$$\ce{NaH(C2H3O2)2 + H2O -> (C2H4O2)2 + NaOH}$$

But what happens to the sodium hydroxide? It's alkaline in a acidic solution so it should react somehow?

Also if I know that $\pu{100 ml}$ of vinegar contains $\pu{4 g}$ of acetic acid, how much sodium diacetate should I add to substitute the vinegar?

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    $\begingroup$ $\ce{NaH(C2H3O2)2(s) ->[H2O] CH3COOH(aq) + CH3COO-(aq) + Na+(aq)}$ with $\mathrm{pH} \approx 4.75$, forming pH buffer. / The solution will be just slightly acidic. $\endgroup$
    – Poutnik
    May 22, 2023 at 13:04
  • $\begingroup$ so the result will have positive and negative ions in solution? I find it hard to believe that they will not react (but I haven't touched chemistry in 15 years). Are you telling me that sodium diacetate is a poor substitute for acetic acid? $\endgroup$
    – Mascarpone
    May 22, 2023 at 13:10
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    $\begingroup$ Yes, it is a poor substitute. Sodium diacetate is in a way just a rearranged mixture of acetic acid and sodium acetate, with the latter being mildly alkalic. I would suggest using citrone juice instead of vinegar. $\endgroup$
    – Poutnik
    May 22, 2023 at 13:17
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    $\begingroup$ What is bad with vinegar? Mixing equivalent amounts of hydrochloric acid and sodium diacetate would be the same as mixing vinegar with table salt. But it would be hard not to overdose the acid. I strongly advice against it. $\endgroup$
    – Poutnik
    May 22, 2023 at 13:41
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    $\begingroup$ Let us continue this discussion in chat. $\endgroup$
    – Poutnik
    May 22, 2023 at 13:46

2 Answers 2

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You can use citric acid with sodium diacetate:

$\ce{(CH3COO)2HNa + H3Citr -> 2 CH3COOH + NaH2Citr}$

You could use premixed or rather separate 2 solids. Premixed is more practical, but I would avoid its longer storage to prevent acetic acid creation.

It could help if a desiccant could be used, like silicagel balls in cups of effervescent tablets. But it should be tested. For myself, I would use empty containers from such tablets, recently used.

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Note that there are 2 Acetic acid molecules and 1 Sodium Hydroxide molecule in the reaction so there will be an extra 1 Acetic acid molecule left after the complete reaction so, your reaction will always result an acidic medium.

To find how much sodium diacetate you should add to substitute the vinegar, you should first find how many moles of Acetic acid are in a 4g sample (divide the mass of sample from the molar mass of Acetic acid). Then according to your reaction, find how many moles of Sodium Diacetate are needed to get the same amount of Acetic acid you previously calculated using stochiometric ratios. Find the required mass of Sodium Diacetate by multiplying the amount of moles you calculated for Sodium Diacetate before with the molar mass of Sodium Diacetate.

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