When a bottle of wine is opened, its hydrogen ion concentration, [H3O+]=4.1×104molL1; what is its pH? How does the pH evolve after the wine is left to stand?

1 Answer
May 7, 2017

pH=log10[H3O+]

Explanation:

And thus............when freshly opened pH=log10(4.1×104)=3.39.

(And in fact most wines have a pH around this level.) See here for more detail on the definition of pH.

And later [H3O+]=0.0023molL1;pH=2.64

The wine must not have been very good, because most wine is consumed within 12 hours after opening. What likely occurred is that the ethyl alcohol air-oxidized up to acetic acid, which is a carboxylic acid, and thus likely to have a lower pH in aqueous solution. (Note that this oxidation is why we seal wine bottles with an air-tight cork/cap).

For the oxidation of ethyl alcohol to acetic acid we could write the equation:

H3CCH2OH(aq)+O2(g)H3CCO2H(aq)+H2O(l)