When a bottle of wine is opened, its hydrogen ion concentration, #[H_3O^+]=4.1xx10^-4*mol*L^-1#; what is its #pH#? How does the #pH# evolve after the wine is left to stand?

1 Answer
anor277
May 7, 2017

#pH=-log_10[H_3O^+]#

Explanation:

And thus............when freshly opened #pH=-log_10(4.1xx10^-4)=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 #[H_3O^+]=0.0023*mol*L^-1; 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:

#"H"_3"CCH"_2"OH(aq)" +"O"_2"(g)" rarr "H"_3"CCO"_2"H(aq)"+"H"_2"O(l)"#

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