The [H3O+] in a wine bottle is 3.1 10–2 M. What is the [–OH] in this wine?
You need to know the Kw for water at the temperature of the wine.
There is a table of Kw versus temperature here
http://www.chemguide.co.uk/physical/acidbaseeqia/kw.html
then use
[H+][OH-]=Kw
to find [OH-]
To determine the concentration of the hydroxide ion, [OH-], in the wine, we can use the relationship between [H3O+] (hydronium ion concentration) and [OH-] (hydroxide ion concentration) in water. In neutral water, these two concentrations are equal, so we can use the equation:
[H3O+] x [OH-] = 1.0 x 10^-14
Given that the [H3O+] in the wine bottle is 3.1 × 10–2 M, we can substitute this value into the equation:
(3.1 × 10–2) x [OH-] = 1.0 × 10^-14
Now, we can solve for [OH-]:
[OH-] = (1.0 × 10^-14) ÷ (3.1 × 10–2)
Calculating this expression gives us the concentration of hydroxide ions, [OH-], in the wine bottle.