# Is it possible to calculated the concentration of hydroxide ions from the known concentration of hydronium ions?

Chapter 15 (Acids and Bases) of Holt High School Chemistry:

Neutralizing $$\pu{5.00 L}$$ of an acid rain sample required $$\pu{11.3 mL}$$ of $$\pu{0.0102 M}\ \ce{KOH}$$. Calculate the hydronium ion $$[\ce{H3O+}]$$ concentration in the rain sample.

We can derive the required concentration by substituting into:
$$c_1V_1 = c_2V_2,$$

Can we, after getting the concentration of $$\ce{H3O+}$$) use the equation with the ionization constant of water
$$K_\mathrm{w} = [\ce{H3O+}][\ce{OH-}]$$ to also get the $$\ce{OH-}$$ concentration?

• Of course we can. Commented Sep 10, 2017 at 16:19

So if your question had asked for the hydroxide concentration, you would indeed calculate the hydronium concentration first (because that is actually accessible) and then invert and multiply $10^{-14}$ to get the desired one as you suggest.
• " you would indeed calculate the hydronium concentration first (because that is actually" Which balanced equation we can use in order to calculate $[\ce{H3O+}]$? Commented May 4, 2021 at 18:56