Question

How do you calculate the pOH of a solution?

Answer 1

In water you use the relationship `pH+pOH=14`.

Explanation:

We know that at `298*K`, equilibrium obtains between hydronium ion and hydroxide ions in water:

`K_w=10^(-14)=[HO^-][H_3O^+]`. We can take `-log_10` of both sides:

`-log_10(K_w)=-log_10[HO^-]-log_10[H_3O^+]=-log_10(10^-14)`

i.e. `-log_10[HO^-]-log_10[H_3O^+]=14` by definition of the log function. And again by definition `pH=-log_10[H_3O^+]` etc.

Thus `pH+pOH=14`. There should be many problems here that use this relationship. Of course, you have to find them. Good luck.