What is the pOH of a solution with a pH of .7?

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Answer 1 · 2016-12-11T07:48:01

And it's an aqueous solution?

We know that in water the following equilibrium operates:

#2H_2O(l) rightleftharpoonsH_3O^+ + HO^-# #K_"eq"=10^-14#

#[H_3O^+][HO^-]=10^-14#

We take #log_10# of both sides:

#log_10[H_3O^+]+log_10[HO^-]=log_10[10^-14]#

#log_10[H_3O^+]+log_10[HO^-]=-14#, and multiply both sides by #-1#,

#-log_10[H_3O^+]-log_10[HO^-]=14#

But #-log_10[H_3O^+]=pH#, and #pOH=-log_10[HO^-]# by definition.

And thus #pH+pOH=14# (for water under standard conditions). This is something that you have to know.

You have #pH=0.7#, and thus #pOH=13.3#. What is #[H_3O^+]#?