What is sum of `pH + pOH " at " 25^(@) C` ?

If a solution has of a pOH value of 14 at 25^(@)C , H^(+) ion concentration in mol L^(-1) should be

pH of heavy water at 25^(@)C

The potential of a hydrogen electrode in a solution with pOH=4 at 25^(@)C is

The potential of a hydrogen electrode in a solution with pOH=4 at 25^(@)C is

What is the [OH^(-)] concentration of an acid whose pH is 5 at 25^@C ?^(**"**)

Shall phenolpthalein be used in neutralisation of Na_2 CO_3 by HC1 ? Why the solubility of AgCN be increased by addition of KCN. What is the sum of PH & POH of a solution.