pOH can be calculated by the negative logarithm of [OH⁻] .
pOH = -log [OH⁻]
pH scale is used to determine how acidic/ neutral or basic a solution is. By knowing the pOH the pH can be calculated, as;
pH + pOH = 14
pH = 14 - pOH
dissociation of Ba(OH)₂ is as follows;
Ba(OH₂) ---> Ba²⁺ + 2OH⁻
1 mol Ba(OH₂) dissociates into 2 OH⁻ moles
Therefore molarity of OH⁻ is twice as much as the molarity of Ba(OH₂).
[OH⁻] = 2 x 2.80 M
= 5.6 M
pOH = -log 5.6
= -0.75
pH = 14 - - 0.75
= 14.75
when the pOH is a negative value this means that the pH is greater than 14.
Usually pH scale is from 1-14, with 1 being very acidic and 14 being very basic. Since pH is greater than 14 this means that the solution is strongly basic.