Barium Hydroxide is a strong base, so it would completely dissociate to Ba²⁺ and OH⁻. But it is crucial to know the concentration of the Ba(OH)₂ solution. For example, if you dissolve 1 g in 1 L of solution, then the concentration would be:
C = (1 g)(1 mol Ba(OH)₂/171.34 g)/ 1 L = 5.84×10⁻³ M
So, the concentration of [OH⁻] is
[OH⁻] = 5.84×10⁻³*2 = 0.0117 M
pH = 14 - -log(0.0117)
pH = 12.07
