Answer:
pH = 12.90
Explanation:
The TSP is in equilibrium with water as follows:
Na₃PO₄(aq) + H₂O(l) ⇄ Na₂HPO₄⁻Na⁺(aq) + OH⁻(aq)
Where Kb = 0.0208 is defined as:
Kb = 0.0208 = [Na₂HPO₄⁻Na⁺] [OH⁻] / [Na₃PO₄]
As both Na₂HPO₄⁻Na⁺ OH⁻ comes from the same equilibrium:
[Na₂HPO₄⁻Na⁺] = [OH⁻] = X
[Na₃PO₄] is -molar mass: 163.94g/mol:
50.0g * (1mol / 163.94g) =0.305moles / 1L =
0.305M
Replacing:
0.0208 = [X] [X] / [0.305M]
6.344x10⁻³ = X²
0.0796M = X = [OH⁻]
As pOH = -log [OH⁻]
pOH = 1.099
pH = 14 - pOH
