Trisodium phosphate (Na3PO4) is available in hardware stores as TSP and is used as a cleaning agent. The label warns that the su

Question

3 years ago

14

bstance is very basic. What is the pH of a solution containing 50.0 g of of TSP in a liter of solution

1 answer:

dexar [7] · Answer 1 · 2022-12-02T19:30:46+03:00

Answer:

pH = 12.90

Explanation:

The TSP is in equilibrium with water as follows:

Na₃PO₄(aq) + H₂O(l) ⇄ Na₂HPO₄⁻Na⁺(aq) + OH⁻(aq)

<em>Where Kb = 0.0208 is defined as:</em>

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