Phosphoric acid is a triprotic acid, ionizing in the following sequential steps:
H₃PO₄ + H₂O $\leftrightarrows$ H₂PO₄^- + H₃O⁺ $K _ { a _ { 1 } }$
H₂PO₄^- + H₂O $\leftrightarrows$ HPO₄²^- + H₃O⁺ $K _ { a_{2} }$

HPO₄²^- + H₂O $\leftrightarrows$ PO₄³^- + H₃O⁺ $K _ { a _ { 1 } }$
Which equilibrium is most important in determining the pH of a solution of sodium phosphate?

Question

Phosphoric acid is a triprotic acid, ionizing in the following sequential steps:
H₃PO₄ + H₂O

\leftrightarrows

H₂PO₄^- + H₃O⁺

K _ { a _ { 1 } }

H₂PO₄^- + H₂O

\leftrightarrows

HPO₄²^- + H₃O⁺

K _ { a_{2} }

HPO₄²^- + H₂O

\leftrightarrows

PO₄³^- + H₃O⁺

K _ { a _ { 1 } }

Which equilibrium is most important in determining the pH of a solution of sodium phosphate?

Quizplus · Accepted Answer

In a solution of sodium phosphate, the predominant species is PO₄³⁻. The equilibrium that involves PO₄³⁻ gaining a proton to form HPO₄²⁻ and OH⁻ is most relevant for determining the pH, as it directly affects the hydroxide ion concentration.

Phosphoric Acid Is a Triprotic Acid, Ionizing in the Following ⇆\leftrightarrows⇆

Phosphoric Acid Is a Triprotic Acid, Ionizing in the Following $\leftrightarrows$