Fill in the left side of this equilibrium constant equation

Question

Fill in the left side of this equilibrium constant equation for the reaction of phosphoric acid (H₃PO₄) with water.

__ = K_a

Answer 1

The equation for the acid-base reaction is

H₂O + H₃PO₄ ⇌ H₃O⁺ + H₂PO₄^–

The acid-dissociation constant (K_a) is given by

K_a = [H₃O⁺][H₂PO₄^–]/[H₃PO₄]

K_a is like the equilibrium constant for the acid base reaction, with the solvent concentration, [H₂O], removed from the denominator.