Is Calcium Oxalate a base or an acid?

Question

Is Calcium Oxalate (CaC₂O₄) an acid or a base, specifically would it dissolve in an acid like HCl or a base like NaOH?

Answer 1

It should be more soluble in an acid because the oxalate anion is the conjugate base of a weak acid.

CaC₂O₄(s) <==> Ca²⁺(aq) + C₂O₄^2-(aq)

Adding acid (H⁺) will have the following effect:

C₂O₄^2-(aq) + H⁺(aq) ==> HC₂O₄^-(aq) + H⁺(aq) ==> H₂C₂O₄(aq)

According to Le Chatelier, as you remove C₂O₄^2- by forming H₂C₂O₄, the equilibrium shifts to the right, allowing more CaC₂O₄ to become aqueous.

To answer you other question, an aqueous solution of calcium oxalate will be very slightly alkaline (basic), because of slight basic nature of the oxalate anion (conjugate base of a weak acid). Since the concentrations of both Ca²⁺ and C₂O₄^2- will be rather low, the pH would probably be between 7 and 8.