Question

Solubility of calcium oxalate is ________ in the presence of ammonium oxalate because of _______ .

Answer 1

Solubility of calcium oxalate is decreased in the presence of ammonium oxalate because of common ion effect.
$Ca{C}_2{O}_4\to C{a}^{2+}+C_2{O}_4^{2-}$
$(N{H}_4{)}_2{C}_2{O}_4\to 2N{H}_4^{+}+C_2{O}_4^{2-}$
Calcium ion dissociates to a small extent but ammonium oxalate completely dissociates and provides oxalate ions that are common ions. These oxlate ions shift the equilibrium for the dissociation of calcium oxalate towards left. This suppresses the dissociation of calcium oxalate.