How to obtain Cr3+ precipitate

The precipitate of chromium(III) carbonate can be obtained by adding a solution containing Cr^3+ ions to a solution of sodium carbonate solution.

The ionic equation is:
2Cr^3+(aq) + 3CO32-(aq) → Cr2(CO3)3(s)

Since the anions in the solution containing Cr^3+ ions are unknown, only ionic equation can be written and we are unable to write the full equation. However, if the anions are known, we can write the full equation. For example, when a solution of chromium(III) chloride is added to sodium carbonate solution, the equation of the reaction is:
2CrCl3(aq) + 3Na2CO3(aq) → Cr2(CO3)3(s) + 6NaCl(aq)