Question

What is the formula for CO3 2- and Al3+ ?

Answer 1

The formula for the given above is obtained by cross multiplying the charges of the given set of atoms. The element with a positive value for the charge should be written first. This may be shown through the formula,
Al2(CO3)2.

Answer 2

Answer is: formula is Al₂(CO₃)₃.

Aluminium carbonate (Al₂(CO₃)₃) has neutral charge. Because aluminium cation has positive charge 3+ and carbonate anion has negative charge 2-, for right chemical formula, we need two aluminium cations and three carbonate anion:

charge of the molecule = 2 · (3+) + 3 · (-2).

charge of the molecule = 0.