Question

What is the formula of ammonium carbonate?

Answer 1

The name of the cation is always added first to the name of the ionic compound. Likewise, the cation is added first to the compound's chemical formula. In this case, you know that you have ammonium, $N{H}_4^{+}$ as the cation.

The name of the anion follows the name of the cation. In this case, you know that you have the carbonate ion,$C{O}_3^{2-}$ as the anion.

$2\times \left[N{H}_4^{+}\right]$ and $1\times \left[C{O}_3^{2-}\right]$

Which means that the chemical formula for this compound will be:

$(N{H}_4{)}_{2}C{O}_3\to$ ammonium carbonate