How many moles of ammonium ions are in 6.985 g of ammonium carbonate?

 (NH4)2CO3 -> 96.09 g/mol 

(6.995g ammonium carbonate)(1mol ammonium carbonate/ 96.09 g ammonium carbonate) = 0.072796 mol ammonium carbonate 

In this conversion, the 'grams' unit is crossed out because it is in both the numerator and the denominator, which leaves the 'mol' unit left. 

Looking at the formula (NH4)2CO3, you can look at it as if it were: 
2 mol (NH4) + 1 mol (CO3) = 1 mol (NH4)2CO3 

For every 1 mol of ammonium carbonate, you have 1 mol of carbonate ions and 2 moles of ammonium ions. 

(0.072796 mol ammonium carbonate) = (0.072796 mol carbonate ion)+(0.363981 mol ammonium ion)