Ammonium Sulfate has the formula `(NH_4)_2SO_4`
The ammonium ion is `NH_4^+` . Each formula unit of ammonium sulfate contains two ammoniun ions. The total number of ammonium ions is therefore 2 times the number of formula units:
(2)(2.9 x 10^30) = 5.8 x 10^30 ammonium ions
To solve this type of problem, start by writing the formula of the compound. Ammonium and sulfate are both polyatomic ions, so their formulas can be found on a table of ions. Since ammonium is a +1 ion and sulfate is a -2 ion, the formula will have one ammonium and two sulfate ions to produce a neutral compound.
The term formula unit is used because ionic compound don't exist as discrete molecules. The formula unit is the simplest whole-number ratio of ions in the crystal lattice.