# How many ammonium ions are in 2.9x 10^30 formula units of ammonium sulfate?

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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.