Question

Question

Answer 1

Blank #1: Polyatomic

Blank #2: 2 (see explanation)

Blank #3: 1 (see explanation)

Explanation

Both the ammonium ion $\text{NH}_4^{+}$ and the sulfate ion $\text{SO}_4^{2-}$ contain more than one atom in each ion. The two species are thus polyatomic. The chloride ion $\text{Cl}^{-}$, for example, is monoatomic.

Superscripts above formulae of the ions indicate their charge. Each ammonium ion carries a positive one (+1) charge. Each sulfate ion carries a charge of negative two (-2).

Ammonium sulfate is an ionic compound. A sample of this compound contain myriads of ammonium ions and sulfate ions. The ions are packed in three-dimensional lattices. Thus unlike water, ammonium sulfate does not exist as molecules in nature.

Assuming that the second and third blanks refers to a formula unit, rather than a molecule, of ammonium sulfate. The empirical formula of ammonium sulfate gives the minimum whole-number ratio between the two ions in a sample.

Charges shall balance between the two ions. Ammonium ions are of charge +1. Sulfate ions are of charge -2. The sample shall thus contain two ammonium ions for every one sulfate ion.

The empirical formula of ammonium sulfate is therefore $(\text{NH}_4)_2\text{SO}_4$.

There are thus two ammonium ions $\text{NH}_4^{+}$ and one sulfate ion $\text{SO}_4^{2-}$ in each formula unit of ammonium sulfate.