# Question #6cfbd

Apr 16, 2015

A phosphate ion has a 3- charge and a potassium ion has a 1+ charge.
In order to form a neutral compound, 3 potassium ions are needed to satisfy the 3- charge on the phosphate ion.

Apr 16, 2015

Three potassium ions (${\text{K}}^{+}$) are needed to bond with a phosphate ion ($\text{PO"_4^(3-)}$) in order to produce a neutral compound. Since there are no molecules of ionic compounds, this is actually a ratio of ions.

An ionic compound is composed of positive and negative ions such that the overall charge is zero. If the positive and negative ions do not have the same magnitude of charge, then they will need to combine in a ratio which will produce an equal positive and negative charge.

In the case of the potassium and phosphate ions, potassium ions have a charge of ${1}^{+}$, and phosphate ions have a charge of ${3}^{-}$. So we need three potassium ions ($3 \times {1}^{+} = {3}^{+}$) to balance the ${3}^{-}$ charge on the phosphate ion. The formula will be $\text{K"_3"PO"_4}$.