# Question #ac64e

Dec 4, 2017

Here's what I got.

#### Explanation:

Interestingly enough, the name sodium phosphate is actually used to describe a family of salts that contain sodium cations and phosphate anions in various ratios.

My guess is that you are supposed to treat "sodium phosphate" as trisodium phosphate, ${\text{Na"_3"PO}}_{4}$.

The idea here is that a formula unit of sodium phosphate, ${\text{Na"_3"PO}}_{4}$, contains

• three sodium cations, $3 \times {\text{Na}}^{+}$
• one phosphate anion, $1 \times {\text{PO}}_{4}^{3 -}$

This, of course, implies that $1$ mole of sodium phosphate will contain $3$ moles of sodium cations and $1$ mole of phosphate anions.

In other words, you have

• ${\text{no. of moles of Na"^(+) = 3 xx "no. of moles of Na"_3"PO}}_{4}$
• ${\text{no. of moles of PO"_4^(3-) = "no. of moles of Na"_3"PO}}_{4}$

Since you know that your sample contains $0.500$ moles of sodium phosphate, you can say that it contains $1.50$ moles of sodium cations and $0.500$ moles of phosphate anions.