Question

Write the correct formula for the ionic compound, sodium phosphate. The phosphate ion is a polyatomic anion with the formula (PO_4^3-)

A. Na(PO₄)3

B. NaPO₄

C. Na₂(PO₄)3

D. Na3(PO4)2

E. Na₃PO4

Can you explain why which answer is correct? I'm very unsure.

Answer 1

The correct formula is Na₃PO₄ . option E is correct.

In writing ionic formulae we have to balance the charge of ions in order to get a neutral compound.

Here, the anion is PO₄^3- . The charge of anion is -3 so the charge of cation should be +3. Then only both get cancelled and produce a neutral compound.

Here, the cation is Na. The charge of Na is +1. So we have to take 3 Na⁺ ions to get +3 charge.

Finally, the cation is 3 Na⁺ and anion is PO₄^3- .

So the formula of ionic compound is Na₃PO₄