Phosphate; PO4- is a polyatomic ion that can combine with any cation to form an ionic compound. Identify all the formulas below that correctly represent phosphate compounds. Select one or more: Combined with magnesium: Mg3(PO4)2 Combined with iron(III): FePO4 Combined with magnesium: Mg(PO4)2 Combined with copper(II): Cu3(PO4)2 Combined with lithium: Li3PO4 Combined with iron(III): Fe3(PO4)2 Combined with copper(II): Cu3(PO4)2 Combined with lithium: Li3PO4
The Correct Answer and Explanation is:
The correct formulas for phosphate compounds, based on the provided options, are:
- Mg₃(PO₄)₂ (Magnesium phosphate)
- FePO₄ (Iron(III) phosphate)
- Cu₃(PO₄)₂ (Copper(II) phosphate)
- Li₃PO₄ (Lithium phosphate)
Explanation:
Phosphate is a polyatomic ion with the formula PO₄³⁻. When phosphate combines with cations to form ionic compounds, the cation’s charge must balance the charge of the phosphate ion.
- Magnesium phosphate (Mg₃(PO₄)₂):
- Magnesium (Mg²⁺) has a +2 charge. To balance the 3− charge of the phosphate ion, three magnesium ions are needed for every two phosphate ions. This gives the formula Mg₃(PO₄)₂.
- Iron(III) phosphate (FePO₄):
- Iron(III) (Fe³⁺) has a +3 charge. To balance the 3− charge of the phosphate ion, one iron(III) ion is needed for every one phosphate ion. This results in the formula FePO₄.
- Copper(II) phosphate (Cu₃(PO₄)₂):
- Copper(II) (Cu²⁺) has a +2 charge. To balance the 3− charge of the phosphate ion, three copper(II) ions are needed for every two phosphate ions. This gives the formula Cu₃(PO₄)₂.
- Lithium phosphate (Li₃PO₄):
- Lithium (Li⁺) has a +1 charge. To balance the 3− charge of the phosphate ion, three lithium ions are needed for every one phosphate ion. This results in the formula Li₃PO₄.
Incorrect formulas:
- Mg(PO₄)₂ is incorrect because magnesium typically forms a 2+ charge and would need 3 phosphate ions to balance. This formula does not balance the charges correctly.
- Fe₃(PO₄)₂ is incorrect for the same reason; it implies a different stoichiometry than the proper formula for iron(III) phosphate, which is FePO₄.
Thus, the correct formulas are Mg₃(PO₄)₂, FePO₄, Cu₃(PO₄)₂, and Li₃PO₄.
