Phosphate; PO4 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): Fe3(PO4)2 Combined with iron(II): FePO4 Combined with lithium: Li3PO4 Combined with copper(V): Cu3(PO4)2 Combined with copper(II): CuPO4 Combined with magnesium: Mg3(PO4)2
The Correct Answer and Explanation is:
The formula for phosphate is PO₄³⁻. When phosphate combines with a cation, the charges of the cation and anion must balance out to form a neutral compound. Let’s analyze each option based on the charges of the cations involved:
- Mg₃(PO₄)₂ (Combined with magnesium):
- Magnesium has a charge of +2 (Mg²⁺).
- To balance the charge of the phosphate ion (PO₄³⁻), three magnesium ions (+2 each) will balance the charge of two phosphate ions, which each have a charge of -3. Therefore, Mg₃(PO₄)₂ is correct.
- Fe₃(PO₄)₂ (Combined with iron(III)):
- Iron(III) has a charge of +3 (Fe³⁺).
- Three iron(III) ions (each with a charge of +3) balance the charge of two phosphate ions (each with a charge of -3). Therefore, Fe₃(PO₄)₂ is correct.
- FePO₄ (Combined with iron(II)):
- Iron(II) has a charge of +2 (Fe²⁺).
- To balance the charge of the phosphate ion (PO₄³⁻), only one iron(II) ion (+2) will not be sufficient to balance the charge of phosphate, which is -3. Therefore, FePO₄ is incorrect.
- Li₃PO₄ (Combined with lithium):
- Lithium has a charge of +1 (Li⁺).
- To balance the charge of one phosphate ion (PO₄³⁻), three lithium ions are required. Therefore, Li₃PO₄ is correct.
- Cu₃(PO₄)₂ (Combined with copper(V)):
- Copper(V) is a rare oxidation state, with a charge of +5 (Cu⁵⁺).
- To balance the charge of two phosphate ions (each with a charge of -3), three copper ions (each with a charge of +5) would be needed. Therefore, Cu₃(PO₄)₂ is correct.
- CuPO₄ (Combined with copper(II)):
- Copper(II) has a charge of +2 (Cu²⁺).
- One copper(II) ion and one phosphate ion would not balance, as the charges do not match. Therefore, CuPO₄ is incorrect.
Correct answers:
- Mg₃(PO₄)₂
- Fe₃(PO₄)₂
- Li₃PO₄
- Cu₃(PO₄)₂
