The formula for the compound formed from the polyatomic ions NH4+ and PO43- is Group of answer choices NH4PO4 (NH4)3PO4 (NH4)2(PO4)2 NH4(PO4)3
The Correct Answer and Explanation is:
Correct Answer: (NH₄)₃PO₄
When determining the formula for a compound formed from polyatomic ions, the charges of the ions involved must be balanced. The ammonium ion (NH₄⁺) carries a single positive charge (+1), while the phosphate ion (PO₄³⁻) carries a triple negative charge (–3). For a neutral compound to form, the total positive and negative charges must cancel out.
Each ammonium ion contributes +1. Three ammonium ions are needed to match the –3 charge from one phosphate ion. Multiplying the +1 charge of ammonium by three results in +3. This exactly offsets the –3 charge from one phosphate ion. Therefore, the correct stoichiometric ratio is 3 ammonium ions to 1 phosphate ion.
To express this properly in a chemical formula, the ammonium ion must be enclosed in parentheses when more than one is present, to indicate that the whole polyatomic ion is repeated. The result is (NH₄)₃PO₄.
The incorrect choices can be eliminated by examining their charge balance:
- NH₄PO₄: Contains only one NH₄⁺, total charge +1; does not balance –3 from PO₄³⁻.
- (NH₄)₂(PO₄)₂: Contains 2 NH₄⁺ (+2) and 2 PO₄³⁻ (–6); overall charge –4, not neutral.
- NH₄(PO₄)₃: Contains 1 NH₄⁺ (+1) and 3 PO₄³⁻ (–9); overall charge –8, not neutral.
Only (NH₄)₃PO₄ achieves a total net charge of zero, fulfilling the requirement for a stable ionic compound. Proper chemical formulas rely on accurate balancing of ion charges to reflect the structure and stability of the resulting compound.
