Silver Nitrate (AgNO3) forms a yellow precipitate when added to Sodium Phosphate (Na3PO4). Which is the correct Net Ionic Equation for the reaction? 3Ag+ + PO43- → Ag3PO4(s) Ag+ + PO43- → Ag2PO4(s) + NO3- AgNO3 + Na3PO4 → Ag3PO4(s)
The Correct Answer and Explanation is:
Correct Answer: ✅ 3Ag⁺ + PO₄³⁻ → Ag₃PO₄(s)
Explanation
When two aqueous ionic compounds are mixed and a solid forms, this is known as a precipitation reaction. The question involves Silver Nitrate (AgNO₃) and Sodium Phosphate (Na₃PO₄), both of which are soluble in water and dissociate into their respective ions:
- AgNO₃ → Ag⁺ + NO₃⁻
- Na₃PO₄ → 3Na⁺ + PO₄³⁻
When Ag⁺ (silver ion) and PO₄³⁻ (phosphate ion) come together in solution, they form an insoluble salt, silver phosphate (Ag₃PO₄), which precipitates out as a yellow solid. The net ionic equation includes only the ions that participate in forming the precipitate, excluding spectator ions like Na⁺ and NO₃⁻, which do not change during the reaction.
The correct net ionic equation shows the combination of 3 Ag⁺ ions and 1 PO₄³⁻ ion to form solid Ag₃PO₄:
3Ag⁺ + PO₄³⁻ → Ag₃PO₄(s)
Let’s analyze the incorrect options:
- ❌ Ag⁺ + PO₄³⁻ → Ag₃PO₄(s): Incorrect stoichiometry; 3 Ag⁺ ions are needed to balance the -3 charge of PO₄³⁻.
- ❌ Ag⁺ + NO₃⁻ + Na⁺ + PO₄³⁻ → Ag₃PO₄(s): Includes all ions; not a net ionic equation.
- ❌ AgNO₃ + Na₃PO₄ → Ag₃PO₄(s): This is the molecular equation, not the net ionic one.
The net ionic equation strips the reaction down to its essence, showing only the species that actually form the precipitate. This not only simplifies the chemistry but also emphasizes the key reaction: the formation of the insoluble Ag₃PO₄ from free ions in solution.
