Which of the following is the correct net ionic equation for the reaction of phosphoric acid and sodium hydroxide.
The correct answer and explanation is:
The reaction between phosphoric acid (H₃PO₄) and sodium hydroxide (NaOH) is an acid-base neutralization reaction. The balanced molecular equation for this reaction is:
H₃PO₄ (aq)+3NaOH (aq)→Na₃PO₄ (aq)+3H₂O (l)\text{H₃PO₄ (aq)} + 3\text{NaOH (aq)} \rightarrow \text{Na₃PO₄ (aq)} + 3\text{H₂O (l)}
To derive the net ionic equation, we first split the reactants into their ions, considering that both H₃PO₄ and NaOH are strong electrolytes, meaning they dissociate completely in aqueous solution. Phosphoric acid dissociates in steps, while sodium hydroxide dissociates completely into sodium ions (Na⁺) and hydroxide ions (OH⁻).
Full Ionic Equation:
H₃PO₄ (aq)+3Na⁺ (aq)+3OH⁻ (aq)→Na₃PO₄ (aq)+3H₂O (l)\text{H₃PO₄ (aq)} + 3\text{Na⁺ (aq)} + 3\text{OH⁻ (aq)} \rightarrow \text{Na₃PO₄ (aq)} + 3\text{H₂O (l)}
However, sodium ions (Na⁺) and water (H₂O) are spectator ions in this reaction because they do not participate in the actual chemical change. Spectator ions do not affect the formation of the products. Therefore, we remove the spectator ions from both sides to get the net ionic equation.
Net Ionic Equation:
H₃PO₄ (aq)+3OH⁻ (aq)→PO₄³⁻ (aq)+3H₂O (l)\text{H₃PO₄ (aq)} + 3\text{OH⁻ (aq)} \rightarrow \text{PO₄³⁻ (aq)} + 3\text{H₂O (l)}
In this net ionic equation, the hydroxide ions (OH⁻) from sodium hydroxide neutralize the hydrogen ions (H⁺) from phosphoric acid, leading to the formation of water and phosphate ions (PO₄³⁻).
Explanation:
Phosphoric acid is a triprotic acid, which means it has three acidic protons (H⁺) that can react with hydroxide ions (OH⁻) from the sodium hydroxide. The net ionic equation shows the neutralization of all three hydrogen ions from phosphoric acid, resulting in the production of phosphate ions (PO₄³⁻). Each hydroxide ion (OH⁻) combines with a hydrogen ion (H⁺) to form water (H₂O), and this is the essence of an acid-base neutralization reaction. The sodium ions (Na⁺) and phosphate ions (PO₄³⁻) remain in solution, and only the change in the hydrogen ions is significant in the net ionic equation.