Understanding the Reaction
Sodium hydroxide (NaOH) is a strong base, and phosphoric acid (H₃PO₄) is a weak acid. When they react, a neutralization reaction occurs, forming water (H₂O) and a salt. However, because phosphoric acid has three acidic hydrogens, it can react with sodium hydroxide in two different ways, forming two distinct salts.
Salt 1: Sodium Dihydrogen Phosphate (NaH₂PO₄)
* Reaction: NaOH + H₃PO₄ → NaH₂PO₄ + H₂O
* Explanation: In this reaction, one hydroxide ion (OH-) from NaOH combines with one hydrogen ion (H+) from H₃PO₄, forming water. The remaining ions, Na+ and H₂PO₄-, combine to form sodium dihydrogen phosphate.
Salt 2: Disodium Hydrogen Phosphate (Na₂HPO₄)
* Reaction: 2 NaOH + H₃PO₄ → Na₂HPO₄ + 2 H₂O
* Explanation: In this reaction, two hydroxide ions (OH-) from NaOH combine with two hydrogen ions (H+) from H₃PO₄, forming two molecules of water. The remaining ions, 2Na+ and HPO₄²-, combine to form disodium hydrogen phosphate.
Important Note: It's also possible to form the third salt, trisodium phosphate (Na₃PO₄), by reacting three moles of NaOH with one mole of H₃PO₄. However, this is less likely to form in a typical reaction.
