H3PO4 + 3NaOH → Na3PO4 + 3H2O
Phosphoric acid and sodium hydroxide — balanced chemical equation, step by step.
Phosphoric acid is triprotic, so full neutralization needs three moles of sodium hydroxide.
How to balance H3PO4 + NaOH = Na3PO4 + H2O
An acid–base (neutralization) reaction combines an acid and a base to produce a salt and water. Balancing means choosing coefficients so that every element has the same number of atoms on both sides of the arrow — the Law of Conservation of Mass. Here is how it's done, step by step.
Step 1 — Write the unbalanced equation
Start with the correct formulas for every reactant and product:
H3PO4 + NaOH = Na3PO4 + H2O
Step 2 — Count the atoms of each element
With no coefficients yet (everything counted once), the atoms do not match. The ✗ marks show which elements are unbalanced:
| Element | Reactants | Products | Equal? |
|---|---|---|---|
| H | 4 | 2 | ✗ |
| P | 1 | 1 | ✓ |
| O | 5 | 5 | ✓ |
| Na | 1 | 3 | ✗ |
Step 3 — Add the smallest whole-number coefficients
Adjust the coefficients in front of each formula until every element balances. The smallest whole-number coefficients are 1 H3PO4, 3 NaOH, 1 Na3PO4, 3 H2O, giving:
H3PO4 + 3NaOH = Na3PO4 + 3H2O
For an acid–base neutralization, balance the metal and the acid anion first, then balance hydrogen and oxygen using the water produced.
Step 4 — Verify the balance
Recount every element. Each one now matches on both sides:
| Element | Reactants | Products | Balanced |
|---|---|---|---|
| H | 6 | 6 | ✓ |
| P | 1 | 1 | ✓ |
| O | 7 | 7 | ✓ |
| Na | 3 | 3 | ✓ |
All elements are balanced and the coefficients are the smallest whole numbers, so H3PO4 + 3NaOH = Na3PO4 + 3H2O is the correct balanced equation.
Molar masses and mole ratio
The balanced coefficients are also the mole ratio of the reaction. Using standard atomic masses, the molar mass of each substance is:
| Substance | Role | Molar mass (g/mol) | Moles |
|---|---|---|---|
| H3PO4 | reactant | 97.99 | 1 |
| NaOH | reactant | 40 | 3 |
| Na3PO4 | product | 163.94 | 1 |
| H2O | product | 18.02 | 3 |
For this reaction the mole ratio is 1 : 3 : 1 : 3. Combine these molar masses with the ratio in the free stoichiometry calculator to convert between moles, grams, and the number of particles for any reactant or product.
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