Molar mass of NaOH (Sodium hydroxide)
The molar mass of NaOH is 40.00 g/mol.
A strong alkali (caustic soda) used in titrations and soap-making.
Step-by-step calculation
Add up the atomic masses of every atom in the formula:
1 × 22.99 + 1 × 15.999 + 1 × 1.008 = 40.00 g/mol
| Element | Atoms | Atomic mass (u) | Subtotal (g/mol) | % by mass |
|---|---|---|---|---|
| Sodium (Na) | 1 | 22.99 | 22.990 | 57.48% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 40.00% |
| Hydrogen (H) | 1 | 1.008 | 1.008 | 2.52% |
| Molar mass of NaOH | 40.00 g/mol | |||
Moles to grams for NaOH
Multiply the number of moles by 40.00 g/mol to get the mass, and divide a mass by 40.00 g/mol to get the moles.
| Amount (mol) | Mass (g) | Mass (g) | Amount (mol) |
|---|---|---|---|
| 0.1 mol | 4.00 g | 1 g | 0.0250 mol |
| 0.25 mol | 10.00 g | 5 g | 0.1250 mol |
| 0.5 mol | 20.00 g | 10 g | 0.2500 mol |
| 1 mol | 40.00 g | 50 g | 1.2501 mol |
| 2 mol | 79.99 g | 100 g | 2.5002 mol |
| 5 mol | 199.99 g | 500 g | 12.5009 mol |
Experiments that use sodium hydroxide
🧪 Acid–base titration
Find the end-point of HCl vs NaOH with phenolphthalein and plot the titration curve.
🧂 Electrolysis of brine
Chlorine at the anode, hydrogen at the cathode, sodium hydroxide left behind.
⚪ Amphoteric hydroxides
Aluminium hydroxide precipitates, then dissolves again in excess NaOH.
🧊 Hot & cold packs
Dissolving salts can absorb heat (NH₄NO₃) or release it (CaCl₂, NaOH).
Frequently asked questions
What is the molar mass of NaOH?
The molar mass of NaOH (sodium hydroxide) is 40.00 g/mol, so one mole of sodium hydroxide weighs 40.00 grams.
How do you calculate the molar mass of NaOH?
Multiply each element’s atomic mass by the number of atoms in the formula and add the results: 1 × 22.99 + 1 × 15.999 + 1 × 1.008 = 40.00 g/mol.
What percentage of NaOH is sodium?
Sodium makes up 57.48% of the mass of NaOH.
How many grams are in one mole of NaOH?
One mole of NaOH has a mass of 40.00 grams, and contains 6.022 × 10²³ formula units.