Molar Mass Formula
Calculate the molar mass of a compound by summing atomic masses.
Includes examples for water, glucose, and NaCl.
The Formula
Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance. It is expressed in grams per mole (g/mol).
To find it, add up the atomic masses of every atom in the chemical formula. Atomic masses are found on the periodic table.
Variables
| Symbol | Meaning |
|---|---|
| M | Molar mass (g/mol) |
| n | Number of atoms of each element in the formula |
| A | Atomic mass of each element (from periodic table, in amu) |
Common Atomic Masses
| Element | Symbol | Atomic Mass (amu) |
|---|---|---|
| Hydrogen | H | 1.008 |
| Carbon | C | 12.011 |
| Nitrogen | N | 14.007 |
| Oxygen | O | 15.999 |
| Sodium | Na | 22.990 |
| Chlorine | Cl | 35.453 |
| Calcium | Ca | 40.078 |
| Iron | Fe | 55.845 |
Example 1 — Water (H₂O)
Find the molar mass of water (H₂O)
Hydrogen: 2 × 1.008 = 2.016
Oxygen: 1 × 15.999 = 15.999
M = 2.016 + 15.999 = 18.015 g/mol
Example 2 — Table Salt (NaCl)
Find the molar mass of sodium chloride (NaCl)
Sodium: 1 × 22.990 = 22.990
Chlorine: 1 × 35.453 = 35.453
M = 22.990 + 35.453 = 58.443 g/mol
Example 3 — Glucose (C₆H₁₂O₆)
Find the molar mass of glucose (C₆H₁₂O₆)
Carbon: 6 × 12.011 = 72.066
Hydrogen: 12 × 1.008 = 12.096
Oxygen: 6 × 15.999 = 95.994
M = 72.066 + 12.096 + 95.994 = 180.156 g/mol
When to Use It
- Converting between grams and moles in chemistry problems
- Calculating the amount of reactants needed for a chemical reaction
- Determining concentration of solutions (molarity = moles / liters)
- Stoichiometry — balancing chemical equations in terms of mass
- Pharmaceutical dosing calculations
Converting Between Grams and Moles
For example, 36.03 grams of water = 36.03 / 18.015 = 2.0 moles of water.