The ethanol molar mass is the mass of exactly 1 mole of ethanol molecules. It is found by adding the atomic masses of all atoms in ethanol’s chemical formula.
1) Identify the ethanol formula and atom counts
Ethanol is commonly written as C2H6O (equivalently C2H5OH). The atom counts per molecule are:
- Carbon: 2 atoms
- Hydrogen: 6 atoms
- Oxygen: 1 atom
2) Multiply each atom count by its atomic mass
Using a typical set of standard atomic weights (C = 12.01, H = 1.008, O = 16.00), each element’s contribution to the molar mass is computed by: \[ \text{contribution} = (\text{number of atoms}) \cdot (\text{atomic mass}) \]
| Element | Count in C2H6O | Atomic mass (g/mol) | Contribution (g/mol) |
|---|---|---|---|
| Carbon (C) | 2 | 12.01 | \(2 \cdot 12.01 = 24.02\) |
| Hydrogen (H) | 6 | 1.008 | \(6 \cdot 1.008 = 6.048\) |
| Oxygen (O) | 1 | 16.00 | \(1 \cdot 16.00 = 16.00\) |
3) Add the contributions to get the ethanol molar mass
\[ M(\text{C}_2\text{H}_6\text{O}) = 24.02 + 6.048 + 16.00 = 46.068\ \text{g/mol} \] Rounded to an appropriate number of significant figures for these atomic masses: \[ M(\text{ethanol}) \approx 46.07\ \text{g/mol} \]
Small differences in the reported ethanol molar mass (for example, 46.07 vs 46.069 g/mol) come from using atomic weights with different rounding or precision. The method is unchanged: sum all atomic contributions from C2H6O.
Visualization: mass contribution by element in ethanol
Common use of the ethanol molar mass
Converting between grams of ethanol and moles uses: \[ n = \frac{m}{M} \] For example, if \(m = 15.0\ \text{g}\) ethanol and \(M = 46.07\ \text{g/mol}\), then: \[ n = \frac{15.0}{46.07} \approx 0.326\ \text{mol} \]