Molar MassMolar mass of ethanol (C2H5OH)
The molar mass of ethanol, C2H5OH, is 46.07 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 46.07 grams.
46.07 g/mol
2 × 12.011 + 6 × 1.0080 + 15.999 = 46.069 · 9 atoms in the formula · also called ethyl alcohol
About ethanol
Ethanol is the alcohol in drinks, made by fermenting sugars, and is also used as a fuel, solvent and antiseptic. Written as C2H5OH, it has six hydrogen atoms in all: do not miss the one on the oxygen.
Other names: ethyl alcohol.
The working
The formula C2H5OH has 2 carbon atoms, 6 hydrogen atoms and 1 oxygen atom, 9 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Carbon (C) | 2 | 12.011 | 24.022 | 52.14% |
| Hydrogen (H) | 6 | 1.0080 | 6.048 | 13.13% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 34.73% |
2 × 12.011 + 6 × 1.0080 + 15.999 = 46.069 g/mol
With the rounded atomic masses used in many school books (C = 12, H = 1, O = 16) the answer is 46 g/mol. The difference from 46.07 is too small to matter in most school sums.
Percentage composition
By mass, C2H5OH is 52.14% carbon, 13.13% hydrogen and 34.73% oxygen. The largest share comes from carbon. In a 100 g sample there are 52.1 g of carbon, 13.1 g of hydrogen and 34.7 g of oxygen.
Notice that hydrogen has more atoms in the formula (6) than carbon (2), yet gives a smaller share of the mass. Percentage by mass depends on how heavy each atom is, not only on how many there are.
Worked examples
Grams to moles. How many moles are in 100 g of C2H5OH? Divide the mass by the molar mass: 100 ÷ 46.07 = 2.171 mol.
Moles to grams. What is the mass of 2 mol of C2H5OH? Multiply: 2 × 46.07 = 92.14 g.
Counting particles. 100 g contains 2.171 mol × 6.022 × 1023 = 1.307 × 1024 molecules, and 1.176 × 1025 atoms in all.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 4.607 g |
| 0.5 mol | 23.03 g |
| 1 mol | 46.07 g |
| 2 mol | 92.14 g |
| 5 mol | 230.3 g |
| Mass | Moles |
|---|---|
| 1 g | 0.02171 mol |
| 10 g | 0.2171 mol |
| 100 g | 2.171 mol |
| 1 kg | 21.71 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of C2H5OH?
The molar mass of ethanol (C2H5OH) is 46.07 g/mol, or 46.069 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of C2H5OH?
100 ÷ 46.07 = 2.171 mol.
What is the mass of one molecule of C2H5OH?
Divide the molar mass by the Avogadro constant: 46.07 ÷ 6.022 × 1023 = 7.650 × 10-23 g.
What is the percentage of carbon in C2H5OH?
Carbon makes up 52.14% of the mass of C2H5OH: 2 × 12.011 ÷ 46.069 × 100.
Which values? This site uses the abridged standard atomic weights published by IUPAC (CIAAW), read on 12 November 2026. Your textbook or question paper may round them differently, for example H = 1 and O = 16, so its answer can differ slightly. In an exam, use the values the paper gives.