Molar MassMolar mass of acetone (CH3COCH3)
The molar mass of acetone, CH3COCH3, is 58.08 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 58.08 grams.
58.08 g/mol
3 × 12.011 + 6 × 1.0080 + 15.999 = 58.080 · 10 atoms in the formula · also called propanone
About acetone
Acetone is a fast-drying solvent used in nail polish remover and for rinsing laboratory glassware. It is the simplest ketone.
Other names: propanone.
The working
The formula CH3COCH3 has 3 carbon atoms, 6 hydrogen atoms and 1 oxygen atom, 10 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) | 3 | 12.011 | 36.033 | 62.04% |
| Hydrogen (H) | 6 | 1.0080 | 6.048 | 10.41% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 27.55% |
3 × 12.011 + 6 × 1.0080 + 15.999 = 58.080 g/mol
With the rounded atomic masses used in many school books (C = 12, H = 1, O = 16) the answer is 58 g/mol. The difference from 58.08 is too small to matter in most school sums.
Percentage composition
By mass, CH3COCH3 is 62.04% carbon, 10.41% hydrogen and 27.55% oxygen. The largest share comes from carbon. In a 100 g sample there are 62.0 g of carbon, 10.4 g of hydrogen and 27.5 g of oxygen.
Notice that hydrogen has more atoms in the formula (6) than carbon (3), 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 250 g of CH3COCH3? Divide the mass by the molar mass: 250 ÷ 58.08 = 4.304 mol.
Moles to grams. What is the mass of 0.2 mol of CH3COCH3? Multiply: 0.2 × 58.08 = 11.62 g.
Counting particles. 250 g contains 4.304 mol × 6.022 × 1023 = 2.592 × 1024 molecules, and 2.592 × 1025 atoms in all.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 5.808 g |
| 0.5 mol | 29.04 g |
| 1 mol | 58.08 g |
| 2 mol | 116.2 g |
| 5 mol | 290.4 g |
| Mass | Moles |
|---|---|
| 1 g | 0.01722 mol |
| 10 g | 0.1722 mol |
| 100 g | 1.722 mol |
| 1 kg | 17.22 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of CH3COCH3?
The molar mass of acetone (CH3COCH3) is 58.08 g/mol, or 58.080 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of CH3COCH3?
100 ÷ 58.08 = 1.722 mol.
What is the mass of one molecule of CH3COCH3?
Divide the molar mass by the Avogadro constant: 58.08 ÷ 6.022 × 1023 = 9.644 × 10-23 g.
What is the percentage of carbon in CH3COCH3?
Carbon makes up 62.04% of the mass of CH3COCH3: 3 × 12.011 ÷ 58.080 × 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.