Molar MassMolar mass of acetic acid (CH3COOH)
The molar mass of acetic acid, CH3COOH, is 60.05 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 60.05 grams.
60.05 g/mol
2 × 12.011 + 4 × 1.0080 + 2 × 15.999 = 60.052 · 8 atoms in the formula · also called ethanoic acid
About acetic acid
Acetic acid is the acid in vinegar, which is a solution of about 5 to 8 percent in water. Only the hydrogen of the COOH group is acidic; the three on the methyl group are not. The pure acid freezes just below room temperature and is then called glacial acetic acid.
Other names: ethanoic acid.
The working
The formula CH3COOH has 2 carbon atoms, 4 hydrogen atoms and 2 oxygen atoms, 8 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 | 40.00% |
| Hydrogen (H) | 4 | 1.0080 | 4.032 | 6.71% |
| Oxygen (O) | 2 | 15.999 | 31.998 | 53.28% |
2 × 12.011 + 4 × 1.0080 + 2 × 15.999 = 60.052 g/mol
With the rounded atomic masses used in many school books (C = 12, H = 1, O = 16) the answer is 60 g/mol. The difference from 60.05 is too small to matter in most school sums.
Percentage composition
By mass, CH3COOH is 40.00% carbon, 6.71% hydrogen and 53.28% oxygen. The largest share comes from oxygen. In a 100 g sample there are 40.0 g of carbon, 6.7 g of hydrogen and 53.3 g of oxygen.
Notice that hydrogen has more atoms in the formula (4) than oxygen (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 CH3COOH? Divide the mass by the molar mass: 100 ÷ 60.05 = 1.665 mol.
Moles to grams. What is the mass of 2 mol of CH3COOH? Multiply: 2 × 60.05 = 120.1 g.
Counting particles. 100 g contains 1.665 mol × 6.022 × 1023 = 1.003 × 1024 molecules, and 8.023 × 1024 atoms in all.
Making a solution. A 0.1 mol/L solution contains 0.1 × 60.05 = 6.005 g of CH3COOH in each litre. For 250 mL, weigh 1.501 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 6.005 g |
| 0.5 mol | 30.03 g |
| 1 mol | 60.05 g |
| 2 mol | 120.1 g |
| 5 mol | 300.3 g |
| Mass | Moles |
|---|---|
| 1 g | 0.01665 mol |
| 10 g | 0.1665 mol |
| 100 g | 1.665 mol |
| 1 kg | 16.65 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of CH3COOH?
The molar mass of acetic acid (CH3COOH) is 60.05 g/mol, or 60.052 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of CH3COOH?
100 ÷ 60.05 = 1.665 mol.
What is the mass of one molecule of CH3COOH?
Divide the molar mass by the Avogadro constant: 60.05 ÷ 6.022 × 1023 = 9.972 × 10-23 g.
What is the percentage of oxygen in CH3COOH?
Oxygen makes up 53.28% of the mass of CH3COOH: 2 × 15.999 ÷ 60.052 × 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.