OneTaskBy Tim King · Updated
Grams to Moles Converter
Molar Mass Worked Out for Any Formula, Plus Particle and Atom Counts
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How the Grams to Moles Converter works
Convert grams to moles or moles to grams for any substance. Type its chemical formula and the calculator works out the molar mass, or type the molar mass itself if you already know it. Each answer shows the working along with the number of molecules or formula units and the total number of atoms.
Balances measure grams, but chemical equations count particles in moles, so converting between the two is the most common step in chemistry homework and lab prep. One mole is 6.02214076 × 10²³ particles, and the molar mass tells you how many grams that is for a given substance.
How grams to moles conversion works
The formula is moles = grams ÷ molar mass, and going the other way, grams = moles × molar mass. The molar mass comes from adding the atomic masses in the formula. Multiply moles by Avogadro's number to get particles, and by the atoms per formula unit to get atoms.
First example. 25 g of sodium chloride, NaCl at 58.44 g/mol, is 25 ÷ 58.44 = 0.428 mol, which is 2.58 × 10²³ formula units and 5.15 × 10²³ ions.
Second example. 0.75 mol of carbon dioxide, CO2 at 44.009 g/mol, weighs 0.75 × 44.009 = 33.0 g.
How many moles are in 100 g of water? 100 ÷ 18.015 = 5.55 mol, about 3.34 × 10²⁴ molecules.
Grams and moles for common substances
| Substance | Formula | Molar mass (g/mol) | Moles in 1 g | Moles in 100 g | Grams in 1 mol |
|---|---|---|---|---|---|
| Water | H2O | 18.015 | 0.05551 | 5.551 | 18.02 |
| Carbon dioxide | CO2 | 44.009 | 0.02272 | 2.272 | 44.01 |
| Oxygen | O2 | 31.998 | 0.03125 | 3.125 | 32.00 |
| Nitrogen | N2 | 28.014 | 0.0357 | 3.57 | 28.01 |
| Methane | CH4 | 16.043 | 0.06233 | 6.233 | 16.04 |
| Ammonia | NH3 | 17.031 | 0.05872 | 5.872 | 17.03 |
| Sodium chloride | NaCl | 58.440 | 0.01711 | 1.711 | 58.44 |
| Ethanol | C2H5OH | 46.069 | 0.02171 | 2.171 | 46.07 |
| Glucose | C6H12O6 | 180.156 | 0.005551 | 0.5551 | 180.16 |
| Sucrose | C12H22O11 | 342.297 | 0.002921 | 0.2921 | 342.30 |
| Sulfuric acid | H2SO4 | 98.072 | 0.0102 | 1.02 | 98.07 |
| Hydrochloric acid | HCl | 36.458 | 0.02743 | 2.743 | 36.46 |
| Nitric acid | HNO3 | 63.012 | 0.01587 | 1.587 | 63.01 |
| Sodium hydroxide | NaOH | 39.997 | 0.025 | 2.5 | 40.00 |
| Calcium carbonate | CaCO3 | 100.086 | 0.009991 | 0.9991 | 100.09 |
| Sodium bicarbonate | NaHCO3 | 84.006 | 0.0119 | 1.19 | 84.01 |
| Acetic acid | CH3COOH | 60.052 | 0.01665 | 1.665 | 60.05 |
| Hydrogen peroxide | H2O2 | 34.014 | 0.0294 | 2.94 | 34.01 |
| Propane | C3H8 | 44.097 | 0.02268 | 2.268 | 44.10 |
| Copper(II) sulfate pentahydrate | CuSO4·5H2O | 249.677 | 0.004005 | 0.4005 | 249.68 |
| Potassium permanganate | KMnO4 | 158.032 | 0.006328 | 0.6328 | 158.03 |
| Calcium hydroxide | Ca(OH)2 | 74.092 | 0.0135 | 1.35 | 74.09 |
| Iron(III) oxide | Fe2O3 | 159.687 | 0.006262 | 0.6262 | 159.69 |
| Aspirin | C9H8O4 | 180.159 | 0.005551 | 0.5551 | 180.16 |
| Caffeine | C8H10N4O2 | 194.194 | 0.005149 | 0.5149 | 194.19 |
Tips and pitfalls
- Divide for moles, multiply for grams. If your answer in moles is bigger than the mass for a heavy compound, you probably multiplied.
- Diatomic gases. Oxygen gas is O2 at 31.998 g/mol, not O at 15.999. Use the formula of the substance as it exists.
- Units first. Convert milligrams or kilograms to grams before dividing.
- Particles are not atoms. One mole of CO2 has 6.022 × 10²³ molecules but three times as many atoms.
FAQ
How do you convert grams to moles?
Divide the mass in grams by the molar mass in grams per mole. For 10 g of calcium carbonate, CaCO3 at 100.09 g/mol, that is 10 ÷ 100.09 = 0.0999 mol. The calculator finds the molar mass from the formula so you only need the mass.
How do you convert moles to grams?
Multiply the number of moles by the molar mass. Two moles of sodium hydroxide, NaOH at 39.997 g/mol, weigh 2 × 39.997 = 80.0 g. This is how you work out how much of a reagent to weigh for a reaction.
What is a mole in chemistry?
A mole is exactly 6.02214076 × 10²³ particles, a number chosen so that one mole of carbon-12 weighs 12 g. It lets chemists count atoms and molecules by weighing them, because the molar mass in grams matches the particle mass in daltons.
Can I enter a molar mass instead of a formula?
Yes. If you type a plain number such as 342.3 the calculator uses it as the molar mass in g/mol. This is handy for large molecules such as proteins or polymers, or when your textbook gives a rounded molar mass you want to match.
How many molecules are in a gram of water?
One gram of water is 1 ÷ 18.015 = 0.0555 mol. Multiplying by Avogadro's number gives about 3.34 × 10²² molecules, which is roughly 33 thousand billion billion molecules in a single gram.
See also: all Chemistry tools, Physics, Electronics.
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