To prepare a solution of ethanol you need the grams, and grams is molarity × volume in litres × 46.069 g/mol. A litre of 1 M takes 46.069 g; 500 mL of 0.1 M takes 2.3035 g; 250 mL of 0.01 M takes 115.17 mg. Enter the strength you want and the volume you want it in, and the calculator returns the mass to weigh together with the same figure in milligrams and as a percentage strength.
The figure comes from the formula. Ethanol is 2 × 12.011 (C) + 6 × 1.008 (H) + 15.999 (O), which is 46.069 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Carbon makes up the largest share of the mass: 2 of the 9 atoms in a formula unit are carbon, and they account for 24.022 g of the 46.069 g, or 52.14% by mass. The derivation table below breaks the whole molecule down element by element.
Order of operations matters more than precision here. Dissolve the solid in rather less than the final volume, then make up to the mark once it has all gone into solution and come back to room temperature — warm solutions read low when they cool. If the calculated mass is under about 20 mg, prepare ten times the strength and dilute it tenfold by pipette instead, because C₁V₁ = C₂V₂ carries less error than a marginal weighing.
Drinking alcohol and a solvent. Strength is quoted as percent by volume, and because ethanol is less dense than water that is not percent by weight. At 46.069 g/mol it is heavier than 1 of the 21 organic compounds covered here, and that ranking matters more than it looks: methanol has a molar mass of 32.042 g/mol, so a gram of it contains 43.8% more formula units than a gram of ethanol. Weigh by mass and you are not weighing equal amounts of substance.
Two practical things move the result. Purity below 100% means the weighed mass overstates how much compound you have — at 98% assay, 0.92138 g of every 46.069 g is not the compound — and any water picked up from the air does the same. Both are systematic, so they shift every solution made from that jar in the same direction.
The formula
c- The molarity you want, in mol/L
V- The volume you want to make, in millilitres
46.069- The molar mass of ethanol in g/mol, derived from its formula
m- The mass of ethanol to weigh out, in grams
How it works, step by step
- Enter the molarity you want, in mol/L.
- Enter the volume you want to make, in millilitres.
- The two are multiplied together and by 46.069 g/mol.
- The result is the mass to weigh; dissolve it in part of the volume and then make up to the mark.
Worked examples
250 mL of 0.1 M ethanol
Weigh 1.15173 g. That is 0.1 M × 0.25 L × 46.069 g/mol, and it comes to 1151.73 mg if your balance is set to milligrams. Dissolve in about 175 mL first, then make up to 250 mL.
500 mL of 0.5 M ethanol
Weigh 11.5173 g. That is 0.5 M × 0.5 L × 46.069 g/mol, and it comes to 11,517.2 mg if your balance is set to milligrams. Dissolve in about 350 mL first, then make up to 500 mL.
1000 mL of 1 M ethanol
Weigh 46.069 g. That is 1 M × 1 L × 46.069 g/mol, and it comes to 46,069 mg if your balance is set to milligrams. Dissolve in about 700 mL first, then make up to 1000 mL.
How to read your score
Frequently asked questions
What is the molar mass of ethanol (C2H6O)?
It is 46.069 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 2 × 12.011 (C) + 6 × 1.008 (H) + 15.999 (O). One mole of ethanol therefore weighs 46.069 g, and a gram of it is 21.707 mmol.
What percentage of ethanol is carbon?
52.14% by mass. Each formula unit contains 2 carbon atoms contributing 24.022 g of the 46.069 g total, so 100 g of ethanol contains 52.14 g of carbon and a kilogram contains 521.44 g of it.
How much ethanol do I need for 1 litre of 1 M solution?
46.069 g — the molar mass in grams, which is what a 1 molar solution means. For 1 L of 0.1 M it is 4.6069 g, and for 1 L of 0.01 M it is 0.46069 g.
How much for 100 mL of 0.1 M?
0.46069 g. The volume is a tenth of a litre and the strength a tenth of molar, so the mass is a hundredth of 46.069 g. In milligrams that is 460.69 mg.
Do I dissolve the solid first or make up the volume first?
Dissolve first, in perhaps 70% of the final volume, then make up to the mark. Adding solid to a full flask overshoots the volume and leaves the solution weak, and undissolved solid at the mark means the strength keeps changing as it goes in.
Can I dilute a stock solution instead of weighing?
Yes, and it is more accurate for small amounts. C₁V₁ = C₂V₂: to get 500 mL of 0.01 M from a 0.5 M stock, take 10 mL of stock and make up to 500 mL. Weighing the 230.35 mg that 500 mL of 0.01 M needs directly is the harder of the two.
Solution recipes for ethanol
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 2 | 12.011 | 24.022 | 52.14% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 34.73% |
| Hydrogen (H) | 6 | 1.008 | 6.048 | 13.13% |
| Total — one mole of ethanol | 46.069 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 46.069 g/mol.
| Target | for 100 mL | for 250 mL | for 500 mL | for 1 L |
|---|---|---|---|---|
| 0.001 M | 4.6069 mg | 11.5173 mg | 23.0345 mg | 46.069 mg |
| 0.005 M | 23.0345 mg | 57.5863 mg | 115.173 mg | 230.345 mg |
| 0.01 M | 46.069 mg | 115.173 mg | 230.345 mg | 460.69 mg |
| 0.05 M | 230.345 mg | 575.863 mg | 1.15173 g | 2.30345 g |
| 0.1 M | 460.69 mg | 1.15173 g | 2.30345 g | 4.6069 g |
| 0.15 M | 691.035 mg | 1.72759 g | 3.45518 g | 6.91035 g |
| 0.2 M | 921.38 mg | 2.30345 g | 4.6069 g | 9.2138 g |
| 0.25 M | 1.15173 g | 2.87931 g | 5.75863 g | 11.5173 g |
| 0.5 M | 2.30345 g | 5.75863 g | 11.5173 g | 23.0345 g |
| 1 M | 4.6069 g | 11.5173 g | 23.0345 g | 46.069 g |
| 2 M | 9.2138 g | 23.0345 g | 46.069 g | 92.138 g |
Each cell is molarity × volume in litres × 46.069 g/mol. Dissolve the solid first and then make up to the marked volume — adding solid to a full volume overshoots it.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Methanol | CH4O | 32.042 | 31.209 |
| Ethanol (this page) | C2H6O | 46.069 | 21.707 |
| Acetone | C3H6O | 58.08 | 17.218 |
| Urea | CH4N2O | 60.056 | 16.651 |
| Isopropyl alcohol | C3H8O | 60.096 | 16.64 |
| Ethylene glycol | C2H6O2 | 62.068 | 16.111 |
| Glycine | C2H5NO2 | 75.067 | 13.321 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.