To prepare a solution of methanol you need the grams, and grams is molarity × volume in litres × 32.042 g/mol. A litre of 1 M takes 32.042 g; 500 mL of 0.1 M takes 1.6021 g; 250 mL of 0.01 M takes 80.105 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. Methanol is 12.011 (C) + 4 × 1.008 (H) + 15.999 (O), which is 32.042 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Oxygen makes up the largest share of the mass: 1 of the 6 atoms in a formula unit is oxygen, and they account for 15.999 g of the 32.042 g, or 49.93% 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.
Wood alcohol: a solvent, a fuel and the feedstock for biodiesel. Toxic by ingestion, absorption and inhalation, unlike the ethanol it resembles. At 32.042 g/mol it is the lightest of the 21 organic compounds covered here, and that ranking matters more than it looks: ethanol has a molar mass of 46.069 g/mol, so a gram of it contains 30.4% fewer formula units than a gram of methanol. Weigh by mass and you are not weighing equal amounts of substance.
Purity is the usual gap between the calculation and the balance. A reagent sold at 98% means 0.64084 g of a nominal 32.042 g is something else, so for exact work you divide the weighed mass by the assay figure on the certificate. For most purposes the difference is smaller than the error in reading the meniscus, but it is systematic rather than random, so it does not average out.
The formula
c- The molarity you want, in mol/L
V- The volume you want to make, in millilitres
32.042- The molar mass of methanol in g/mol, derived from its formula
m- The mass of methanol 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 32.042 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 methanol
Weigh 0.80105 g. That is 0.1 M × 0.25 L × 32.042 g/mol, and it comes to 801.05 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 methanol
Weigh 8.0105 g. That is 0.5 M × 0.5 L × 32.042 g/mol, and it comes to 8010.5 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 methanol
Weigh 32.042 g. That is 1 M × 1 L × 32.042 g/mol, and it comes to 32,042 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 methanol (CH4O)?
It is 32.042 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 12.011 (C) + 4 × 1.008 (H) + 15.999 (O). One mole of methanol therefore weighs 32.042 g, and a gram of it is 31.209 mmol.
What percentage of methanol is oxygen?
49.93% by mass. Each formula unit contains 1 oxygen atom contributing 15.999 g of the 32.042 g total, so 100 g of methanol contains 49.93 g of oxygen and a kilogram contains 499.31 g of it.
How much methanol do I need for 1 litre of 1 M solution?
32.042 g — the molar mass in grams, which is what a 1 molar solution means. For 1 L of 0.1 M it is 3.2042 g, and for 1 L of 0.01 M it is 0.32042 g.
How much for 100 mL of 0.1 M?
0.32042 g. The volume is a tenth of a litre and the strength a tenth of molar, so the mass is a hundredth of 32.042 g. In milligrams that is 320.42 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 160.21 mg that 500 mL of 0.01 M needs directly is the harder of the two.
Solution recipes for methanol
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 1 | 15.999 | 15.999 | 49.93% |
| Carbon (C) | 1 | 12.011 | 12.011 | 37.49% |
| Hydrogen (H) | 4 | 1.008 | 4.032 | 12.58% |
| Total — one mole of methanol | 32.042 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 32.042 g/mol.
| Target | for 100 mL | for 250 mL | for 500 mL | for 1 L |
|---|---|---|---|---|
| 0.001 M | 3.2042 mg | 8.0105 mg | 16.021 mg | 32.042 mg |
| 0.005 M | 16.021 mg | 40.0525 mg | 80.105 mg | 160.21 mg |
| 0.01 M | 32.042 mg | 80.105 mg | 160.21 mg | 320.42 mg |
| 0.05 M | 160.21 mg | 400.525 mg | 801.05 mg | 1.6021 g |
| 0.1 M | 320.42 mg | 801.05 mg | 1.6021 g | 3.2042 g |
| 0.15 M | 480.63 mg | 1.20158 g | 2.40315 g | 4.8063 g |
| 0.2 M | 640.84 mg | 1.6021 g | 3.2042 g | 6.4084 g |
| 0.25 M | 801.05 mg | 2.00263 g | 4.00525 g | 8.0105 g |
| 0.5 M | 1.6021 g | 4.00525 g | 8.0105 g | 16.021 g |
| 1 M | 3.2042 g | 8.0105 g | 16.021 g | 32.042 g |
| 2 M | 6.4084 g | 16.021 g | 32.042 g | 64.084 g |
Each cell is molarity × volume in litres × 32.042 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 (this page) | CH4O | 32.042 | 31.209 |
| Ethanol | 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.