To prepare a solution of isopropyl alcohol you need the grams, and grams is molarity × volume in litres × 60.096 g/mol. A litre of 1 M takes 60.096 g; 500 mL of 0.1 M takes 3.0048 g; 250 mL of 0.01 M takes 150.24 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. Isopropyl alcohol is 3 × 12.011 (C) + 8 × 1.008 (H) + 15.999 (O), which is 60.096 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: 3 of the 12 atoms in a formula unit are carbon, and they account for 36.033 g of the 60.096 g, or 59.96% 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.
Rubbing alcohol, sold at 70% for disinfection and 99% for electronics. The 70% strength is the more effective disinfectant, not the weaker one. At 60.096 g/mol it is heavier than 4 of the 21 organic compounds covered here, and that ranking matters more than it looks: urea has a molar mass of 60.056 g/mol, so a gram of it contains 0.0666% more formula units than a gram of isopropyl alcohol. 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 1.2019 g of a nominal 60.096 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
60.096- The molar mass of isopropyl alcohol in g/mol, derived from its formula
m- The mass of isopropyl alcohol 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 60.096 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 isopropyl alcohol
Weigh 1.5024 g. That is 0.1 M × 0.25 L × 60.096 g/mol, and it comes to 1502.4 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 isopropyl alcohol
Weigh 15.024 g. That is 0.5 M × 0.5 L × 60.096 g/mol, and it comes to 15,024 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 isopropyl alcohol
Weigh 60.096 g. That is 1 M × 1 L × 60.096 g/mol, and it comes to 60,096 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 isopropyl alcohol (C3H8O)?
It is 60.096 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 3 × 12.011 (C) + 8 × 1.008 (H) + 15.999 (O). One mole of isopropyl alcohol therefore weighs 60.096 g, and a gram of it is 16.64 mmol.
What percentage of isopropyl alcohol is carbon?
59.96% by mass. Each formula unit contains 3 carbon atoms contributing 36.033 g of the 60.096 g total, so 100 g of isopropyl alcohol contains 59.96 g of carbon and a kilogram contains 599.59 g of it.
How much isopropyl alcohol do I need for 1 litre of 1 M solution?
60.096 g — the molar mass in grams, which is what a 1 molar solution means. For 1 L of 0.1 M it is 6.0096 g, and for 1 L of 0.01 M it is 0.60096 g.
How much for 100 mL of 0.1 M?
0.60096 g. The volume is a tenth of a litre and the strength a tenth of molar, so the mass is a hundredth of 60.096 g. In milligrams that is 600.96 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 300.48 mg that 500 mL of 0.01 M needs directly is the harder of the two.
Solution recipes for isopropyl alcohol
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 3 | 12.011 | 36.033 | 59.96% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 26.62% |
| Hydrogen (H) | 8 | 1.008 | 8.064 | 13.42% |
| Total — one mole of isopropyl alcohol | 60.096 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 60.096 g/mol.
| Target | for 100 mL | for 250 mL | for 500 mL | for 1 L |
|---|---|---|---|---|
| 0.001 M | 6.0096 mg | 15.024 mg | 30.048 mg | 60.096 mg |
| 0.005 M | 30.048 mg | 75.12 mg | 150.24 mg | 300.48 mg |
| 0.01 M | 60.096 mg | 150.24 mg | 300.48 mg | 600.96 mg |
| 0.05 M | 300.48 mg | 751.2 mg | 1.5024 g | 3.0048 g |
| 0.1 M | 600.96 mg | 1.5024 g | 3.0048 g | 6.0096 g |
| 0.15 M | 901.44 mg | 2.2536 g | 4.5072 g | 9.0144 g |
| 0.2 M | 1.20192 g | 3.0048 g | 6.0096 g | 12.0192 g |
| 0.25 M | 1.5024 g | 3.756 g | 7.512 g | 15.024 g |
| 0.5 M | 3.0048 g | 7.512 g | 15.024 g | 30.048 g |
| 1 M | 6.0096 g | 15.024 g | 30.048 g | 60.096 g |
| 2 M | 12.0192 g | 30.048 g | 60.096 g | 120.192 g |
Each cell is molarity × volume in litres × 60.096 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 |
|---|---|---|---|
| Ethanol | C2H6O | 46.069 | 21.707 |
| Acetone | C3H6O | 58.08 | 17.218 |
| Urea | CH4N2O | 60.056 | 16.651 |
| Isopropyl alcohol (this page) | C3H8O | 60.096 | 16.64 |
| Ethylene glycol | C2H6O2 | 62.068 | 16.111 |
| Glycine | C2H5NO2 | 75.067 | 13.321 |
| Benzene | C6H6 | 78.114 | 12.802 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.