To prepare a solution of ammonia you need the grams, and grams is molarity × volume in litres × 17.031 g/mol. A litre of 1 M takes 17.031 g; 500 mL of 0.1 M takes 0.85155 g; 250 mL of 0.01 M takes 42.578 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. Ammonia is 14.007 (N) + 3 × 1.008 (H), which is 17.031 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Nitrogen makes up the largest share of the mass: 1 of the 4 atoms in a formula unit is nitrogen, and they account for 14.007 g of the 17.031 g, or 82.24% 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.
A refrigerant, a fertiliser feedstock and a cleaner. Household ammonia is a 5 to 10% solution of the gas in water, sold as ammonium hydroxide. At 17.031 g/mol it is heavier than 1 of the 11 gases and small molecules covered here, and that ranking matters more than it looks: methane has a molar mass of 16.043 g/mol, so a gram of it contains 6.16% more formula units than a gram of ammonia. Weigh by mass and you are not weighing equal amounts of substance.
Because this is a gas, volume is often the easier measure. One mole of any ideal gas occupies 22.414 L at 0 °C and 1 atm and 24.4655 L at 25 °C, so 17.031 g of ammonia — one mole — fills about 24.47 litres at room temperature. Real gases depart from that by a percent or so, more near their boiling point, but for ordinary work the molar volume is the quickest route from grams to litres.
The formula
c- The molarity you want, in mol/L
V- The volume you want to make, in millilitres
17.031- The molar mass of ammonia in g/mol, derived from its formula
m- The mass of ammonia 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 17.031 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 ammonia
Weigh 0.425775 g. That is 0.1 M × 0.25 L × 17.031 g/mol, and it comes to 425.775 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 ammonia
Weigh 4.25775 g. That is 0.5 M × 0.5 L × 17.031 g/mol, and it comes to 4257.75 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 ammonia
Weigh 17.031 g. That is 1 M × 1 L × 17.031 g/mol, and it comes to 17,031 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 ammonia (NH3)?
It is 17.031 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 14.007 (N) + 3 × 1.008 (H). One mole of ammonia therefore weighs 17.031 g, and a gram of it is 58.716 mmol.
What percentage of ammonia is nitrogen?
82.24% by mass. Each formula unit contains 1 nitrogen atom contributing 14.007 g of the 17.031 g total, so 100 g of ammonia contains 82.24 g of nitrogen and a kilogram contains 822.44 g of it.
How much ammonia do I need for 1 litre of 1 M solution?
17.031 g — the molar mass in grams, which is what a 1 molar solution means. For 1 L of 0.1 M it is 1.7031 g, and for 1 L of 0.01 M it is 0.17031 g.
How much for 100 mL of 0.1 M?
0.17031 g. The volume is a tenth of a litre and the strength a tenth of molar, so the mass is a hundredth of 17.031 g. In milligrams that is 170.31 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 85.155 mg that 500 mL of 0.01 M needs directly is the harder of the two.
Solution recipes for ammonia
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Nitrogen (N) | 1 | 14.007 | 14.007 | 82.24% |
| Hydrogen (H) | 3 | 1.008 | 3.024 | 17.76% |
| Total — one mole of ammonia | 17.031 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 17.031 g/mol.
| Target | for 100 mL | for 250 mL | for 500 mL | for 1 L |
|---|---|---|---|---|
| 0.001 M | 1.7031 mg | 4.25775 mg | 8.5155 mg | 17.031 mg |
| 0.005 M | 8.5155 mg | 21.2888 mg | 42.5775 mg | 85.155 mg |
| 0.01 M | 17.031 mg | 42.5775 mg | 85.155 mg | 170.31 mg |
| 0.05 M | 85.155 mg | 212.888 mg | 425.775 mg | 851.55 mg |
| 0.1 M | 170.31 mg | 425.775 mg | 851.55 mg | 1.7031 g |
| 0.15 M | 255.465 mg | 638.662 mg | 1.27732 g | 2.55465 g |
| 0.2 M | 340.62 mg | 851.55 mg | 1.7031 g | 3.4062 g |
| 0.25 M | 425.775 mg | 1.06444 g | 2.12887 g | 4.25775 g |
| 0.5 M | 851.55 mg | 2.12887 g | 4.25775 g | 8.5155 g |
| 1 M | 1.7031 g | 4.25775 g | 8.5155 g | 17.031 g |
| 2 M | 3.4062 g | 8.5155 g | 17.031 g | 34.062 g |
Each cell is molarity × volume in litres × 17.031 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 |
|---|---|---|---|
| Methane | CH4 | 16.043 | 62.332 |
| Ammonia (this page) | NH3 | 17.031 | 58.716 |
| Water | H2O | 18.015 | 55.509 |
| Carbon monoxide | CO | 28.01 | 35.702 |
| Nitrogen | N2 | 28.014 | 35.696 |
| Oxygen | O2 | 31.998 | 31.252 |
| Hydrogen peroxide | H2O2 | 34.014 | 29.4 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.