To prepare a solution of hydrochloric acid you need the grams, and grams is molarity × volume in litres × 36.458 g/mol. A litre of 1 M takes 36.458 g; 500 mL of 0.1 M takes 1.8229 g; 250 mL of 0.01 M takes 91.145 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. Hydrochloric acid is 1.008 (H) + 35.45 (Cl), which is 36.458 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Chlorine makes up the largest share of the mass: 1 of the 2 atoms in a formula unit is chlorine, and they account for 35.45 g of the 36.458 g, or 97.24% 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.
Muriatic acid, sold as a percentage solution rather than a solid. Concentrated acid is about 37% w/w, which works out near 12 mol/L. At 36.458 g/mol it is the lightest of the 12 acids covered here, and that ranking matters more than it looks: formic acid has a molar mass of 46.025 g/mol, so a gram of it contains 20.8% fewer formula units than a gram of hydrochloric acid. Weigh by mass and you are not weighing equal amounts of substance.
One more step applies if you are starting from a concentrated bottle. Concentrated acids are labelled as a percentage by weight together with a density, not as a molarity, so getting to mol/L means multiplying density by that percentage and dividing by 36.458 g/mol. A page like this one gives you the last of those three numbers; the first two are on the bottle, and they vary between grades.
The formula
c- The molarity you want, in mol/L
V- The volume you want to make, in millilitres
36.458- The molar mass of hydrochloric acid in g/mol, derived from its formula
m- The mass of hydrochloric acid 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 36.458 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 hydrochloric acid
Weigh 0.91145 g. That is 0.1 M × 0.25 L × 36.458 g/mol, and it comes to 911.45 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 hydrochloric acid
Weigh 9.1145 g. That is 0.5 M × 0.5 L × 36.458 g/mol, and it comes to 9114.5 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 hydrochloric acid
Weigh 36.458 g. That is 1 M × 1 L × 36.458 g/mol, and it comes to 36,458 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 hydrochloric acid (HCl)?
It is 36.458 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 1.008 (H) + 35.45 (Cl). One mole of hydrochloric acid therefore weighs 36.458 g, and a gram of it is 27.429 mmol.
What percentage of hydrochloric acid is chlorine?
97.24% by mass. Each formula unit contains 1 chlorine atom contributing 35.45 g of the 36.458 g total, so 100 g of hydrochloric acid contains 97.24 g of chlorine and a kilogram contains 972.35 g of it.
How much hydrochloric acid do I need for 1 litre of 1 M solution?
36.458 g — the molar mass in grams, which is what a 1 molar solution means. For 1 L of 0.1 M it is 3.6458 g, and for 1 L of 0.01 M it is 0.36458 g.
How much for 100 mL of 0.1 M?
0.36458 g. The volume is a tenth of a litre and the strength a tenth of molar, so the mass is a hundredth of 36.458 g. In milligrams that is 364.58 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 182.29 mg that 500 mL of 0.01 M needs directly is the harder of the two.
Solution recipes for hydrochloric acid
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Chlorine (Cl) | 1 | 35.45 | 35.45 | 97.24% |
| Hydrogen (H) | 1 | 1.008 | 1.008 | 2.765% |
| Total — one mole of hydrochloric acid | 36.458 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 36.458 g/mol.
| Target | for 100 mL | for 250 mL | for 500 mL | for 1 L |
|---|---|---|---|---|
| 0.001 M | 3.6458 mg | 9.1145 mg | 18.229 mg | 36.458 mg |
| 0.005 M | 18.229 mg | 45.5725 mg | 91.145 mg | 182.29 mg |
| 0.01 M | 36.458 mg | 91.145 mg | 182.29 mg | 364.58 mg |
| 0.05 M | 182.29 mg | 455.725 mg | 911.45 mg | 1.8229 g |
| 0.1 M | 364.58 mg | 911.45 mg | 1.8229 g | 3.6458 g |
| 0.15 M | 546.87 mg | 1.36718 g | 2.73435 g | 5.4687 g |
| 0.2 M | 729.16 mg | 1.8229 g | 3.6458 g | 7.2916 g |
| 0.25 M | 911.45 mg | 2.27863 g | 4.55725 g | 9.1145 g |
| 0.5 M | 1.8229 g | 4.55725 g | 9.1145 g | 18.229 g |
| 1 M | 3.6458 g | 9.1145 g | 18.229 g | 36.458 g |
| 2 M | 7.2916 g | 18.229 g | 36.458 g | 72.916 g |
Each cell is molarity × volume in litres × 36.458 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 |
|---|---|---|---|
| Hydrochloric acid (this page) | HCl | 36.458 | 27.429 |
| Formic acid | CH2O2 | 46.025 | 21.727 |
| Acetic acid | CH3COOH | 60.052 | 16.652 |
| Boric acid | H3BO3 | 61.831 | 16.173 |
| Nitric acid | HNO3 | 63.012 | 15.87 |
| Oxalic acid | C2H2O4 | 90.034 | 11.107 |
| Lactic acid | C3H6O3 | 90.078 | 11.101 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.