Moles to grams for magnesium chloride is a multiplication by 95.205 g/mol. A mole weighs 95.205 g, 100 mmol weighs 9.5205 g, 10 mmol weighs 0.95205 g and a millimole is 95.205 mg. Those four figures cover most of what gets weighed out in practice, and the table below extends them from a micromole up to ten moles.
The figure comes from the formula. Magnesium chloride is 24.305 (Mg) + 2 × 35.45 (Cl), which is 95.205 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: 2 of the 3 atoms in a formula unit are chlorine, and they account for 70.9 g of the 95.205 g, or 74.47% by mass. The derivation table below breaks the whole molecule down element by element.
Two habits make the weighed mass match the calculation. Weigh into a container you have tared rather than onto paper, because what stays behind on paper is a real loss — on a 100 mg weighing it is easily a percent. And when the target is under about 20 mg, weigh ten times that and dilute, since the absolute error of the balance does not shrink with the sample.
Used for de-icing, tofu coagulation and magnesium supplementation. The hexahydrate is what shops sell, and it weighs more than twice as much. At 95.205 g/mol it is heavier than 8 of the 34 salts covered here, and that ranking matters more than it looks: sodium nitrate has a molar mass of 84.99377 g/mol, so a gram of it contains 12% more formula units than a gram of magnesium chloride. 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, 1.9041 g of every 95.205 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
n- The amount of magnesium chloride you need, in moles
95.205- The molar mass of magnesium chloride in g/mol, derived from its formula
m- The mass to weigh out, in grams
How it works, step by step
- Enter the amount you need, in moles.
- It is multiplied by 95.205 g/mol.
- The result is the mass to weigh out, also given in milligrams.
- Weigh into a tared container; anything left in the boat is a real loss from the amount you calculated.
Worked examples
5 mmol of magnesium chloride in grams
5 mmol × 95.205 g/mol = 0.476025 g, which is 476.025 mg. Doubling the amount doubles the mass to 0.95205 g, because the relationship is a plain proportion once the molar mass is fixed.
250 mmol of magnesium chloride in grams
250 mmol × 95.205 g/mol = 23.8013 g, which is 23,801.3 mg. Doubling the amount doubles the mass to 47.6025 g, because the relationship is a plain proportion once the molar mass is fixed.
2 mol of magnesium chloride in grams
2 mol × 95.205 g/mol = 190.41 g, which is 190,410 mg. Doubling the amount doubles the mass to 380.82 g, because the relationship is a plain proportion once the molar mass is fixed.
How to read your score
Frequently asked questions
What is the molar mass of magnesium chloride (MgCl2)?
It is 95.205 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 24.305 (Mg) + 2 × 35.45 (Cl). One mole of magnesium chloride therefore weighs 95.205 g, and a gram of it is 10.504 mmol.
What percentage of magnesium chloride is chlorine?
74.47% by mass. Each formula unit contains 2 chlorine atoms contributing 70.9 g of the 95.205 g total, so 100 g of magnesium chloride contains 74.47 g of chlorine and a kilogram contains 744.71 g of it.
How many grams is one mole of magnesium chloride?
95.205 g, by definition of the molar mass. Two moles is 190.41 g and half a mole is 47.6025 g.
How many grams is 0.1 mol, and how many milligrams is 1 mmol?
0.1 mol of magnesium chloride is 9.5205 g. One millimole is 95.205 mg and one micromole is 95.205 µg, which is the range most bench work sits in.
How do I weigh out an amount too small for my balance?
Weigh a larger mass and dilute it. To get 0.9521 mg of magnesium chloride, weigh 9.521 mg into 100 mL, then take 10 mL of that: the absolute error of the balance stays the same while the amount delivered falls by a factor of ten.
Should I use the hydrate or the anhydrous molar mass?
This page is the anhydrous form, MgCl2, at 95.205 g/mol. If your jar is the other form the molar mass differs and so will every mass you weigh, so check the label before using the figure. Salts that are sold as hydrates weigh more per mole because the water is part of the crystal.
Moles to grams reference for magnesium chloride
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Chlorine (Cl) | 2 | 35.45 | 70.9 | 74.47% |
| Magnesium (Mg) | 1 | 24.305 | 24.305 | 25.53% |
| Total — one mole of magnesium chloride | 95.205 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 95.205 g/mol.
| Wanted | Weigh (g) | Weigh (mg) | With 2% over (g) |
|---|---|---|---|
| 1 µmol | 0.000095 | 0.095205 | 0.000097 |
| 10 µmol | 0.00095205 | 0.95205 | 0.000971091 |
| 100 µmol | 0.0095205 | 9.5205 | 0.00971091 |
| 1 mmol | 0.095205 | 95.205 | 0.0971091 |
| 10 mmol | 0.95205 | 952.05 | 0.971091 |
| 50 mmol | 4.76025 | 4760.25 | 4.85546 |
| 100 mmol | 9.5205 | 9520.5 | 9.71091 |
| 250 mmol | 23.8013 | 23,801.3 | 24.2773 |
| 500 mmol | 47.6025 | 47,602.5 | 48.5546 |
| 750 mmol | 71.4038 | 71,403.8 | 72.8318 |
| 1 mol | 95.205 | 95,205 | 97.1091 |
| 2 mol | 190.41 | 190,410 | 194.218 |
| 5 mol | 476.025 | 476,025 | 485.546 |
| 10 mol | 952.05 | 952,050 | 971.091 |
Weigh is the amount multiplied by 95.205 g/mol. The last column carries a 2% allowance, which is what you take when some of the solid will be left in the weighing boat.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Ammonium nitrate | NH4NO3 | 80.043 | 12.493 |
| Sodium bicarbonate | NaHCO3 | 84.00577 | 11.904 |
| Sodium nitrate | NaNO3 | 84.99377 | 11.766 |
| Magnesium chloride (this page) | MgCl2 | 95.205 | 10.504 |
| Calcium carbonate | CaCO3 | 100.086 | 9.9914 |
| Potassium nitrate | KNO3 | 101.1023 | 9.891 |
| Sodium carbonate | Na2CO3 | 105.9875 | 9.4351 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.