Moles to grams for potassium sulfate is a multiplication by 174.2526 g/mol. A mole weighs 174.2526 g, 100 mmol weighs 17.4253 g, 10 mmol weighs 1.74253 g and a millimole is 174.253 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. Potassium sulfate is 2 × 39.0983 (K) + 32.06 (S) + 4 × 15.999 (O), which is 174.2526 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Potassium makes up the largest share of the mass: 2 of the 7 atoms in a formula unit are potassium, and they account for 78.1966 g of the 174.2526 g, or 44.88% 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.
A chloride-free potassium fertiliser, preferred where salt sensitivity matters. It is much less soluble than the chloride, about 120 g per litre. At 174.2526 g/mol it is heavier than 25 of the 34 salts covered here, and that ranking matters more than it looks: gypsum has a molar mass of 172.164 g/mol, so a gram of it contains 1.21% more formula units than a gram of potassium sulfate. 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 3.4851 g of a nominal 174.2526 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
n- The amount of potassium sulfate you need, in moles
174.2526- The molar mass of potassium sulfate 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 174.2526 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 potassium sulfate in grams
5 mmol × 174.2526 g/mol = 0.871263 g, which is 871.263 mg. Doubling the amount doubles the mass to 1.74253 g, because the relationship is a plain proportion once the molar mass is fixed.
250 mmol of potassium sulfate in grams
250 mmol × 174.2526 g/mol = 43.5632 g, which is 43,563.2 mg. Doubling the amount doubles the mass to 87.1263 g, because the relationship is a plain proportion once the molar mass is fixed.
2 mol of potassium sulfate in grams
2 mol × 174.2526 g/mol = 348.505 g, which is 348,505 mg. Doubling the amount doubles the mass to 697.01 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 potassium sulfate (K2SO4)?
It is 174.2526 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 2 × 39.0983 (K) + 32.06 (S) + 4 × 15.999 (O). One mole of potassium sulfate therefore weighs 174.2526 g, and a gram of it is 5.7388 mmol.
What percentage of potassium sulfate is potassium?
44.88% by mass. Each formula unit contains 2 potassium atoms contributing 78.1966 g of the 174.2526 g total, so 100 g of potassium sulfate contains 44.88 g of potassium and a kilogram contains 448.75 g of it.
How many grams is one mole of potassium sulfate?
174.2526 g, by definition of the molar mass. Two moles is 348.5052 g and half a mole is 87.1263 g.
How many grams is 0.1 mol, and how many milligrams is 1 mmol?
0.1 mol of potassium sulfate is 17.4253 g. One millimole is 174.253 mg and one micromole is 174.253 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 1.743 mg of potassium sulfate, weigh 17.43 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, K2SO4, at 174.2526 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 potassium sulfate
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Potassium (K) | 2 | 39.0983 | 78.1966 | 44.88% |
| Oxygen (O) | 4 | 15.999 | 63.996 | 36.73% |
| Sulfur (S) | 1 | 32.06 | 32.06 | 18.4% |
| Total — one mole of potassium sulfate | 174.2526 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 174.2526 g/mol.
| Wanted | Weigh (g) | Weigh (mg) | With 2% over (g) |
|---|---|---|---|
| 1 µmol | 0.000174253 | 0.174253 | 0.000177738 |
| 10 µmol | 0.00174253 | 1.74253 | 0.00177738 |
| 100 µmol | 0.0174253 | 17.4253 | 0.0177738 |
| 1 mmol | 0.174253 | 174.253 | 0.177738 |
| 10 mmol | 1.74253 | 1742.53 | 1.77738 |
| 50 mmol | 8.71263 | 8712.63 | 8.88688 |
| 100 mmol | 17.4253 | 17,425.3 | 17.7738 |
| 250 mmol | 43.5632 | 43,563.2 | 44.4344 |
| 500 mmol | 87.1263 | 87,126.3 | 88.8688 |
| 750 mmol | 130.689 | 130,689 | 133.303 |
| 1 mol | 174.253 | 174,253 | 177.738 |
| 2 mol | 348.505 | 348,505 | 355.475 |
| 5 mol | 871.263 | 871,263 | 888.688 |
| 10 mol | 1742.53 | 1742526.000000 | 1777.38 |
Weigh is the amount multiplied by 174.2526 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 |
|---|---|---|---|
| Potassium iodide | KI | 166.0028 | 6.024 |
| Silver nitrate | AgNO3 | 169.8722 | 5.8868 |
| Gypsum | CaSO4·2H2O | 172.164 | 5.8084 |
| Potassium sulfate (this page) | K2SO4 | 174.2526 | 5.7388 |
| Epsom salt | MgSO4·7H2O | 246.466 | 4.0574 |
| Sodium thiosulfate pentahydrate | Na2S2O3·5H2O | 248.1715 | 4.0295 |
| Copper(II) sulfate pentahydrate | CuSO4·5H2O | 249.677 | 4.0052 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.