Moles to grams for trisodium phosphate is a multiplication by 163.93907 g/mol. A mole weighs 163.9391 g, 100 mmol weighs 16.3939 g, 10 mmol weighs 1.63939 g and a millimole is 163.939 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. Trisodium phosphate is 3 × 22.9898 (Na) + 30.9738 (P) + 4 × 15.999 (O), which is 163.93907 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Sodium makes up the largest share of the mass: 3 of the 8 atoms in a formula unit are sodium, and they account for 68.9693 g of the 163.9391 g, or 42.07% 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 heavy-duty cleaner and degreaser, and a food additive. Its solutions are strongly alkaline — around pH 12 at 1% — which is what does the cleaning. At 163.9391 g/mol it is heavier than 21 of the 34 salts covered here, and that ranking matters more than it looks: iron(III) chloride has a molar mass of 162.195 g/mol, so a gram of it contains 1.08% more formula units than a gram of trisodium phosphate. 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, 3.2788 g of every 163.9391 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 trisodium phosphate you need, in moles
163.93907- The molar mass of trisodium phosphate 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 163.93907 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 trisodium phosphate in grams
5 mmol × 163.9391 g/mol = 0.819695 g, which is 819.695 mg. Doubling the amount doubles the mass to 1.63939 g, because the relationship is a plain proportion once the molar mass is fixed.
250 mmol of trisodium phosphate in grams
250 mmol × 163.9391 g/mol = 40.9848 g, which is 40,984.8 mg. Doubling the amount doubles the mass to 81.9695 g, because the relationship is a plain proportion once the molar mass is fixed.
2 mol of trisodium phosphate in grams
2 mol × 163.9391 g/mol = 327.878 g, which is 327,878 mg. Doubling the amount doubles the mass to 655.756 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 trisodium phosphate (Na3PO4)?
It is 163.93907 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 3 × 22.9898 (Na) + 30.9738 (P) + 4 × 15.999 (O). One mole of trisodium phosphate therefore weighs 163.9391 g, and a gram of it is 6.0998 mmol.
What percentage of trisodium phosphate is sodium?
42.07% by mass. Each formula unit contains 3 sodium atoms contributing 68.9693 g of the 163.9391 g total, so 100 g of trisodium phosphate contains 42.07 g of sodium and a kilogram contains 420.7 g of it.
How many grams is one mole of trisodium phosphate?
163.93907 g, by definition of the molar mass. Two moles is 327.8781 g and half a mole is 81.96953 g.
How many grams is 0.1 mol, and how many milligrams is 1 mmol?
0.1 mol of trisodium phosphate is 16.3939 g. One millimole is 163.939 mg and one micromole is 163.939 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 1.639 mg of trisodium phosphate, weigh 16.39 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, Na3PO4, at 163.93907 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 trisodium phosphate
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Sodium (Na) | 3 | 22.98977 | 68.96931 | 42.07% |
| Oxygen (O) | 4 | 15.999 | 63.996 | 39.04% |
| Phosphorus (P) | 1 | 30.97376 | 30.97376 | 18.89% |
| Total — one mole of trisodium phosphate | 163.93907 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 163.93907 g/mol.
| Wanted | Weigh (g) | Weigh (mg) | With 2% over (g) |
|---|---|---|---|
| 1 µmol | 0.000163939 | 0.163939 | 0.000167218 |
| 10 µmol | 0.00163939 | 1.63939 | 0.00167218 |
| 100 µmol | 0.0163939 | 16.3939 | 0.0167218 |
| 1 mmol | 0.163939 | 163.939 | 0.167218 |
| 10 mmol | 1.63939 | 1639.39 | 1.67218 |
| 50 mmol | 8.19695 | 8196.95 | 8.36089 |
| 100 mmol | 16.3939 | 16,393.9 | 16.7218 |
| 250 mmol | 40.9848 | 40,984.8 | 41.8045 |
| 500 mmol | 81.9695 | 81,969.5 | 83.6089 |
| 750 mmol | 122.954 | 122,954 | 125.413 |
| 1 mol | 163.939 | 163,939 | 167.218 |
| 2 mol | 327.878 | 327,878 | 334.436 |
| 5 mol | 819.695 | 819,695 | 836.089 |
| 10 mol | 1639.39 | 1639390.698380 | 1672.18 |
Weigh is the amount multiplied by 163.93907 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 permanganate | KMnO4 | 158.0323 | 6.3278 |
| Copper(II) sulfate | CuSO4 | 159.602 | 6.2656 |
| Iron(III) chloride | FeCl3 | 162.195 | 6.1654 |
| Trisodium phosphate (this page) | Na3PO4 | 163.9391 | 6.0998 |
| Potassium iodide | KI | 166.0028 | 6.024 |
| Silver nitrate | AgNO3 | 169.8722 | 5.8868 |
| Gypsum | CaSO4·2H2O | 172.164 | 5.8084 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.