Moles to grams for sodium citrate is a multiplication by 258.06831 g/mol. A mole weighs 258.0683 g, 100 mmol weighs 25.8068 g, 10 mmol weighs 2.58068 g and a millimole is 258.068 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. Sodium citrate is 3 × 22.9898 (Na) + 6 × 12.011 (C) + 5 × 1.008 (H) + 7 × 15.999 (O), which is 258.06831 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Oxygen makes up the largest share of the mass: 7 of the 21 atoms in a formula unit are oxygen, and they account for 111.993 g of the 258.0683 g, or 43.4% 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.
The anticoagulant in blood bags, the emulsifying salt in smooth cheese sauce, and the buffer in effervescent tablets. The dihydrate is 294.10 g per mole. At 258.0683 g/mol it is heavier than 29 of the 34 salts covered here, and that ranking matters more than it looks: copper(II) sulfate pentahydrate has a molar mass of 249.677 g/mol, so a gram of it contains 3.36% more formula units than a gram of sodium citrate. 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, 5.1614 g of every 258.0683 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 sodium citrate you need, in moles
258.06831- The molar mass of sodium citrate 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 258.06831 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 sodium citrate in grams
5 mmol × 258.0683 g/mol = 1.29034 g, which is 1290.34 mg. Doubling the amount doubles the mass to 2.58068 g, because the relationship is a plain proportion once the molar mass is fixed.
250 mmol of sodium citrate in grams
250 mmol × 258.0683 g/mol = 64.5171 g, which is 64,517.1 mg. Doubling the amount doubles the mass to 129.034 g, because the relationship is a plain proportion once the molar mass is fixed.
2 mol of sodium citrate in grams
2 mol × 258.0683 g/mol = 516.137 g, which is 516,137 mg. Doubling the amount doubles the mass to 1032.27 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 sodium citrate (Na3C6H5O7)?
It is 258.06831 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 3 × 22.9898 (Na) + 6 × 12.011 (C) + 5 × 1.008 (H) + 7 × 15.999 (O). One mole of sodium citrate therefore weighs 258.0683 g, and a gram of it is 3.8749 mmol.
What percentage of sodium citrate is oxygen?
43.4% by mass. Each formula unit contains 7 oxygen atoms contributing 111.993 g of the 258.0683 g total, so 100 g of sodium citrate contains 43.4 g of oxygen and a kilogram contains 433.97 g of it.
How many grams is one mole of sodium citrate?
258.06831 g, by definition of the molar mass. Two moles is 516.1366 g and half a mole is 129.0342 g.
How many grams is 0.1 mol, and how many milligrams is 1 mmol?
0.1 mol of sodium citrate is 25.8068 g. One millimole is 258.068 mg and one micromole is 258.068 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 2.581 mg of sodium citrate, weigh 25.81 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, Na3C6H5O7, at 258.06831 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 sodium citrate
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 7 | 15.999 | 111.993 | 43.4% |
| Carbon (C) | 6 | 12.011 | 72.066 | 27.93% |
| Sodium (Na) | 3 | 22.98977 | 68.96931 | 26.73% |
| Hydrogen (H) | 5 | 1.008 | 5.04 | 1.953% |
| Total — one mole of sodium citrate | 258.06831 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 258.06831 g/mol.
| Wanted | Weigh (g) | Weigh (mg) | With 2% over (g) |
|---|---|---|---|
| 1 µmol | 0.000258068 | 0.258068 | 0.00026323 |
| 10 µmol | 0.00258068 | 2.58068 | 0.0026323 |
| 100 µmol | 0.0258068 | 25.8068 | 0.026323 |
| 1 mmol | 0.258068 | 258.068 | 0.26323 |
| 10 mmol | 2.58068 | 2580.68 | 2.6323 |
| 50 mmol | 12.9034 | 12,903.4 | 13.1615 |
| 100 mmol | 25.8068 | 25,806.8 | 26.323 |
| 250 mmol | 64.5171 | 64,517.1 | 65.8074 |
| 500 mmol | 129.034 | 129,034 | 131.615 |
| 750 mmol | 193.551 | 193,551 | 197.422 |
| 1 mol | 258.068 | 258,068 | 263.23 |
| 2 mol | 516.137 | 516,137 | 526.459 |
| 5 mol | 1290.34 | 1290341.539200 | 1316.15 |
| 10 mol | 2580.68 | 2580683.078400 | 2632.3 |
Weigh is the amount multiplied by 258.06831 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 |
|---|---|---|---|
| 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 |
| Sodium citrate (this page) | Na3C6H5O7 | 258.0683 | 3.8749 |
| Iron(II) sulfate heptahydrate | FeSO4·7H2O | 278.006 | 3.597 |
| Zinc sulfate heptahydrate | ZnSO4·7H2O | 287.541 | 3.4778 |
| Potassium dichromate | K2Cr2O7 | 294.1818 | 3.3993 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.