Going from grams to moles for Tris base means dividing by its molar mass, 121.136 g/mol. One gram is 0.00825518 mol, or 8.25518 mmol; 100 mg is 0.82552 mmol; and a 121.136 g portion is exactly one mole. The division is the whole calculation, but the molar mass has to be the one for the exact formula you have, C4H11NO3, which is where these figures come from.
The figure comes from the formula. Tris base is 4 × 12.011 (C) + 11 × 1.008 (H) + 14.007 (N) + 3 × 15.999 (O), which is 121.136 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Carbon makes up the largest share of the mass: 4 of the 19 atoms in a formula unit are carbon, and they account for 48.044 g of the 121.136 g, or 39.66% by mass. The derivation table below breaks the whole molecule down element by element.
Balance resolution is the practical limit here. On a two-decimal balance the smallest step is 10 mg, which is 0.08255 mmol of Tris base; on a three-decimal balance it is 1 mg, or 8.255 µmol. To hit a target within 1% you therefore need to weigh at least a gram on the first and at least 100 mg on the second, and below that a stock solution measured by pipette beats weighing.
The buffer of molecular biology, working between pH 7 and 9. Its pKa moves with temperature, so a buffer set at 25 degrees C is not the same in the cold. At 121.136 g/mol it is heavier than 12 of the 21 organic compounds covered here, and that ranking matters more than it looks: octane has a molar mass of 114.232 g/mol, so a gram of it contains 6.04% more formula units than a gram of Tris base. 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, 2.4227 g of every 121.136 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
m- The mass you weighed, in grams
121.136- The molar mass of Tris base in g/mol, derived from its formula
n- The amount of substance in moles
How it works, step by step
- Enter the mass you weighed, in grams.
- It is divided by 121.136 g/mol, the molar mass of Tris base.
- The result is the amount of substance in moles, with millimoles and micromoles beneath it.
- Check it against the table if you want the figure for a standard weighing rather than a typed mass.
Worked examples
0.25 g of Tris base in moles
0.25 ÷ 121.136 = 0.0020638 mol, or 2.0638 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 8.255 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
2 g of Tris base in moles
2 ÷ 121.136 = 0.0165104 mol, or 16.51 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 8.255 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
25 g of Tris base in moles
25 ÷ 121.136 = 0.20638 mol, or 206.38 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 8.255 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
How to read your score
Frequently asked questions
What is the molar mass of Tris base (C4H11NO3)?
It is 121.136 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 4 × 12.011 (C) + 11 × 1.008 (H) + 14.007 (N) + 3 × 15.999 (O). One mole of Tris base therefore weighs 121.136 g, and a gram of it is 8.2552 mmol.
What percentage of Tris base is carbon?
39.66% by mass. Each formula unit contains 4 carbon atoms contributing 48.044 g of the 121.136 g total, so 100 g of Tris base contains 39.66 g of carbon and a kilogram contains 396.61 g of it.
How do I convert grams of Tris base to moles?
Divide the mass in grams by 121.136 g/mol. So 1 g is 0.00825518 mol, 10 g is 0.0825518 mol and 100 g is 0.825518 mol. Nothing else enters the calculation — no volume, no temperature, no concentration.
How many moles is 100 g of Tris base?
0.825518 mol, which is 825.518 mmol. Read the other way, one mole of Tris base is 121.136 g, so 100 g is 0.8255 of a mole.
What about milligrams and micromoles?
The same division, scaled. A milligram of Tris base is 8.2552 µmol, 10 mg is 82.552 µmol and 100 mg is 0.82552 mmol. Working in µmol per mg avoids the string of leading zeros that mol per g produces at this scale.
Does purity change the number of moles?
Yes, in proportion. A 98% pure sample weighing 1 g contains 0.98 g of Tris base, which is 0.00809008 mol rather than 0.00825518 mol. The calculator assumes the mass you enter is the compound itself, so divide by the assay figure first if you need the corrected amount.
Grams to moles reference for Tris base
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 4 | 12.011 | 48.044 | 39.66% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 39.62% |
| Nitrogen (N) | 1 | 14.007 | 14.007 | 11.56% |
| Hydrogen (H) | 11 | 1.008 | 11.088 | 9.153% |
| Total — one mole of Tris base | 121.136 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 121.136 g/mol.
| On the balance | Moles | Millimoles | Micromoles |
|---|---|---|---|
| 1 mg | 0.000008 | 0.00825518 | 8.25518 |
| 5 mg | 0.000041 | 0.0412759 | 41.2759 |
| 10 mg | 0.000083 | 0.0825518 | 82.5518 |
| 25 mg | 0.00020638 | 0.20638 | 206.38 |
| 50 mg | 0.000412759 | 0.412759 | 412.759 |
| 100 mg | 0.000825518 | 0.825518 | 825.518 |
| 250 mg | 0.0020638 | 2.0638 | 2063.8 |
| 500 mg | 0.00412759 | 4.12759 | 4127.59 |
| 1 g | 0.00825518 | 8.25518 | 8255.18 |
| 2 g | 0.0165104 | 16.5104 | 16,510.4 |
| 5 g | 0.0412759 | 41.2759 | 41,275.9 |
| 10 g | 0.0825518 | 82.5518 | 82,551.8 |
| 25 g | 0.20638 | 206.38 | 206,380 |
| 50 g | 0.412759 | 412.759 | 412,759 |
| 100 g | 0.825518 | 825.518 | 825,518 |
| 250 g | 2.0638 | 2063.8 | 2063796.063928 |
| 500 g | 4.12759 | 4127.59 | 4127592.127856 |
Every row is the mass divided by 121.136 g/mol. A balance reading to 1 mg resolves 8.255 µmol of this compound, which is the smallest step the middle columns can really move in.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Toluene | C7H8 | 92.141 | 10.853 |
| Creatinine | C4H7N3O | 113.12 | 8.8402 |
| Octane | C8H18 | 114.232 | 8.7541 |
| Tris base (this page) | C4H11NO3 | 121.136 | 8.2552 |
| Paracetamol | C8H9NO2 | 151.165 | 6.6153 |
| Uric acid | C5H4N4O3 | 168.112 | 5.9484 |
| Glucose | C6H12O6 | 180.156 | 5.5507 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.