The molar mass of Tris base, C4H11NO3, is 121.136 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 121.136 g, and a gram of it is 4.971e+21 formula units. The calculator turns any weighed mass into that count, and reports the amount in moles, millimoles and the mass of a single formula unit alongside it.
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.
The numbers a bench actually uses sit at the millimole scale. One millimole of Tris base is 121.136 mg and one micromole is 121.136 µg, so a balance reading to a milligram places you within 8.255 µmol. A single formula unit weighs 2.0115e-22 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
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 of Tris base in grams
121.136- The molar mass of Tris base in g/mol, derived from its formula
N- The number of formula units that mass contains
How it works, step by step
- Enter a mass of Tris base in grams.
- It is divided by the molar mass, 121.136 g/mol, giving the amount in moles.
- That amount is multiplied by the Avogadro constant, 6.02214076 × 10²³ per mole, to give the number of formula units.
- The panel also reports the amount in moles and millimoles and the mass of one formula unit.
Worked examples
0.5 g of Tris base as a molecule count
0.5 g divided by 121.136 g/mol is 0.00412759 mol, and multiplying by the Avogadro constant gives 2.486e+21 formula units of Tris base. The same mass is 4.1276 mmol, which is the figure a reaction is actually planned in.
5 g of Tris base as a molecule count
5 g divided by 121.136 g/mol is 0.0412759 mol, and multiplying by the Avogadro constant gives 2.486e+22 formula units of Tris base. The same mass is 41.276 mmol, which is the figure a reaction is actually planned in.
50 g of Tris base as a molecule count
50 g divided by 121.136 g/mol is 0.412759 mol, and multiplying by the Avogadro constant gives 2.486e+23 formula units of Tris base. The same mass is 412.76 mmol, which is the figure a reaction is actually planned in.
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 many molecules are in one gram of Tris base?
About 4.971e+21. One gram is 0.00825518 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 121.136.
How much does a single molecule of Tris base weigh?
2.0115e-22 g, which is 121.136 daltons. It is the molar mass divided by the Avogadro constant, and the number in daltons is numerically the same as the molar mass in g/mol — that equivalence is what makes the mole convenient.
Is molar mass the same as molecular weight?
They are the same number in ordinary use but not the same quantity. Molecular weight, properly relative molecular mass, is a ratio and has no unit: for Tris base it is 121.136. Molar mass carries grams per mole: 121.136 g/mol. Because the mole is defined so those agree, you can read one off the other.
Why is the molar mass not a whole number?
Because standard atomic weights are averages over the isotopes found in nature. Carbon is quoted as 12.011 rather than a whole number for that reason, and the same applies to the other elements here, which is why Tris base comes out at 121.136 g/mol rather than 121.
Molar mass, composition and mole equivalents of 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.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000121136 | 0.121136 | 6.022e+17 |
| 10 µmol | 0.00121136 | 1.21136 | 6.022e+18 |
| 100 µmol | 0.0121136 | 12.1136 | 6.022e+19 |
| 1 mmol | 0.121136 | 121.136 | 6.022e+20 |
| 10 mmol | 1.21136 | 1211.36 | 6.022e+21 |
| 50 mmol | 6.0568 | 6056.8 | 3.011e+22 |
| 100 mmol | 12.1136 | 12,113.6 | 6.022e+22 |
| 250 mmol | 30.284 | 30,284 | 1.506e+23 |
| 500 mmol | 60.568 | 60,568 | 3.011e+23 |
| 750 mmol | 90.852 | 90,852 | 4.517e+23 |
| 1 mol | 121.136 | 121,136 | 6.022e+23 |
| 2 mol | 242.272 | 242,272 | 1.204e+24 |
| 5 mol | 605.68 | 605,680 | 3.011e+24 |
| 10 mol | 1211.36 | 1211360.000000 | 6.022e+24 |
Mass is the amount multiplied by 121.136 g/mol. The last column is that amount multiplied by the Avogadro constant, 6.02214076 × 10²³ per mole.
| 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.