Going from grams to moles for uric acid means dividing by its molar mass, 168.112 g/mol. One gram is 0.00594842 mol, or 5.94842 mmol; 100 mg is 0.59484 mmol; and a 168.112 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, C5H4N4O3, which is where these figures come from.
The figure comes from the formula. Uric acid is 5 × 12.011 (C) + 4 × 1.008 (H) + 4 × 14.007 (N) + 3 × 15.999 (O), which is 168.112 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: 5 of the 16 atoms in a formula unit are carbon, and they account for 60.055 g of the 168.112 g, or 35.72% 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 0.05948 mmol of uric acid; on a three-decimal balance it is 1 mg, or 5.948 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 end point of purine metabolism and the crystal that causes gout. Barely soluble in water, which is precisely why it crystallises in joints. At 168.112 g/mol it is heavier than 14 of the 21 organic compounds covered here, and that ranking matters more than it looks: paracetamol has a molar mass of 151.165 g/mol, so a gram of it contains 11.2% more formula units than a gram of uric acid. 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 3.3622 g of a nominal 168.112 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
m- The mass you weighed, in grams
168.112- The molar mass of uric acid 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 168.112 g/mol, the molar mass of uric acid.
- 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 uric acid in moles
0.25 ÷ 168.112 = 0.0014871 mol, or 1.4871 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 5.948 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
2 g of uric acid in moles
2 ÷ 168.112 = 0.0118968 mol, or 11.897 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 5.948 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
25 g of uric acid in moles
25 ÷ 168.112 = 0.14871 mol, or 148.71 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 5.948 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 uric acid (C5H4N4O3)?
It is 168.112 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 5 × 12.011 (C) + 4 × 1.008 (H) + 4 × 14.007 (N) + 3 × 15.999 (O). One mole of uric acid therefore weighs 168.112 g, and a gram of it is 5.9484 mmol.
What percentage of uric acid is carbon?
35.72% by mass. Each formula unit contains 5 carbon atoms contributing 60.055 g of the 168.112 g total, so 100 g of uric acid contains 35.72 g of carbon and a kilogram contains 357.23 g of it.
How do I convert grams of uric acid to moles?
Divide the mass in grams by 168.112 g/mol. So 1 g is 0.00594842 mol, 10 g is 0.0594842 mol and 100 g is 0.594842 mol. Nothing else enters the calculation — no volume, no temperature, no concentration.
How many moles is 100 g of uric acid?
0.594842 mol, which is 594.842 mmol. Read the other way, one mole of uric acid is 168.112 g, so 100 g is 0.5948 of a mole.
What about milligrams and micromoles?
The same division, scaled. A milligram of uric acid is 5.9484 µmol, 10 mg is 59.484 µmol and 100 mg is 0.59484 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 uric acid, which is 0.00582945 mol rather than 0.00594842 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 uric acid
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 5 | 12.011 | 60.055 | 35.72% |
| Nitrogen (N) | 4 | 14.007 | 56.028 | 33.33% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 28.55% |
| Hydrogen (H) | 4 | 1.008 | 4.032 | 2.398% |
| Total — one mole of uric acid | 168.112 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 168.112 g/mol.
| On the balance | Moles | Millimoles | Micromoles |
|---|---|---|---|
| 1 mg | 0.000006 | 0.00594842 | 5.94842 |
| 5 mg | 0.000030 | 0.0297421 | 29.7421 |
| 10 mg | 0.000059 | 0.0594842 | 59.4842 |
| 25 mg | 0.00014871 | 0.14871 | 148.71 |
| 50 mg | 0.000297421 | 0.297421 | 297.421 |
| 100 mg | 0.000594842 | 0.594842 | 594.842 |
| 250 mg | 0.0014871 | 1.4871 | 1487.1 |
| 500 mg | 0.00297421 | 2.97421 | 2974.21 |
| 1 g | 0.00594842 | 5.94842 | 5948.42 |
| 2 g | 0.0118968 | 11.8968 | 11,896.8 |
| 5 g | 0.0297421 | 29.7421 | 29,742.1 |
| 10 g | 0.0594842 | 59.4842 | 59,484.2 |
| 25 g | 0.14871 | 148.71 | 148,710 |
| 50 g | 0.297421 | 297.421 | 297,421 |
| 100 g | 0.594842 | 594.842 | 594,842 |
| 250 g | 1.4871 | 1487.1 | 1487103.835538 |
| 500 g | 2.97421 | 2974.21 | 2974207.671076 |
Every row is the mass divided by 168.112 g/mol. A balance reading to 1 mg resolves 5.948 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 |
|---|---|---|---|
| Octane | C8H18 | 114.232 | 8.7541 |
| Tris base | C4H11NO3 | 121.136 | 8.2552 |
| Paracetamol | C8H9NO2 | 151.165 | 6.6153 |
| Uric acid (this page) | C5H4N4O3 | 168.112 | 5.9484 |
| Glucose | C6H12O6 | 180.156 | 5.5507 |
| Aspirin | C9H8O4 | 180.159 | 5.5507 |
| Caffeine | C8H10N4O2 | 194.194 | 5.1495 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.