Molar MassMolar mass of citric acid (C6H8O7)
The molar mass of citric acid, C6H8O7, is 192.12 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 192.12 grams.
192.12 g/mol
6 × 12.011 + 8 × 1.0080 + 7 × 15.999 = 192.123 · 21 atoms in the formula
About citric acid
Citric acid gives lemons, oranges and other citrus fruit their sour taste. It is a weak acid with three acidic hydrogen atoms, and it is widely used in food, soft drinks and cleaning products. The formula here is for the anhydrous acid; it is also sold as a monohydrate.
The working
The formula C6H8O7 has 6 carbon atoms, 8 hydrogen atoms and 7 oxygen atoms, 21 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Carbon (C) | 6 | 12.011 | 72.066 | 37.51% |
| Hydrogen (H) | 8 | 1.0080 | 8.064 | 4.20% |
| Oxygen (O) | 7 | 15.999 | 111.993 | 58.29% |
6 × 12.011 + 8 × 1.0080 + 7 × 15.999 = 192.123 g/mol
With the rounded atomic masses used in many school books (C = 12, H = 1, O = 16) the answer is 192 g/mol. The difference from 192.12 is too small to matter in most school sums.
Percentage composition
By mass, C6H8O7 is 37.51% carbon, 4.20% hydrogen and 58.29% oxygen. The largest share comes from oxygen. In a 100 g sample there are 37.5 g of carbon, 4.2 g of hydrogen and 58.3 g of oxygen.
Notice that hydrogen has more atoms in the formula (8) than oxygen (7), yet gives a smaller share of the mass. Percentage by mass depends on how heavy each atom is, not only on how many there are.
Worked examples
Grams to moles. How many moles are in 5 g of C6H8O7? Divide the mass by the molar mass: 5 ÷ 192.12 = 0.02602 mol.
Moles to grams. What is the mass of 0.25 mol of C6H8O7? Multiply: 0.25 × 192.12 = 48.03 g.
Counting particles. 5 g contains 0.02602 mol × 6.022 × 1023 = 1.567 × 1022 molecules, and 3.291 × 1023 atoms in all.
Making a solution. A 0.1 mol/L solution contains 0.1 × 192.12 = 19.21 g of C6H8O7 in each litre. For 250 mL, weigh 4.803 g and make it up to the mark with water.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 19.21 g |
| 0.5 mol | 96.06 g |
| 1 mol | 192.1 g |
| 2 mol | 384.2 g |
| 5 mol | 960.6 g |
| Mass | Moles |
|---|---|
| 1 g | 0.005205 mol |
| 10 g | 0.05205 mol |
| 100 g | 0.5205 mol |
| 1 kg | 5.205 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of C6H8O7?
The molar mass of citric acid (C6H8O7) is 192.12 g/mol, or 192.123 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of C6H8O7?
100 ÷ 192.12 = 0.5205 mol.
What is the mass of one molecule of C6H8O7?
Divide the molar mass by the Avogadro constant: 192.12 ÷ 6.022 × 1023 = 3.190 × 10-22 g.
What is the percentage of oxygen in C6H8O7?
Oxygen makes up 58.29% of the mass of C6H8O7: 7 × 15.999 ÷ 192.123 × 100.
Which values? This site uses the abridged standard atomic weights published by IUPAC (CIAAW), read on 12 November 2026. Your textbook or question paper may round them differently, for example H = 1 and O = 16, so its answer can differ slightly. In an exam, use the values the paper gives.