Molar MassMolar mass of naphthalene (C10H8)
The molar mass of naphthalene, C10H8, is 128.17 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 128.17 grams.
About naphthalene
Naphthalene is the white solid of traditional mothballs. It is made of two benzene rings joined side by side and it sublimes.
The working
The formula C10H8 has 10 carbon atoms and 8 hydrogen atoms, 18 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) | 10 | 12.011 | 120.110 | 93.71% |
| Hydrogen (H) | 8 | 1.0080 | 8.064 | 6.29% |
10 × 12.011 + 8 × 1.0080 = 128.174 g/mol
With the rounded atomic masses used in many school books (C = 12, H = 1) the answer is 128 g/mol. The difference from 128.17 is too small to matter in most school sums.
Percentage composition
By mass, C10H8 is 93.71% carbon and 6.29% hydrogen. The largest share comes from carbon. In a 100 g sample there are 93.7 g of carbon and 6.3 g of hydrogen.
Worked examples
Grams to moles. How many moles are in 10 g of C10H8? Divide the mass by the molar mass: 10 ÷ 128.17 = 0.07802 mol.
Moles to grams. What is the mass of 1.5 mol of C10H8? Multiply: 1.5 × 128.17 = 192.3 g.
Counting particles. 10 g contains 0.07802 mol × 6.022 × 1023 = 4.698 × 1022 molecules, and 8.457 × 1023 atoms in all.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 12.82 g |
| 0.5 mol | 64.09 g |
| 1 mol | 128.2 g |
| 2 mol | 256.3 g |
| 5 mol | 640.9 g |
| Mass | Moles |
|---|---|
| 1 g | 0.007802 mol |
| 10 g | 0.07802 mol |
| 100 g | 0.7802 mol |
| 1 kg | 7.802 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of C10H8?
The molar mass of naphthalene (C10H8) is 128.17 g/mol, or 128.174 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of C10H8?
100 ÷ 128.17 = 0.7802 mol.
What is the mass of one molecule of C10H8?
Divide the molar mass by the Avogadro constant: 128.17 ÷ 6.022 × 1023 = 2.128 × 10-22 g.
What is the percentage of carbon in C10H8?
Carbon makes up 93.71% of the mass of C10H8: 10 × 12.011 ÷ 128.174 × 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.