Molar MassMolar mass of zinc oxide (ZnO)
The molar mass of zinc oxide, ZnO, is 81.38 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 81.38 grams.
About zinc oxide
Zinc oxide is a white powder that turns yellow when hot. It is used in ointments, sunscreens and rubber. It is amphoteric.
The working
The formula ZnO has 1 zinc atom and 1 oxygen atom, 2 atoms in all. Multiply each count by the atomic weight of the element and add:
65.38 + 15.999 = 81.379 g/mol
With the rounded atomic masses used in many school books (Zn = 65, O = 16) the answer is 81 g/mol. The difference from 81.38 is small, but it shows why you should use the values your question paper gives.
Percentage composition
By mass, ZnO is 80.34% zinc and 19.66% oxygen. The largest share comes from zinc. In a 100 g sample there are 80.3 g of zinc and 19.7 g of oxygen.
Worked examples
Grams to moles. How many moles are in 10 g of ZnO? Divide the mass by the molar mass: 10 ÷ 81.38 = 0.1229 mol.
Moles to grams. What is the mass of 1.5 mol of ZnO? Multiply: 1.5 × 81.38 = 122.1 g.
Counting particles. 10 g contains 0.1229 mol × 6.022 × 1023 = 7.400 × 1022 formula units.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 8.138 g |
| 0.5 mol | 40.69 g |
| 1 mol | 81.38 g |
| 2 mol | 162.8 g |
| 5 mol | 406.9 g |
| Mass | Moles |
|---|---|
| 1 g | 0.01229 mol |
| 10 g | 0.1229 mol |
| 100 g | 1.229 mol |
| 1 kg | 12.29 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of ZnO?
The molar mass of zinc oxide (ZnO) is 81.38 g/mol, or 81.379 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of ZnO?
100 ÷ 81.38 = 1.229 mol.
What is the mass of one formula unit of ZnO?
Divide the molar mass by the Avogadro constant: 81.38 ÷ 6.022 × 1023 = 1.351 × 10-22 g.
What is the percentage of zinc in ZnO?
Zinc makes up 80.34% of the mass of ZnO: 1 × 65.38 ÷ 81.379 × 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.