Molar MassMolar mass of calcium carbide (CaC2)
The molar mass of calcium carbide, CaC2, is 64.10 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 64.10 grams.
About calcium carbide
Calcium carbide reacts with water to give acetylene gas. It was used in miners' lamps and is still used to make acetylene for welding.
The working
The formula CaC2 has 1 calcium atom and 2 carbon atoms, 3 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Calcium (Ca) | 1 | 40.078 | 40.078 | 62.52% |
| Carbon (C) | 2 | 12.011 | 24.022 | 37.48% |
40.078 + 2 × 12.011 = 64.100 g/mol
With the rounded atomic masses used in many school books (Ca = 40, C = 12) the answer is 64 g/mol. The difference from 64.10 is too small to matter in most school sums.
Percentage composition
By mass, CaC2 is 62.52% calcium and 37.48% carbon. The largest share comes from calcium. In a 100 g sample there are 62.5 g of calcium and 37.5 g of carbon.
Notice that carbon has more atoms in the formula (2) than calcium (1), 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 10 g of CaC2? Divide the mass by the molar mass: 10 ÷ 64.10 = 0.156 mol.
Moles to grams. What is the mass of 1.5 mol of CaC2? Multiply: 1.5 × 64.10 = 96.15 g.
Counting particles. 10 g contains 0.156 mol × 6.022 × 1023 = 9.395 × 1022 formula units.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 6.41 g |
| 0.5 mol | 32.05 g |
| 1 mol | 64.1 g |
| 2 mol | 128.2 g |
| 5 mol | 320.5 g |
| Mass | Moles |
|---|---|
| 1 g | 0.0156 mol |
| 10 g | 0.156 mol |
| 100 g | 1.56 mol |
| 1 kg | 15.6 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of CaC2?
The molar mass of calcium carbide (CaC2) is 64.10 g/mol, or 64.100 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of CaC2?
100 ÷ 64.10 = 1.56 mol.
What is the mass of one formula unit of CaC2?
Divide the molar mass by the Avogadro constant: 64.10 ÷ 6.022 × 1023 = 1.064 × 10-22 g.
What is the percentage of calcium in CaC2?
Calcium makes up 62.52% of the mass of CaC2: 1 × 40.078 ÷ 64.100 × 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.