Molar MassMolar mass of calcium phosphate (Ca3(PO4)2)
The molar mass of calcium phosphate, Ca3(PO4)2, is 310.17 g/mol. One mole of it, which is 6.022 × 1023 formula units, has a mass of 310.17 grams.
310.17 g/mol
3 × 40.078 + 2 × 30.974 + 8 × 15.999 = 310.174 · 13 atoms in the formula · also called tricalcium phosphate
About calcium phosphate
Calcium phosphate is the main mineral of bones and teeth and of phosphate rock, from which fertilisers are made. The formula has three calcium atoms and two phosphate groups, so two phosphorus and eight oxygen atoms.
Other names: tricalcium phosphate.
The working
The formula Ca3(PO4)2 has 3 calcium atoms, 2 phosphorus atoms and 8 oxygen atoms, 13 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) | 3 | 40.078 | 120.234 | 38.76% |
| Phosphorus (P) | 2 | 30.974 | 61.948 | 19.97% |
| Oxygen (O) | 8 | 15.999 | 127.992 | 41.26% |
3 × 40.078 + 2 × 30.974 + 8 × 15.999 = 310.174 g/mol
With the rounded atomic masses used in many school books (Ca = 40, P = 31, O = 16) the answer is 310 g/mol. The difference from 310.17 is too small to matter in most school sums.
Percentage composition
By mass, Ca3(PO4)2 is 38.76% calcium, 19.97% phosphorus and 41.26% oxygen. The largest share comes from oxygen. In a 100 g sample there are 38.8 g of calcium, 20.0 g of phosphorus and 41.3 g of oxygen.
Worked examples
Grams to moles. How many moles are in 10 g of Ca3(PO4)2? Divide the mass by the molar mass: 10 ÷ 310.17 = 0.03224 mol.
Moles to grams. What is the mass of 1.5 mol of Ca3(PO4)2? Multiply: 1.5 × 310.17 = 465.3 g.
Counting particles. 10 g contains 0.03224 mol × 6.022 × 1023 = 1.942 × 1022 formula units.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 31.02 g |
| 0.5 mol | 155.1 g |
| 1 mol | 310.2 g |
| 2 mol | 620.3 g |
| 5 mol | 1551 g |
| Mass | Moles |
|---|---|
| 1 g | 0.003224 mol |
| 10 g | 0.03224 mol |
| 100 g | 0.3224 mol |
| 1 kg | 3.224 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of Ca3(PO4)2?
The molar mass of calcium phosphate (Ca3(PO4)2) is 310.17 g/mol, or 310.174 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of Ca3(PO4)2?
100 ÷ 310.17 = 0.3224 mol.
What is the mass of one formula unit of Ca3(PO4)2?
Divide the molar mass by the Avogadro constant: 310.17 ÷ 6.022 × 1023 = 5.151 × 10-22 g.
What is the percentage of oxygen in Ca3(PO4)2?
Oxygen makes up 41.26% of the mass of Ca3(PO4)2: 8 × 15.999 ÷ 310.174 × 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.