CaCO₃ Molar Mass
Calcium carbonate
The molar mass of CaCO₃ (calcium carbonate) is approximately 100.09 g/mol. Each formula unit combines one calcium atom, one carbon atom, and three oxygen atoms, so the exact sum is 40.078 + 12.011 + (3 × 15.999) = 100.086 g/mol — about 40.0% calcium, 12.0% carbon, and 48.0% oxygen by mass. Because CaCO₃ is an ionic compound, this same number is properly called the formula mass.
Molar mass of CaCO₃
100.09 g/mol
Exact value from IUPAC standard atomic weights: 100.086 g/mol
| Formula | CaCO₃ |
|---|---|
| Molar Mass | 100.09 g/mol |
| Formula Mass | ≈ 100.086 u |
| Calcium Atoms | 1 |
| Carbon Atoms | 1 |
| Oxygen Atoms | 3 |
| Atoms per Formula Unit | 5 |
Good to know
CaCO₃ is an ionic compound: a crystal lattice of Ca²⁺ and CO₃²⁻ ions with no discrete molecules. That is why chemists quote a formula mass per formula unit rather than a molecular mass.
How to Calculate the Molar Mass of CaCO₃
The calcium carbonate molar mass is the sum of one calcium atomic weight, one carbon atomic weight, and three oxygen atomic weights. The IUPAC standard atomic weights give exactly 100.086 g/mol — rounded to 100.09 g/mol for classroom use. The same number also goes by "formula mass of calcium carbonate", because CaCO₃ is an ionic compound counted in formula units rather than discrete molecules.
CaCO₃
- Calcium: 1 × 40.078 = 40.078
- Carbon: 1 × 12.011 = 12.011
- Oxygen: 3 × 15.999 = 47.997
40.078 + 12.011 + 47.997 = 100.086 g/mol
≈ 100.09 g/mol
Step 1 Read the chemical formula
CaCO₃ contains 1 calcium atom, 1 carbon atom and 3 oxygen atoms. Subscripts count atoms, and a symbol without a subscript counts one.
Step 2 Find the atomic masses
Look up each element's IUPAC standard atomic weight on the periodic table: Ca = 40.078, C = 12.011 and O = 15.999. Most atomic weights are not whole numbers — each one averages an element's naturally occurring isotopes.
Step 3 Multiply by the atom counts
Each element contributes its atomic weight once per atom: Ca: 1 × 40.078 = 40.078; C: 1 × 12.011 = 12.011; O: 3 × 15.999 = 47.997.
Step 4 Add the contributions
40.078 + 12.011 + 47.997 = 100.086 g/mol. The IUPAC total is 100.086 g/mol, usually reported as 100.09 g/mol. One mole of CaCO₃ — 6.022 × 10²³ formula units, 5 atoms each — has exactly this mass in grams.
CaCO₃ Formula Breakdown
CaCO₃
- Ca = Calcium × 1
- C = Carbon × 1
- O = Oxygen × 3
- Total atoms = 5
CaCO₃ reads as two charged pieces, not four separate atoms glued in a row: a Ca²⁺ ion paired with a carbonate unit, CO₃²⁻. The subscript ₃ belongs to that carbonate unit — one carbon bonded to three oxygens, which travel together as a single 2− ion — so the oxygen count multiplies by 3 while Ca and C each count once. Add the pieces up: 1 + 1 + 3 = 5 atoms per formula unit.
Elemental Composition of CaCO₃
Each element's share of the total mass of one mole of CaCO₃. One mole — about 100.09 g — contains 40.078 g of calcium, 12.011 g of carbon and 47.997 g of oxygen, and every sample scales by the same ratio. Stated as percent composition, CaCO₃ is 40.04% calcium, 12.00% carbon and 47.96% oxygen by mass.
| Element | Atoms | Atomic Weight | Mass Contribution | Mass % |
|---|---|---|---|---|
| Calcium (Ca) | 1 | 40.078 | 40.078 | 40.04% |
| Carbon (C) | 1 | 12.011 | 12.011 | 12.00% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 47.96% |
| Total | 5 | 100.086 | 100% |
What Is the Formula Mass of CaCO₃?
The formula mass of CaCO₃ is approximately 100.09 u per formula unit — numerically the same number as the molar mass, 100.09 g/mol, because one mole of formula units weighs as many grams as one formula unit weighs in unified atomic mass units. A formula unit here is one Ca²⁺ ion paired with one CO₃²⁻ ion. Like solid NaCl, calcium carbonate is a crystal lattice in which the ions alternate in a fixed ratio, so there are no discrete "CaCO₃ molecules" to weigh — the formula unit is the counting unit that plays the molecule's role.
You will still see "molecular mass of CaCO₃" in search results and homework questions. It is used informally, and it always expects the number 100.09 — but the more precise terms are formula mass and formula weight, which describe exactly what CaCO₃ has: a mass per formula unit. Reference tables such as Wikipedia list 100.0869 g/mol, computed from a slightly older atomic-weight set; the current IUPAC weights give 100.086, and both round to the classroom value 100.09.
| Molar mass | 100.09 g/mol — the mass of one mole of CaCO₃ formula units |
|---|---|
| Formula mass | ≈ 100.086 u (Da) — the mass of one single CaCO₃ formula unit |
What Is the Chemical Formula for Calcium Carbonate?
The chemical formula for calcium carbonate is CaCO₃. The compound is built from ions, not neutral atoms: each calcium atom loses two electrons to become a Ca²⁺ ion, and the carbonate ion CO₃²⁻ — one carbon bonded to three oxygens — carries a matching 2− charge.
The charges cancel in a 1 : 1 ratio, so one Ca²⁺ pairs with one CO₃²⁻ and the formula needs no extra subscripts: Ca²⁺ + CO₃²⁻ → CaCO₃. That 1 : 1 pairing is also why a formula unit contains exactly five atoms — one calcium plus the carbonate unit's one carbon and three oxygens.
How Many Grams Are in One Mole of CaCO₃?
One mole of CaCO₃ has a mass of approximately 100.09 grams. That is the whole conversion — the molar mass is the conversion factor between moles and grams. 1 mol × 100.09 g/mol = 100.09 g, and half a mole weighs 0.5 × 100.09 = 50.045 g. Going the other way, divide by the same factor: 200.18 g of CaCO₃ is 200.18 ÷ 100.09 = 2 mol. Type an amount below to convert either way; the calculation uses 100.09 g/mol.
1 mol of CaCO₃ has a mass of 100.09 g
Need a full reaction calculation? Open the Stoichiometry Calculator →
CaCO₃ Molar Mass Units and Conversions
Molar mass is normally quoted in grams per mole (g/mol), but the same number scales across units: 100.09 g/mol = 100,090 mg/mol = 0.10009 kg/mol. Per formula unit, the same value appears in unified atomic mass units — one CaCO₃ formula unit has a formula mass of about 100.09 u. The number never changes; only the unit — and the amount of CaCO₃ it describes — does.
CaCO₃ molar mass in every unit
- grams per mole: 100.09 g/mol
- milligrams per mole: 100,090 mg/mol
- kilograms per mole: 0.10009 kg/mol
- per formula unit: ≈ 100.086 u
Try Another Formula
Enter any formula to get its molar mass, elemental composition, and the full step-by-step calculation.
Related Chemistry
- Molar Mass CalculatorMolar mass, molecular weight, and composition for any formula.
- Stoichiometry CalculatorConvert between moles, mass, and reaction amounts.
- Empirical Formula CalculatorTurn percent composition into a formula.
- Chemical Equation BalancerBalance equations with coefficients and atom checks.
Frequently Asked Questions
What is the molar mass of CaCO₃?
Approximately 100.09 g/mol. Using IUPAC standard atomic weights, the sum is 1 × 40.078 (calcium) + 1 × 12.011 (carbon) + 3 × 15.999 (oxygen) = 100.086 g/mol, which rounds to 100.09 g/mol.
How do you calculate the molar mass of CaCO₃?
Add one calcium, one carbon, and three oxygen atomic-mass contributions: 40.078 + 12.011 + 47.997 = 100.086 ≈ 100.09 g/mol. In general: read the subscripts in the formula, multiply each element's atomic weight by its atom count, then add the contributions — exactly what the worked example above shows.
What is the formula mass of CaCO₃?
Approximately 100.09 u per formula unit. One formula unit is one Ca²⁺ ion paired with one CO₃²⁻ ion; numerically, formula mass in u and molar mass in g/mol are the same number.
How many atoms are in CaCO₃?
Five in total: one calcium atom, one carbon atom, and three oxygen atoms in every formula unit. The three oxygens belong to the carbonate unit, CO₃²⁻, which travels as a single 2− ion.
What percentage of CaCO₃ is calcium?
About 40% by mass — exactly 40.04% using IUPAC atomic weights (40.078 of 100.086). Carbon contributes 12.00%, and the three oxygens carry the remaining 47.96%, which is why nearly half of any calcium carbonate sample's mass is oxygen.
How many grams are in one mole of CaCO₃?
About 100.09 grams. One mole contains 6.022 × 10²³ formula units, and the molar mass converts that amount directly to mass: 1 mol × 100.09 g/mol = 100.09 g.
What is CaCO₃ called?
Calcium carbonate. The name comes straight from the ions: the Ca²⁺ cation is calcium and the CO₃²⁻ anion is carbonate.
Does CaCO₃ have an atomic number?
No — atomic number is a property of elements, not compounds. The elements inside CaCO₃ each have one: calcium is 20, carbon is 6, and oxygen is 8. A compound like CaCO₃ is identified by its formula, not an atomic number.