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Molar mass of calcium carbonate

The molar mass of calcium carbonate (CaCO₃) is 100.086 g/mol: the sum of the atomic weights 40.078 + 12.011 + 3 × 15.999. School problems round it to 100 g/mol (Ca = 40, C = 12, O = 16).

CaCO3 calcium carbonate

Molar mass

100.086 g/mol

For school problems (Ca = 40, C = 12, O = 16): 100 g/mol

Breakdown by element

M(CaCO3) = 40.078 + 12.011 + 3 × 15.999 = 100.086 g/mol

The result is rounded to the precision of the least precise atomic weight. Atomic weights from IUPAC (CIAAW). Agrees with PubChem: 100.09 g/mol. PubChem CID 10112

What is calcium carbonate?

Chalk, limestone and marble are made mostly of calcium carbonate. It also builds mollusc shells, eggshells and corals.

CaCO₃ hardly dissolves in water, but it reacts with acids, giving off carbon dioxide. When heated it does not melt: it breaks down into quicklime, CaO, and CO₂, which is how limestone is burned to make lime.

Properties

State at 25 °C
Solid
Density
2.71 g/cm³ calcite
Melting point
does not melt: decomposes on heating
Solubility in water
practically insoluble

Sources: PubChem (HSDB, NIOSH), Wikipedia (CRC Handbook), NIST Chemistry WebBook; each value agrees in two of them.

Molar mass problems with calcium carbonate

For school problems (Ca = 40, C = 12, O = 16): M(CaCO₃) = 100 g/mol

  1. Problem 1

    How many moles are in 150 g of CaCO₃?

    n = m ÷ M = 150 g ÷ 100 g/mol

    Answer: 1.5 mol

  2. Problem 2

    What is the mass of 2 mol of CaCO₃?

    m = n × M = 2 mol × 100 g/mol

    Answer: 200 g

  3. Problem 3

    What is the mass percentage of Ca in CaCO₃?

    w(Ca) = M(Ca) ÷ M(CaCO₃) = 40 ÷ 100 = 0.4

    Answer: 40.0%

  4. Problem 4

    How many Ca²⁺ ions are in 3 mol of CaCO₃?

    N = n × NA = 3 mol × 6.02 × 10²³ mol⁻¹

    Answer: 1.806 × 10²⁴

What is molar mass?

Molar mass M is the mass of one mole of a substance, about 6.022 × 10²³ of its particles. It is measured in grams per mole (g/mol).

To find it, add up the atomic weights of all the atoms in the formula: multiply each element’s atomic weight by its subscript, the number of its atoms. In g/mol, the molar mass equals the relative molecular mass Mr.

For water: M(H₂O) = 2 × 1.0080 + 15.999 = 18.015 g/mol.