Molar Mass of Calcium Carbonate (CaCO₃)
Learn how chemists calculate the molar mass of Calcium Carbonate (CaCO₃), with a clear formula breakdown, worked steps, and study notes · IUPAC name: Calcium carbonate.
Quick answer
The molar mass of Calcium Carbonate (CaCO₃) is
100.086g/mol
One mole of Calcium Carbonate therefore has a mass of 100.086 grams—the value you use for stoichiometry and laboratory preparation.
Reviewed for educational accuracy · Accuracy policy
- CAS Registry Number
- 471-34-1
- PubChem CID
- 10112
- SMILES
- [Ca+2].[O-]C(=O)[O-]
Step-by-step calculation
Let's find the molar mass of Calcium Carbonate (CaCO₃) together—step by step, as if you are seeing the formula for the first time.
Step 1 — Look at the chemical formula
The formula is CaCO₃. Each letter stands for an element. The little number after a letter (the subscript) tells you how many atoms of that element are in one molecule or formula unit.
- 1 Calcium atom (Ca)
- 1 Carbon atom (C)
- 3 Oxygen atoms (O)
Step 2 — Look up each atomic mass
Atomic mass comes from the periodic table. It is the average mass of one mole of atoms of that element, in grams per mole (g/mol). Think of it as the "price tag" for one mole of that element.
- Calcium (Ca) = 40.078 g/mol
- Carbon (C) = 12.011 g/mol
- Oxygen (O) = 15.999 g/mol
Step 3 — Multiply atoms × atomic mass
Why multiply? If one oxygen atom "costs" about 16 g/mol, then two oxygen atoms cost twice as much. Each element's contribution is: number of atoms × atomic mass.
- 1 × 40.078 = 40.078 g/mol (Calcium)
- 1 × 12.011 = 12.011 g/mol (Carbon)
- 3 × 15.999 = 47.997 g/mol (Oxygen)
Step 4 — Add the contributions
Why add? The molar mass of the whole compound is simply the total mass of every atom in the formula. Add each element's contribution:
40.078 + 12.011 + 47.997 = 100.086 g/mol
Step 5 — Final answer
Molar mass of Calcium Carbonate = 100.086 g/mol
That means one mole of Calcium Carbonate (CaCO₃) has a mass of about 100.09 grams.
Quick summary
Read the formula → count atoms → look up atomic masses → multiply → add → report g/mol. For CaCO₃, the total is 100.086 g/mol.
Common beginner mistakes
- Assuming CaCO₃ is soluble in water — it is very insoluble (Ksp ≈ 3.3 × 10⁻⁹).
- Forgetting factor of 2 for HCl in acid–carbonate stoichiometry.
- Confusing CaCO₃ (100.09) with CaO (56.08) or Ca(OH)₂ (74.09) molar masses.
Memory trick
Use 100 g/mol round number for quick percent yield from decomposition.
Mini practice
Without looking above, list the atoms in CaCO₃ and write one multiplication line for the heaviest element. Then check your work against Step 3.
Real-world example
If a recipe asks for 0.100 mol of Calcium Carbonate, mass needed = 0.100 × 100.086 = 10.009 g. That is how chemists turn a mole amount into a weighable sample.
Atomic contribution table
Each row shows how much mass one element contributes to the total for CaCO₃.
| Element | Atoms | Atomic mass | Contribution | Mass % |
|---|---|---|---|---|
| Ca | 1 | 40.078 | 40.078 g/mol | 40.0% |
| C | 1 | 12.011 | 12.011 g/mol | 12.0% |
| O | 3 | 15.999 | 47.997 g/mol | 48.0% |
| Total molar mass | 100.086 g/mol | 100% | ||
Mass contribution chart
Teal and blue circles alternate like positive and negative ions in a crystal lattice. Formula mass is the mass of one formula unit, not a single molecule.
Download study sheets
Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Calcium Carbonate (CaCO₃).
Practice this calculation
Without looking above, write the atom count for CaCO₃, then compute the molar mass. Check your answer against 100.086 g/mol.
Next challenge: how many grams are in 0.250 mol of Calcium Carbonate? Multiply 0.250 × 100.086 to get 25.021 g.
Physical and chemical properties
Physical properties
| Appearance | White crystalline solid or powder; marble as polished stone |
| Color | White (pure); colored when impure (iron oxides, organic matter) |
| Odor | Odorless |
| State (STP) | Solid |
| Density | 2.71 g/cm³ (calcite); 2.93 g/cm³ (aragonite) |
| Melting point | Decomposes at ~825–840 °C (no true melting under 1 atm) |
| Boiling point | Decomposes before boiling |
| Solubility | 0.013 g/L water at 25 °C; soluble in acid; more soluble in CO₂-saturated water |
| Crystal structure | Trigonal (calcite, R-3c); orthorhombic (aragonite, Pmcn) |
Chemical properties
| Classification | Ionic carbonate salt / alkaline earth carbonate |
| Family | Group 2 carbonate (alkaline earth carbonate) |
| Basicity | Weakly basic (carbonate anion hydrolyzes water) |
| Polarity | Ionic |
| Oxidation states | Ca: +2, C: +4, O: −2 |
Applications
Industrial uses
- Portland cement manufacture (limestone + clay heated in kiln)
- Paper filler and coating pigment
- Construction aggregate and dimension stone (marble)
- Flue gas desulfurization (scrubbing SO₂)
Laboratory uses
- Primary standard for EDTA titrations (after drying)
- CO₂ generation by acid addition
- Demonstration of thermal decomposition and polymorphism
Ocean acidification threatens CaCO₃ shell formation; geological carbon storage as carbonate minerals; limestone neutralizes acid rain in soils.
Eggshells, snail shells, coral reefs, and foraminifera tests are predominantly CaCO₃; antacid (Tums) neutralizes stomach HCl.
Preparation and production
Mining natural limestone deposits. Precipitated CaCO₃ by combining Ca(OH)₂ with CO₂: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. Laboratory: precipitate from CaCl₂ + Na₂CO₃.
Global limestone production exceeds 3 billion tonnes annually. Precipitated calcium carbonate (PCC) is synthesized for paper and plastics with controlled particle size.
Important reactions of Calcium Carbonate
CaCO₃(s) + 2 HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
- Reaction type
- Acid–carbonate
- Conditions
- Room temperature, dilute acid
- Explanation
- Strong acid protonates carbonate, decomposing to CO₂ and water — definitive carbonate test with effervescence.
- Products
- Calcium chloride, water, carbon dioxide
- Why it matters
- CO₂ preparation, carbonate identification, antacid action
Related ideas: Gas evolution · Qualitative analysis · Stoichiometry
CaCO₃(s) → CaO(s) + CO₂(g)
- Reaction type
- Thermal decomposition (calcination)
- Conditions
- ~900 °C in lime kiln
- Explanation
- High temperature breaks ionic lattice, releasing CO₂ and forming quicklime (CaO) — endothermic, ΔH ≈ +178 kJ/mol.
- Products
- Calcium oxide (quicklime) and carbon dioxide
- Why it matters
- Cement and lime production, historical mortar
Related ideas: Thermal decomposition · Industrial chemistry · Mass loss calculations
CaCO₃(s) + CO₂(g) + H₂O(l) → Ca(HCO₃)₂(aq)
- Reaction type
- Carbonation (soluble bicarbonate formation)
- Conditions
- Water containing dissolved CO₂
- Explanation
- Rainwater with dissolved CO₂ dissolves limestone slowly, forming caves and karst topography; process reverses when CO₂ degasses.
- Products
- Calcium bicarbonate (soluble)
- Why it matters
- Cave formation, hard water chemistry, stalactite/stalagmite deposition
Related ideas: Equilibrium · Geochemistry · Solubility
CaCO₃(s) → Ca²⁺(aq) + CO₃²⁻(aq)
- Reaction type
- Dissolution equilibrium
- Conditions
- Aqueous, 25 °C
- Explanation
- Very sparingly soluble; Ksp = 3.3 × 10⁻⁹ governs carbonate concentration in saturated solutions.
- Products
- Calcium and carbonate ions
- Why it matters
- Water hardness, scaling in pipes, ocean chemistry
Related ideas: Solubility product · Equilibrium · Precipitation
History and discovery
Limestone used in pyramids (~2580 BCE). Lavoisier studied CO₂ from acid–carbonate reactions. Geological understanding of chalk formations linked to marine microorganisms in the 19th century.
Known since prehistoric use of limestone; chemical composition established through acid reaction producing 'fixed air' (CO₂) studied by Black and Lavoisier.
Interesting facts
- CaCO₃ molar mass ~100 g/mol makes stoichiometry convenient — 100 g = 1 mol.
- The White Cliffs of Dover are compacted coccolithophore CaCO₃ from Cretaceous seas.
- Marble and limestone are both CaCO₃ — marble is metamorphosed, recrystallized limestone.
- Hard-boiled eggs sometimes show green ring (ferrous sulfide) unrelated to CaCO₃ shell (~94% CaCO₃).
Comparison with similar compounds
CaCO₃ (100.09 g/mol) decomposes at ~840 °C; MgCO₃ (84.31 g/mol) decomposes at lower temperature (~540 °C) due to smaller cation polarizing carbonate less.
Storage, handling, and safety
Stable indefinitely in dry conditions. Avoid prolonged exposure to acidic atmospheres (CO₂ + moisture forms soluble bicarbonate on surface).
Low toxicity. Dust may irritate lungs (silicosis risk if contaminated with silica in mined limestone). Eye protection when handling powder.
Generally non-toxic; used as food additive (E170) and antacid. Dust inhalation may irritate respiratory tract.
- Respiratory irritation from fine dust
- Eye irritation from powder
- Thermal hazard during calcination (releases CO₂ at high temperature)
Classification: Not classified as hazardous (pure CaCO₃)
Exam notes and student tips
Exam notes
- Molar mass CaCO₃ = 40.08 + 12.01 + 3(16.00) = 100.09 g/mol.
- Acid test: CaCO₃ + 2 HCl → CaCl₂ + H₂O + CO₂ (effervescence).
- Thermal decomposition: CaCO₃ → CaO + CO₂ (mass loss = 44 g CO₂ per 100 g CaCO₃).
- Percent composition: Ca 40.0%, C 12.0%, O 48.0%.
Student tips
- Use 100 g/mol round number for quick percent yield from decomposition.
- Link acid test CO₂ to limewater turbidity for complete identification chain.
- Remember calcite vs. aragonite as polymorphs — same molar mass, different density.
Common mistakes
- Assuming CaCO₃ is soluble in water — it is very insoluble (Ksp ≈ 3.3 × 10⁻⁹).
- Forgetting factor of 2 for HCl in acid–carbonate stoichiometry.
- Confusing CaCO₃ (100.09) with CaO (56.08) or Ca(OH)₂ (74.09) molar masses.
Misconceptions
- Chalkboard chalk is often gypsum (CaSO₄·2H₂O), not CaCO₃ — true chalk is CaCO₃.
- CaCO₃ antacids do not ' absorb' acid — they neutralize HCl chemically.
- All limestone is pure CaCO₃ — dolomite contains MgCO₃ as well.
Practice questions
1. Calculate the molar mass of CaCO₃.
Show answer
40.08 + 12.01 + 3(16.00) = 100.09 g/mol
2. What mass of CO₂ from complete decomposition of 50.0 g CaCO₃?
Hint: 1:1 mole ratio; CO₂ molar mass 44.01 g/mol.
Show answer
50.0 g ÷ 100.09 g/mol = 0.500 mol CaCO₃ → 0.500 mol CO₂ = 22.0 g
3. How many mL of 2.0 M HCl to react with 10.0 g CaCO₃?
Show answer
10.0 g ÷ 100.09 g/mol = 0.100 mol CaCO₃; needs 0.200 mol HCl; 0.200/2.0 = 0.100 L = 100 mL
4. Why do antacid tablets fizz in water?
Show answer
Some formulations include carbonate/bicarbonate that react with acid; pure CaCO₃ fizzes with stomach HCl, not necessarily in plain water.
Frequently asked questions about Calcium Carbonate
100.09 g/mol.
Chemistry of Calcium Carbonate
The sections above give the number you need for calculations. Here we look more closely at how Calcium Carbonate (CaCO₃) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.
Calcium carbonate (CaCO₃) is an ionic compound with molar mass 100.09 g/mol (Ca 40.08 + C 12.01 + 3 × 16.00), the principal mineral in limestone, chalk, and marble. It crystallizes primarily as calcite (trigonal) or aragonite (orthorhombic), polymorphs with identical formula but different crystal packing — aragonite is denser and less stable at surface conditions, converting to calcite over geological time.
CaCO₃ reacts with acids to release CO₂: CaCO₃ + 2 HCl → CaCl₂ + H₂O + CO₂ — the effervescence test for carbonates. It undergoes thermal decomposition above ~840 °C: CaCO₃ → CaO + CO₂ (lime production). In oceans, CaCO₃ forms shells and coral skeletons; rising CO₂ lowers pH and threatens calcifying organisms through reduced carbonate ion availability (ocean acidification).
CaCO₃ contains Ca²⁺ and CO₃²⁻ ions in a 1:1 ratio. The carbonate ion is planar with sp² hybridized carbon and three equivalent C–O bonds (resonance). The formula unit represents one calcium ion paired with one carbonate ion in the crystal lattice.
CaCO₃ is basic ( carbonate hydrolyzes water slightly) and reacts with strong acids. It is insoluble in pure water (~0.013 g/L at 25 °C) but solubility increases in acidic conditions and in water containing dissolved CO₂ (forms soluble calcium bicarbonate). It does not decompose at room temperature but calcines to quicklime (CaO) industrially.
Limestone and marble: one compound, two rocks
Limestone and marble are both composed almost entirely of CaCO₃, but limestone is a sedimentary rock formed from compacted marine shell and skeletal debris, while marble is metamorphosed limestone that has recrystallized under heat and pressure into a denser, more uniformly crystalline stone prized for sculpture and construction — the same chemical formula producing dramatically different textures and uses depending purely on geological history.
Antacid neutralization and CO₂ release
Calcium carbonate antacids (such as Tums) neutralize excess stomach acid through the reaction CaCO₃ + 2 HCl → CaCl₂ + H₂O + CO₂, and the carbon dioxide byproduct is responsible for the occasional burping sensation some people notice after taking calcium-carbonate-based antacid tablets — a direct, everyday illustration of the same acid-carbonate chemistry used in laboratory qualitative tests.
Hard water and calcium carbonate scale formation
Water hardness is largely measured in terms of dissolved calcium (and magnesium) carbonate/bicarbonate content; when hard water is heated or its dissolved CO₂ escapes, calcium bicarbonate reverts to insoluble CaCO₃, precipitating as the familiar limescale that builds up in kettles, pipes, and water heaters — the reverse of the same dissolution equilibrium that carves limestone caves underground.
The CO₂ effervescence test as a universal carbonate fingerprint
Because virtually all metal carbonates release CO₂ gas when treated with acid, the vigorous fizzing observed when acid contacts CaCO₃ (limestone, chalk, or marble) serves as one of the most reliable and visually unambiguous qualitative tests in introductory chemistry and geology, used both in classroom demonstrations and in the field to quickly identify carbonate rocks and minerals.
Recalculate any formula with the molar mass calculator, compare atoms on the periodic table, or browse more compounds in the salt library.
References and further reading
- USGS: Limestone and crushed stone statistics
- NIST Chemistry WebBook: CaCO₃ thermodynamic data
- PubChem CID 10112: Calcium carbonate identifiers