⚗️ Molar Mass Calculator

Calculate molecular weight and elemental composition of chemical compounds

⚡ Live calculation enabled
🧪 Common Compounds
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🧬 Visual Formula Builder (Periodic Table)
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📚 How to Use & Examples
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Formula Syntax:

  • Elements: Use element symbols (H, O, C, Na, etc.)
  • Subscripts: Use numbers after elements (H2O, CO2)
  • Coefficients: Leading numbers for multiple molecules (3H2SO4, 2NaCl)
  • Parentheses: For groups: Ca(OH)2, Al2(SO4)3
  • Brackets: For complex groups: [Cu(NH3)4]SO4
  • Hydrates: Use dot (·) for water: CuSO4·5H2O

Examples:

  • Water: H2O → 18.015 g/mol
  • Sulfuric Acid: H2SO4 → 98.079 g/mol
  • 3 moles of Sulfuric Acid: 3H2SO4 → 294.237 g/mol
  • Calcium Hydroxide: Ca(OH)2 → 74.093 g/mol
  • Glucose: C6H12O6 → 180.156 g/mol
  • Copper Sulfate Pentahydrate: CuSO4·5H2O → 249.685 g/mol

Understanding Coefficients:

The coefficient (number before the formula) represents the number of molecules or moles. For example, 3H₂SO₄ means 3 separate molecules of sulfuric acid, so the total mass is 3 × 98.079 = 294.237 g/mol.

📖 What is Molar Mass?
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Definition

Molar mass is the mass of one mole of a substance (chemical element or compound). It is expressed in grams per mole (g/mol). One mole contains exactly 6.022 × 10²³ particles (Avogadro's number), whether they are atoms, molecules, ions, or electrons.

Key Points

  • Unit: Grams per mole (g/mol)
  • Symbol: M or m
  • Purpose: Converts between mass (grams) and amount (moles)
  • Application: Essential for stoichiometry calculations in chemistry

Why is Molar Mass Important?

Molar mass allows chemists to:

  • Convert between grams and moles in chemical reactions
  • Determine the amount of reactants needed in experiments
  • Calculate theoretical yields in chemical synthesis
  • Analyze the composition of unknown substances
  • Prepare solutions with precise concentrations

Formula

Molar Mass = Sum of (Atomic Mass × Number of Atoms)

For all elements in the compound

⚖️ Molar Mass vs. Molecular Weight
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While often used interchangeably, molar mass and molecular weight have subtle differences:

Molar Mass

  • Unit: g/mol (grams per mole)
  • Refers to: Mass of 1 mole
  • Has units: Yes
  • Example: H₂O = 18.015 g/mol
  • Used for: Practical calculations

Molecular Weight

  • Unit: amu or Da (atomic mass units)
  • Refers to: Mass of 1 molecule
  • Has units: Technically, but often unitless
  • Example: H₂O = 18.015 amu
  • Used for: Relative comparisons

📌 Key Insight: Numerically, they are the same! The molar mass in g/mol equals the molecular weight in amu. The difference is mainly in the units and context of use.

Terminology by Substance Type

  • Molecular compounds: Molecular mass or molecular weight (H₂O, CO₂)
  • Ionic compounds: Formula mass or formula weight (NaCl, CaCO₃)
  • Elements: Atomic mass or atomic weight (Fe, Au, C)
  • All substances: Molar mass (universal term)
🧮 How to Calculate Molar Mass - Step by Step
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General Steps

  1. Write the chemical formula of the compound
  2. Identify all elements and count their atoms
  3. Find atomic masses from the periodic table
  4. Multiply atomic mass by number of atoms for each element
  5. Add all values to get total molar mass

Example 1: Water (H₂O)

Step 1: Formula = H₂O

Step 2: Count atoms

  • Hydrogen (H): 2 atoms
  • Oxygen (O): 1 atom

Step 3: Atomic masses

  • H = 1.008 g/mol
  • O = 15.999 g/mol

Step 4: Calculate

  • H: 2 × 1.008 = 2.016 g/mol
  • O: 1 × 15.999 = 15.999 g/mol

Step 5: Total = 2.016 + 15.999 = 18.015 g/mol

Example 2: Sulfuric Acid (H₂SO₄)

Formula: H₂SO₄

Atomic composition:

  • H: 2 atoms × 1.008 = 2.016 g/mol
  • S: 1 atom × 32.06 = 32.06 g/mol
  • O: 4 atoms × 15.999 = 63.996 g/mol

Total: 2.016 + 32.06 + 63.996 = 98.072 g/mol

Example 3: Compound with Parentheses - Calcium Hydroxide Ca(OH)₂

Formula: Ca(OH)₂

Understanding parentheses: The subscript 2 applies to everything inside (OH)

  • Ca: 1 atom
  • O: 1 atom × 2 = 2 atoms
  • H: 1 atom × 2 = 2 atoms

Calculation:

  • Ca: 1 × 40.078 = 40.078 g/mol
  • O: 2 × 15.999 = 31.998 g/mol
  • H: 2 × 1.008 = 2.016 g/mol

Total: 40.078 + 31.998 + 2.016 = 74.092 g/mol

Example 4: Hydrate - Copper(II) Sulfate Pentahydrate CuSO₄·5H₂O

Formula: CuSO₄·5H₂O

Understanding hydrates: Calculate CuSO₄ and 5H₂O separately, then add

Part 1: CuSO₄

  • Cu: 1 × 63.546 = 63.546 g/mol
  • S: 1 × 32.06 = 32.06 g/mol
  • O: 4 × 15.999 = 63.996 g/mol
  • Subtotal: 159.602 g/mol

Part 2: 5H₂O (5 water molecules)

  • H₂O = 18.015 g/mol
  • 5 × 18.015 = 90.075 g/mol

Total: 159.602 + 90.075 = 249.677 g/mol

Example 5: With Coefficient - 3H₂SO₄ (3 moles)

Formula: 3H₂SO₄

Understanding coefficients: Calculate one molecule first, then multiply by coefficient

Step 1: Molar mass of H₂SO₄ = 98.079 g/mol

Step 2: Multiply by coefficient 3

Total: 3 × 98.079 = 294.237 g/mol

💡 Note: This represents the mass of 3 separate molecules of sulfuric acid, which is useful in stoichiometry when balancing chemical equations.

🔬 Real-World Applications
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1. Laboratory Preparation

Problem: How many grams of NaCl are needed to make 1 mole?

Solution: Molar mass of NaCl = 58.443 g/mol, so you need exactly 58.443 grams.

2. Chemical Reactions

Example: 2H₂ + O₂ → 2H₂O

If you have 4 grams of H₂:

  • Molar mass of H₂ = 2.016 g/mol
  • Moles = 4 ÷ 2.016 = 1.98 moles
  • From equation: 1.98 moles H₂ produces 1.98 moles H₂O
  • Mass of water = 1.98 × 18.015 = 35.67 grams

3. Pharmaceutical Industry

Drug manufacturers use molar mass to:

  • Calculate precise dosages
  • Determine active ingredient concentrations
  • Ensure quality control in production

4. Environmental Science

Used to measure:

  • CO₂ emissions (molar mass = 44.01 g/mol)
  • Pollutant concentrations in air and water
  • Chemical composition of samples

5. Forensic Science

Forensic chemists use molar mass calculations to:

  • Identify unknown substances
  • Analyze drug compositions
  • Determine poison concentrations
💡 Tips & Common Mistakes
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✅ Pro Tips

  • Use this calculator! Save time and avoid arithmetic errors
  • Round at the end: Keep full precision during calculation, round final answer
  • Check units: Always include g/mol in your answer
  • Double-check parentheses: Multiply subscripts correctly
  • Use IUPAC values: Atomic masses are standardized (2021 values in this calculator)

❌ Common Mistakes

Mistake 1: Forgetting to multiply by subscripts

Wrong: H₂O = 1.008 + 15.999 = 17.007 g/mol ❌

Right: H₂O = (2 × 1.008) + 15.999 = 18.015 g/mol ✅

Mistake 2: Ignoring parentheses distribution

Wrong: Ca(OH)₂ = 40.078 + 15.999 + (1.008 × 2) ❌

Right: Ca(OH)₂ = 40.078 + (15.999 × 2) + (1.008 × 2) ✅

Mistake 3: Using outdated atomic masses

Atomic masses are periodically updated by IUPAC. Always use current values!

Mistake 4: Confusing coefficient with subscript

2H₂O: Coefficient = 2 molecules of water (2 × 18.015 = 36.030 g/mol)

H₂O₂: Subscript = 1 molecule with 2 oxygen atoms (34.015 g/mol)

🎯 Quick Reference

Compound Formula Molar Mass
Water H₂O 18.015 g/mol
Carbon Dioxide CO₂ 44.009 g/mol
Table Salt NaCl 58.443 g/mol
Glucose C₆H₁₂O₆ 180.156 g/mol
Sulfuric Acid H₂SO₄ 98.079 g/mol

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