Molecular Formula Calculator

Find the molecular formula from empirical formula and molar mass. Determine the true molecular formula by finding the ratio n = molar mass / empirical formula mass.

⚗️ Analysis📐 n = M_molecular / M_empirical🧪 Chemistry
Empirical formula (e.g. CH2O)
Molar mass of compound (g/mol)
Please enter valid values.

Formula & Reference

VariableSymbolFormulaUnits
Molecular Formula Calculator—n = M_molecular / M_empiricalintegers

Step-by-Step Examples

Example 1
Glucose

Empirical formula CH2O, M = 180.16 g/mol.

  • M(CH2O) = 12.011+2(1.008)+15.999 = 30.026
  • n = 180.16/30.026 = 5.999 ~ 6
  • Molecular formula: C6H12O6
✓ Molecular formula = C6H12O6 (glucose)
Example 2
Benzene

Empirical formula CH, M = 78.11 g/mol.

  • M(CH) = 12.011+1.008 = 13.019
  • n = 78.11/13.019 = 6
  • Molecular: C6H6
✓ Molecular formula = C6H6 (benzene)
Example 3
Hydrogen Peroxide

Empirical formula HO, M = 34.01 g/mol.

  • M(HO) = 1.008+15.999 = 17.007
  • n = 34.01/17.007 = 2
  • Molecular: H2O2
✓ Molecular formula = H2O2

Real-World Applications

🧪
Analytical Chemistry
Molecular formula determined from empirical formula (elemental analysis) + molar mass (MS).
💊
Drug Identification
Pharmaceutical identification: molecular formula confirms compound identity.
📚
Organic Chemistry
Structural determination starts with molecular formula from combustion analysis.
🏭
Quality Control
Correct molecular formula ensures correct molar mass calculations in manufacturing.

Common Mistakes to Avoid

⚠️
n must be an integer

n = M_molecular / M_empirical must be a whole number. If not: recheck empirical formula or molar mass.

⚠️
Molar mass from mass spectrometry

Use MS parent ion peak (M+) for molar mass. Exact mass from high-resolution MS.

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Empirical and molecular can be same

If n=1: molecular formula = empirical formula. H2O, CO2, CH4 are both empirical and molecular.

Frequently Asked Questions

What is the difference between empirical and molecular formula? ▾
Empirical: simplest whole-number ratio (CH2O). Molecular: actual atoms per molecule (C6H12O6). n = molecular/empirical mass.
How do I find both empirical and molecular formula? ▾
From combustion analysis: find empirical formula. From mass spectrometry: find molar mass. Divide to find n.
What if n is not exactly an integer? ▾
Round to nearest integer. Small deviations due to rounding in molar mass or impure sample. If n = 2.5 or similar: recheck data.
What are examples where molecular = empirical? ▾
Water H2O, carbon dioxide CO2, methane CH4, glucose could not (C6H12O6 simplifies to CH2O). Any molecule where atoms share no common factor.
How is molar mass measured experimentally? ▾
Mass spectrometry (most accurate). Boiling point elevation or freezing point depression (colligative, less precise). Osmotic pressure. SEC/GPC for polymers.

Related Chemistry Calculators

📊 Empirical Formula📊 Percent Composition⚗️ Molar Mass🔥 Combustion Analysis⚖️ Stoichiometry

Formula Explorer connections

Interpretation: This relationship converts chemical amount, mass, composition or balanced-equation ratios into a reaction quantity. Assumption: Use a balanced reaction, consistent units and the correct molar mass. Purity, side reactions and limiting reagents can change experimental results.

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