Chemical Formula Calculator
Analyze molecular formulas, calculate molecular weights, and determine compound properties
Chemical Formula Input
Examples: H2O, C6H12O6, NaCl, H2SO4
Chemical Formula Calculator: Molecular Weight, Composition & Compound Properties
Our Chemical Formula Calculator determines molecular weight, percent composition by mass, empirical formula, and compound type from any chemical formula you enter. Ideal for chemistry students, teachers, lab scientists, and pharmacists working with stoichiometry and molar calculations.
Common Compounds Reference Table
| Compound | Formula | Mol. Weight | Type |
|---|---|---|---|
| Water | H₂O | 18.015 g/mol | Polar covalent |
| Sodium chloride (table salt) | NaCl | 58.44 g/mol | Ionic |
| Glucose (blood sugar) | C₆H₁₂O₆ | 180.16 g/mol | Organic polar |
| Carbon dioxide | CO₂ | 44.01 g/mol | Nonpolar covalent |
| Ammonia | NH₃ | 17.03 g/mol | Polar covalent |
| Sulfuric acid | H₂SO₄ | 98.08 g/mol | Strong acid |
| Ethanol | C₂H₅OH | 46.07 g/mol | Polar organic |
| Aspirin | C₉H₈O₄ | 180.16 g/mol | Organic acid |
| Calcium carbonate (limestone) | CaCO₃ | 100.09 g/mol | Ionic salt |
| Sucrose (table sugar) | C₁₂H₂₂O₁₁ | 342.30 g/mol | Organic polar |
How to Use the Chemical Formula Calculator
- Enter the formula — type the chemical formula using standard notation (e.g., H2O, C6H12O6, Ca(OH)2). Subscripts are entered as regular numbers.
- Verify element recognition — all elements detected are listed with their atomic weights from the IUPAC 2021 atomic weight table.
- Read molecular weight — the molar mass is shown in g/mol (grams per mole), the standard unit for stoichiometry.
- View percent composition — each element's contribution to total mass is shown as a percentage, useful for empirical formula verification.
Example Calculations
Example 1 — Molecular Weight of Glucose (C₆H₁₂O₆)
- C: 6 × 12.011 = 72.066
- H: 12 × 1.008 = 12.096
- O: 6 × 15.999 = 95.994
- Total = 180.156 g/mol
Percent composition: C = 40.0%, H = 6.7%, O = 53.3%
Example 2 — Stoichiometry for Aspirin Synthesis
Making 10 g of aspirin (C₉H₈O₄, MW = 180.16 g/mol):
- Moles of aspirin = 10 ÷ 180.16 = 0.0555 mol
- Requires 0.0555 mol salicylic acid (MW 138.12) = 7.67 g
Frequently Asked Questions
What is molecular weight and why does it matter?
Molecular weight (molar mass) is the mass in grams of one mole (6.022 × 10²³ molecules) of a substance, expressed in g/mol. It is the conversion factor between the number of moles and the mass in grams — fundamental for stoichiometry, preparing solutions of known concentration (molarity), and pharmaceutical dosing calculations.
How do I calculate percentage composition by mass?
For each element, divide (number of atoms × atomic weight) by the total molecular weight, then multiply by 100. For CO₂ (MW = 44.01): %C = (1 × 12.011) ÷ 44.01 × 100 = 27.3%; %O = (2 × 15.999) ÷ 44.01 × 100 = 72.7%. This is useful for verifying lab results against theoretical composition and for determining empirical formulas from combustion analysis.
What is the difference between empirical and molecular formulas?
The empirical formula shows the simplest whole-number ratio of atoms (e.g., CH for benzene). The molecular formula shows the actual number of each atom in one molecule. Benzene's molecular formula is C₆H₆ — six times the empirical formula. To find the molecular formula, divide the known molecular weight by the empirical formula weight to get the multiplier.
What is stoichiometry?
Stoichiometry is the calculation of the quantities of reactants and products in chemical reactions using the balanced equation and molar masses. For example, burning methane: CH₄ + 2O₂ → CO₂ + 2H₂O tells you that 1 mole of CH₄ (16 g) reacts with 2 moles of O₂ (64 g) to produce 1 mole of CO₂ (44 g) and 2 moles of H₂O (36 g). Molar mass is the bridge between atom counts and measurable grams.
How do I identify ionic vs covalent compounds from a formula?
Ionic compounds are typically formed between metals and nonmetals (e.g., NaCl, CaCO₃, Fe₂O₃). Covalent compounds form between nonmetals only (e.g., H₂O, CO₂, NH₃). Polyatomic ions like SO₄²⁻, NO₃⁻, and OH⁻ are groups of covalently bonded atoms that carry charge and often appear in ionic compounds. If a formula contains a metal cation paired with a nonmetal or polyatomic anion, it is ionic.
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