Molecular Weight Calculator - Molar Mass & Chemical Formula
Free online molecular weight and molar mass calculator. Intelligently parse chemical formulas with parentheses, polyatomic groups, and hydrates (e.g. Al2(SO4)3, CuSO4·5H2O) using official IUPAC standard atomic weights to generate molar mass and elemental mass percent composition bar charts.
Molecular Weight & Molar Mass Calculator
Parse chemical formulas, calculate molar mass (g/mol), element mass percent composition, and stoichiometric mole conversions.
Enter Chemical Formula
Elemental Mass Composition
| Element | Symbol | Atoms | Atomic Mass | Total Mass | Mass % |
|---|---|---|---|---|---|
| Aluminum | Al | 2 | 26.982 | 53.964 | 15.77% |
| Sulfur | S | 3 | 32.060 | 96.180 | 28.11% |
| Oxygen | O | 12 | 15.999 | 191.988 | 56.12% |
Molecular Weight & Chemical Formula Guide: IUPAC Atomic Weights, Hydrates & Mass Composition
Molecular weight (molar mass) represents the combined atomic masses of all atoms present in a chemical formula, expressed in grams per mole (g/mol). This guide explains chemical formula stoichiometry, polyatomic ions, hydrates, and mass percent composition.
Calculating Molar Mass and Mass Percent Composition
Molar Mass: M_total = Σ (Atom Count_i × Atomic Weight_i)
Elemental Mass % = [ (Atom Count_i × Atomic Weight_i) / M_total ] × 100
Sample Moles = Sample Mass (g) / M_total (g/mol)
Step-by-Step Instructions
Enter Chemical Formula
Input chemical molecular formula using standard elemental symbols and capitalization (e.g. `H2O`, `C6H12O6`, `NaCl`, `CuSO4*5H2O`, `(NH4)2SO4`).
Automatic Formula Parsing & Element Breakdown
The parser resolves nested parentheses, hydrate water crystals (`*5H2O`), and subatomic stoichiometry.
Compute Molar Mass & Elemental Percentage
Review calculated Molecular Weight in grams per mole (`g/mol` or `Da`) with exact elemental mass percentage composition.
Calculate Solute Mass for Solutions
Use the built-in stoichiometry engine to determine exact grams required for preparing molar laboratory solutions.
Key Features & Capabilities
- IUPAC standard atomic weight table integration featuring all 118 elements with high-precision atomic masses
- Advanced chemical formula parser supporting nested parentheses (e.g. `Ca3(PO4)2`), brackets, and crystal hydrates (`FeSO4*7H2O`)
- Mass percentage composition table displaying exact weight contribution and mole ratio for every element in the molecule
- Outputs molar mass in Grams per Mole (`g/mol`), Daltons (`Da`), and Unified Atomic Mass Units (`u`)
- Common chemical presets library (Glucose, Caffeine, Aspirin, Ethanol, Sulfuric Acid, Sodium Hydroxide)
- Instant laboratory-grade precision with step-by-step stoichiometric breakdown
Frequently Asked Questions
What is Molecular Weight (Molar Mass) and how is it calculated?
Molecular Weight (Molar Mass) is the mass of one mole of a chemical substance measured in grams per mole (`g/mol`). It is calculated by summing the standard atomic weights of all constituent atoms in the chemical formula. For example, for Glucose (`C6H12O6`): `(6 * 12.011) + (12 * 1.008) + (6 * 15.999) = 72.066 + 12.096 + 95.994 = 180.156 g/mol`.
How does the parser handle hydrate crystal formulas like CuSO4*5H2O?
The parser recognizes the dot/asterisk notation (`*` or `·`) indicating coordinated water of crystallization. It computes the anhydrous salt (`CuSO4` = 159.61 g/mol) and adds the mass of 5 water molecules (`5 * 18.015 = 90.075 g/mol`), yielding a total molecular weight of 249.685 g/mol.
How is elemental mass percentage (mass fraction) calculated?
The mass percent of an element is: `Mass % = (Total Atomic Mass of Element in Molecule / Total Molecular Weight) * 100`. For water (`H2O`, MW = 18.015 g/mol): Hydrogen is `(2.016 / 18.015) * 100 = 11.19%`, and Oxygen is `(15.999 / 18.015) * 100 = 88.81%`.
What is the difference between Molecular Weight and Formula Weight?
Molecular weight applies strictly to discrete covalent molecules (like `H2O` or `CO2`). Formula weight applies to ionic crystal lattices (like `NaCl` or `CaCO3`) which do not exist as isolated single molecules. However, both are calculated identically and expressed in g/mol.
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