Molecular Weight Calculator

Understanding Molecular Weight and Molar Mass

Molecular weight (also called molecular mass or molar mass) is the mass of one molecule of a substance. It is calculated by adding up the atomic weights of all atoms in the molecular formula. This is an essential concept in chemistry for stoichiometry, solution preparation, and chemical reaction calculations.

The Molecular Weight Formula

To calculate the molecular weight of a compound, sum the atomic weights of each element multiplied by the number of atoms of that element in the molecule:

Molecular Weight = Sum of (Atomic Weight x Number of Atoms)

For example, water (H2O) has a molecular weight of 2 x 1.008 + 15.999 = 18.015 g/mol.

How to Use This Calculator

Enter a chemical formula in the molecular formula field. The formula is case-sensitive, so use uppercase for the first letter and lowercase for the second letter of each element symbol. For example, write "H2O" for water, "C6H12O6" for glucose, and "NaCl" for sodium chloride. You can also select common chemicals from the dropdown menu. The calculator will instantly compute the molecular weight and show a detailed breakdown of each element's contribution.

Supported Formula Syntax

The calculator supports standard chemical formula notation including element symbols with subscript numbers, parentheses for polyatomic groups like Al2(SO4)3, and hydrate notation like CuSO4.5H2O. The formula parser correctly handles nested parentheses and calculates the total molecular weight accurately.

Applications of Molecular Weight

Molecular weight is used in many practical applications. Chemists use it to prepare solutions of specific concentrations, determine the composition of unknown compounds, and balance chemical equations. In industry, molecular weight is essential for quality control, pharmaceutical formulation, and material science.

Frequently Asked Questions

How is molecular weight calculated?

Molecular weight is calculated by summing the atomic weights (from the periodic table) of each element in the chemical formula, multiplied by the number of atoms of that element. For water (H2O), this is (2 x 1.008) + 15.999 = 18.015 g/mol.

What is the difference between molecular weight and molar mass?

In most practical contexts, molecular weight and molar mass are used interchangeably. Molecular weight is technically the ratio of the mass of a molecule to the atomic mass constant (dimensionless), while molar mass is the mass of one mole of a substance in grams per mole (g/mol). However, they have the same numerical value.

Why is the formula case-sensitive?

Chemical element symbols are written with an uppercase first letter and lowercase second letter. For example, "Co" is cobalt, while "CO" would mean carbon and oxygen. The calculator follows standard chemical notation to correctly distinguish between different elements.

What atomic weight data does this calculator use?

This calculator uses the standard atomic weights published by IUPAC (International Union of Pure and Applied Chemistry). These are the most widely accepted values used in chemistry and industry worldwide.

Can I calculate molecular weight for hydrates?

Yes, you can enter hydrate formulas like CuSO4.5H2O (copper sulfate pentahydrate). The calculator correctly parses the dot notation and includes the water of crystallization in the total molecular weight.

What is the molecular weight of common salt?

Sodium chloride (NaCl) has a molecular weight of 58.44 g/mol. This comes from adding the atomic weight of sodium (22.99 g/mol) and chlorine (35.45 g/mol).

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