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Calculate the molecular weight (molar mass) of a chemical compound from its formula. Supports parentheses and multi-element formulas.
Molecular Weight:
MW = sum of (atomic mass x count) for each element
Example: H2O = 2(1.008) + 15.999 = 18.015 g/mol
Molecular weight (molar mass) is the sum of the atomic masses of all atoms in a molecule, expressed in grams per mole (g/mol). It equals the mass of one mole (6.022 x 10^23 molecules) of a substance.
Water (H2O) has a molecular weight of 18.015 g/mol: 2 hydrogen atoms (2 x 1.008) plus 1 oxygen atom (15.999).
A mole is the SI unit for amount of substance. One mole contains exactly 6.02214076 x 10^23 particles (Avogadro's number). It allows chemists to count atoms by weighing them.
In a chemical formula, element symbols start with a capital letter followed by optional lowercase letters. Subscript numbers indicate how many atoms of that element are in the molecule. Parentheses group repeated units.
Molecular weight refers to actual discrete molecules, while formula weight is used for ionic compounds (like NaCl) that exist as lattices, not individual molecules. Numerically they are calculated the same way.
Molecular weight is used to convert between mass and moles, to prepare solutions of specific molarity, to determine stoichiometric ratios in reactions, and to identify unknown compounds.