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Formula Weight

FW = Σ(atomic masses)
Quick Reference
Formula / NotationFW = Σ(atomic masses)
Also Known AsMolar mass, molecular weight, gram formula mass, gram formula weight

What is Formula Weight?

Formula weight (FW) is the sum of the atomic weights of all atoms in the chemical formula of a compound, expressed in atomic mass units (amu) or grams per mole (g/mol). It is equivalent to molar mass for ionic compounds and molecular weight for molecular compounds. Formula weight is used to convert between mass and moles of a substance.

Formula & Notation

FW = Σ(atomic masses)

Other Names / Synonyms: Molar mass, molecular weight, gram formula mass, gram formula weight

Properties & Characteristics

FW = sum of all atomic masses in formula. Units: g/mol or amu. Example: H₂O FW = 2(1.008) + 15.999 = 18.015 g/mol. NaCl FW = 22.990 + 35.453 = 58.443 g/mol. Used interchangeably with molar mass in many contexts. Calculated from periodic table atomic weights.

Uses & Applications

Preparing solutions of known concentration (molarity). Stoichiometric calculations in reactions. Converting mass to moles and vice versa. Analytical chemistry calculations. Pharmaceutical dosing calculations. Quality control in manufacturing.

Safety Information

Theoretical calculation — no direct safety concerns. Accuracy important for preparing reagent solutions of correct concentration.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Formula Weight
Formula FW = Σ(atomic masses)
Synonyms Molar mass, molecular weight, gram formula mass, gram formula weight

Frequently Asked Questions

Formula weight (FW) is the sum of the atomic weights of all atoms in the chemical formula of a compound, expressed in atomic mass units (amu) or grams per mole (g/mol). It is equivalent to molar mass for ionic compounds and molecular weight for molecular compounds. Formula weight is used to convert between mass and moles of a substance.

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