Science & Lab Tools
Molecular Weight Calculator
Calculate the molecular weight (molar mass) of any chemical compound
Enter a chemical formula to calculate its molecular weight
Related to Molecular Weight Calculator
The Molecular Weight Calculator determines the total mass of a molecule by summing the atomic weights of all atoms in the chemical formula. Each element has a specific atomic weight (measured in g/mol), and the calculator uses these standardized values to compute the total molecular weight. The process involves parsing the chemical formula to identify individual elements and their quantities, then multiplying each element's atomic weight by its count in the molecule.
Formula Parsing
The calculator breaks down chemical formulas into their constituent elements and quantities. For example, H2O is parsed as two hydrogen atoms (H×2) and one oxygen atom (O×1). The calculator recognizes both single-letter elements (H, N, O) and two-letter elements (He, Na, Cl).
Calculation Method
For each element identified, the calculator multiplies its standard atomic weight by the number of atoms present. These individual masses are then summed to give the total molecular weight. For example, in H2O: (1.008 × 2) + (15.999 × 1) = 18.015 g/mol.
The molecular weight result is expressed in grams per mole (g/mol), which represents the mass of one mole of the molecule. This value is crucial for various chemical calculations, including stoichiometry, solution preparation, and concentration determinations. The calculator provides both the total molecular weight and a detailed breakdown showing the contribution of each element.
Understanding g/mol
The unit g/mol (grams per mole) indicates how many grams of a substance are present in one mole. One mole contains exactly 6.022 × 10²³ molecules (Avogadro's number). This means that a molecular weight of 18.015 g/mol for water (H2O) indicates that one mole of water molecules weighs 18.015 grams.
1. What is molecular weight?
Molecular weight, also known as molecular mass, is the sum of the atomic weights of all atoms in a molecule. It represents the mass of one mole of molecules and is typically expressed in grams per mole (g/mol).
2. How do I write chemical formulas correctly?
Chemical formulas should be written with correct capitalization (e.g., Na for sodium, not NA or na) and numbers (e.g., H2O for water). Uppercase letters start element symbols, and when present, lowercase letters follow (e.g., Fe for iron, He for helium).
3. Why are molecular weights important?
Molecular weights are essential for calculating quantities in chemical reactions, preparing solutions of specific concentrations, and determining the amount of substance needed in chemical processes. They are fundamental to stoichiometry and chemical analysis.
4. What does g/mol mean?
g/mol (grams per mole) is the standard unit for molecular weight. It represents the mass in grams of one mole of a substance, where a mole is a specific number (6.022 × 10²³) of molecules.
5. What is the scientific source for this calculator?
This calculator uses atomic weights from the International Union of Pure and Applied Chemistry (IUPAC) standards, which are based on extensive scientific measurements and periodic reviews. The atomic weights used are the standard atomic weights as defined by IUPAC's Commission on Isotopic Abundances and Atomic Weights (CIAAW). These values represent the most accurate and internationally accepted measurements of atomic masses, taking into account the natural isotopic composition of elements.