Molecular Weight Calculator
Enter a chemical formula to calculate its molecular weight (molar mass). The calculator provides an elemental breakdown and mass percentages.
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What is Molecular Weight?
Molecular Weight, also known as **molar mass**, is the mass of one mole of a substance (a chemical element or chemical compound). It is one of the most fundamental concepts in chemistry, providing the critical link between the mass of a substance and the number of molecules or atoms it contains. The standard unit for molecular weight is grams per mole (g/mol).
How to Calculate Molecular Weight Manually
To calculate the molecular weight of a compound, you need a periodic table and the chemical formula. Follow these steps:
- List the elements: Identify every chemical element present in the formula.
- Count the atoms: For each element, count the number of atoms. Remember to multiply by the subscript outside any parentheses. For example, in (NH₄)₂SO₄, there are 2 Nitrogen (N) atoms, 8 Hydrogen (H) atoms, 1 Sulfur (S) atom, and 4 Oxygen (O) atoms.
- Find atomic weights: Look up the atomic weight (also called atomic mass) of each element on the periodic table.
- Multiply and Sum: For each element, multiply its atom count by its atomic weight. Then, add up all these totals to get the final molecular weight of the compound.
Our calculator automates this entire process instantly, parsing the formula and handling all the lookups and calculations for you.
Why is Molecular Weight Important?
- Stoichiometry: It is the basis for all stoichiometric calculations, which relate the quantities of reactants and products in chemical reactions.
- Solution Preparation: It allows chemists to weigh out a specific mass of a compound to create a solution with a desired concentration (molarity). You can perform these calculations with our Molarity Calculator.
- Converting Between Mass and Moles: Molecular weight is the conversion factor between the mass of a substance (in grams) and the amount of substance (in moles). For a tool focused on this, try our Mass Calculator.
- Determining Empirical Formulas: It is used in combination with mass percentage data to determine the simplest whole-number ratio of atoms in a compound.