Nearly every chemistry calculation that starts in grams runs through molar mass: the mass of one mole of a substance. Type a formula and this calculator adds up its atoms, shows each element’s share of the mass, and turns a mass in grams into moles.
How to Use It
- Type the Chemical Formula exactly as written, capitals included: H2O, Ca(OH)2, Al2(SO4)3.
- For a hydrate, add a period or a middle dot before the water: CuSO4.5H2O.
- Optionally enter a Mass in grams to convert it to moles.
- Press Calculate to see the molar mass and a table of each element’s atoms, mass and percent by mass.
How It Works
Molar mass is the sum, over every element, of its atom count times its atomic weight:
A number after parentheses multiplies everything inside, and a hydrate’s leading number multiplies the water that follows. Moles come from dividing a mass by the molar mass:
The atomic weights are IUPAC’s abridged standard values, such as H = 1.008 and O = 15.999.
Worked Example
Copper(II) sulfate pentahydrate, CuSO₄·5H₂O, has 1 Cu, 1 S, 9 O (4 + 5) and 10 H:
So 25 g of it is .
Tips and Common Mistakes
- Capitals matter. Co is cobalt; CO is carbon monoxide.
- Multiply through parentheses. In Al₂(SO₄)₃, there are 3 sulfur and 12 oxygen atoms.
- Don’t forget the water in a hydrate. Its mass is part of the compound you weigh out.
- Molar mass and molecular weight are the same number, in g/mol and u respectively.
- Round at the end. Keep full atomic weights until the final answer.