Free tool
Type a chemical formula to get its molar mass in g/mol, plus how many atoms of each element it contains, each element's mass contribution and its mass percent. Parentheses and hydrates work.
Built for General Chemistry ISymbols are case sensitive (Co is cobalt, CO is carbon monoxide). For a hydrate, use a dot or an asterisk: CuSO4·5H2O or CuSO4*5H2O.
Enter a formula such as H2O or Ca(OH)2.
Molar mass is the first step of almost every stoichiometry problem. Encodr keeps the steps on a spaced-repetition schedule so they are automatic by exam day.
Get started freeMolar mass is the mass of one mole of a substance in grams per mole. Add up the atomic weight of every atom
in the formula: molar mass = sum of (number of atoms × atomic weight). A subscript after a
parenthesis multiplies everything inside it, and the coefficient in front of a hydrate's water multiplies the
whole water molecule.
Worked example: Ca(OH)2 has 1 Ca, 2 O and 2 H. That is 40.078 + 2(15.999) + 2(1.008) = 74.092 g/mol. Calcium's mass percent is 40.078 ÷ 74.092 × 100 = 54.09%.
Hydrate example: CuSO4·5H2O is CuSO4 (159.602 g/mol) plus 5 waters (5 × 18.015 = 90.075 g/mol), so 249.677 g/mol. Water is 36.08% of its mass.
Atomic weights here are the IUPAC abridged standard atomic weights (H 1.008, C 12.011, O 15.999), so answers can differ in the second decimal from a textbook that rounds to H 1.01 or O 16.00. Use whatever values your course's periodic table gives on an exam. Next step: turning grams into moles in the stoichiometry walkthrough, and the free General Chemistry I flashcards.
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