Chemical Composition Mole (mol) – The number equal to the number of carbon atoms in 12.01 grams of carbon. Avogadro’s number – The number of atoms in exactly 12 grams of pure 12C; 6.022 x 1023. One mole of anything contains 6.022 x 1023 units of that substance.

Molar mass – The mass in grams of 1 mol of the substance. Molar Mass of an element is the mass in grams of 6.022 x 1023 atoms. Molar Mass of an compound is the mass in grams of 6.022 x 1023 molecules or units.

% Composition = grams of element of element by mass grams of compound X 100 % Composition = molar mass of element__ of element by molar mass of compound X 100 molar mass

Hydrate – Molecule with water attached to crystalline structure. Ex Hydrate – Molecule with water attached to crystalline structure. Ex. CuSO4 * 5H2O molar mass of H2O % Comp. H2O = molar mass of X 100 hydrate compound

Percent to mass Mass to mole Divide by small Multiply 'til whole Empirical Formula – Expressed the smallest whole-number ratio of the atoms present in a compound. Percent to mass Mass to mole Divide by small Multiply 'til whole

Molecular Formula – The exact formula of a molecule, giving the types of atoms and the number of each. Compare empirical formula mass to known molar mass. Molecular formula = (empirical formula)n n = molar mass empirical formula mass