% Composition, Empirical and Molecular Formulas notes

Percent Composition % by mass of each element in a compound Formula: Mass of element in a sample Total mass of sample X 100 = % composition

Empirical Formula The symbols of the elements in a compound with subscripts showing the smallest whole-number ratio of the different atoms in a compound. (most reduced form) Example Diborane= B 2 H 6 (molecular formual (actual formula of the compound)) EF for Diborane = BH 3

Steps to calculate EF from % comp 1.Convert % comp data to mass composition (assume out of 100 g) 2.Find moles of each atom 3.Divide moles of each atom by the smallest mole value to give you a ratio 4.Apply ratio to compound.

Molecular formula You already know the molecular formula is the actual formula of a covalent compound. If you have the EF and the molar mass you can determine the molecular formula of a compound.

Steps to determine MF from EF and % comp data. 1.Figure out molar mass of EF. 2.Get the molar mass of MF (given in the problem) 3.Molar mass MF Molar mass EF 4. Multiply answer from step 3 by the EF to give you MF.