Molar Mass & Percent Composition

The mass of 1 mole of an element or compound – The mass in grams from the Periodic Table Unit = grams per mole (g/mol)

Step One – Identify the molecular formula Ex: calcium fluoride Step Two – Determine the number of atoms of each element Ca = F = Step Three – Multiply the atomic mass by the number of atoms Ca = x = F = x = 78.08g/mol CaF

1)PbCl 2 Pb = x = Cl = x = 2)Aluminum sulfate Al = S = O = g/mol Al 2 (SO 4 ) x 2= x 3= x 12= g/mol

3) Copper (II) chloride Cu = x 1 = Cl = x 2 = ) NH 4 Cl N = x 1 = H = 1.01 x 4 = 4.04 Cl = x 1 = g/mol CuCl g/mol

Step One – Identify the molecular formula Ex: iron (III) oxide Step Two – Calculate the molar mass of the compound Fe = x 2 = O = x 3 = Step Three – Divide the mass of the individual elements by the total, then multiply by 100 Fe = O = Fe 2 O g/mol x 100 =69.9% x 100 =30.1%

1)H 2 O 2 H = 1.01 x 2 = 2.02 O = x 2 = )Sn(OH) 4 Sn = x 1 = O = x 4 = H = 1.01 x 4 = g/mol / 34.02x 100= 5.9 % / 34.02x 100 = 94.1 % g/mol / x 100= 63.6 % / x 100= 34.3 % / x 100= 2.2 %