CHEM 103 MOLECULAR WEIGHT study guide

A compound is made up of two or more elements combined in a definite ratio that is represented by a molecular formula. Each of these elements has a certain atomic weight, which can be found in the periodic table. The sum of the atomic weights of the atoms in the molecular formula is called the formula weight or molecular weight or formula mass. We will use the term molecular weight for this number in our work. Here are three examples of molecular weight determination: Ca3(PO4)2 Molecular Weight = 3 Ca = 3 x 40.08 = 120.24 2 P = 2 x 30.97 = 61.94 8 O = 8 x 16.00 = 128.00 310.1 8 C3H5O2Cl Molecular Weight = 3 C = 3 x 12.01 = 36.03 5 H = 5 x 1.008 = 5.04 2 O = 2 x 16.00 = 32.00 1 Cl = 1 x 35.45 = 35.45 108.5 2 Al2(SO4)3 Molecular Weight = 2 Al = 2 x 26.98 = 53.96 3 S = 3 x 32.07 = 96.21 12 O = 12 x 16.00 = 192.00 Problem Set #1 1. Na2SO4 = 142.05 Na = 22.99 x 2 = 45.98 S = 32.07 x 1 = 32.07 O = 16 x 4 = 64 2. O2F2 = 70 O = 16 x 2 = 32 F = 19 x 2 = 38 3. Ca(NO3)2 =164.1 Ca = 40.08 x 1 = 40.08 N = 14.01 x 2 = 28.02 O = 16 x 6