1. MOLAR MASS Molar mass of a substance = mass in grams of one mole of the substance. A compound’s molar mass is NUMERICALLY equal to its formula mass. Formula mass is expressed in atomic mass units (amu) found on the periodic table. Ex. 2 mol H x 1.01 g H = 2.02 g H 1 mol H 1 mol O x 16.00 g O = 16.00 g O 1 mol O molar mass H 2 O = 18.02 g/mol Formula mass H 2 O = 18.02 amu Molar mass H 2 O = 18.02 g/mol

2. Molar Mass Summary Mathematically, formula mass = molar mass. Units are different. It is acceptable to round average atomic mass to 2 decimal places for most applications. Multiply each atom present by its mass and add all masses together to find molar mass.

3. NaCl 1 Na = 23.00 g/mol +1 Cl = 35.45 g/mol 58.45 g/mol MgCl 2 1 Mg = 24.31 g/mol +2 Cl = 70.90 g/mol(2 x 35.45 = 70.90) 95.21 g/mol 11 Na 23.00 Atomic # Symbol Avg. atomic mass 17 Cl 35.45 16 O 16.00 12 Mg 24.31

4. NaClO 3 1 Na = 23.00 g/mol 1 Cl = 35.45 g/mol (3 x 16 = 48) +3 O = 48.00 g/mol 106.45 g/mol Mg(ClO 2 ) 2 1 Mg = 24.31 g/mol (2 x 35.45 = 70.90) +2 Cl = 70.90 g/mol (4 x 16.00 = 64.0) +4 O = 64.00 g/mol 159.21 g/mol 11 Na 23.00 Atomic # Symbol Avg. atomic mass 17 Cl 35.45 16 O 16.00 12 Mg 24.31