1. Use of Formulae Masses and Moles (but no badgers)

2. Formula Mass Sum of all the average atomic masses of all the atoms in the formula for the compound Example: Find formula mass for potassium chlorate First: find formula!

3. Formula mass problem continued Then: Mass of K: 1 atom/mole x 39.10 amu/atom = 39.10 amu Mass of Cl: 1 atom/mole x 35.45 amu/atom = 35.45 amu Mass of O: 3 atoms/mole x 16.00 amu/atom=48.00 amu Formula mass = 39.10 amu + 35.45 amu + 48.00 amu = 122.55 amu

4. Molar Mass Mass of one mole of the compound Numerical value is equal to formula mass Units are grams!

5. Problem: Find molar mass of barium nitrate First, find formula! Then: Barium: 1 mole x 137.33 g/mole = 137.33 g Nitrogen: 2 mole x 14.01 g/mole = 28.02 g Oxygen: 6 mole x 16.00 g/mole = 96.00 g Sum: 137.33 g + 28.02 g + 96.00 g = 261.35 g/mole

6. Conversion: Molar mass can be used to convert from grams to moles and back again Show all your work! Do Sample problem 7-8 and 7-9