1. Molar Mass = mass in grams of one mole –Units grams/mole Molar Mass = atomic mass Why aren’t all atomic masses whole numbers? –Remember that atomic masses are averages of all the isotopes H 1.0 C 12.0 O 16.0 Mg 24.3

2. Molecular mass = protons + neutrons = amu (amu = atomic mass units) Hydrogen atom has 1 proton = 1 amu Oxygen atom has 8 protons and 8 neutrons = 16 amu

3. Calculate the molar mass HCl(think H 1 Cl 1 ) 1* 1.0 + 1* 35.5 = 36.0 g/mol Al 2 O 3 2 * 27.0 + 3 * 16.0 = 102 g/mol C 25 H 52 25 * 12.0 + 52 * 1.0 = 352 g/mol C 6 H 12 O 6 6 * 12.0 + 12 * 1.0 + 6 * 16.0 = 180 g/mol Mg(ClO 3 ) 2 1* 24.3 + 2 * 35.5 + 6 * 16.0 = 191.3 g/mol

4. Calculate the molar mass K 3 PO 4 212.3 g/mol Ca 3 (PO 4 ) 2 310.3 g/mol H 2 SO 4 98.1 g/mol (NH 4 ) 3 PO 4 149 g/mol BaSO 4 233.4 g/mol

5. Now we can use molar mass to convert between moles and grams Particles (atoms or molecules) Moles Avogadro’s Number 6.02 x 10 23 particles/mole ÷ x

6. How many grams are in 2 moles of carbon? –Molar mass of carbon = atomic mass = 12 g/mol How many moles are in 27 grams of water? –Molar mass of water = 2 x 1.0 + 1 x 16.0 = 18.0 g/mol –Essentially what you have 27 ÷ 18 = 1.5 moles