1. CHAPTER 10 THE MOLE

2. The mole is a number (6.02 x 10 23 ) It is a term like the term “dozen” It was chosen by chemists to make working with atomic weights easier. It is the number of atoms in one atomic weight (in grams) of an element. 10.81 grams of boron contains one mole of boron atoms. 1.0 gram of H contains one mole of H atoms.

3. Molecular weights When using atomic weights we can choose the units (AMU/atom or grams/mole) 18 grams of H 2 O contains one mole of water molecules. Molecular weight of H 2 O = grams/mole 1g +1g +16g H +H +O

4. What is the molecular weight of ethanol (C 2 H 6 O)? 2 carbons 12 + 1224 6 H6 (1)6 1 oxygen1616 ----- molecular weight of ethanol =46 g/mole or46 AMU/molecule

5. empirical formula It is the formula of a substance in terms of the lowest combining ratio of the elements. Hydrogen peroxide molecular formula is H 2 O 2 The empirical formula is HO Formulas of ionic compounds are always empirical

6. Experimentally determining an empirical formula Determine the mass of each element in a sample of the compound. From the mass determine the moles of each element. Use the mole ratio of the elements to determine the empirical formula.

7. Example: What is the empirical formula of a liquid if it was found to contain 1.2 grams of hydrogen and 19 grams of oxygen?

8. Avogadro’s relationship Equal volumes of any gas at the same temperature and pressure will have the same number of molecules. One mole of gas at standard temperature and pressure (25 o C, 1 atm) will have a volume of 22.4 L