2. Chapter 11 The Mole A chemists best friend

3.  Counting units in groups is common  Dozen  Case  Gross  Mole - a particular number of atoms, ions, molecules or formula units It is a large number

4. 6.02 X 10 23 Just like dozen = 12 Mole = 6.02 x 10 23 particles

5.  Use atomic masses to 3 significant digits or to the hundredths' place, which ever gives you more digits Avogadro constant - 6.02  10 23 It is an SI standard (symbol = N ) A

6. The Mole- 6.02  10 “things” In chemistry “things” are atoms, ions, molecules, or formula units. 23  One mole of particles has a mass in grams equivalent to that of one particle in atomic mass units 1 mole of particles contains 6.02  10 particles 23

7.  Molar mass- the mass of one mole of molecules, atoms, ions, or formula units Examples:  grams to moles  molecules to grams  grams to atoms

8. Percent Composition- used to identify unknowns Example: Find the percentage composition of aluminum oxide 2 Al atoms = 53.96 u 3 O atoms = 48.00 u 101.96 u % Al = 53.96  100 = 52.92% 101.96 % O = 48.00  100 = 47.08% 101.96 Practice prob pg 331

9. Empirical Formulas The decomposition of 11.47 g of a compound of copper and oxygen yields 9.16 g of copper. What is the empirical formula? 2.31 g oxygen 9.16 g Cu 1 mole Cu =.144 mole Cu 63.55 g Cu 2.31 g O 1 mole O =.144 mole O 16.00 g O Ratio 1:1 hence CuO

10. A compound contains carbon 81.7% and Hydrogen 18.3%. Find the empirical formula 81.7 g C 1 mole C = 6.80 moles C 12.01 g C 18.3 g H 1 mole H = 18.1 moles H 1.01 g H Ratio = 6.81 : 18.1 6.81 6.81 = 1:2.66 = 1:2 3 = 1: 8 3:8 C H 2 3 3 3 3 8 Exercises Pg 333

11.  Molecular Formulas~ Must know molar mass Example: analysis of a compound reveals this composition: 80.0% C 20.0% H Molar mass = 30.0 g What is the molecular formula? 80.0 g C 1 mole C= 6.66 mole C 12.01 g C 20.0 g H 1 mole H = 19.8 mole H 1.01 g H C H 1 3 C2H6C2H6

12. Ascorbic acid, vitamin C, is 40.9% carbon, 4.58% hydrogen and 54.5% oxygen. Its molar mass is 176.1 g/mole. What is the molecular formula?

13. Hydrates ~ water molecules are part of the crystal structure Example: 5.20 g of hydrated BaI 2 is heated. The dry sample has a mass of 4.76 g. What is the formula of the hydrate?.44 g H O 2 5.20 g – 4.76 g =.44 g H O 2

14. 4.76 g BaI 1 mole BaI=.0122 mole BaI 391.13 g BaI 2 2 2.44 g H O 1 mole H O=.024 mole H O 18.02 g H O 2 2 2.0122 mole = 1.00.024 mole = 2.0.0122 2 1:2 RatioBaI 2H O 22

15. Atomic mass unit ( u ) a.m.u. H = 1.01 u O = 16.00 u C = 12.00 u  Molecular Mass- the sum of all the atomic masses of the atoms in a molecule  Formula Mass- used for ionic compounds