2. The Mole 1

3. Molecular and Formula Mass 2 What is the average atomic mass of the following atoms? What unit is used? Oxygen 16.00amu Zinc 65.38amu Silver 107.87 amu How about oxygen gas, O 2 16.00amu x 2 = 32.00 amu

4. Molecular Mass (used for Covalent compounds) This is the mass of one molecule expressed in unified atomic mass units (amu). It is calculated by adding up the average atomic mass of each atom found in a compound 3

5. Calculate the molecular mass of H 2 O. mass of H 2 O = 2 H + 1 O = (2 x 1.01 amu) + (1 x 16.00 amu) = 18.02 amu Practice 1: Calculate the molecular mass of C 3 H 8. mass of C 3 H 8 = (3 x 12.01 amu) + (8 x 1.01 amu) = 44.11 amu 4

6. Formula Mass (Used for Ionic Compounds) Since ionic compounds do not actually consist of individual molecules, the mass is referred to as formula mass. The smallest unit of an ionic compound is called a formula unit. This is the total mass of each atom written in the formula for an ionic compound expressed in unified atomic mass units (amu) 5

7. Calculate the formula mass of MgO. mass of MgO = 1 Mg + 1 O = (1 x 24.31amu) + (1 x 16.00amu) = 40.31 amu Practice 2: Calculate the formula mass of CaCl 2. mass of CaCl 2 = (1 x 40.08 amu) + (2 x 35.45 amu) = 110.98 amu 6

8. We have a problem! How can you measure 44.01 amu in the lab? We do not have an electronic scale which can measure in amu, only g, kg or lb. 7

9. Introducing the MOLE and Molar Mass In 1811, a chemist named Amedeo Avogadro realized that any convenient quantity of matter must contain an enormous number of chemical entities. 8

10. Josef Loschmidt latter showed that approx. 602 000 000 000 000 000 000 000, or 6.02 x 10 23 atoms was a convenient and measurable number of entities to work with. 9

11. How Big is a Mole? Mole Video 10

12. Grouping Items ItemUnitNumber sockspair2 eggsdozen12 pencilsgross (12 dozen)144 paperream500 entities (atoms, molecules, ions, formula units) mole6.02 x 10 23 11

13. 6.02 x 10 23 This number is called Avogadro’s constant ( N A ) One mole of an entity has 6.02 x 10 23 entities in it. 1 mole = 6.02 x 10 23 entities The symbol for mole is ‘ n ’ not ‘m’ like you would think… because??? 12

14. Why 6.02 x 10 23 ? Many experiments have shown that 6.02 x 10 23 atoms of an element has approx. the same mass in grams, g, as the relative atomic mass in unified atomic mass units, u. ElementAtomic Mass (amu) Molar Mass (g/mol) Argon39.95 amu39.95 g/mol Uranium238.03 amu238.03 g/mol Carbon12.01 amu12.01 g/mol 13

15. Molar Mass is the mass, in grams per mole, of one mole of a substance. The SI unit for molar mass is g/mol. The SI symbol for molar mass is “M”. Example: The mass of an ammonia molecule is 17.04 amu The mass of one mole of ammonia molecules is 17.04 g 14

16. How large is 6.02 x 10 23 ? One mole of pennies would make at least seven stacks that would reach the moon. One mole of TimBits would cover the Earth and be 8 kilometers deep. Astronomers estimate that there is a mole of stars in the Universe. 15

17. Practice 3 What is the molecular mass of glucose? 180.18 amu What is the molar mass of glucose? 180.18 g/mol What is the mass of 1 mole of table salt? 58.44 g What is the mass of 3 moles of table salt? 175.32 g 16

18. Textbook Reference pp. 167 - 171 Assigned Questions p. 168 # 2, 4, 5, 6 p. 170 # 8, 11, 12 17