1. To Do… http://chem.illinois.edu Lab tomorrow. Read Chapter 13. Lon-Capa (HW2 Type 2 due Wednesday, February 5 by 7 pm). 1

2. Polyatomic Ions Ammonium Nitrate Sulfate Hydroxide Phosphate Carbonate 2

3. The Mole Concept: Why?  We can count by weighing (relative masses).  Reactions occur by number of particles, we must deal with masses, so we must have a way of converting between number and mass.  Atoms/molecules are very small! 3

4. Calculate… You have 50.0 g of water. How many moles of H 2 O molecules do you have? How many moles of hydrogen atoms are present in this sample? 4

5. Consider This… Does a methane molecule (CH 4 ) contain more hydrogen or more carbon? 5

6. Clicker Question Determine the percent by mass of hydrogen in a sample of 2 moles of methane (CH 4 ). a) 12.57% by mass hydrogen b) 25.13% by mass hydrogen c) 50.26% by mass hydrogen d) I have no idea. 6

7. Clicker Question Determine the percent by mass of hydrogen in a sample of 2 moles of methane (CH 4 ). a) 12.57% by mass hydrogen b) 25.13% by mass hydrogen c) 50.26% by mass hydrogen 7

8. Calculate… Determine the percent mass of oxygen in each of the following substances: H 2 O (water) H 2 O 2 (hydrogen peroxide) 8

9. Determining a Formula You have some “nitrogen oxide” compound and you want to figure out what it is (both the formula and the name). You know it’s 30.4% nitrogen by mass. N x O y = formula? name? 9

10. Calculate… Determine the percent mass of nitrogen in: dinitrogen tetroxide 10

11. Calculate… Octane (a constituent of gasoline) is a hydrocarbon (consists only of carbon and hydrogen). It has a molar mass of about 114 g/mol and is 84.12% carbon by mass. Determine the molecular formula for octane. 11

12. Calculate… You have equal masses of each of the following compounds: Sulfuric acid: H 2 SO 4 Sucrose (table sugar): C 12 H 22 O 11 Potassium chlorate: KClO 3 Which one has the greatest number of oxygen atoms? 12

13. Formulas for Ionic Compounds are Empirical Formulas 13