1. Chemistry 102 Dr. Don DeCoste 367J Noyes Lab decoste@illinois.edu 3-4 pm Tuesdays and Thursdays By appointment; open door policy http://chem.illinois.edu 1

2. To Do Continue reading Chapter 3. Text homework for Chapter 3. Quiz on Friday (1-3.4) Lon-Capa assignment #1. 2

3. Consider This… Does a methane molecule (CH 4 ) contain more hydrogen or more carbon? 3

4. Calculate… Determine the percent mass of oxygen in each of the following substances: H 2 O (water) H 2 O 2 (hydrogen peroxide) 4

5. Determining a Formula You have some “nitrogen oxide” and you want to figure out what it is (both the formula and the name). You know it is 30.4% nitrogen by mass. N x O y = formula? name? 5

6. Percent Mass Nitrogen in N 2 O 4 Note: we need the molar mass to determine the molecular formula. 6

7. A Question For You… 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. 7

8. Clicker Question Substance AB 2 is 42.86% A by mass. Determine the percent B by mass for substance A 2 B. a) 14.28% B b) 25.00% B c) 28.57% B d) 57.14% B e) I do not know/I can’t get any of the above answers. 8

9. Clicker Question Consider a compound consisting of Co, N, and O that is 32.21% Co and 15.32% N by mass. Is it possible to determine the name of the compound? a) Yes, and it is cobalt nitrate. b) Yes, and it is cobalt(I) nitrate. c) Yes, and it is cobalt(II) nitrate. d) Yes, and it is cobalt(III) nitrate. e) Not without a molar mass. 9

10. Formulas for Ionic Compounds are Empirical Formulas 10

11. Clicker Question You have separate equal mass samples of each of the three compounds listed below. Which sample has the greatest mass of nitrogen? a) Ammonium nitrate b) Nitrogen monoxide c) Magnesium nitride d) I do not know. 11

12. Clicker Question For which of the following is the percent by mass of carbon equal to the percent by mass of oxygen? a) COb) C 8 H 15 O 3 c) C 2 H 4 O 2 d) C 4 H 6 O 3 e) CO 2 12