1. HW = Study for Wednesday’s Ch 8 Exam a)1.0 mol zinc b)1.0 mol copper c)1.0 mol potassium d)1.0 mol sulfur e)all have the same mass Which of the following has the greatest mass?

2. How many mol of CO 2 are in 3.3 g of carbon dioxide? (a) 145.233 mol (b) 0.075 mol (c) 150 mol (d) 13 mol (e) none of the above

3. 3.3 g CO 2 ( )‏ 1 mol CO2 = 0.075 mol CO 2 44.01 g CO 2 MOLE (mol)‏ Mass (g)‏ Particles (atoms or molecules)‏ How many mol of CO 2 are in 3.3 g of carbon dioxide?

4. How many grams of uranium are in 5.00 X 10 22 atoms of pure uranium? (a) 19.8 g (b) 0.0830 g (c) 0.000349 g (d) 1.19 x 10 25 g (e) none of the above

5. 5.00 x 10 22 atoms U ()‏ 6.022 x 10 23 atoms U 1 mol U ()‏ 1 mol U 238.00g U = 19.8 g U MOLE (mol)‏ Mass (g)‏ Particles (atoms or molecules)‏ How many grams of uranium are in 5.00 X 10 22 atoms of pure uranium?

6. In order to determine the molecular formula of a compound you only need to know its empirical formula? a)True b)False Find n = molar mass = 192.92g/mol empirical mass 95.96 g/mol n = 2

7. To find molecular formula… A. Find empirical formula. B. Find empirical mass C. Find n = molar mass empirical mass D. Multiply all parts of empirical formula by n

8. A compound having an approximate molar mass of 165- 170g/mol has the following percent composition by mass. Determine its molecular formula. 42.87% C 3.598% H 28.55 % O 25.00% N a)C 2 H 2 ON b)C 4 H 4 O 2 N 2 c)C 6 H 6 O 3 N 3 d)CHON e)none of the above

9. = 3.57 mol C = 3.56 mol H = 1.78 mol O / 1.78 mol = 2 C = 2 H = 1 O 42.87% C 3.598% H 28.55% O 42.87g C 3.598g H 28.55g O Step 1) %  gStep 2) g  mol Step 3) mol mol Step 4) return to whole XXXXXX = 1.78 mol N= 1 N/ 1.78 mol 25.00% N 25.00g N C 2 H 2 ON n = molar mass empirical mass = 167g mol = 2.98 56.05 g/mol C6H6O3N3C6H6O3N3

10. Determine the percent composition of sulfuric acid. a) 28.57% H, 14.29 % S, 57.14% O b) 2.055% H, 32.70 % S, 65.25% O c) 1.02% H, 32.70 % S, 16.31% O d) none of the above

11. Determine the percent composition of sulfuric acid. MOLAR MASS of H 2 SO 4 = 98.09 g/mol % H = mass H = 2.02 g. = 0.02055 molar mass 98.09 g 2.055% H, 32.70 % S, 65.25% O % S = mass S = 32.07 g. = 0.3270 molar mass 98.09 g molar mass 98.09 g % H = mass O = 64.00 g. = 0.6525 molar mass 98.09 g

12. Percent Abundance Practice – Part I Silicon has three naturally ocurring stable isotopes, silicon-28, silicon-29 and silicon-30 with respective percent abundances of 92.23%, 4.69% and 3.08%. What is the average atomic mass of silcon? Weighted Average = Value A (%A) + Value B (% B) + Value C (% C) + … 28amu (.9223) + 29amu (.0469) + 30 amu (.0308) = 28.11 amu

13. Percent Abundance Practice – Part II Gallium has an average atomic mass of 69.79 amu and its stable isotopes are 71 Ga and 69 Ga. Find the percent abundances of gallium’s isotopes. 71 Ga 69 Ga Difference between average and each isotope = 1.21 amu and 0.79 amu Difference in mass between 71 Ga and 69 Ga = 2.00 amu 0.79 amu 2.00 amu x 100 = 39.5 % 1.21 amu 2.00 amu x 100 = 60.5 %