3. Friday, March 21 st : “A” Day Monday, March 24 th : “B” Day Agenda  Homework Questions/Collect  Finish section 7.1…finally!  In-class: Practice pg. 231: #1-4 Practice pg. 232: #1-3  Homework: Practice worksheet pg 24/25 Must SHOW WORK for credit!

4. Homework “Grams/Moles Calculations” worksheet  Questions/Problems?  Hand in

5. Changing Particles Mass  Now that you know how to change particles into moles and moles into mass (in grams), we can put these two steps together to convert from Particles Mass!

6. Changing Particles Mass  You need 2 steps to change number of particles to mass, in grams: 1. Change particles to moles using Avogadro’s number 2. Change moles to mass using the molar mass  Two different conversion factors must be used!

7. Particles Mass Sample Problem C, pg. 231  Find the mass in grams of 2.44 X 10 24 atoms of carbon, whose molar mass is 12.01 g/mol. 1.Start with what you know: 2.44 X 10 24 atoms C 2.Use Avogadro’s number as a conversion factor to change atoms C moles C:  2.44 X 10 24 atoms C X 1 mol C 6.022 X 10 23 atoms C = 4.05 mol C

8. Particles Mass Sample Problem C, pg. 231, cont. 3. Now, use molar mass of carbon to change moles C mass (in grams) of C:  4.05 moles C X 12.01 g C 1 mole C 48.6 g C (3 sig figs)

9. Particles Mass Practice #1  Find the mass in grams of 6.12 X 10 14 formula units of rhenium dioxide, ReO 2, 218.21 g/mol. 1.Start with what you know: 6.12 X 10 14 form. units ReO 2 2.Use Avogadro’s number as a conversion factor to change form. units ReO 2 moles ReO 2 :  6.12 X 10 14 form. units X 1 mol ReO 2 6.022 X 10 23 form. units = 1.02 X 10 -9 mole ReO 2

10. Particles Mass Practice #1, cont. 3. Now, use molar mass of ReO 2 to change moles ReO 2 mass (in grams) of ReO 2 :  1.02 X 10 -9 mole ReO 2 X 218.21 g ReO 2 1 mole ReO 2 2.23 X 10 -7 g ReO 2 (3 sig figs)

11. Changing Mass Particles  Converting from mass to number of particles is simply the opposite of what you’ve just done.  You need 2 steps to change number of particles to mass: 1.Change mass to moles using molar mass 2.Second, change moles to particles using Avogadro’s number  Two different conversion factors must be used!

12. Mass Particles Sample Problem D, pg. 232  Find the number of molecules present in 47.5 g of glycerol, C 3 H 8 O 3. The molar mass of glycerol is 92.11 g/mol. 1.Start with what you know: 47.5 g C 3 H 8 O 3 2. Use molar mass of C 3 H 8 O 3 to change mass C 3 H 8 O 3 moles C 3 H 8 O 3 : 47.5 g C 3 H 8 O 3 X 1 mol C 3 H 8 O 3 =.516 mol C 3 H 8 O 3 92.11 g C 3 H 8 O 3

13. Mass Particles Sample Problem D, cont. 3.Now, use Avogadro’s number to change moles molecules:  0.516 mol C 3 H 8 O 3 X 6.022 X 10 23 molecules C 3 H 8 O 3 1 mole C 3 H 8 O 3 3.11 X 10 23 molecules C 3 H 8 O 3 (3 sig figs)

14. Mass Particles Additional Practice  Determine the number of atoms present in 54.3 grams of cobalt, Co. 1. Start with what you know: 54.3 g Co 2.Use molar mass of Co to change mass Co mole Co:  54.3 g Co X 1 mol Co =.921 mole Co 58.93 g Co

15. Mass Particles Additional Practice, cont. 3.Now, use Avogadro’s number to change moles Co atoms Co:  0.921 moles Co X 6.022 X 10 23 atoms Co 1 mole Co 5.55 X 10 23 atoms Co

16. In-Class Assignments/Homework You Must SHOW WORK!  Practice pg. 231: #1-4  Practice pg. 232: #1-3  Practice worksheet, pg. 24/25  Concept Review: “Avogadro’s Number & Molar Conversions”