2. Thursday, April 7th : “A” Day Friday, April 8th: “A” Day Agenda
Finish Section 7.1: “Avogadro’s Number & Molar Conversions”
In-Class:
Practice pg. 231: #1-4
Practice pg. 232: #1-3
Concept Review: “Avogadro’s Number & Molar Conversions”: #6-10
Section 7.1 quiz next time…

3. Finish 7.1: “Avogadro’s Number and Molar Conversions”
6.022 X 1023 atoms
1 mole

4. Molar Mass Relates Moles to Grams
Molar mass: the mass in grams of one mole of an element or compound.
Molar mass is numerically equal to the atomic mass of elements (Fe, Al, etc.) and the formula mass of compounds (H2O, CH4, etc. ) and diatomic elements. (O2, F2, etc.)
The units for molar mass are grams
mole

5. Molar mass of water = 18.02 g H2O
Molar Mass Example #1
What is the molar mass of water, H2O?
To determine the molar mass, look up the atomic mass of each element present in the compound and add them up. This is the molar mass.
H = 1.01 g/mol
O = 16.0 g/mol
Molar mass of water = g H2O
1 mole

6. Molar Mass Example #2
What is the molar mass of sulfuric acid, H2SO4? H = 1.01 g/mol S = g/mol O = 16.0 g/mol Molar mass of sulfuric acid = g H2SO4 1 mole

7. So, why do we need to know the molar mass…
Molar mass can be used as a conversion factor in problems converting between mass and amount!!!

8. Converting Number of Particles to Mass
To convert from number of particles to mass, you must use a two-step process:
First, convert number of particles to amount in moles using Avogadro’s number.
Second, convert amount in moles to mass in grams using the molar mass.
Two different conversion factors must be used!

9. Converting Between Mass, Amount, and Number of Particles

10. Sample Problem C, pg. 231 Converting Number of Particles to Mass
Find the mass in grams of 2.44 X 1024 atoms of carbon, whose molar mass is g/mol.
Known: X 1024 atoms of carbon
Unknown: Mass in grams of carbon
Two conversion factors:
1 mole C AND g C
6.022 X 1023 atoms C mole C

11. Sample Problem C, continued Converting Number of Particles to Mass
Step 1: Convert # of particles amount in moles:
2.44 X 1024 C atoms X mole C
6.022 X 1023 atoms C
= moles C
Step 2: Convert amount in moles mass (in grams)
4.05 moles C X g C
1 mole C
= g C

12. Additional Practice
Find the mass in grams of 6.12 X 1014 formula units of rhenium dioxide, ReO2, g/mol.
Known: X 1014 formula units ReO2
Unknown: Mass in grams of ReO2
Two conversion Factors:
1 mole ReO AND g ReO2
6.022 X 1023 form unit ReO mole ReO2

13. = 2.23 X 10 -7 g ReO2 Additional Practice
Step 1: Convert # of particles amount in moles:
6.12 X 1014 form. unit X _1 mol_ReO2__
6.022 X 1023 form. unit ReO2
= 1.02 X mole ReO2
Step 2: Convert amount in moles mass (in grams)
1.02 X mole ReO2 X g ReO2
1 mole ReO2
= 2.23 X g ReO2

14. Converting Mass to Number of Particles
Converting from mass to number of particles is simply the opposite of the previous problems.
To convert from mass to number of particles, you must use a two-step process:
First, convert mass in grams to amount in moles using molar mass.
Second, convert amount in moles to number of particles using Avogadro’s number.
Two different conversion factors must be used!

15. Sample Problem D, pg. 232 Converting Mass to Number of Particles
Find the number of molecules present in 47.5 g of glycerol, C3H8O3. The molar mass of glycerol is g/mol.
Known: g glycerol, C3H8O3
Unknown: # of molecules present
Two conversion factors:
1 mole C3H8O3 AND X 1023 molecules C3H8O3
92.11 g C3H8O mole C3H8O3

16. Sample Problem D, cont. Converting Mass to Number of Particles
Step 1: Convert mass (in grams) amount in moles:
47.5 g C3H8O3 X 1 mole C3H8O3 = mol C3H8O3
92.11 g C3H8O3
Step 2: Convert amount in moles # of molecules:
0.516 mol C3H8O3 X X 1023 molecules C3H8O3
1 mole C3H8O3
= 3.11 X 1023 molecules C3H8O3

17. Additional Practice
Determine the number of atoms present in
54.3 grams of cobalt, Co.
Known: g of cobalt, Co.
Unknown: # of atoms
Two conversion Factors:
1 mole Co AND X 1023 atoms Co
58.93 g Co mole Co

18. = 5.55 X 1023 atoms Co Additional Practice
Step 1: Convert mass (in grams) amount in moles:
54.3 g Co X 1 mol Co = mol Co
58.93 g Co
Step 2: Convert amount in moles # of atoms:
0.921 moles Co X X 1023 atoms Co
1 mole Co
= X 1023 atoms Co

19. In-Class Assignments/Homework You Must SHOW WORK!
Practice pg. 231: #1-4
Practice pg. 232: #1-3
Concept Review: “Avogadro’s Number & Molar Conversions”: #6-10
Section 7.1 quiz next time…