1. 3.3b
The Mole

2. POINT > Explain the concept of the mole
POINT > Define Avagadro’s number
POINT > Perform conversions using the mole
POINT > Define molar mass

3. POINT > Explain the concept of the mole
Recall that each element has an atomic mass. For example, the atomic mass of a C atom is U What is the mass of a C atom in grams? Answer: approx. 2 x grams; g

4. POINT > Explain the concept of the moleg
Masses on this scale are not very useful, so chemists invented the mole (mol)
Just like a “dozen” represents a specific number, so does a mole
A mole is the number of atoms in g of carbon
= × 1023

5. POINT > Define Avagadro’s number
A mole is 6.02 × 1023 This is Avagadro’s number Avagadro’s work with gas particles helped inspire the development of the mole How large is this number….?

6. POINT > Define Avagadro’s number
If you had $6.02 x 1023 …
and spent $1,000,000,000 per second
= 6.02 x 1014 seconds
6.02 x 1014 seconds / 60 = x 1013 minutes
1.003 x 1013 minutes / 60 = x 1011 hours
1.672 x 1011 hours / 24 = x 109 days
6.968 x 109 days / = x 107 years
It would take 19 million years

7. WB CHECK:
What is Avagadro’s number?
A mole is what number?

8. POINT > Explain the concept of the mole
1 dozen cookies = 12 cookies 1 mole of cookies = 6.02 x 1023 cookies 1 dozen cars = 12 cars 1 mole of cars = 6.02 x 1023 cars 1 dozen Al atoms = 12 Al atoms 1 mole of Al atoms = 6.02 x 1023 Al atoms Note that the number is always the same, but the mass is very different!

9. POINT > Explain the concept of the mole
We use the mole (mol) as a unit of measure for an amount of a chemical substance
We use the mole to convert between the number of particles and the mass of a substance:
Recall that 6.02 x 1023 atoms of C = 1.0 mol C
Also recall: 12.01g C = 1.0 mol C
We can now convert between number of atoms, grams, and moles

10. POINT > Perform conversions using the mole
We can now convert between number of atoms, grams, and moles using these conversion factors:
1 mol C g C g C mol C
1 mol C x 1023 atoms C x 1023 atoms C mol C

11. POINT > Perform conversions using the mole
Ex. How many carbon atoms are in mol C?
Step 1: we are given mol C
Step 2: we want the number of atoms of C
Step 3: conversion: 1 mole C = 6.02 × 1023 atoms C =
0.120 mol C ×
1 mol C
6.02 × 1023 atoms C
7.22 × 1022 atoms C

12. POINT > Perform conversions using the mole
Ex. How many moles of carbon are in 1.25 × 1021 atoms C?
Step 1: we are given 1.25 × 1021 atoms C
Step 2: we want the number of moles of C
Step 3: conversion : 1 mole C = 6.02 × 1023 atoms C
1.25 × 1021 atoms C ×
1 mol C
6.02 × 1023 atoms C
= 2.08 × 10-3 mol C

13. WB CHECK:
How many atoms in mol C?
3.0 x 1022 C atoms
How many moles is 7.63 x 1024 C atoms?
12.7 moles carbon

14. POINT > Perform conversions using the mole
How many atoms in 2.7 g carbon?
2.7g C x
0.225 mol C x
= 1.4 x 1023 C atoms
1 mol C
= mol C
12.0g C
6.02 x 1023 atoms C
1 mol C
= 1.35 x 1023 atoms C

15. POINT > Perform conversions using the mole
How many grams is 4.9 x carbon atoms?
4.9 x 1026 atoms C x
8.14 x 102 mol C x
= 9.8 x 103 g C
1 mol C
= 8.14 x 102 mol C
6.02 x 1023 atoms C
12.0g C
= 9.77 x 103 g C
1 mol C

16. WB CHECK: How many atoms in 10.0g carbon? 10.0g C x 1 mol C
0.833 mol C x
= 5.01 x C atoms
1 mol C
= mol C
12.0g C
6.02 x 1023 atoms C
= 5.02 x 1023 C atoms
1 mol C

17. POINT > Define molar mass
12.01g carbon = 1.0 mol carbon
12.01g is the molar mass of carbon
The atomic mass of any element in grams = molar mass of the element
Ex. the molar mass of sulfur is 32.06g
32.06g sulfur has 6.02 x 1023 sulfur atoms and is one mole of sulfur

18. WB CHECK:
What is the molar mass of calcium (Ca)?
What is the molar mass of iron?
What is the mass of 2.0 mol helium (He)?
How many zinc atoms are in 65.4g of zinc (Zn)?

19. Homework:
Finish reading Ch 3.3 pages 78-84
Practice #1-4 page 81
#1-3 page 81
#1-3 page 82
#1-3 page 83
F.A. #1-7 page 83