1. Unit V: The Mole Concept

4. The Mole Concept
1 mole =
A really BIG number
1 mole = 6.02 x 1023 molecules = Avagadro’s Number

5. Avagadro’s Number
It was long after Avogadro that the idea of a mole was introduced.
Since a molecular weight in grams (mole) of any substance contains the same number of molecules, then according to Avogadro's Principle, the molar volumes of all gases should be the same.
The number of molecules in one mole is now called Avogadro's number.

6. How big is Avogadro’s number?
An Avogadro's number of standard soft drink cans would cover the surface of the earth to a depth of over 200 miles

7. How big is Avogadro’s number?
One mole of Kit-Kat bars (~1cm thick) piled high would reach 6.02X 1018 km
Pile of Kit-Kat bars is 1 billion times
the radius of the solar system
6 x 109 km

8. How big is Avogadro’s number?
If Aliens came to Earth to distribute $1 mole (Canadian)
Each Canadian would get

9. Mole Redefined
Strictly speaking a mole is the number of carbon atoms in exactly 12 g of carbon having a mass of 12 [C-12 isotopes]

10. Atomic Mass The mass of 1 mole of atoms of an element Eg.
Remember: 1 mole: 6.02 x 1023
Eg.
The mass of 1 mole of “C” atoms is 12.0 g
The mass of 1 mole of “Ca” atoms is 40.1g

11. Molar Mass (Molecular Mass)
The mass in grams of 1 mole of molecules of an element or compound
In most cases the molar mass of an element is the mass shown on the periodic table expressed in grams
Be careful here !!!!

12. Diatomic Elements: Molar Mass
Molar Mass of our diatomic elements will be different from their Atomic Masses
H2(g)
O2(g)
N2(g)
F2(g)
Cl2(g)
Br2(l)
I2(s)

13. Special Elements: Molar Mass
Sometime Phosphorus is P
And Sometimes it is P4
Sometimes sulphur is S
And sometimes it is S8
Assume all the other elements are monatomic

14. Atomic Mass vs. Molar Mass
Element
Symbol
Formula
Atomic
Mass
Molar
Neon Ne
Bromine Br
Silicon Si
Hydrogen H
Iodine I
Iron Fe

15. Atomic Mass vs. Molar Mass
Element
Symbol
Formula
Atomic
Mass
Molar
Neon Ne
20.2
Bromine Br
Br2
79.9
159.8
Silicon Si
28.1
Hydrogen H H2
1.0
2.0
Iodine I I2
126.9
253.8
Iron Fe
55.8

16. Finding the Molar Mass of Compounds
Finding the molar mass of a compound involves:
using the periodic table to look up the mass of every atom involved
Adding up the masses of the atoms and expressing the resulting mass in g/mol

17. Calculating Molar Mass of a Compound
H20
2(1.0) + 1(16.0) = 18.0 g/mol
Note: the units for molar mass = g/mol
All atomic masses on the periodic table are expressed to one decimal place
Therefore, your answers should be expressed to one decimal place as well

18. Finding the Molar Mass of Compounds
Ca(NO3)2
1 Ca: 40.1 g/mol
2 N: 2(14.0 g/mol)
6 O: 6(16.0) g/mol
164.1 g/mol

19. Finding the Molar Mass of Compounds
ammonium phosphate
(NH4)3PO4
3 N: 3(14.0 g/mol)
12 H: 12(1.0 g/mol)
1 P: 1(31.0 g/mol)
4 O: 4(16.0 g/mol)
149.0 g/mol

20. Calculate the Molar Mass
Of ammonium dichromate (NH4)2Cr2O7
252.0 g/mol

21. Hydrated Compounds
Treat water like an element with a molar mass of 18.0g/mol
H20
2(1.0) + 1(16.0) = 18.0 g/mol

22. Find the molar mass of cobalt (II) chloride hexahydrate?
CoCl2 ●6H20
(35.5) (18.0) = g/mol

23. Do Hebden Questions 6 (a-h) and 7 (a-b) on page 80

24. Grams Moles Conversion
Units
MM = molar mass
g = grams
mol = mole
Conversion Factors
MM g
1 mol
1 mol
MM g OR

25. Example 1a: grams  moles
Find the number of moles in a 30.0g sample of NH3
1.76 mol NH3

26. Example 1b: grams  moles
How many moles are present in 6.34 x 10-5 g of K2SO4?
3.64x 10-7 mol of K2SO4

27. Example 1c: grams  moles
Find the number of moles in a 391 g sample of nitrogen dioxide (NO2)
8.50 mol of NO2

28. Example 2a: moles  grams
Find the mass of 2.5 moles of H2O?
45 g of H2O

29. Example 2b: moles  grams
Find the mass of mol of H2O?
5.40 g of H2O

30. Recall
X 1000
X 1000 Kg g mg
÷ 1000
÷ 1000

31. Example 3a: mg  moles 62.6 mg of C12H22O11 = ? moles
Plan: mg  g  mol
mol or 1.83x10-4 mol of C12H22O11

32. Example 3b: mg  moles 14.3 mg of SO2 = ? moles Plan: mg  g  moles
2.23 x 10-4 mol or mol

33. Example 4a: kg  moles 3.6kg of sulphur trioxide = ? mol
44.9 mol or 45 mol of SO3

34. Example 4b: kg  moles 2.75 Kg H2SO4 = ? Moles Plan: kg  g  mol
28.0 mol H2SO4

35. Example 5: moles  mg 0.00462 moles of ammonium chromate= ? mg
702 mg of (NH4)2CrO4

36. Finding the molar mass given mass and moles
Trick to these questions is that there is no formula given – it is an unknown compound containing
MM = mm (g)
moles

37. Example
For a compound of phosphorus and chlorine, it is found that moles of the gas has a mass of 27.5 g
Find the molar mass of the gas
137.5 g/mol

38. Example
Guess molecular formula g/mol
P (31.0)
Cl (35.5)
PCl3

39. Hebden
Do Exercises 8 (a- d, e); 9 (a-f); 10 (a-c) on page 82 of Hebden

40. Unit V: The Mole Concept
V.2. Number of moles and volume of Gas

41. Gases and Moles
The volume occupied by a certain amount of gas depends on the temperature and the pressure
Standard Temperature and Pressure (STP)
Standard temperature 0◦C (273 K)
Standard Pressure kPa (1 atm)

42. Gases and Moles
The volume of one mole of ANY STP is 22.4 Litres

43. ONLY FOR GASES AT STP Gases and Moles 22.4 L 1 mol 1 mol 22.4 L
The Molar STP is
22.4 L
1 mol
1 mol
22.4 L OR
ONLY FOR GASES AT STP

44. Example 1a: Moles  Litres Conversion
Find the volume (L) occupied by moles of CO2 at STP
1.344 L

45. Example 1b: Moles  Litres Conversion
mol NH3 = is ? L at STP
1.46 L NH3

46. Example 1c: Moles  Litres Conversion
3.96 x 10-5 mol N2O4 (g) = ? L at STP
8.87 x 10-4 L or L

47. Example 2a: Litres to Moles Conversion
60.2 L of CO2 (STP) = ? mol
2.69 mol CO2

48. Example 2b: Litres to Moles Conversion
Find the number of moles in a ml sample of NO2 at 0◦C and kPa.
mol

49. Hebden
Do Exercises 11 (a- c); 12 (a-c) on page 83 of Hebden

50. Mass  Moles  Volume
grams
moles
Litres
@STP

51. Mass  Moles  Volume
Find the volume occupied by 22.0 g of CO2 (g) at STP?
Plan: g  mol  L
11.2 L

52. Mass  Moles  Volume 5.463 g CO2 @STP = ? L Plan: g  moles  Litres

53. Volume  Moles Grams 204.6 L NH3 (g) (STP) = ? Grams
Plan: L  mol  g
155 g of NH3 (g)

54. More Practice Find the mass of a 200.00 mL sample of NO2 (g) at STP
Plan: L  mol g
0.41 g

55. More Practice Find the volume occupied by 3.60 kg of fluorine at STP?
Plan: g  mol  L
2122 L

56. Hebden
Do Exercises 22 (b, i); 24 (a, c, g) on page of Hebden

57. Atoms and Molecules A molecule = an atom Ne = Ne
For a monatomic element
A molecule = an atom
Ne = Ne

58. Atoms and Molecules A molecule ≠ an atom Cl2 ≠ Cl
This is not the case for our diatomic elements
A molecule ≠ an atom
Cl ≠ Cl

59. Molecules of Compounds
H2O
Total Atoms in one Molecule
3 Atoms
1 molecule

60. Molecules of Compounds
H2O
How many “H” atoms in one Molecule
2 “H” Atoms
1 molecule

61. Molecules of Compounds
H2O
How many “O” atoms in one Molecule
1 “O” Atoms
1 molecule

62. Atoms and Molecules 2 “N” Atoms 1 “C” Atoms (NH4)2CO3 1 molecule
8 “H” Atoms
1 molecule
1 “C” Atoms
1 molecule
14 Atoms
1 molecule
3 “O” Atoms
1 molecule

63. Moles ↔ Molecules Conversions
How many molecules are there in a mole?
6.02 X 1023 MAN!

64. Moles ↔ Molecules Conversions
6.02 x1023 molecules
1 mol OR
1 mol____
6.02 x1023 molecules

65. Example 1a. Moles  molecules
How many molecules are there in a 0.25 mol sample of CO2?
1.505 X 1023 molecules

66. Example 1b. Moles  molecules
3.00 moles of N2H4 = ? Molecules
1.81 X 1024 molecules

67. Example 2. Molecules  moles
x 1024 molecules of H2O = ? Moles
8.6 moles

68. Moles  Molecules  atoms

69. Molely Practice
Find the number of “H” atoms in 4.0 moles of ammonia (NH3).
Plan: moles  molecules atoms
7.224 x 1024 “H” atoms

70. Find that MOLE!!!!

71. Hebden
Do Exercises 15 (a- d); 16 (a-b); 17 (a-b); 18 (a-c) and 19 on pages of Hebden
Mole Practice Man!