1. Chemical Calculations 7.1-7.7
CHAPTER 7
Chemical Calculations 1

2. The Mole
A number of atoms, ions, or molecules that is large enough to see and handle.
A mole = number of things
Just like a dozen = 12 things
One mole = x 1023 things
Avogadro’s number = x 1023
Symbol for Avogadro’s number is NA. 16

3. The Mole 17

4. The Mole How do we know when we have a mole?
count it out
weigh it out
Molar mass - mass in grams numerically equal to the atomic weight of the element in grams.
H has an atomic weight of g
g of H atoms = x 1023 H atoms
Mg has an atomic weight of g
g of Mg atoms = x 1023 Mg atoms 17

5. The Mole 17

6. The Mole
Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures. 18

7. The Mole
Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures. 19

8. The Mole
Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures. 20

9. The Mole
Example 2-1: Calculate the mass of a single Mg atom, in grams, to 3 significant figures. 21

10. The Mole
Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures. 22

11. The Mole
Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures. 23

12. The Mole
Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures. 24

13. The Mole
Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures. 25

14. The Mole
Example 2-3. How many atoms are contained in 1.67 moles of Mg? 28

15. The Mole
Example 2-3. How many atoms are contained in 1.67 moles of Mg? 28

16. The Mole
Example 2-3. How many atoms are contained in 1.67 moles of Mg? 28

17. The Mole
Example 2-3. How many atoms are contained in 1.67 moles of Mg? 28

18. The Mole
Example 2-3. How many atoms are contained in 1.67 moles of Mg? 28

19. The Mole
Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg?
You do it! 29

20. The Mole
Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? 31

21. The Mole
Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? 31

22. IT IS IMPERATIVE THAT YOU KNOW HOW TO DO THESE PROBLEMS
The Mole
Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg?
IT IS IMPERATIVE THAT YOU KNOW
HOW TO DO THESE PROBLEMS 31

23. Formula Weights, Molecular Weights, and Moles
How do we calculate the molar mass of a compound?
add atomic weights of each atom
The molar mass of propane, C3H8, is: 32

24. Formula Weights, Molecular Weights, and Moles
The molar mass of calcium nitrate, Ca(NO3)2 , is:
You do it! 32

25. Formula Weights, Molecular Weights, and Moles33

26. Formula Weights, Molecular Weights, and Moles
One Mole of Contains
Cl2 or 70.90g x 1023 Cl2 molecules
2(6.022 x 1023 ) Cl atoms
C3H8 You do it! 34

27. Formula Weights, Molecular Weights, and Moles
One Mole of Contains
Cl2 or 70.90g x 1023 Cl2 molecules
2(6.022 x 1023 ) Cl atoms
C3H8 or g x 1023 C3H8 molecules
3 (6.022 x 1023 ) C atoms
8 (6.022 x 1023 ) H atoms 34

28. Formula Weights, Molecular Weights, and Moles
Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane. 38

29. Formula Weights, Molecular Weights, and Moles
Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane. 38

30. Formula Weights, Molecular Weights, and Moles
Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane. 38

31. Formula Weights, Molecular Weights, and Moles
Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane. 38

32. Formula Weights, Molecular Weights, and Moles
Example 2-8. Calculate the number of O atoms in 26.5 g of Li2CO3.
You do it! 40

33. Formula Weights, Molecular Weights, and Moles
Example 2-8. Calculate the number of O atoms in 26.5 g of Li2CO3. 41

34. Percent Composition
% composition = mass of an individual element in a compound divided by the total mass of the compound x 100%
Determine the percent composition of C in C3H8. 45

35. Percent Composition and Formulas of Compounds
What is the percent composition of H in C3H8?
You do it! 46

36. Percent Composition
What is the percent composition of H in C3H8? 47

37. Percent Composition
Example 2-10: Calculate the percent composition of Fe2(SO4)3 to 3 significant figures.
You do it! 48

38. Percent Composition
Example 2-10: Calculate the percent composition of Fe2(SO4)3 to 3 sig. fig. 49

39. Percent Composition 49

40. Empirical and Molecular Formulas
Empirical Formula - smallest whole-number ratio of atoms present in a compound
Molecular Formula - actual numbers of atoms of each element present in a molecule of the compound
We determine the empirical and molecular formulas of a compound from the percent composition of the compound. 50

41. Empirical And Molecular Formulas51

42. Empirical Formulas
Example 2-11: A compound contains 24.74% K, 34.76% Mn, and 40.50% O by mass. What is its empirical formula?
Make the simplifying assumption that we have g of compound.
In g of compound there are:
24.74 g of K
34.76 g of Mn
40.50 g of O 51

43. Empirical Formulas 52

44. Empirical Formulas 53

45. Empirical Formulas 54

46. Empirical Formulas 55

47. Empirical Formulas 56

48. Empirical Formulas
Example 2-12: A sample of a compound contains 6.541g of Co and 2.368g of O. What is empirical formula for this compound?
You do it! 57

49. Empirical Formulas
Example 2-12: A sample of a compound contains 6.541g of Co and 2.368g of O. What is empirical formula for this compound? 58

50. Empirical Formulas
Example 2-12: A sample of a compound contains 6.541g of Co and 2.368g of O. What is empirical formula for this compound? 59

51. Molecular Formulas
Example 2-13: A compound is found to contain 85.63% C and 14.37% H by mass. In another experiment its molar mass is found to be 56.1 g/mol. What is its molecular formula?
short cut method 61

52. Determination of Molecular Formulas62

53. Calculations Based on Chemical Equations

54. Calculations Based on Chemical Equations
Example 3-1: How many CO molecules are required to react with 25 formula units of Fe2O3?

55. Calculations Based on Chemical Equations
Example 3-2: How many iron atoms can be produced by the reaction of 2.50 x 105 formula units of iron (III) oxide with excess carbon monoxide?

56. Calculations Based on Chemical Equations
Example 3-2: How many iron atoms can be produced by the reaction of 2.50 x 105 formula units of iron (III) oxide with excess carbon monoxide?

57. Calculations Based on Chemical Equations
Example 3-2: How many iron atoms can be produced by the reaction of 2.50 x 105 formula units of iron (III) oxide with excess carbon monoxide?

58. Calculations Based on Chemical Equations
Example 3-3: What mass of CO is required to react with 146 g of iron (III) oxide?

59. Calculations Based on Chemical Equations
Example 3-3: What mass of CO is required to react with 146 g of iron (III) oxide?

60. Calculations Based on Chemical Equations
Example 3-3: What mass of CO is required to react with 146 g of iron (III) oxide?

61. Calculations Based on Chemical Equations
Example 3-4: What mass of carbon dioxide can be produced by the reaction of mole of iron (III) oxide with carbon monoxide?

62. Calculations Based on Chemical Equations
Example 3-4: What mass of carbon dioxide can be produced by the reaction of mole of iron (III) oxide with carbon monoxide?

63. Calculations Based on Chemical Equations
Example 3-4: What mass of carbon dioxide can be produced by the reaction of mole of iron (III) oxide with carbon monoxide?

64. Calculations Based on Chemical Equations
Example 3-5: What mass of iron (III) oxide reacted with carbon monoxide if the carbon dioxide produced by the reaction had a mass of 8.65 grams?
You do it!

65. Calculations Based on Chemical Equations
Example 3-5: What mass of iron (III) oxide reacted with carbon monoxide if the carbon dioxide produced by the reaction had a mass of 8.65 grams?

66. Calculations Based on Chemical Equations
Example 3-6: How many pounds of carbon monoxide would react with 125 pounds of iron (III) oxide?
You do it!

67. Calculations Based on Chemical Equations
YOU MUST BE PROFICIENT WITH THESE
TYPES OF PROBLEMS!!!

68. Limiting Reactant Concept
Kitchen example of limiting reactant concept.
1 packet of muffin mix + 2 eggs + 1 cup of milk
12 muffins
How many muffins can we make with the following amounts of mix, eggs, and milk?

69. Limiting Reactant Concept
Mix Packets Eggs Milk
1 1 dozen 1 gallon
limiting reactant is the muffin mix
2 1 dozen 1 gallon
3 1 dozen 1 gallon
4 1 dozen 1 gallon
5 1 dozen 1 gallon
6 1 dozen 1 gallon
7 1 dozen 1 gallon
limiting reactant is the dozen eggs

70. Limiting Reactant Concept
Example 3-7: Suppose a box contains 87 bolts, 110 washers, and 99 nuts. How many sets, each consisting of one bolt, two washers, and one nut, can you construct from the contents of one box?

71. Limiting Reactant Concept
Example 3-8: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g of carbon disulfide with 110. g of oxygen?

72. Limiting Reactant Concept
Example 3-8: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g of carbon disulfide with 110. g of oxygen?

73. Limiting Reactant Concept
Example 3-8: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g of carbon disulfide with 110. g of oxygen?

74. Limiting Reactant Concept
Example 3-8: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g of carbon disulfide with 110. g of oxygen?
Determine which mass makes the most product

75. Limiting Reactant Concept

76. Limiting Reactant Concept
Which is limiting reactant?
Limiting reactant is O2.
What is maximum mass of sulfur dioxide?
Maximum mass is 147 g.

77. Percent Yields from Reactions
Theoretical yield is calculated by assuming that the reaction goes to completion.
Determined from the limiting reactant calculation.
Actual yield is the amount of a specified pure product made in a given reaction.
In the laboratory, this is the amount of product that is formed in your beaker, after it is purified and dried.
Percent yield indicates how much of the product is obtained from a reaction.

78. Percent Yields from Reactions
Example 3-9: A 10.0 g sample of ethanol, C2H5OH, was boiled with excess acetic acid, CH3COOH, to produce 14.8 g of ethyl acetate, CH3COOC2H5. What is the percent yield?

79. Percent Yields from Reactions

80. Percent Yields from Reactions

81. Percent Yields from Reactions