1. Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Introductory Chemistry, 3 rd Edition Nivaldo Tro Chapter 6 Chemical Composition 2009, Prentice Hall

2. Tro's "Introductory Chemistry", Chapter 6 2 Why Is Knowledge of Composition Important? Everything in nature is either chemically or physically combined with other substances. To know the amount of a material in a sample, you need to know what fraction of the sample it is. Some Applications: The amount of sodium in sodium chloride for diet. The amount of iron in iron ore for steel production. The amount of hydrogen in water for hydrogen fuel. The amount of chlorine in freon to estimate ozone depletion.

3. Tro's "Introductory Chemistry", Chapter 6 3 Counting Nails by the Pound I want to buy a certain number of nails for a project, but the hardware store sells nails by the pound. How do I know how many nails I am buying when I buy a pound of nails? Analogy: How many atoms in a given mass of an element?

4. Tro's "Introductory Chemistry", Chapter 6 4 Counting Nails by the Pound, Continued A hardware store customer buys 2.60 pounds of nails. A dozen nails has a mass of 0.150 pounds. How many nails did the customer buy? 1 dozen nails = 0.150 lbs. 12 nails = 1 dozen nails Solution map:

5. Tro's "Introductory Chemistry", Chapter 6 5 Counting Nails by the Pound, Continued The customer bought 2.60 lbs of nails and received 208 nails. He counted the nails by weighing them!

6. Tro's "Introductory Chemistry", Chapter 6 6 Counting Nails by the Pound, Continued What if he bought a different size nail? Would the mass of a dozen be 0.150 lbs? Would there still be 12 nails in a dozen? Would there be 208 nails in 2.60 lbs? How would this effect the conversion factors?

7. Tro's "Introductory Chemistry", Chapter 6 7 Counting Atoms by Moles If we can find the mass of a particular number of atoms, we can use this information to convert the mass of an element sample to the number of atoms in the sample. The number of atoms we will use is 6.022 x 10 23 and we call this a mole. 1 mole = 6.022 x 10 23 things.  Like 1 dozen = 12 things. Avogadro’s number.

8. Tro's "Introductory Chemistry", Chapter 6 8 Chemical Packages—Moles Mole = Number of things equal to the number of atoms in 12 g of C-12. 1 atom of C-12 weighs exactly 12 amu. 1 mole of C-12 weighs exactly 12 g. In 12 g of C-12 there are 6.022 x10 23 C-12 atoms.

9. Tro's "Introductory Chemistry", Chapter 6 9 Example 6.1—A Silver Ring Contains 1.1 x 10 22 Silver Atoms. How Many Moles of Silver Are in the Ring? Since the number of atoms given is less than Avogadro’s number, the answer makes sense. 1 mol = 6.022 x 10 23 atoms 1.1 x 10 22 atoms Ag moles Ag Check: Solution: Solution Map: Relationships: Given: Find: atoms Agmol Ag

10. Tro's "Introductory Chemistry", Chapter 6 10 Example 6.1: A silver ring contains 1.1 x 10 22 silver atoms. How many moles of silver are in the ring?

11. Tro's "Introductory Chemistry", Chapter 6 11 Example: A silver ring contains 1.1 x 10 22 silver atoms. How many moles of silver are in the ring? Write down the given quantity and its units. Given:1.1 x 10 22 Ag atoms

12. Tro's "Introductory Chemistry", Chapter 6 12 Write down the quantity to find and/or its units. Find: ? moles Information: Given:1.1 x 10 22 Ag atoms Example: A silver ring contains 1.1 x 10 22 silver atoms. How many moles of silver are in the ring?

13. Tro's "Introductory Chemistry", Chapter 6 13 Collect needed conversion factors: 1 mole Ag atoms = 6.022 x 10 23 Ag atoms. Information: Given:1.1 x 10 22 Ag atoms Find:? moles Example: A silver ring contains 1.1 x 10 22 silver atoms. How many moles of silver are in the ring?

14. Tro's "Introductory Chemistry", Chapter 6 14 Write a solution map for converting the units: Information: Given:1.1 x 10 22 Ag atoms Find:? moles Conversion Factor: 1 mole = 6.022 x 10 23 Example: A silver ring contains 1.1 x 10 22 silver atoms. How many moles of silver are in the ring? atoms Ag moles Ag

15. Tro's "Introductory Chemistry", Chapter 6 15 Apply the solution map: = 1.8266 x 10 22 moles Ag = 1.8 x 10 22 moles Ag Significant figures and round: Information: Given:1.1 x 10 22 Ag atoms Find:? moles Conversion Factor: 1 mole = 6.022 x 10 23 Solution Map: atoms  mole Example: A silver ring contains 1.1 x 10 22 silver atoms. How many moles of silver are in the ring?

16. Tro's "Introductory Chemistry", Chapter 6 16 Check the solution: 1.1 x 10 22 Ag atoms = 1.8 x 10 -2 moles Ag The units of the answer, moles, are correct. The magnitude of the answer makes sense since 1.1 x 10 22 is less than 1 mole. Information: Given:1.1 x 10 22 Ag atoms Find:? moles Conversion Factor: 1 mole = 6.022 x 10 23 Solution Map: atoms  mole Example: A silver ring contains 1.1 x 10 22 silver atoms. How many moles of silver are in the ring?

17. Tro's "Introductory Chemistry", Chapter 6 17 Practice—Calculate the Number of Atoms in 2.45 Mol of Copper.

18. Tro's "Introductory Chemistry", Chapter 6 18 Practice—Calculate the Number of Atoms in 2.45 Mol of Copper, Continued. Since atoms are small, the large number of atoms makes sense. 1 mol = 6.022 x 10 23 atoms 2.45 mol Cu atoms Cu Check: Solution: Solution Map: Relationships: Given: Find: mol Cuatoms Cu

19. Tro's "Introductory Chemistry", Chapter 6 19 Relationship Between Moles and Mass The mass of one mole of atoms is called the molar mass. The molar mass of an element, in grams, is numerically equal to the element’s atomic mass, in amu. The lighter the atom, the less a mole weighs. The lighter the atom, the more atoms there are in 1 g.

20. Tro's "Introductory Chemistry", Chapter 6 20 Mole and Mass Relationships 1 mole carbon 12.01 g 1 mole sulfur 32.06 g

21. Tro's "Introductory Chemistry", Chapter 6 21 Example 6.2—Calculate the Moles of Sulfur in 57.8 G of Sulfur. Since the given amount is much less than 1 mol S, the number makes sense. 1 mol S = 32.07 g 57.8 g S mol S Check: Solution: Solution Map: Relationships: Given: Find: g Smol S

22. Tro's "Introductory Chemistry", Chapter 6 22 Example 6.2: Calculate the number of moles of sulfur in 57.8 g of sulfur.

23. Tro's "Introductory Chemistry", Chapter 6 23 Example: Calculate the number of moles of sulfur in 57.8 g of sulfur. Write down the given quantity and its units. Given:57.8 g S

24. Tro's "Introductory Chemistry", Chapter 6 24 Write down the quantity to find and/or its units. Find: ? moles S Information: Given:57.8 g S Example: Calculate the number of moles of sulfur in 57.8 g of sulfur.

25. Tro's "Introductory Chemistry", Chapter 6 25 Collect needed conversion factors: 1 mole S atoms = 32.07 g Information: Given:57.8 g S Find:? moles S Example: Calculate the number of moles of sulfur in 57.8 g of sulfur.

26. Tro's "Introductory Chemistry", Chapter 6 26 Write a solution map for converting the units: Information: Given:57.8 g S Find:? moles S Conversion Factor: 1 mole S = 32.07 g g S moles S Example: Calculate the number of moles of sulfur in 57.8 g of sulfur.

27. Tro's "Introductory Chemistry", Chapter 6 27 Apply the solution map: = 1.802307 moles S = 1.80 moles S Significant figures and round: Information: Given:57.8 g S Find:? moles S Conversion Factor: 1 mole S = 32.07 g Solution Map:g  moles Example: Calculate the number of moles of sulfur in 57.8 g of sulfur.

28. Tro's "Introductory Chemistry", Chapter 6 28 Check the solution: 57.8 g sulfur = 1.80 moles sulfur The units of the answer, moles, are correct. The magnitude of the answer makes sense since 57.8 g is more than 1 mole. Information: Given:57.8 g S Find:? moles S Conversion Factor: 1 mole S = 32.07 g Solution Map:g  moles Example: Calculate the number of moles of sulfur in 57.8 g of sulfur.

29. Tro's "Introductory Chemistry", Chapter 6 29 Practice—Calculate the Moles of Carbon in 0.0265 g of Pencil Lead.

30. Tro's "Introductory Chemistry", Chapter 6 30 Practice—Calculate the Moles of Carbon in 0.0265 g of Pencil Lead, Continued. Since the given amount is much less than 1 mol C, the number makes sense. 1 mol C = 12.01 g 0.0265 g C mol C Check: Solution: Solution Map: Relationships: Given: Find: g Cmol C

31. Tro's "Introductory Chemistry", Chapter 6 31 Example 6.3—How Many Aluminum Atoms Are in a Can Weighing 16.2 g? Since the given amount is much less than 1 mol Cu, the number makes sense. 1 mol Al = 26.98 g, 1 mol = 6.022 x 10 23 16.2 g Al atoms Al Check: Solution: Solution Map: Relationships: Given: Find: g Almol Alatoms Al

32. Tro's "Introductory Chemistry", Chapter 6 32 Example 6.3: How many aluminum atoms are in an aluminum can with a mass of 16.2 g?

33. Tro's "Introductory Chemistry", Chapter 6 33 Example: How many aluminum atoms are in an aluminum can with a mass of 16.2 g? Write down the given quantity and its units. Given:16.2 g Al

34. Tro's "Introductory Chemistry", Chapter 6 34 Write down the quantity to find and/or its units. Find: ? atoms Al Information: Given:16.2 g Al Example: How many aluminum atoms are in an aluminum can with a mass of 16.2 g?

35. Tro's "Introductory Chemistry", Chapter 6 35 Collect needed conversion factors: 1 mole Al atoms = 26.98 g Al 1 mole = 6.022 x 10 23 Information: Given:16.2 g Al Find:? atoms Al Example: How many aluminum atoms are in an aluminum can with a mass of 16.2 g?

36. Tro's "Introductory Chemistry", Chapter 6 36 Write a solution map for converting the units: g Almol Alatoms Al Information: Given:16.2 g Al Find:? atoms Al Conversion Factors: 1 mol Al = 26.98 g 1 mol = 6.022 x 10 23 Example: How many aluminum atoms are in an aluminum can with a mass of 16.2 g?

37. Tro's "Introductory Chemistry", Chapter 6 37 Apply the solution map: = 3.6159 x 10 23 atoms Al = 3.62 x 10 23 atoms Al Significant figures and round: Information: Given:16.2 g Al Find:? atoms Al Conversion Factors: 1 mol Al = 26.98 g 1 mol = 6.022 x 10 23 Solution Map: g  mol  atoms Example: How many aluminum atoms are in an aluminum can with a mass of 16.2 g?

38. Tro's "Introductory Chemistry", Chapter 6 38 Check the solution: 16.2 g Al = 3.62 x 10 23 atoms Al The units of the answer, atoms, are correct. The magnitude of the answer makes sense since 16.2 g is less than the mass of 1 mole, 26.98 g. Information: Given:16.2 g Al Find:? atoms Al Conversion Factors: 1 mol Al = 26.98 g 1 mol = 6.022 x 1023 Solution Map: g  mol  atoms Example: How many aluminum atoms are in an aluminum can with a mass of 16.2 g?

39. Tro's "Introductory Chemistry", Chapter 6 39 Practice—How Many Copper Atoms Are in a Penny Weighing 3.10 g?

40. Tro's "Introductory Chemistry", Chapter 6 40 Practice—How Many Copper Atoms Are in a Penny Weighing 3.10 g?, Continued Since the given amount is much less than 1 mol Cu, the number makes sense. 1 mol Cu = 63.55 g, 1 mol = 6.022 x 10 23 3.10 g Cu atoms Cu Check: Solution: Solution Map: Relationships: Given: Find: g Cumol Cuatoms Cu

41. Tro's "Introductory Chemistry", Chapter 6 41 Molar Mass of Compounds The relative weights of molecules can be calculated from atomic weights. Formula mass = 1 molecule of H 2 O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu. Since 1 mole of H 2 O contains 2 moles of H and 1 mole of O. Molar mass = 1 mole H 2 O = 2(1.01 g H) + 16.00 g O = 18.02 g.

42. Tro's "Introductory Chemistry", Chapter 6 42 Example 6.4—Calculate the Mass of 1.75 Mol of H 2 O. Since the given amount is more than 1 mol, the mass being > 18 g makes sense. 1 mol H 2 O = 18.02 g 1.75 mol H 2 O g H 2 O Check: Solution: Solution Map: Relationships: Given: Find: mol H 2 Og H 2 O

43. Tro's "Introductory Chemistry", Chapter 6 43 Example 6.4: Calculate the mass (in grams) of 1.75 mol of water.

44. Tro's "Introductory Chemistry", Chapter 6 44 Example: Calculate the mass (in grams) of 1.75 mol of water. Write down the given quantity and its units. Given:1.75 mol H 2 O

45. Tro's "Introductory Chemistry", Chapter 6 45 Write down the quantity to find and/or its units. Find: ? g H 2 O Information: Given:1.75 mol H 2 O Example: Calculate the mass (in grams) of 1.75 mol of water.

46. Tro's "Introductory Chemistry", Chapter 6 46 Collect needed conversion factors: Molar mass H 2 O = 2(atomic mass H) + 1(atomic mass O) = 2(1.01) + 1(16.00) = 18.02 g/mol 1 mol H 2 O = 18.02 g H 2 O Information: Given:1.75 mol H 2 O Find:? g H 2 O Example: Calculate the mass (in grams) of 1.75 mol of water.

47. Tro's "Introductory Chemistry", Chapter 6 47 Write a solution map for converting the units: Information: Given:1.75 mol H 2 O Find:? g H 2 O Conversion Factor: 1 mole H 2 O = 18.02 g H 2 O mol H 2 O g H 2 O Example: Calculate the mass (in grams) of 1.75 mol of water.

48. Tro's "Introductory Chemistry", Chapter 6 48 Apply the solution map: = 31.535 g H 2 O = 31.5 g H 2 O Significant figures and round: Information: Given:1.75 mol H 2 O Find:? g H 2 O Conversion Factor: 1 mole H 2 O = 18.02 g H 2 O Solution Map:mol  g Example: Calculate the mass (in grams) of 1.75 mol of water.

49. Tro's "Introductory Chemistry", Chapter 6 49 Check the solution: 1.75 mol H 2 O = 31.5 g H 2 O The units of the answer, g, are correct. The magnitude of the answer makes sense since 31.5 g is more than 1 mole. Information: Given:1.75 mol H 2 O Find:? g H 2 O Conversion Factor: 1 mole H 2 O = 18.02 g H 2 O Solution Map:mol  g Example: Calculate the mass (in grams) of 1.75 mol of water.

50. Tro's "Introductory Chemistry", Chapter 6 50 Practice—How Many Moles Are in 50.0 g of PbO 2 ? (Pb = 207.2, O = 16.00)

51. Tro's "Introductory Chemistry", Chapter 6 51 Practice—How Many Moles Are in 50.0 G of PbO 2 ? (Pb = 207.2, O = 16.00), Continued Since the given amount is less than 239.2 g, the moles being < 1 makes sense. 1 mol PbO 2 = 239.2 g 50.0 g mol PbO 2 moles PbO 2 Check: Solution: Solution Map: Relationships: Given: Find: g PbO 2 mol PbO 2

52. Tro's "Introductory Chemistry", Chapter 6 52 Example 6.5—What Is the Mass of 4.78 x 10 24 NO 2 Molecules? Since the given amount is more than Avogadro’s number, the mass > 46 g makes sense. 1 mol NO 2 = 46.01 g, 1 mol = 6.022 x 10 23 4.78 x 10 24 NO 2 molecules g NO 2 Check: Solution: Solution Map: Relationships: Given: Find: molecules mol NO 2 g NO 2

53. Tro's "Introductory Chemistry", Chapter 6 53 Example 6.5: Find the mass of 4.78 x 10 24 NO 2 molecules?

54. Tro's "Introductory Chemistry", Chapter 6 54 Example: Find the mass of 4.78 x 10 24 NO 2 molecules. Write down the given quantity and its units. Given:4.78 x 10 24 NO 2 molecules

55. Tro's "Introductory Chemistry", Chapter 6 55 Write down the quantity to find and/or its units. Find: ? g NO 2 Information: Given:4.78 x 10 24 molec NO 2 Example: Find the mass of 4.78 x 10 24 NO 2 molecules.

56. Tro's "Introductory Chemistry", Chapter 6 56 Collect needed conversion factors: Molar mass NO 2 = 1(atomic mass N) + 2(atomic mass O) = 1(14.01) + 2(16.00) = 46.01 g/mol 1 mole NO 2 molec = 46.01 g NO 2 1 mole = 6.022 x 10 23 Information: Given:4.78 x 10 24 molec NO 2 Find:? g NO 2 Example: Find the mass of 4.78 x 10 24 NO 2 molecules.

57. Tro's "Introductory Chemistry", Chapter 6 57 Write a solution map for converting the units: molec NO 2 mol NO 2 g NO 2 Information: Given:4.78 x10 24 NO 2 molec Find:? g NO 2 Conversion Factor: 1 mol NO 2 = 46.01 g NO 2 1 mol = 6.022 x 10 23 Example: Find the mass of 4.78 x 10 24 NO 2 molecules.

58. Tro's "Introductory Chemistry", Chapter 6 58 Apply the solution map: = 365.21 g NO 2 = 365 g NO 2 Significant figures and round: Information: Given:4.78 x 10 24 molec NO 2 Find:? g NO 2 Conversion Factors: 1 mol NO 2 = 46.01 g 1 mol = 6.022 x 10 23 Solution Map: molec  mol  g Example: Find the mass of 4.78 x 10 24 NO 2 molecules.

59. Tro's "Introductory Chemistry", Chapter 6 59 Check the solution: 4.78 x 10 24 molecules NO 2 = 365 g NO 2 The units of the answer, g, are correct. The magnitude of the answer makes sense since 4.78 x 10 24 is more than 1 mole. Information: Given:4.78 x 10 24 molec NO 2 Find:? g NO 2 Conversion Factors: 1 mol NO 2 = 46.01 g 1 mol = 6.022 x 10 23 Solution Map: molec  mol  g Example: Find the mass of 4.78 x 10 24 NO 2 molecules.

60. Tro's "Introductory Chemistry", Chapter 6 60 Practice—How Many Formula Units Are in 50.0 g of PbO 2 ? (PbO 2 = 239.2)

61. Tro's "Introductory Chemistry", Chapter 6 61 Practice—How Many Formula Units Are in 50.0 g of PbO 2 ? (PbO 2 = 239.2), Continued Since the given amount is much less than 1 mol PbO 2, the number makes sense. 1 mol PbO 2 = 239.2 g,1 mol = 6.022 x 10 23 50.0 g PbO 2 formula units PbO 2 Check: Solution: Solution Map: Relationships: Given: Find: g PbO 2 mol PbO 2 units PbO 2

62. Tro's "Introductory Chemistry", Chapter 6 62 Chemical Formulas as Conversion Factors 1 spider  8 legs. 1 chair  4 legs. 1 H 2 O molecule  2 H atoms  1 O atom.

63. Tro's "Introductory Chemistry", Chapter 6 63 Counting Parts If we know how many parts are in the whole unit, by counting the number of whole units, we can effectively count the parts. For example, when all the desks in the room have 4 legs, if there are 30 desks in the room, there will be 120 legs (4 x 30). Since every H 2 O molecule has 2 H atoms, in 100 H 2 O molecules, there are 200 H atoms. In 1 mole of H 2 O molecules, there are 2 moles of H atoms.

64. Tro's "Introductory Chemistry", Chapter 6 64 Mole Relationships in Chemical Formulas Since we count atoms and molecules in mole units, we can find the number of moles of a constituent element if we know the number of moles of the compound. Moles of compoundMoles of constituents 1 mol NaCl1 mol Na, 1 mol Cl 1 mol H 2 O2 mol H, 1 mol O 1 mol CaCO 3 1 mol Ca, 1 mol C, 3 mol O 1 mol C 6 H 12 O 6 6 mol C, 12 mol H, 6 mol O

65. Tro's "Introductory Chemistry", Chapter 6 65 Example 6.6—Calculate the Moles of Oxygen in 1.7 Moles of CaCO 3. Since the given amount is much less than 1 mol S, the number makes sense. 1 mol CaCO 3 = 3 mol O 1.7 mol CaCO 3 mol O Check: Solution: Solution Map: Relationships: Given: Find: mol CaCO 3 mol O

66. Tro's "Introductory Chemistry", Chapter 6 66 1 mol C 10 H 14 O = 150.2 g, 1 mol C = 12.01 g, 10 mol C : 1 mol C 10 H 14 O Example 6.7—Find the Mass of Carbon in 55.4 g C 10 H 14 O. Since the amount of C is less than the amount of C 10 H 14 O, the answer makes sense. 55.4 g C 10 H 14 O g C Check: Solution: Solution Map: Relationships: Given: Find: g C 10 H 14 Omol C 10 H 14 Omol Cg C

67. Tro's "Introductory Chemistry", Chapter 6 67 Example 6.7: Carvone (C 10 H 14 O) is the main component in spearmint oil. It has a pleasant odor and mint flavor. It is often added to chewing gum, liqueurs, soaps, and perfumes. Find the mass of carbon in 55.4 g of carvone.

68. Tro's "Introductory Chemistry", Chapter 6 68 Example: Find the mass of carbon in 55.4 g of carvone, (C 10 H 14 O). Write down the given quantity and its units. Given:55.4 g C 10 H 14 O

69. Tro's "Introductory Chemistry", Chapter 6 69 Write down the quantity to find and/or its units. Find: ? g C Information: Given:55.4 g C 10 H 14 O Example: Find the mass of carbon in 55.4 g of carvone, (C 10 H 14 O).

70. Tro's "Introductory Chemistry", Chapter 6 70 Collect needed conversion factors: Molar mass C 10 H 14 O = 10(atomic mass C) + 14(atomic mass H) + 1(atomic mass O) = 10(12.01) + 14(1.01) + (16.00) = 150.2 g/mol 1 mole C 10 H 14 O = 150.2 g C 10 H 14 O 1 mole C 10 H 14 O  10 mol C 1 mole C = 12.01 g C Information: Given:55.4 g C 10 H 14 O Find: g C Example: Find the mass of carbon in 55.4 g of carvone, (C 10 H 14 O).

71. Tro's "Introductory Chemistry", Chapter 6 71 Write a solution map for converting the units: g C 10 H 14 O mol C 10 H 14 O mol C Information: Given:55.4 g C 10 H 14 O Find: g C Conversion Factors: 1 mol C 10 H 14 O = 150.2 g 1 mol C 10 H 14 O  10 mol C 1 mol C = 12.01 g Example: Find the mass of carbon in 55.4 g of carvone, (C 10 H 14 O). gCgC

72. Tro's "Introductory Chemistry", Chapter 6 72 Apply the solution map: = 44.2979 g C = 44.3 g C Significant figures and round: Information: Given:55.4 g C 10 H 14 O Find: g C Conversion Factors: 1 mol C 10 H 14 O = 150.2 g 1 mol C 10 H 14 O  10 mol C 1 mol C = 12.01 g Solution Map: g C 10 H 14 O  mol C 10 H 14 O  mol C  g C Example: Find the mass of carbon in 55.4 g of carvone, (C 10 H 14 O).

73. Tro's "Introductory Chemistry", Chapter 6 73 Check the solution: 55.4 g C 10 H 14 O = 44.3 g C The units of the answer, g C, are correct. The magnitude of the answer makes sense since the amount of C is less than the amount of C 10 H 14 O. Information: Given:55.4 g C 10 H 14 O Find: g C Conversion Factors: 1 mol C 10 H 14 O = 150.2 g 1 mol C 10 H 14 O  10 mol C 1 mol C = 12.01 g Solution Map: g C 10 H 14 O  mol C 10 H 14 O  mol C  g C Example: Find the mass of carbon in 55.4 g of carvone, (C 10 H 14 O).

74. Tro's "Introductory Chemistry", Chapter 6 74 Practice—Find the Mass of Sodium in 6.2 g of NaCl (MM: Na = 22.99, Cl = 35.45)

75. Tro's "Introductory Chemistry", Chapter 6 75 1 mol NaCl = 58.44 g, 1 mol Na = 22.99 g, 1 mol Na : 1 mol NaCl Practice—Find the Mass of Sodium in 6.2 g of NaCl, Continued Since the amount of Na is less than the amount of NaCl, the answer makes sense. 6.2 g NaCl g Na Check: Solution: Solution Map: Relationships: Given: Find: g NaClmol NaClmol Nag Na

76. Tro's "Introductory Chemistry", Chapter 6 76 Percent Composition Percentage of each element in a compound. By mass. Can be determined from: The formula of the compound. The experimental mass analysis of the compound. The percentages may not always total to 100% due to rounding.

77. Example 6.9—Find the Mass Percent of Cl in C 2 Cl 4 F 2. Since the percentage is less than 100 and Cl is much heavier than the other atoms, the number makes sense. C 2 Cl 4 F 2 % Cl by mass Check: Solution: Solution Map: Relationships: Given: Find:

78. Tro's "Introductory Chemistry", Chapter 6 78 Practice—Determine the Mass Percent Composition of the Following: CaCl 2 (Ca = 40.08, Cl = 35.45)

79. Tro's "Introductory Chemistry", Chapter 6 79 Practice—Determine the Percent Composition of the Following, Continued: CaCl 2

80. Tro's "Introductory Chemistry", Chapter 6 80 Mass Percent as a Conversion Factor The mass percent tells you the mass of a constituent element in 100 g of the compound. The fact that NaCl is 39% Na by mass means that 100 g of NaCl contains 39 g Na. This can be used as a conversion factor. 100 g NaCl  39 g Na

81. Tro's "Introductory Chemistry", Chapter 6 81 Empirical Formulas The simplest, whole-number ratio of atoms in a molecule is called the empirical formula. Can be determined from percent composition or combining masses. The molecular formula is a multiple of the empirical formula. % A mass A (g) moles A 100g MM A % B mass B (g) moles B 100g MM B moles A moles B

82. 82 Empirical Formulas, Continued Benzene Molecular formula = C 6 H 6 Empirical formula = CH Glucose Molecular formula = C 6 H 12 O 6 Empirical formula = CH 2 O Hydrogen Peroxide Molecular formula = H 2 O 2 Empirical formula = HO

83. Tro's "Introductory Chemistry", Chapter 6 83 Practice—Determine the Empirical Formula of Benzopyrene, C 20 H 12.

84. Tro's "Introductory Chemistry", Chapter 6 84 Practice—Determine the Empirical Formula of Benzopyrene, C 20 H 12, Continued Find the greatest common factor (GCF) of the subscripts. 20 factors = (10 x 2), (5 x 4) 12 factors = (6 x 2), (4 x 3) GCF = 4 Divide each subscript by the GCF to get the empirical formula. C 20 H 12 = (C 5 H 3 ) 4 Empirical formula = C 5 H 3

85. Tro's "Introductory Chemistry", Chapter 6 85 Finding an Empirical Formula 1.Convert the percentages to grams. a.Skip if already grams. 2.Convert grams to moles. a.Use molar mass of each element. 3.Write a pseudoformula using moles as subscripts. 4.Divide all by smallest number of moles. 5.Multiply all mole ratios by number to make all whole numbers, if necessary. a.If ratio ?.5, multiply all by 2; if ratio ?.33 or ?.67, multiply all by 3, etc. b.Skip if already whole numbers after Step 4.

86. Tro's "Introductory Chemistry", Chapter 6 86 Example 6.11—Finding an Empirical Formula from Experimental Data

87. Tro's "Introductory Chemistry", Chapter 6 87 Example: A laboratory analysis of aspirin determined the following mass percent composition. Find the empirical formula. C = 60.00% H = 4.48% O = 35.53%

88. Tro's "Introductory Chemistry", Chapter 6 88 Example: Find the empirical formula of aspirin with the given mass percent composition. Write down the given quantity and its units. Given:C = 60.00% H = 4.48% O = 35.53% Therefore, in 100 g of aspirin there are 60.00 g C, 4.48 g H, and 35.53 g O.

89. Tro's "Introductory Chemistry", Chapter 6 89 Write down the quantity to find and/or its units. Find: empirical formula, C x H y O z Information: Given:60.00 g C, 4.48 g H, 35.53 g O Example: Find the empirical formula of aspirin with the given mass percent composition.

90. Tro's "Introductory Chemistry", Chapter 6 90 Collect needed conversion factors: 1 mole C = 12.01 g C 1 mole H = 1.01 g H 1 mole O = 16.00 g O Information: Given:60.00 g C, 4.48 g H, 35.53 g O Find: empirical formula, C x H y O z Example: Find the empirical formula of aspirin with the given mass percent composition.

91. Tro's "Introductory Chemistry", Chapter 6 91 Write a solution map: Information: Given:60.00 g C, 4.48 g H, 35.53 g O Find: empirical formula, C x H y O z Conversion Factors: 1 mol C = 12.01 g; 1 mol H = 1.01 g; 1 mol O = 16.00 g Example: Find the empirical formula of aspirin with the given mass percent composition. g C mol C g H mol H pseudo- formula pseudo- formula empirical formula empirical formula mole ratio whole number ratio g O mol O

92. Tro's "Introductory Chemistry", Chapter 6 92 Apply the solution map: Calculate the moles of each element. Information: Given:60.00 g C, 4.48 g H, 35.53 g O Find: empirical formula, C x H y O z Conversion Factors: 1 mol C = 12.01 g; 1 mol H = 1.01 g; 1 mol O = 16.00 g Solution Map: g C,H,O  mol C,H,O  mol ratio  empirical formula Example: Find the empirical formula of aspirin with the given mass percent composition.

93. Tro's "Introductory Chemistry", Chapter 6 93 Apply the solution map: Write a pseudoformula. Information: Given:4.996 mol C, 4.44 mol H, 2.221 mol O Find: empirical formula, C x H y O z Conversion Factors: 1 mol C = 12.01 g; 1 mol H = 1.01 g; 1 mol O = 16.00 g Solution Map: g C,H,O  mol C,H,O  mol ratio  empirical formula Example: Find the empirical formula of aspirin with the given mass percent composition. C 4.996 H 4.44 O 2.221

94. Tro's "Introductory Chemistry", Chapter 6 94 Apply the solution map: Find the mole ratio by dividing by the smallest number of moles. Information: Given:C 4.996 H 4.44 O 2.221 Find: empirical formula, C x H y O z Conversion Factors: 1 mol C = 12.01 g; 1 mol H = 1.01 g; 1 mol O = 16.00 g Solution Map: g C,H,O  mol C,H,O  mol ratio  empirical formula Example: Find the empirical formula of aspirin with the given mass percent composition.

95. Tro's "Introductory Chemistry", Chapter 6 95 Apply the solution map: Multiply subscripts by factor to give whole number. Information: Given:C 2.25 H 2 O 1 Find: empirical formula, C x H y O z Conversion Factors: 1 mol C = 12.01 g; 1 mol H = 1.01 g; 1 mol O = 16.00 g Solution Map: g C,H,O  mol C,H,O  mol ratio  empirical formula Example: Find the empirical formula of aspirin with the given mass percent composition. { } x 4 C9H8O4C9H8O4

96. Tro's "Introductory Chemistry", Chapter 6 96 Example 6.12—Finding an Empirical Formula from Experimental Data

97. Tro's "Introductory Chemistry", Chapter 6 97 Example: A 3.24-g sample of titanium reacts with oxygen to form 5.40 g of the metal oxide. What is the formula of the oxide?

98. Tro's "Introductory Chemistry", Chapter 6 98 Example: Find the empirical formula of oxide of titanium with the given elemental analysis. Write down the given quantity and its units. Given:Ti = 3.24 g compound = 5.40 g

99. Tro's "Introductory Chemistry", Chapter 6 99 Write down the quantity to find and/or its units. Find: empirical formula, Ti x O y Information: Given: 3.24 g Ti, 5.40 g compound Example: Find the empirical formula of oxide of titanium with the given elemental analysis.

100. Tro's "Introductory Chemistry", Chapter 6 100 Collect needed conversion factors: 1 mole Ti = 47.88 g Ti 1 mole O = 16.00 g O Information: Given: 3.24 g Ti, 5.40 g compound Find: empirical formula, Ti x O y Example: Find the empirical formula of oxide of titanium with the given elemental analysis.

101. Tro's "Introductory Chemistry", Chapter 6 101 Write a solution map: Information: Given: 3.24 g Ti, 5.40 g compound Find: empirical formula, Ti x O y Conversion Factors: 1 mol Ti = 47.88g;1 mol O = 16.00g Example: Find the empirical formula of oxide of titanium with the given elemental analysis. g Ti mol Ti pseudo- formula pseudo- formula empirical formula empirical formula mole ratio whole number ratio g O mol O

102. Tro's "Introductory Chemistry", Chapter 6 102 Apply the solution map: Calculate the mass of each element. Information: Given: 3.24 g Ti, 5.40 g compound Find: empirical formula, Ti x O y Conversion Factors: 1 mol Ti= 47.88g;1 mol O= 16.00g Solution Map: g Ti,O  mol Ti,O  mol ratio  empirical formula Example: Find the empirical formula of oxide of titanium with the given elemental analysis. 5.40 g compound − 3.24 g Ti = 2.6 g O

103. Tro's "Introductory Chemistry", Chapter 6 103 Apply the solution map: Calculate the moles of each element. Information: Given: 3.24 g Ti, 2.16 g O Find: empirical formula, Ti x O y Conversion Factors: 1 mol Ti= 47.88g;1 mol O= 16.00g Solution Map: g Ti,O  mol Ti,O  mol ratio  empirical formula Example: Find the empirical formula of oxide of titanium with the given elemental analysis.

104. Tro's "Introductory Chemistry", Chapter 6 104 Apply the solution map: Write a pseudoformula. Information: Given: 0.0677 mol Ti, 0.135 mol O Find: empirical formula, Ti x O y Conversion Factors: 1 mol Ti= 47.88g;1 mol O= 16.00g Solution Map: g Ti,O  mol Ti,O  mol ratio  empirical formula Example: Find the empirical formula of oxide of titanium with the given elemental analysis. Ti 0.0677 O 0.135

105. Tro's "Introductory Chemistry", Chapter 6 105 Apply the solution map: Find the mole ratio by dividing by the smallest number of moles. Information: Given: 0.0677 mol Ti, 0.135 mol O Find: empirical formula, Ti x O y Conversion Factors: 1 mol Ti= 47.88g;1 mol O= 16.00g Solution Map: g Ti,O  mol Ti,O  mol ratio  empirical formula Example: Find the empirical formula of oxide of titanium with the given elemental analysis.

106. Tro's "Introductory Chemistry", Chapter 6 106 Practice—Determine the Empirical Formula of Stannous Fluoride, which Contains 75.7% Sn (118.70) and the Rest Fluorine (19.00).

107. Tro's "Introductory Chemistry", Chapter 6 107 Practice—Determine the Empirical Formula of Stannous Fluoride, which Contains 75.7% Sn (118.70) and the Rest Fluorine (19.00), Continued. Given: 75.7% Sn, (100 – 75.3) = 24.3% F  in 100 g stannous fluoride there are 75.7 g Sn and 24.3 g F. Find: Sn x F y Conversion Factors:1 mol Sn = 118.70 g; 1 mol F = 19.00 g Solution Map: g Sn mol Sn g F mol F pseudo- formula pseudo- formula empirical formula empirical formula mole ratio whole number ratio

108. Tro's "Introductory Chemistry", Chapter 6 108 Practice—Determine the Empirical Formula of Stannous Fluoride, which Contains 75.7% Sn (118.70) and the Rest Fluorine (19.00), Continued. Apply solution map: Sn 0.638 F 1.28 SnF 2

109. Tro's "Introductory Chemistry", Chapter 6 109 Practice—Determine the Empirical Formula of Hematite, which Contains 72.4% Fe (55.85) and the Rest Oxygen (16.00).

110. Tro's "Introductory Chemistry", Chapter 6 110 Practice—Determine the Empirical Formula of Hematite, which Contains 72.4% Fe (55.85) and the Rest Oxygen (16.00), Continued. Given: 72.4% Fe, (100 – 72.4) = 27.6% O  in 100 g hematite there are 72.4 g Fe and 27.6 g O. Find: Fe x O y Conversion Factors:1 mol Fe = 55.85 g; 1 mol O = 16.00 g Solution Map: g Fe mol Fe g O mol O pseudo- formula pseudo- formula empirical formula empirical formula mole ratio whole number ratio

111. Tro's "Introductory Chemistry", Chapter 6 111 Practice—Determine the Empirical Formula of Hematite, which Contains 72.4% Fe (55.85) and the Rest Oxygen (16.00), Continued. Apply solution map: Fe 1.30 O 1.73

112. Tro's "Introductory Chemistry", Chapter 6 112 All These Molecules Have the Same Empirical Formula. How Are the Molecules Different? NameMolecular Formula Empirical Formula GlyceraldehydeC3H6O3C3H6O3 CH 2 O ErythroseC4H8O4C4H8O4 CH 2 O ArabinoseC 5 H 10 O 5 CH 2 O GlucoseC 6 H 12 O 6 CH 2 O

113. Tro's "Introductory Chemistry", Chapter 6 113 All These Molecules Have the Same Empirical Formula. How Are the Molecules Different?, Continued NameMolecular Formula Empirical Formula Molar Mass, g GlyceraldehydeC3H6O3C3H6O3 CH 2 O90 ErythroseC4H8O4C4H8O4 CH 2 O120 ArabinoseC 5 H 10 O 5 CH 2 O150 GlucoseC 6 H 12 O 6 CH 2 O180

114. Tro's "Introductory Chemistry", Chapter 6 114 Molecular Formulas The molecular formula is a multiple of the empirical formula. To determine the molecular formula, you need to know the empirical formula and the molar mass of the compound. Molar mass real formula Molar mass empirical formula = Factor used to multiply subscripts

115. Tro's "Introductory Chemistry", Chapter 6 115 Example—Determine the Molecular Formula of Cadinene if it has a Molar Mass of 204 g and an Empirical Formula of C 5 H 8. 1.Determine the empirical formula. May need to calculate it as previous. C5H8C5H8 2.Determine the molar mass of the empirical formula. 5 C = 60.05, 8 H = 8.064 C 5 H 8 = 68.11 g/mol

116. Tro's "Introductory Chemistry", Chapter 6 116 3.Divide the given molar mass of the compound by the molar mass of the empirical formula. Round to the nearest whole number. Example—Determine the Molecular Formula of Cadinene if it has a Molar Mass of 204 g and an Empirical Formula of C 5 H 8, Continued.

117. Tro's "Introductory Chemistry", Chapter 6 117 4.Multiply the empirical formula by the factor above to give the molecular formula. (C 5 H 8 ) 3 = C 15 H 24 Example—Determine the Molecular Formula of Cadinene if it has a Molar Mass of 204 g and an Empirical Formula of C 5 H 8, Continued.

118. Tro's "Introductory Chemistry", Chapter 6 118 Practice—Benzopyrene has a Molar Mass of 252 g and an Empirical Formula of C 5 H 3. What is its Molecular Formula? (C = 12.01, H=1.01)

119. Tro's "Introductory Chemistry", Chapter 6 119 Practice—Benzopyrene has a Molar Mass of 252 g and an Empirical Formula of C 5 H 3. What is its Molecular Formula? (C = 12.01, H=1.01), Continued C 5 =5(12.01 g) = 60.05 g H 3 =3(1.01 g) = 3.03 g C 5 H 3 =63.08 g Molecular formula = {C 5 H 3 } x 4 = C 20 H 12

120. Tro's "Introductory Chemistry", Chapter 6 120 Practice—Determine the Molecular Formula of Nicotine, which has a Molar Mass of 162 g and is 74.0% C, 8.7% H, and the Rest N. (C=12.01, H=1.01, N=14.01)

121. Tro's "Introductory Chemistry", Chapter 6 121 Practice—Determine the Molecular Formula of Nicotine, which has a Molar Mass of 162 g and is 74.0% C, 8.7% H, and the Rest N, Continued Given: 74.0% C, 8.7% H, {100 – (74.0+8.7)} = 17.3% N  in 100 g nicotine there are 74.0 g C, 8.7 g H, and 17.3 g N. Find: C x H y N z Conversion Factors: 1 mol C = 12.01 g; 1 mol H = 1.01 g; 1 mol N = 14.01 g Solution Map: g C mol C g H mol H pseudo- formula pseudo- formula empirical formula empirical formula mole ratio whole number ratio g N mol N

122. Tro's "Introductory Chemistry", Chapter 6 122 Practice—Determine the Molecular Formula of Nicotine, which has a Molar Mass of 162 g and is 74.0% C, 8.7% H, and the Rest N, Continued. Apply solution map: C 6.16 H 8.6 N 1.23 C 5 =5(12.01 g) = 60.05 g N 1 =1(14.01 g) = 14.01 g H 7 =7(1.01 g) = 7.07 g C 5 H 7 N=81.13 g {C 5 H 7 N} x 2 = C 10 H 14 N 2