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Introduction to the Mole and Molar Mass Revised 9/05/06 Purpose At the completion of this unit students will • Have a conceptual understanding of the mole as the method of “counting” items and finding the mass of items that can’t be seen. • Be able to calculate the number of items (molecules, atoms, ions, and formula units) if given the number of moles. • Be able to calculate the number of moles if given the number of items. • Be able to calculate the mass of a sample if given the number of moles in a sample. • Be able to calculate the number of moles in a sample if given the mass of a sample. • Be able to prepare a sample containing a given number of moles. • Be able to determine the molar mass of a compound. Background • When you buy eggs you usually Dozen ask for a _______ eggs. • You know that one dozen of any item is ______. 12 Paper • Paper is packaged by a ream. • A ream of paper has 500 sheets. • Why is it useful to use units like a dozen or a ream? • What determines how many items should make up a particular unit? • If you were asked to design a new unit to count something, what would you consider when choosing how many items should be included in your new counting unit? Materials • 3 packages of different types of candy, balance, worksheet, calculator, pencil. Part 1 1. 2. 3. 4. Record the number of items in each package. Measure the mass of each package. Record the mass of each package in the data table. Answer questions in Analysis and Interpretations. Record masses your group measured on the board summarizing class data. Data Table 1 Name of the Items in the Number of items in package Mass of the package Package Jolly Ranchers Caramels Hershey's Kisses 4 4 4 26.9 23.03 20.96 ANALYSIS AND INTERPRETATION • As you know, a dozen represents 12 items. • Since I did not have enough items to make a dozen, I decided to make a new counting unit. I called this unit an DART. Each of your packages contains 4 _____ items. 1. A DART of oranges 4 will have _____ oranges. 2. A DART of pretzels 4 has ____ pretzels. 3. A DART of molecules of water has ____ 4 molecules of water. 4. A DART of particles 4 has ___ particles. 5. A DART of atoms of 4 iron has _____ atoms of iron. 26 Fe 55.85 6. A DART of formula units of salt has 4 _______ formula units of salt. 7. How many Hershey’s Kisses are in 2 DARTS? 8 _______ 8. How many caramels are in 10 DARTS? 40 _______ 9. How many Dum Dum Pops are in 400 1600 DARTS? _______ 10. How many Starbursts are in 1/2 2 DART? _____ 11. Write the directions for finding the number of items if given the number of DARTS 12. How many oranges are 20 in 5 DARTS? _______ 13. How many apples are 2 in 0.5 DARTS? _______ 14. How many pencils are in 0.25 (1/4) 1 DARTS? ___ 15. How many atoms of silver are in 20 80 DARTS? _______ 47 Ag 107.9 16. How many molecules of water are 20 in 5 DARTS? _______ 17. How many DARTS are 16 4 Hershey’s Kisses? ______ 18. How many DARTS are 25 100 pretzels? ____ 19. How many DARTS are 100 400 Starbursts? ____ 20. How many DARTS ¼ 0.25 is 1 orange? ________ (Write a fraction or a decimal.) 21. How many DARTS 0.5 are 2 caramels? _____ 22. Write your own directions for finding the number of DARTS given the number of pieces 23. How many DARTS are 48 Hershey’s 12 Kisses? ____ 24. How many DARTS are 32 Hershey’s 8 Kisses? ______ 25. How many DARTS are 24 Jolly Ranchers? 6 ______ 26. How many DARTS are .5 2 Gobstoppers? ______ 27. How many DARTS 5 are 20 caramels? ______ DARTS • DART of molecules of water would be too small to see. • Scientists had to select a bigger unit for counting molecules of substances. • The unit scientists use is called a MOLE. One MOLE of anything has 602,200,000,000,000,000,000,000 items. AVOGADRO’S NUMBER •6.022 x 23 10 • One MOLE of anything 23 items. has 6.022 x 10 28. How many Hershey’s Kisses make up 1 MOLE? 6.022 x 1023 29. How many caramels make up 10 MOLES? 10 [6.022 x 23] 10 60.22 x Or 23 10 24 10 6.022 x 30. Find the number of Jolly Ranchers in 4 MOLES. 4 [6.022 x 23 24.088 x 10 24 2.41 x 10 23] 10 31. Find the number of atoms of sodium in 2 MOLES. 2[6.022 x ] 11 23 Na 12.044 x 10 22.99 24 1.20 x 10 23 10 32. Find the number of molecules of water in 6 MOLES. 23] 6[6.022 x 10 23 36.113 x 10 24 3.61 x 10 33. Find the number of caramels in 0.5 MOLES. .5[6.022 x ] 23 3.011 x 10 23 10 34. How many moles of 23 caramels is 6.022x10 1 of caramels? ___ 35. How many moles of 23 Starbursts is 6.022x10 1 of Starbursts? ___ 36. How many moles of 23 Gobstoppers is 12.04x10 2 of Gobstoppers? ___ 12.04 x 1023 6.022 x 1023 =2 37. How many atoms of potassium make up one MOLE? 6.022 x 1023 19 K 39.10 38. How many atoms of potassium make up 2 MOLES? 2[6.022 x ] 19 23 12.044 x 10 K 24 39.10 1.20 x 10 23 10 39. How many molecules of water make up 1 MOLE? 6.022 x 23 10 40. How many molecules of water make up 5 MOLES? 23 ] 5[6.022 x 10 23 30.110 x 10 24 3.01 x 10 41. How many moles 23 atoms are 6.022 x 10 1 of sodium? _____ 42. How many moles 23 atoms are 12.04 x 10 of carbon? 2 _____ 12.04 x 1023 = 2 6.022 x 1023 43. How many moles 23 atoms are 18.06 x 10 3 of sodium? _____ 18.06 x 1023 = 3 6.022 x 1023 44. How many moles 23 atoms are 60.22 x 10 10 of sodium? _____ 60.22 x 1023 = 10 6.022 x 1023 45. How many moles are 23 molecules 6.022 x 10 1 of water? _____ 46. How many moles are 23 molecules 12.04 x 10 2 of water? _____ 12.04 x 1023 = 2 6.022 x 1023 47. How many moles are 23 molecules 30.10 x 10 5 of water? _____ 30.10 x 1023 = 5 6.022 x 1023 Part 2 Mass • In addition to being able to tell the number of items in an DART, you can now tell the mass of an DART of Hershey’s Kisses, Jolly Ranchers, and caramels. Data Table 1 Name of the Items in the Number of items in package Mass of the package Package Jolly Ranchers Caramels Hershey's Kisses 4 4 4 26.9 23.03 20.96 48. Based on your measurements, the mass of 1 DART of Hershey’s 20.96 Kisses is ______ g. 49. The mass of 2 DARTS of Hershey’s 41.92 Kisses is ______ g. 50. The mass of 1 DART of Jolly Ranchers is 26.9 g. ___ 51. The mass of 1 DART of caramels is 23.03 ____g 52. The mass of 100 DARTS of Hershey’s 2096 Kisses is ____ g. 53. The mass of 1/2 DART of Hershey’s 10.48 Kisses is ____ g. 54. Complete the directions for finding mass of a given number of DARTS 55. The mass of 4 DARTS of Jolly 107.6 Ranchers is ____ g. 56. The mass of 0.5 DARTS of Jolly 13.45 Ranchers is ____ g. 57. The mass of 100 DARTS of caramels is 2303.00 g. _____ 58. The mass of 1/5 DARTS of caramels is 4.606 g. _____ 59. The mass of 60 DARTS of Hershey’s 1257.6 Kisses is _____ g. 60. The mass of 0.1 DARTS of Hershey’s 2.096 Kisses is _____ g. 61. How would you calculate the number of DARTS if you know the mass of a package of Hershey’s Kisses? 260/20.96 = 12.40 62. How would you calculate the number of DARTS if you know the mass of a package of caramels? 198.5/23.03 = 8.62 63. How would you calculate the number of DARTS if you know the mass of a package of Jolly Ranchers? 198/26.9 = 7.36 Molar Mass • Scientists use the Periodic Table to determine the mass of a mole of atom of an element. • For example, a mole of Iron (Fe) atoms would have a mass of 55.85g. Periodic Table 64. The mass of 1 mole of 87.62 Strontium (Sr) is ___ g. 38 Sr 87.62 65. The mass of 1 mole 207.2 of Lead (Pb) is ____ g. 82 Pb 207.2 66. The mass of 1 mole of Nickel (Ni) is ____ g. 58.69 28 Ni 58.69 67. The mass of 4 moles of Strontium (Sr) is 350.48 _____g. 38 Sr 87.62 68. The mass of 0.5 moles of Lead (Pb) is ____ g. 103.6 82 Pb 207.2 69. The mass of 100 moles of (Ni) is _____ g. 5869.00 28 Ni 58.69 Molar Mass • Scientists also use the Periodic Table to determine the molar mass (formula weight) of compounds. • The molar mass of the compound is the sum of the molar masses of the elements that make up the compound. Potassium Chloride • The molar mass of Potassium Chloride is: Potassium (K) 39.10 g/mole Chloride (Cl) +34.45 g/mole 73.55 g/mole Potassium Permanganate • The molar mass of KMnO4 is the sum of all the molar masses times the number of atoms of each element for the molecule (subscript). Potassium Permanganate KMnO4 • Potassium (K) 39.10 g/mole • Manganese (Mn) 54.94g/mole • Oxygen (O) 4[16.00 g/mole] 158.04 g/mole. 70. The molar mass of 1 mole of Sodium Chloride (NaCl) is____ g. 58.44 71. The molar mass of 1 mole of Lead Iodide 461.0 (PbI2) is _____ g. 72. The mass of 100 moles of Nickel Sulfide 9076.00 (NiS) is ________ g. 73. The mass of 1 mole of is Glucose (C6H12O6) 180.156 is ______ g. 74. The mass of 1 mole of is Sucrose (C12H24O12 ) 306.31 _______ g. 75. The mass of 4 moles of Glucose (C6H12 O6) is _________ g. 720.624 Mole Conversions • In chemistry, the mole is the standard measurement of amount. • However, balances DO NOT give readings in moles. Balances give readings in grams. • So the problem is that, while we compare amounts of one substance to another using moles, we must also use grams, since this is the information we get from balances. There are three steps to converting grams of a substance to moles. 1. Determine how many grams are given in the problem. 2. Calculate the molar mass of the substance. 3. Divide step one by step two. The three steps above can be expressed in the following proportion: Grams --------------Molar Mass Moles -------------1 Mole = Example #1 - Convert 25.0 grams of KMnO4 to moles. Step One: The problem will tell you how many grams are present. Look for the unit of grams. The problem gives us 25.0 grams. Step Two: You need to know the molar mass of the substance. The molar mass of KMnO4 is 158.034 grams/mole. Potassium (K) = 39.10 x 1 = 39.10 g Manganese (Mn) = 54.94 x 1 = 54.94 g Oxygen (O) = 16.00 x 4 = 64.00 g --------------158.04 g Step Three: You divide the grams given by the substance's molar mass (25.0/158.04) The answer of 0.16 mole has been rounded off. Example #2 - Calculate how many moles are in 57.0 grams of Mg(NO3)2 Step One: 57.0 grams are given in the text of the problem. Step Two: The molar mass is 148 grams/mole. Mg (Magnesium) = 24 x 1= 24 g N (Nitrogen) = 14 x 2= 28 g O (Oxygen) = 16 x 6= 96 g Step Three: Again you divide the grams by the substances molar mass (57.0 g/148 g). This answer has been rounded to 0.39 moles. Practice Problems 1. Calculate the moles present in: 2.00 grams of H2O .11 moles water 2. Calculate the moles present in: 75.57 grams of KBr .635 moles KBr 3. Calculate the moles present in: 100.0 grams of KClO4 .72 moles KClO4 4. Calculate the moles present in: 225.5 grams of Sucrose (C12H24O12) .63 moles Sucrose 5. Calculate the moles present in: 350.0 grams of Glucose (C6H12O6) 1.943 moles Glucose Homework 1. Calculate the moles present in: 3.00 grams of NaCl .05 moles 2. Calculate the moles present in: 25.0 grams of NH3 1.47 moles NH3 3. Calculate the moles present in: 16.0 grams of KCl .21 moles KCl 4. Calculate the moles present in: 30.25 grams of BeCl2 .38 moles KCl 5. Calculate the moles present in: 175.25 grams of Li2S 3.81 moles Li2S 6. Calculate the moles present in: 75.62 grams of CO2 1.72 moles CO2 7. Calculate the moles present in: 56.5 grams of H2O 3.14 moles H2O 8. Calculate the moles present in: 22.6 grams of CH3COOH .38 moles CH3COOH 9. Calculate the moles present in: 18.4 grams of AgCl .13 moles AgCl 10. Calculate the moles present in: 68.3 grams of HCN 2.53 moles HCN

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posted: | 11/4/2009 |

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