# Introduction to the Mole and Molar Mass

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Introduction to the Mole and Molar Mass

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 ask for a _______ eggs. Dozen
You know that one dozen of any item is ______. Dozen 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? Image source:

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?

ANALYSIS AND INTERPRETATION
As you know, a dozen represents 12 items. What if I decided to make a new counting unit? I called this unit a DART. Each dart is _____ items. 1 Dart = 4 items, just like 1 Dozen = 12 items 4

1. A DART of oranges will have _____ oranges.
4 Image Source:

2. A DART of pretzels has ____ pretzels.
4 Image Source:

3. A DART of molecules of water has ____ molecules of water.
4 Image Source:

4. A DART of particles has ___ particles.
4. A DART of particles has ___ particles. 4

5. A DART of atoms of iron has _____ atoms of iron.
4 26 Fe 55.85 Image Source:

6. A DART of formula units of salt has _______ formula units of salt.
4 Image Source:

7. How many Hershey’s Kisses are in 2 DARTS? _______
8 Image Source: SStevens 2005

8. How many caramels are in 10 DARTS? _______
40 Image source: SStevens 2005

9. How many Dum Dum Pops are in 400 DARTS? _______
1600 Image Source:

10. How many Starbursts are in 1/2 DART? _____
Image source: SStevens 2005

15. How many atoms of silver are in 20 DARTS? _______
80 47 Ag 107.9 Image Source:

Write the directions for finding the number of items if given the number of DARTS

17. How many DARTS are 16 Hershey’s Kisses? ______
4 Image Source: SStevens 2005

18. How many DARTS are 100 pretzels? ____
25 Image Source:

19. How many DARTS are 400 Starbursts? ____
100 Image Source: SStevens 2005

20. How many DARTS is 1 orange? ________
(Write a fraction or a decimal.) ¼ 0.25 Image Source:

21. How many DARTS are 2 caramels? _____
0.5 Image Source: SStevens 2005

23. How many DARTS are 48 Hershey’s Kisses? ____
12 Image Source: SStevens 2005

25. How many DARTS are 24 Jolly Ranchers? ______
6 Image Source: SStevens 2005

27. How many DARTS are 20 caramels? ______
5 Image Source:Sstevens 2005

Write your own directions for finding the number of DARTS given the number of pieces

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.
Image Sources:

AVOGADRO’S NUMBER 6.02 x 1023 One MOLE of anything has 6.02 x 1023 items.

A. What is the Mole? A counting number (like a dozen)
Avogadro’s number (NA) 1 mol = 6.02  1023 items A large amount!!!! VERY

A. What is the Mole? HOW LARGE IS IT??? 1 mole of hockey pucks would equal the mass of the moon! 1 mole of basketballs would fill a bag the size of the earth! 1 mole of pennies would cover the Earth 1/4 mile deep!

28. How many Hershey’s Kisses make up 1 MOLE?
6.02 x 1023 Image Source: SStevens 2005

A mole of Caramels is _____ caramels.
6.02 x 1023 Image Source: SStevens 2005

A mole of Jolly Ranchers is ______ Jolly Ranchers
6.02 x 1023 Image Source: SStevens 2005

A mole of silver atoms is _______ atoms of silver.
6.02 x 1023 47 Ag 107.9 Image Source:

29. How many caramels make up 10 MOLES?
10 [6.02 x 1023] 60.2 x 1023 Which is 6.02 x 1024

30. Find the number of Jolly Ranchers in 4 MOLES.
4 [6.02 x 1023] = 2.408 x 1024

31. Find the number of atoms of sodium in 2 MOLES.
2[6.02 x 1023]= 1.20 x 1024 11 Na

32. Find the number of molecules of water in 6 MOLES.
6[6.02 x 1023]= 3.61 x 1024

33. Find the number of caramels in 0.5 MOLES.
.5[6.02 x 1023 ]= 3.011 x 1023 Image Source: SStevens

34. How many moles of caramels is 6.02x1023 of caramels? ___
Image Source: SStevens 2005

35. How many moles of Starbursts is 6.02x1023 of Starbursts? ___

36. How many moles of Gobstoppers is 12.04x1023 of Gobstoppers? ___

37. How many atoms of potassium make up one MOLE?
6.02 x 1023 19 K 39.10

38. How many atoms of potassium make up 2 MOLES?
2[6.02 x 1023 ] x 1023 1.20 x 1024 19 K 39.10

39. How many molecules of water make up 1 MOLE?
6.02 x 1023 Image Source:

40. How many molecules of water make up 5 MOLES?
5[6.02 x 1023 ]= 3.01 x 1024

41. How many moles are 6.022 x 1023 atoms of sodium? _____
Image source: SStevens 2002

42. How many moles are 12.04 x 1023 atoms of carbon? _____
Image source: SStevens 2002

43. How many moles are 18.06 x 1023 atoms of sodium? _____
Image source: SStevens 2002

44. How many moles are 60.22 x 1023 atoms of sodium? _____
Image source: SStevens 2002

45. How many moles are 6.02 x 1023 molecules of water? _____
Image Source:

46. How many moles are 12.04 x 1023 molecules of water? _____
Image Source:

47. How many moles are 30.10 x 1023 molecules of water? _____
5 30.10 x = 5 6.022 x 1023 Image Source:

Part 2

Molar Mass Scientists use the Periodic Table to determine the mass of a mole of atom of an element. For example, a mole of carbon (C) atoms would have a mass of 12.01g.

Periodic Table Image Source:http://www.webelements.com/

1 mole carbon atoms = __________ atoms = __________ g..
6.02 x 1023 12.01 6 C 12.01

1 mole helium atoms = __________ atoms = _______ g..
6.02 x 1023 4.00 2 He 4.00

1 mole iron atoms = __________ atoms = _______ g..
6.02 x 1023 55.85 26 Fe 55.85

1 mole boron atoms = __________ atoms = _______ g..
6.02 x 1023 10.81 5 B 10.81

1 mole He atoms is 4.00 g, so 2 mole He atoms = ______ g.
8.00 2 He 4.00

1 mole Fe atoms is 55.85 g, so 0.5 mole Fe atoms = ______ g.
27.93 26 Fe 55.85

1 mole C atoms is 12.01 g, so 12 mole C atoms = ______ g
144.12 6 C 12.01

1 mole B atoms is 10.81 g, so 3 mole B atoms = ______ g
32.43 5 B 10.81

120.1 g C atoms = ______ mol 10 6 C 12.01 120.1 ÷ = 10

8.00 g He atoms = ______ mol 2 2 He 4.00 8.00 ÷ 4.00 = 2

g Fe atoms = ______ mol 3 26 Fe 55.85 ÷ = 3

5.405 g B atoms = ______ mol 0.5 5 B 10.81 5.405 ÷ = 0.5

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 _____g.
350.48 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.
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) g/mole Chloride (Cl) 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) g/mole Manganese (Mn) g/mole Oxygen (O) 4[16.00 g/mole] g/mole.

70. The molar mass of 1 mole of Sodium Chloride (NaCl) is____ g.
58.44 Image source: SStevens 2002

71. The molar mass of 1 mole of Lead Iodide (PbI2) is _____ g.
461.0

72. The mass of 100 moles of Nickel Sulfide (NiS) is ________ g.

73. The mass of 1 mole of is Glucose (C6H12O6) is ______ g.
Image source: SStevens 2002

74. The mass of 1 mole of is Sucrose (C12H24O12 ) _______ g.
306.31 Image source:

75. The mass of 4 moles of Glucose (C6H12 O6) is _________ g.
Image source: SStevens 2002

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 Moles = Molar Mass 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 grams/mole. Potassium (K) = x 1 = g Manganese (Mn) = x 1 = g Oxygen (O) = x 4 = g 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

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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