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The Mole: A Shortcut for Chemists. Source: http://en.wikipedia.org/wiki/Mole_(animal). The Mole. The mole is a counting unit for chemists, the same way a baker uses a dozen. 1 dozen = 12 objects 1 mole = 6.02 × 10 23 objects = 602,000,000,000,000,000,000,000 objects - PowerPoint PPT Presentation
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S-C-8-1_The Mole Presentation
The Mole: A Shortcut for Chemists
Source: http://en.wikipedia.org/wiki/Mole_(animal)
The Mole
• The mole is a counting unit for chemists, the same way a baker uses a dozen.
• 1 dozen = 12 objects• 1 mole = 6.02 × 1023 objects • = 602,000,000,000,000,000,000,000 objects• That’s almost a trillion trillion!• 6.02 × 1023 is called Avogadro’s number.• “Mole” in writing; “mol” in calculations.
Representative Particles
• Moles can be used to count “representative particles:” atoms, molecules, ions, and formula units.
• The representative particle of an ionic compound is the formula unit.
• The representative particle of a covalent compound is the molecule.
• The representative particle of an element is the atom unless it is a diatomic element, in which case it is the molecule.
• 1 mole of any of the representative particles = 6.02 × 1023 of those particles.
• How many atoms in 1 mol of aluminum?• How many molecules are in 1 mol of water?• How many formula units are in 1 mol of salt?• How many atoms are in 0.5 mol of aluminum?• How many molecules are in 2 mol of water?• How many formula units are in 2.67 mol of salt?
Dimensional Analysis
Dimensional Analysis(Factor-Unit Method)
• A simple, powerful tool.
• Converts among measurements expressed in different units.
• Develops relationships between units and expresses this relationship as a factor of both units.
Dimensional Analysis(Factor-Unit Method)
• Example:– 500 grams is equivalent to how many pounds?
Dimensional Analysis(Factor-Unit Method)
• Example:– 500 grams is equivalent to how many pounds?
Step 1: Write the statement as a mathematical formula.
pounds______CFgrams500
Dimensional Analysis(Factor-Unit Method)
• Example:– 500 grams is equivalent to how many pounds?
Step 2: Write the relationship between the known and unknown units.
1 pound = 454 grams
Dimensional Analysis(Factor-Unit Method)
• Example:– 500 grams is equivalent to how many pounds?
Step 3: Write the relationship as two ratios.
grams 454pound 1
pound 1grams 454
Dimensional Analysis(Factor-Unit Method)
• Example:– 500 grams is equivalent to how many pounds?
Step 4: Select the relationship that has the unit sought on top.
grams 454pound 1
pound 1grams 454
pounds______CFgrams500
Dimensional Analysis(Factor-Unit Method)
• Example:– 500 grams is equivalent to how many pounds?
Step 4: Select the relationship that has the unit sought on top.
pounds______grams454
pound1grams500
Dimensional Analysis(Factor-Unit Method)
• Example:– 500 grams is equivalent to how many pounds?
Step 5: Perform the calculation.
pounds10.1grams454
pound1grams500
Dimensional Analysis(Factor-Unit Method)
• Example:– 500 grams is equivalent to how many pounds?
Step 6: Check the answer. Is it reasonable?
pounds10.1grams454
pound1grams500
Dimensional Analysis(Factor-Unit Method)
• Example:– A can of Coca-Cola contains 12 fluid ounces (fl oz).
What is the volume of the can in quarts? (Given: 1 qt = 32 fl oz)
Dimensional Analysis(Factor-Unit Method)
• Example: Solution– A can of Coca-Cola contains 12 fluid ounces (fl
oz). What is the volume of the can in quarts? (Given: 1 qt = 32 fl oz)
pounds______CFozfl12
Dimensional Analysis(Factor-Unit Method)
• Example: Solution– A can of Coca-Cola contains 12 fluid ounces (fl
oz). What is the volume of the can in quarts? (Given: 1 qt = 32 fl oz)
1 quart = 32 fl oz
pounds______CFozfl12
Dimensional Analysis(Factor-Unit Method)
• Example: Solution– A can of Coca-Cola contains 12 fluid ounces (fl
oz). What is the volume of the can in quarts? (Given: 1 qt = 32 fl oz)
quarts______oz fl 32
quart 1oz fl 21
quart 1 oz fl 23
oz fl 32quart 1
Dimensional Analysis(Factor-Unit Method)
• Example: Solution– A can of Coca-Cola contains 12 fluid ounces (fl
oz). What is the volume of the can in quarts? (Given: 1 qt = 32 fl oz)
quarts 38.0oz fl 32
quart 1oz fl 21
Atomic Masses
• What do the atomic masses on the periodic table represent?
• Carbon has an atomic mass of 12; this means a carbon atom weighs 12 atomic mass units (amu).
• The actual mass of an atom of carbon is only 2 x 10-23 grams.
• Practice: What is the atomic mass of one molecule of O2?
16.00 + 16.00 = 32.02 amu
Formula Weight
• Formula weight: The weight of a molecule or an ionic compound.
• Molecule: CO2
12.01 + 16.00 + 16.00 = 44.01 amuFor molecules, formula weight is also
called the “molecular weight.”• Ionic compound: NaCl 22.99 + 35.45 = 58.44 amu
Molar Mass
• Molar mass = the mass of one mole.• For atoms, molar mass is the same as atomic mass.• The molar mass of a compound allows you to convert
between the amount of the element (moles) and its mass (grams).
• If you want to convert from amount (moles) to mass (grams):
• If you want to convert from mass (grams) to amount (moles):
# of moles × Formula weight = Mass (in grams) 1 mol
mass (grams) × 1 mol = # of moles formula weight
Molar Mass Examples
• 1 mol N = 14.01 g N• Written as 14.01 g/mol• Calculate the following molar masses:
•Br•CaF2
•NO2
•NaCl
Molar Mass Examples: Solutions
Calculate the following molar masses:• Br
79.90• CaF2
40.08 + 19.00(2) = 78.08 g/mol• NO2
14.01 + 16.00(2) = 46.01 g/mol• NaCl
22.99 + 35.45 = 58.44 g/mol
Conversion Factors: Mole-Mass Problems
• The red portions in the examples above are the conversion factors.
• Conversion factor: A ratio equal to one that expresses the same quality in two different ways.
• Another example: To find the number of eggs in 3 dozen:3 dozen x 12 eggs/dozen = # of eggs
Mole-Mass Problems1. What is the mass of 0.50 mol HCl?
2. What is the mass of 2 mol Zn?
3. How many moles are in 1.5 g of Cu?
4. How many moles are in 50 g H2SO4?
Mole-Mass Answers1. What is the mass of 0.50 mol HCl?
0.50 mol × 36.46 g/mol = 18.23 g HCl
2. What is the mass of 2 mol Zn?2 mol × 65.41 g/mol = 130.82 g
3. How many moles are in 1.5 g of Cu?1.5 g × 1 mol/63.55 g = 0.02 mol
4. How many moles are in 50 g H2SO4?50 g × 1 mol/98.09 g = 0.51 mol
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