Post on 18-Jan-2018
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Chapter 8
The Mole
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I say, “I have a dozen….”• You say....
✓A dozen what?
✓eggs, donuts, pencils, dogs, siblings....whatever.
• What is a dozen?
✓12 items
• How would you label a dozen?
✓12 items/1 dozen
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I’ll give you a dozen rice…
• You might say, “Big deal.”• This would not be useful because rice grains are so
small.• You would still be hungry.
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OK, I’ll give you a dozen gold atoms…
• You might again say, “So what.”• This would not be valuable because a dozen atoms
is so small, so in chemistry we need a much LARGER dozen.
• Introducing...
The really big dozen
The Mole
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Using the Mole Just Like the Dozen• If you had 1 dozen bicycles, you’d have… • how many bicyles, dozen frames, dozens of
wheels, frames, wheels?✓1 dozen bikes*12 bikes/1doz = 12 bikes
✓1 dozen bikes*1frame/1bike = 1 dozen frames
✓1 dozen bikes*2 wh/1 bike = 2 dozen wheels
✓1 dozen bikes*12 bikes/1doz*1frame/1bike✴ 12 frame
✓1 dozen bikes*12 bikes/1doz*2wheels/1bike✴ 24 wheels
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The Chemist’s Dozen - A MoleAvogadro’s Number of “items”
• 6.022 141 99 x 1023 items/mol✓Atoms or molecules or ions or units or whatever
(dogs, donuts, eggs, bicycles, etc)
• 602,214,199,000,000,000,000,000 items/mol• The average atomic mass of any element is
the mass of a mole of atoms of that element.✓H = 1.01 g/mol✓C = 12.01 g/mol✓Fe = 55.85 g/mol
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Molar Mass - The Average Mass in the Periodic Table
• The mass (in grams) of 1 mole of a substance.
• Determine the MM (molar mass) of carbon tetrachloride: CCl4✓1 mole C = 12.01 g✓4 mole Cl = 4 (35.45 g) = 141.8 g✓12.01 g + 141.8 g = 153.81 g/1 mol of CCl4 molecules
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Molar Mass, again• Determine the MM (molar mass) of aluminum
hydroxide: Al(OH)3
✓1 mole Al = 26.98 g✓1 mole O = 16.00 g * 3 = 48.00 g✓1 mole H = 1.01 g * 3 = 3.03 g✓26.98 g/1mol + 48.00 g/1mol + 3.03 g/1mol
78.01 g/1mole of Al(OH)3 formula units aka ionicules
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Molar Mass of Large Compounds• Determine the MM (molar mass) of iron(III) sulfate: Fe2(SO4)3 ✓2 mole Fe = 2 (55.85 g) = 111.70 g✓3 mole S = 3 (32.07 g) = 96.21 g✓12 mole of O = 12 (16.00) = 192.00g✓111.70 g + 96.21 g + 192.00 g =
399.91 g/1mol of iron(III) sulfate ionicules
• So if you had 5 moles of iron(III) sulfate, how much would it weigh?✓5 moles * ~400 g/1mol = ~2000 g
~2000 g of iron(III) sulfate
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So what is the unit label on the molar masses that you look up in the
periodic table?
• g/mol • (or g/1 mole)
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So what is the unit label on Avogadro’s number?
6.02 x 1023
• items/mol
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Mass ↔ Moles• How many moles of Mg in 75.0 g of Mg?✓1 mole Mg = 24.31 g✓(75 g)(1 mol/24.31g) = 3.085150144 moles
3.09 moles of Mg atoms
• What is the mass of 0.732 mole of Cl2 molecules?✓1 mole Cl atoms = 35.45 g✓1 mole Cl2 molecules = 70.90 g✓(0.732 mole)(70.90 g/1mole) = 51.8988 g
51.9 g of Cl2 molecules
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Moles ↔ Items• How many atoms are in 4.7 moles of Mg?✓1 mol Mg = 6.02 x 1023 atoms✓(4.7 mole)(6.02 x 1023 atoms/1mol) =
2.8294 x 1024 atoms2.8 x 1024 atoms of Mg
• How many mole of oxygen molecules in 5.83 x 1022
molecules?✓1 mole O2 = 6.02 x 1023 molecules✓(5.83 x 1022 molecules)(1 mol/6.02 x 1023 molecules)
0.096843853 mole0.0968 mole of O2 molecules
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Mass ↔ Moles ↔ Items• What is the mass of 2.8 x 1024 atoms of Mg?✓1 mole Mg = 6.02 x 1023 atoms, 1 mole Mg = 24.31 g✓This is a two step process: ✓Change to moles, then change to grams✓(2.8 x 1024 atoms)(1 mole/6.02 x 1023 atoms)(24.31 g/1mole) =
113.0697674 g110 g of Mg atoms
• How many ammonia molecules are in 34 g of NH3?✓1 mole NH3 = 17.04 g, 1 mole = 6.02 x 1023 molecules✓This is a two step process:✓Change to moles, then change to molecules✓(34 g)(1 mole/17.04 g)(6.02 x 1023 molecules/1mole) =
1.201173709 x 1024 molecules1.2 x 1024 molecules of NH3
Practice Problem• What would be the mass of 3.75 x 1021 atoms
of iron?✓Change to moles, then change to grams✓(3.75 x 1021 atoms)(1 mole/6.02 x 1023 atoms)(55.85 g/1mole) =
0.3479028 g0.348 g of Fe atoms
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Practice Problem
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• How many water molecules would be found in a 54 gram sample of water?✓1 mole H2O= 18.02 g, 1 mole = 6.02 x 1023 molecules✓This is a two step process:✓Change to moles, then change to molecules✓(54 g)(1 mole/18.02 g)(6.02 x 1023 molecules/1mole) =
1.80459 x 1024 molecules1.8 x 1024 molecules of H2O
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Sometimes in chemistry it is useful to report the percentages of elements in a compound. This is called:
Percent Composition (by mass)aka Elemental Analysis
• Determine the % composition by mass✓(aka an elemental analysis of MgF2)
• Mg = 24.31 g/1mol, F = 19.00 g/1mol• MgF2 = 62.31 g/1mol• Remember that % is✓always part out of total
• Mg = (24.31 / 62.31)(100) = 39.01%• F (all of it) = (38 / 62.31)(100) = 60.99%
Determine the Percent Composition of carbon in the following:
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1. CO2
C = 12.01 g/1mol, O = 16.00 g/1mol MM = 12.01+16.00(2)= 44.01 g/molSo % C = (12.01 / 44.01)(100) = 27.29%
2. C6H12O6
MM = 12.01(6) +1.01(12) +16.00(6) =180.g/molSo % C = (72.06/180)(100) = 40.0%
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Elemental Analysis