Download - Chemical Quantities
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Chapter 7
Chemical Quantities
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2 lb bag of sugar
5 lb bag of potatoes 2 liters of soda-pop
3 gross of M&M’s 10 gallons of gasoline
1 dozen Krispy Kream doughnuts
•We describe quantities by weighing them, how much space they take up, or by counting them.•We do the same in chemistry
2 g of NaCl (weight)
3 mL of H20 (volume)5 moles of MgI (counting)
STOP
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• A mole is a quantity of particles, just as…
1 dozen = 12 things
1 mole = 6.02 x 1023 particles
• “Particles” usually measured in moles are atoms, molecules, ions, and formula units
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Important # to remember…
Avogrado’s Number
1 mole =6.02 x 1023
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Examples: moles atoms
How many atoms of Al are in 1.50 mol of Al?
Conversion:1 mole = 6.02 x 1023 atoms
1.50 mol of Al
1 mole= 9.03 x 1023 atoms
of Al
6.02 x 1023 atoms
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Examples: moles molecules atoms How many atoms of H are there in 3.0 moles
of H2O?Conversions:1 mole = 6.02 x 1023 moleculesH2O molecule = 2 atoms of Hydrogen
1 mole
3 moles of H2O
1 H2O molecule
= 3.6 x 1024 atoms H
6.02 x 1023 molec. 2 atoms H
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Question 1:
• Which contains more molecules:– 1.00 mol H2O2
– 1.00 mol C2H6
– 1.00 mol CO
• H2O2
• C2H6
• CO• All contains 6.02 x 1023 molecules
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Question 2:
• Which contains more atoms:– 1.00 mol H2O2
– 1.00 mol C2H6
– 1.00 mol CO
• H2O2
• C2H6
• CO• All contains 6.02 x 1023 atoms
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Question 3:
• Determine the number of atoms in 3.00 mol Sn
A. 1.81 x 1025 atoms SnB. 1.81 x 1024 atoms SnC. 4.98 x 10-24 atoms SnD. None of the above
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Molar Mass
• Determined simply by looking at the periodic chart
• Molar mass = Atomic Mass
Ca20
40.08 Molar Mass
* Thus, 1 mol Ca = 40 g
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Question 4
• Calculate the mass of 1.00 mol of copper
A. 29 g CuB. 63 g CuC. 64 g CuD. 1 g Cu
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Examples: grams molesCalculate the number of moles in 367 g of silver?
Conversion:1 mole Ag = 108 g
367 g Ag
108 g Ag = 3.40 mol Ag
1 mol Ag
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Molar Mass (compound)• Mass of 1 mole in a compound• Determined by adding the molar mass of
each atom in that compound
What is the gram molecular mass of H2O?2 atoms H = 1 g x 21 atom O = 16 g x 1
= 18 g
Thus… 1 mole of H2O = 18 g
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Question 5:
• Calculate the molar mass of diatomic nitrogen
A. 7 g N
B. 14 g N2
C. 28 g N2
D. 14 g N
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Examples: moles gramsWhat is the mass of 3.40 moles of H2O?
Conversion:1 mole H2O = 18 g
3.4 mol H2O
1 mole H2O = 61.2 g H2O
18 g
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Examples: moles grams What is the mass of 5.60 moles of ammonium
carbonate?
Conversion:ammonium carbonate - (NH4)2CO3
N: 2 x 14 g = 28 gH: 8 x 1 g = 8 gC: 1 x 12 g = 12 gO: 3 x 16 g = 48 g
5.60 mol (NH4)2CO3
1 mol (NH4)2CO3 = 538 g
1 mol (NH4)2CO3 = 96 g
96 g
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Examples: moles atoms How many atoms is this?
Conversions:1 mole = 6.02 x 1023 molecules1 (NH4)2CO3 molecule = 14 atoms
6.02 x 1023 molecules
1 mole (NH4)2CO3
5.6 moles (NH4)2CO3 14 atoms
1 molecule (NH4)2CO3
= 4.72 x 1025 atoms
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• When dealing with gasses, volume is determined by using the conversion:
1 mole = 22.4 L
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Examples: moles volume
How much volume is 5.60 moles of CO2?
Conversion:1 mole = 22.4 L
5.6 mol CO2
1 mol= 125 L CO2
22.4 L
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Review of conversions for moles
1 mole = 6.02 x 1023 particles
1 mole = _____ grams
1 mole = 22.4 L
STOP
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Examples:
How many grams of Al are in 2.0 mol Al?
Conversion:1 mole Al = 27 g
2.0 mol Al 27 g Al
1 mol Al= 54 g Al
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Examples:
How many molecules are in 5 mol of N2O3?
Conversion:1 mole N2O3 = 6.02 x 1023 molecules
5 mol N2O3 6.02 x 1023 molecules
1 mol N2O3
= 3.01 x 1024 molecules N2O3
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Examples:
What is the mass of 8 L of CO2? (Hint: 2 step conversion)
Conversion:1 mol = 22.4 L1 mol CO2 = 44 g
8 L CO2 1 mol
22.4 L
= 15.7 g CO2
44 g CO2
1 mol CO2
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Percent Composition:• Describes the relative amounts of each
element in a compound (% by mass)
% mass of =element
Grams of element in compound
Grams of compoundx 100
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Grams of Compound = 9.41g + 5.99g = 15.40g
What is the % mass of each element when you combine9.41g of Ca with 5.99g of S ?
% Ca =
% S =
9.4115.40
5.9915.40
x 100
x 100
= 61%
= 39%
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If you know the chemical formula, you can calculate % composition using molar mass
Ex.) Calculate the % comp. of ethane (C2H6)
C2 =
H6 =
C2H6 =
24 g
6 g
30 g
% C = % H =
% C = % H =
x 10024
30x 1006
30
80% 20%
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% comp. can be used to calculate the # of grams of an element in a specific amount of a compound
Ex.) Calculate the mass of carbon in 30 g of
ethane (C2H6)
From prev. example: %C in C2H6 = 80% of C
30 g C2H6 .80
(80 %) C
= 24 g Cx
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Empirical Formula• The lowest whole-number ratio of the elements
in a compound
Ie.) The E.F. of hydrogen peroxide (H2O2) is HO
• The E.F. can be determined by % comp.
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• Assume you have 100 g of this compound 67.6 g Hg 10.8 g S 21.6 g O
• Determine the # of moles of each
Ex.) Calculate the formula for a compound that is 67.6% Hg, 10.8% S, & 21.6% O.
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21.6 g O 1 mole O
16 g O= 1.35 mol O
10.8 g S 1 mole S
32 g S= .337 mol S
But the subscripts need to be whole #’s
67.6 g Hg 1 mole Hg
200 g Hg= .337 mol Hg
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• Find the smallest subscript and divide each by it
.337 mol Hg
.337 mol
1.35 mol O
.337 mol
.337 mol S
.337 mol
=
=
=
1 mol Hg
1 mol S
4 mol O
HgSO4
Empirical Formula