4.3 ? APPLICATION EXAMPLE FOR MOLES? Gas Behavior

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4.3 ? APPLICATION EXAMPLE FOR MOLES? Gas
Behavior
How does the behavior of gases affect airbags?
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What is pressure?
Pressure Force of gas particles running into a
surface
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Pressure and Number of Molecules
If pressure is molecular collisions with the
container
As number of molecules increases, there are more
molecules to collide with the wall
Collisions between molecules and the wall increase
Pressure increases
As of molecules increases, pressure increases
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Pressure and Volume
If pressure is molecular collisions with the
container
As volume increases, molecules can travel farther
before hitting the wall
Collisions between molecules and the wall decrease
Pressure decreases
As volume increases, pressure decreases
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Section 4.3Counting Molecules
So the number of molecules affects pressure of an
airbaghow do we count molecules?
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• How do auto makers utilize enough atoms of gas to
  create pressure that inflates the bag,
• But not so many that the pressure is too great
  when it hits you and your face that it causes
  permanent damage
• Count the atoms

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What is a mole?
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Definition
Mole SI unit for counting
The only acceptable abbreviation for mole is
molnot m!!
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What is a counting unit?
Youre already familiar with one counting unita
dozen
A dozen 12
Dozen
12
A dozen doughnuts
12 doughnuts
A dozen books
12 books
A dozen cars
12 cars
A dozen people
12 people
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What does a mole count in?
A mole 6.02 ? 1023 (called Avogadros number)
6.02 ? 1023 602,000,000,000,000,000,000,000
mole
6.02 ? 1023
1 mole of doughnuts
6.02 ? 1023 doughnuts
1 mole of atoms
6.02 ? 1023 atoms
1 mole of molecules
6.02 ? 1023 molecules
This means a 12 ounce bottle of water would have
19.7 moles of watera much easier-to-work-with
number!
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Molar Mass
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Definition
Molar Mass The mass for one mole of an atom or
molecule.
Other terms commonly used for the same
meaning Molecular Weight Molecular Mass Formula
Weight Formula Mass
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Mass for 1 mole of atoms
The average atomic mass grams for 1 mole
Average atomic mass is found on the periodic table
Element
Mass
1 mole of carbon atoms
12.01 g
1 mole of oxygen atoms
16.00 g
1 mole of hydrogen atoms
1.01 g
Unit for molar mass g/mole or g/mol
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Molar mass for molecules
The molar mass for a molecule the sum of the
molar masses of all the atoms
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Calculating a Molecules Mass
To find the molar mass of a molecule
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Count the number of each type of atom
Find the molar mass of each atom on the periodic
table
2
3
Multiple the of atoms ? molar mass for each atom
4
Find the sum of all the masses
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Example Molar Mass
Example Find the molar mass for CaBr2
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Example Molar Mass
1
Count the number of each type of atom
Example Find the molar mass for CaBr2
Ca
1
Br
2
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Example Molar Mass
2
Find the molar mass of each atom on the periodic
table
Example Find the molar mass for CaBr2
Ca
1
40.08 g/mole
Br
2
79.91 g/mole
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Example Molar Mass
3
Multiple the of atoms ? molar mass for each atom
Example Find the molar mass for CaBr2
?
Ca
1
40.08 g/mole

40.08 g/mole
?
Br
2
79.91 g/mole

159.82 g/mole
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Example Molar Mass
4
Find the sum of all the masses
Example Find the molar mass for CaBr2
?
Ca
1
40.08 g/mole

40.08 g/mole

?
Br
2
79.91 g/mole

159.82 g/mole
199.90 g/mole
1 mole of CaBr2 molecules would have a mass of
199.90 g
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Example Molar Mass Parenthesis
Be sure to distribute the subscript outside the
parenthesis to each element inside the
parenthesis.
Example Find the molar mass for Sr(NO3)2
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Example Molar Mass Parenthesis
Be sure to distribute the subscript outside the
parenthesis to each element inside the
parenthesis.
Example Find the molar mass for Sr(NO3)2
?
Sr
1
87.62 g/mole

87.62 g/mole
?
N
2
14.01 g/mole
28.02 g/mole

?

96.00 g/mole
6
16.00 g/mole

O
211.64 g/mole
1 mole of Sr(NO3)2 molecules would have a mass of
211.64 g
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Lets Practice 2
Example Find the molar mass for Al(OH)3
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Lets Practice 2
Be sure to distribute the subscript outside the
parenthesis to each element inside the
parenthesis.
Example Find the molar mass for Al(OH)3
?
Al
1
26.98 g/mole

26.98 g/mole
?
O
3
16.00 g/mole
48.00 g/mole

?

3.03 g/mole
3
1.01 g/mole

H
78.01 g/mole
1 mole of Al(OH)3 molecules would have a mass of
78.01 g
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Using Molar Mass in Conversions
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Example Moles to Grams
Example How many grams are in 1.25 moles of
water?
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Example Moles to Grams
When converting between grams and moles, the
molar mass is needed
Example How many grams are in 1.25 moles of
water?
1 mole H2O molecules 18.02 g
1.25 mol H2O
g H2O
18.02
_______ g H2O
22.53
mol H2O
1
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Lets Practice 3
Example How many moles are in 25.5 g NaCl?
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Lets Practice 3
Example How many moles are in 25.5 g NaCl?
1 mole NaCl molecules 58.44 g
25.5 g NaCl
mole NaCl
1
_______ mole NaCl
0.44
g NaCl
58.44
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Lets Practice 4
Example How many grams is a sample of 2.75
1024 molecules of SrCl2?
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Lets Practice 4
Example How many grams is a sample of 2.75
1024 molecules of SrCl2?
1 moles SrCl2 molecules 158.52 g
1 mol 6.02?1023 molecules
2.75 1024 molecules SrCl2
mol SrCl2
g SrCl2
1
158.52
molecules SrCl2
6.02 1023
mol SrCl2
1
_________ g SrCl2
7.24
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Example Grams to Molecules
Example How many molecules are in 25.5 g NaCl?
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Example Grams to Molecules
Example How many molecules are in 25.5 g NaCl?
1 moles NaCl molecules 58.44 g
1 mol 6.02?1023 molecules
25.5 g NaCl
mol NaCl
molecules NaCl
1
6.02?1023
g NaCl
58.44
mol NaCl
1
_________ molecules NaCl
2.63 ? 1023