Transcript Unit 5 Notes

THE MOLE
General Chemistry
Fall 2009
Chemical Measurements
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Everyday people perform jobs that require the
ability to count and measure
Chef- essential to measure ingredients correctly
Construction worker- measuring cement, sand,
gravel, and water determines the consistency of
concrete
Painter- adding the right mixture of colors creates
new colors.
Chemical Measurements
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Dozen = 12
Can you
Baker’s dozen = 13
imagine a
mole of
Gross= 144
donuts?
23
Mole (mol) = 6.02x10
A mole of water molecules has a volume of only 18
mL!
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Molecules are unbelievably small, so a lot of them doesn’t
take up that much space.
The mole is useful in chemistry because it links the
microscopic world of atoms, molecules, and ions, to the
macroscopic world
Avogadro’s Number
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6.02x1023 is so important in chemistry it’s given its
own name…
 You

guessed it, Avogadro’s Number
In numerical form it looks like this:
 602,000,000,000,000,000,000,000
A
mole of paper would reach passed Pluto
 A mole of basketballs is the size of Earth
 A mole of rice would cover the land masses of Earth to
a depth of 75 meters!
How fast can you count?
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Do you think we can count to 6.02x1023?
Let’s try and figure out how long it would take us to
count to 6.02x1023
Who’s the fastest counter?
 How
should we do this task?
Scientific Notation Practice
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Using the mole requires that we are comfortable
using scientific notation
Write the following in scientific notation
6000
0.0067
78,000,000
698,700
0.000009
0.0090076
6.00x103
6.70x10-3
7.80x107
6.99x105
9.00x10-6
9.01x10-3
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Write the following in standard notation
6.02x104
9.03x109
7.77x10-2
9.21x10-7
60,200
9,030,000,000
0.0777
0.000000921
The mole
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The mole establishes a relationship between the
atomic mass and the gram
The mass in grams of 1 mole of a substance is equal
to its atomic mass
 6.02x1023
atoms Cu = 63.5 g
 6.02x1023 atoms H
= 1.001 g
 6.02x1023 atoms Fe = 55.8 g
What’s in a Mole?
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A mole of particles in an element is usually talking about
atoms.
The number of molecules in a mole of any molecular compound
is 6.02x1023
How many atoms are in a molecule of ammonia (NH3)?
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4 atoms
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1 N atom and 3 H atoms
Each molecule has 4 atoms
So 1 mole of ammonia gas contains 1 mole of NH3 molecules,
but four times as many atoms, or 4 moles of atoms (1 mol N
atoms and 3 mol H atoms)
Mole Conversions
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Chemists measure amounts of substances by volume
or mass.
Because the mole measures both a mass and a
number of particles (and volume, but that’s later), it
is the central unit in converting the amount of
substance from one type of measurement to
another.
Moles to Molecules
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The number of particles in 1 mole of any substance
is always the same- Avogadro’s number.
6.02x1023 particles
or
1 mol
6.02x1023 particles
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Molecules OR atoms
1 mol
How many atoms are in 3 mol of elemental Ne?
3 mol Ne
1
6.02x1023 atoms
1 mol
1.81x1024 atoms Ne
Unit Analysis Method
1.
2.
3.
Write down units asked for in answer to the right
Write down the given value over 1 on the left
Apply one or more unit factors to cancel units
It’s as easy
as 1-2-3!
Moles to Molecules (cont.)
PARTICLES
Atoms
6.02x1023 particles
1 mol
Molecules?
Use the subscript
1 mol
6.02x1023 particles
MOLES
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How many atoms of oxygen are in 6 mol of O2 molecules?
6 mol O2
1
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6.02x1023 molecules O2
1 mol O2
2 atoms O
1 molec. O2
7.22x1024 atoms O
How many moles of I2are in 8.02x1020 molecules of I2?
8.02x1020 molec. I2
1
1 mol I2
6.02x1023 molecules I2
1.33x10-3 mol I2
Discuss in your team
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Make sure everyone understands how to convert
from moles to particles (atoms + molecules) and
vice versa.
You MUST come up with a question in your group
about moles to particles conversions.
Molar Mass
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The mass in grams of 1 mole of a substance is
called the molar mass of the substance.
The molar mass of an element is equal to its atomic
mass.
The unit for molar mass is grams per mole, or g/mol
Molar Mass
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Ne = 20.18 g/mol
O2 = 16.00*2 = 32.00 g/mol
U = 238.03 g/mol
NaOH = 22.99 + 16.00 + 1.008 = 40.00 g/mol
CO2 = 12.01 + 16.00*2 = 44.01 g/mol
Al2(CO3)3 = 26.98*2 + (12.01*3) + (16.00*9) =
233.99 g/mol
Moles to Grams Conversions
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If you know the mass of a substance, you can
calculate the number of moles.
You have 11.2 g of NaCl. How many moles is that?
 1.
determine the molar mass of NaCl (using the
periodic table)
 Na=
23.0 g/mol
Cl= 35.5 g/mol
 23.0 g/mol + 35.5 g/mol = 58.5 g/mol (get these #’s
from the periodic table)
Moles to Grams Conversions
1.
2.
Molar mass of NaCl = 58.5 g/mol
Set up a conversion factor
(a fraction whose value is equal to 1)
1.
The units we need should be in the numerator and the
units you already know in the denominator.
Moles to Grams Conversions
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You can also determine the mass of a sample if you
know the number of moles
2.50 mol of NaCl is how many grams?
Set up a conversion factor 
Moles to Grams Conversions
MASS
moles x
g = g
mol
g x mol = moles
g
MOLES
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How many moles are in 14 g LiOH?
14 g LiOH
1
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1 mol LiOH
23.95 g LiOH
0.58 mol LiOH
How many moles are in 15 g N2?
15 g N2
1
1 mol N2
28.02 g N2
0.54 mol N2
Moles to Grams Conversions
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How many grams are in 4 mol H2O2?
4 mol H2O2
1
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34.016 g H2O2
1 mol H2O2
136.06 g H2O2
How many grams are in 56 mol CaCO3?
56 mol CaCO3
1
100.09 g CaCO3
1 mol CaCO3
5605.04 g CaCO3
Discuss in your Team
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Make sure everyone understands how to convert
from moles to grams and vice versa.
You MUST come up with a question in your group
about moles to grams conversions.
Multistep Conversions
MASS
PARTICLES
Avogadro’s
Number
Use molar
mass
MOLES
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You want to impress your date by boasting you know how many molecules
of table sugar are in the cake you just made. You need 250 g of sugar
(C12H22O11). How many sucrose molecules will be in the cake?
Plan: Convert the mass to moles using the molar mass and then convert to
moles using Avogadro’s number.
250 g C12H22O11
1
1 mol C12H22O11
342.3 g C12H22O11
6.02x1023 molecules
1 mol C12H22O11
4.4x1023 molec. C12H22O11
Multistep Conversions
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If you burned 4.0x1024 molecules of methane (CH4) during a
laboratory experiment, what mass of methane did you use?
Plan: Convert your given # of molecules to moles using
Avogadro’s number, then convert the moles to grams using the
molar mass of methane. (12.00 + 1.004*4)
4.0 x 1024 molec. CH4
1
1 mol CH4
6.02x1023 molec. CH4
16.016 g CH4
1 mol CH4
106.42 g CH4
Moles and Gases
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At the same temperature and pressure, equal
volumes of gases contain the same number of gas
particles.
1 mole of any gas at 0oC and 1 atm (Standard
Temperature and Pressure; STP) has a volume of
22.4 L.
This volume, 22.4 L/mol, is called molar volume.
Moles and Gases
MASS
PARTICLES
Avogadro’s
Number
Molar
Mass
MOLES
Molar Volume
(22.4 L/mol)
VOLUME
of gases at STP
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A student fills a 1.0-L flask with CO2 at STP. How many
molecules of gas are in the flask?
Plan:
1) Convert from volume to moles using molar volume.
2) Then convert from moles to molecules using Avogadro’s
number.
Moles and Gases
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Let’s see how you did…
1.0-L CO2
1
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1 mol CO2
22.4 L CO2
6.02 x 1023 molec CO2
1 mol CO2
2.7 x 1022 molec. CO2
A chemical reaction produces 0.82 mole of oxygen gas. What
volume will that gas occupy at STP?
0.82 mol O2
1
22.4 L O2
1 mol O2
18 L O2
Percent Composition
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In your team discuss…
How many hours of sleep do you get a night?
What percentage of the day do you spend asleep?
 As
a team, write out how you figured out the
percentage of each day you spend sleeping.
Percent Composition
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You can determine what part of the total mass of a
compound is made up by each element in that
compound.
Percent Composition- the mass of each element in
a compound compared to the entire mass of the
compound and multiplied by 100 percent.
Determining % Composition
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First method: Calculate from a given formula
Example: Water
1
mole of water (H2O)
 Molar
mass= 18 grams
 2 moles of hydrogen atoms
 1 mole of oxygen atoms
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To determine percent composition you need to
determine what part of the total mass, 18 g, is
made up of hydrogen atoms and what part is made
up of oxygen atoms.
Determining % Composition
% of element = total mass of element in compound
total mass of compound
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100
% of hydrogen= 2.0 g H
x 100 = 11%
18.0 g H2O
% of oxygen =
16 g O
x 100 = 89%
18.0 g H2O
Determining % Composition
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Second method: Experimental analysis (mass the whole sample,
separate into parts through decomposition, mass the parts, follow same method as before)
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A sample of an unknown compound with a mass of 0.2370 g was extracted
from the roots of a plant. Decomposition produced 0.09480 g of carbon,
0.1264 g of oxygen, and 0.0158 g of hydrogen. What is the percent
composition of the compound?
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Plan: Determine the % of each element in the compound by dividing the
mass of each element by the total mass of the sample, then multiply by
100.
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% C = (0.0948 g / 0.2370 g) x 100% = 40.00% C
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% O = (0.1264 g / 0.2370 g) x 100% = 53.33% O
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% H = (0.0158 g / 0.2370 g) x 100% = 6.67% H
Your Turn
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Find the percent composition of a compound that
contains 2.30 g of sodium, 1.60 g of oxygen, and
0.100 g of hydrogen in a 4.00-g sample of the
compound.
% Na = (2.30 g / 4.00 g) x 100% = 57.5% Na
% O = (1.60g / 4.00 g) x 100% = 40.0% O
% H = (0.100 g / 4.00 g) x 100% = 2.50% H
B
Number of
particles
A
Moles of
substance
E
D
Mass of
substance
C
F
Volume of gas
(STP)
a)
Use N as a unit factor: multiply by 1 mol/6.02x1023
b)
Use N as a unit factor: multiply by 6.02x1023/1 mol
c)
Use molar mass as a unit factor: multiply by 1 mol/#g
d)
Use molar mass as a unit factor: multiply by #g/1 mol
e)
Use molar volume as a unit factor: multiply by 1 mol/22.4L
f)
Use molar volume as a unit factor: multiply by 22.4L/1 mol