9/20/2013

Today

◦ Counting Atoms & Molecules
 The concept of the Mole:
 Avogadro’s Constant
 6.022x1023 particles = 1 mole
 grams → moles
 moles → molecules
 grams → molecules
◦ Concept Check:
 Covers today’s material
 Remember Atomic Masses
 12 g of Carbon-12 = 1 mole
 Unit Conversions:
Next Meeting
◦ Review:
 See CANVAS for exam topics &
review materials
 Spend the weekend reviewing the
practice problems at the end of the
chapters
Relative Masses:
A convenient tool for relating one quantity of particles to another
quantity of particles through measurements of mass
Nut: 1 g
Bolt: 2 g
100 x 12 = 1200
1.2 x 103 objects
1200 g =
100 dozen
=
2400 g
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9/20/2013
Molar Mass:
A connection between Macroscopic and Particulate nature of matter based on
the relative masses of each atom
Carbon-12: 12 amu
Magnesium-24: ~24 amu
Definition of 1 mole
=
1 mol
=
Molar Mass:
Indicates how many grams are in one mole of the substance
12 g/mol
24 g/mol
Mole / Dozen Analogy
• Like the mole, a dozen of something is a convenient way to talk
about the number of items we tend to buy in those quantities:
1 dozen donuts
= 12 donuts
3 dozen eggs
= 36 eggs
• The mole and the dozen make it easier to talk about large
quantities of some specific item. In the case of a dozen, we are
often specifying a quantity of eggs.
• In the case of a mole, we are specifying a quantity of atoms,
molecules or some other particle on the atomic scale.
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9/20/2013
Molar Mass & Avogadro’s Constant:
A connection between Macroscopic and Particulate nature of matter
Relative Masses:
Carbon: 12 amu
Magnesium: ~24 amu
6.022 x 1023
particles
12 g
=
1 mol
=
24 g
Molar Mass:
Indicates how many grams are in one mole of the substance
12 g/mol
24 g/mol
The Mole
•
A mole of anything is 6.02214 x 1023 of that particular thing.
•
In Chemistry, we work with very small particles, so we must work
with a very
large quantity of them.
•
The mole is a convenient number to count a large quantity of
particles.
•
We can talk about a mole of anything, but we usually use it to
talk about atoms, molecules, ions, and formula units – Matter
at the microscopic, atomic, particle level.
6.02214 x 1023 is also called Avogadro’s number.
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9/20/2013
Proceeding clockwise from
the top samples containing
one mole each: copper,
aluminum, iron, sulfur,
iodine, and (in the center)
mercury.
How big is one mole?
Imagine you had 1 mole of US Dollars ($6.022 x 1023). If
you spent $1 billion per second, how many years would it
take you to spend all of the money?
This is the same number of carbon
ATOMS in 12 grams of carbon
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9/20/2013
The mole and counting particles
• We can use Avogadro’s number to convert
between particles and moles:
1 mole = 6.02214 x 1023 particles
• The two possible conversion factors are:
6.022  10 23 particles
1 mol
or
1 mol
6.022  10 23 particles
The heart of CHEMISTRY
The MOLE
Molar Mass:
g/mol
Mass (g)
NA:
6.022 x 1023
particles/mol
# of Particles
Density:
g/mL
• atoms
• molecules
• ions
• formula units
Volume (mL)
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9/20/2013
Unit Conversions
How many moles are in 236.5 g of water (H2O)?
How many molecules of water are in the quantity
above?
iClicker PARTICIPATION Question:
Mole to Mole Conversions
How many moles of Hydrogen atoms are present in 2
moles of ammonium phosphate (NH4)3PO4?
A. 2 moles H
B. 4 moles H
C. 7 moles H
D. 12 moles H
E. 24 moles H
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9/20/2013
Unit Conversions
How many moles are in 2.99 x 1021 molecules of carbon
dioxide?
How many grams of CO2 are in the quantity above?
Mole Conversions
What is the mass of 3.5 x 1022 atoms of gold?
How many formula units are present in 335 mg of
magnesium chloride (one formula unit = MgCl2)? How
many Chlorine atoms are present?
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