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Chemical Quantities
“Counting Particles of Matter”
Estimating Large Numbers
Knowing “how many” of something there
is a nature way to describe it.
Would this be a qualitative or quantitative
description?
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Estimating Large Numbers
Chapter 12 begins with a story of a man
who brought 40 large drums of pennies
into a bank to get them counted.
How could you count these pennies without
touching each one?
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You could put them into equal groups
and see how much is in one group!
Atoms are small,
though they can be
grouped too!
The first man to do
this was a man
named Amedeo
Avogadro.
Avogadro’s Constant
Avogadro realized that the volume of a
gas is proportional to the number of
atoms regardless of the type of gas.
He named his unit of atoms a mole, which
represents 6.02 x 1023 atoms (a lot!)
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That’s a lot of atoms!
This may seem like a lot, but atoms are
tiny!
You have 7x1027 in your body!
Compare that to 10x1021 stars in the
universe!
Do you understand how they get that number
– they didn’t count them!
Remember the parts of an atom?
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A mole
How big is a mole?
There are 6.02 x 1023 atoms in 1
mole of oxygen atoms.
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There are 6.02 x 1023 atoms in 1
mole of carbon atoms.
There are 6.02 x 1023 atoms in 1
mole of chicken nuggets atoms.
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Why this? To let you know that a mole
represents a given number of something,
though one mole may not be the same size
as another mole of something else.
* Warning: ugly
Why a mole?
Scientists need to be able to communicate
about numbers of atoms, so they need a
standard unit of measurement – the mole.
What are other standard units of measure
used by scientists?
Length? Velocity? Time? Force? Temperature?
Volume? Mass?
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Let’s use moles to figure
out quantities of chemicals
for reactions!
Yeah!
Molar Mass
The mass of one mole
of a substance is
listed on the periodic
table
The atomic mass of
an element is the
mass of one mole of
that element.
So one mole of
carbon is 12.011
grams.
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So what would the molar mass of
H2O be?
H 2 atoms x 1 gram = 2 grams
O 1 atom x 16 grams = 16 grams
-------------------------------------------------- Total = 18 grams
The molar mass of water (H2O) is 18
grams!
Try the MM problems on
the handout
Round all answers to one decimal place
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We can use this to quantify atoms!
The mass of an iron bar is 16.8 g. How
many Fe atoms are in the sample?
Let’s work through this one together…
Answer questions 7-9 on
your worksheet
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The End!
Get that homework done!
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