What is the Mole?
Hint: Its not a small mammal…
The Mole in Chemistry
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The mole is a unit of measurement in chemistry.
The mole is similar to other counting units such as 12
eggs equals 1 dozen.
One mole of any substance contains 6.02x10^23
number of particles. (Avogadro's Number)
Therefore, one mole of eggs would have
602000000000000000000000 eggs.
The mole is a great way to count matter without
using really big numbers.
This is important for chemistry because there are
millions of particles in small amounts of substances
The Mole in Chemistry (Cont.)
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The mole is a great way to count matter
without using really big numbers.
This is important for chemistry because there
are millions of particles in small amounts of
substances
Just 18 mL (or grams) of water contains
6.02x10^23 molecules of water
This presentation will help to explain how we
can find out how many moles and molecules
are in a given amount of a substance.
A Mole of Carbon
There are 12 grams in one mole of carbon. All of the other elements
mole number is relative to that of carbons. Amazingly, there are
6.02x10^23 atoms in each of the samples above.
How to Calculate the Mole
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A sample of 12 grams of carbon is equal to one mole.
The amount of moles in a substance can be
determined using that substance’s molar mass.
The molar mass is the amount of grams in one mole
of a substance.
The molar mass is the average atomic mass for a
substance.
Ex. Carbon has an atomic mass of 12 amu so its
molar mass is 12 g/mol
Molar Mass
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The molar mass of an atom, molecule, or
compound is the number of grams in one
mole of the substance.
Molar Mass = Grams/mole
Ex. Molar Mass of pure Sodium (Na)
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Find Sodium on the Periodic Table
The molar mass is equal to the atomic mass
Therefore, the molar mass is 22.99 or 23.0 grams
Calculating Molar Mass for
Compounds
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For compounds, the molar mass is the
combined total of all the atomic masses for
each atom in the compound.
Ex. C6H12O6
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There are 6 carbons, 12 hydrogen, and 6 oxygen
Carbon has an atomic mass of 12, so we multiply
12 by 6 for a total of 72.
We do the same for hydrogen and oxygen and add
them all together for the molar mass.
C: 6(12) = 72, H: 12(1) = 12, O: 6(16) = 96
So, 72+12+96 = 180 grams/mole
You Try!
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A.
B.
C.
D.
What is the molar mass of NH3?
14 g
17 g
4g
25 g
Use the Periodic Table
Try Again
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Use this other example of how to
calculate molar mass.
Try Again
Correct!!!
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Good Answer! Now learn about mole
conversions.
Mole Conversions
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Grams have to be converted to moles
before converting to number of
particles.
Grams x 1mol/molar mass = Moles
Moles x 6.02x10^23/1mol = Particles
Calculating the Moles in a
Given Substance
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Suppose you were given a graduated cylinder with 18 mL of
water in it and you were told to find the number of moles.
(Hint: 18 mL of water is equal to 18 grams of water)
First, we need to find the molar mass for water (H2O) using the
average (or relative) atomic masses on the periodic table.
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2 H @ 1 g each = 2 g
1 O @ 16 g = 16 g
2 g + 16 g = 18 g of water in 1 mole
Second, we set up a conversion factor to convert the grams of
water to moles.
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18 grams H2O x 1 mole H2O/18 grams H2O (the grams cancel and
we are left with moles)
= 1 mole of water
Calculating Number of
Particles from Moles
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You can convert moles to the number of
particles of a substance.
Take the number of moles and multiply it
by Avogadro’s Number (6.02x10^23)
For example, we found that 18 grams of
water is equal to 1 mole.
1mole water x 6.02x10^23 particles/mole
= 6.02x10^23 particles
Let’s Try That Again!
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Suppose that you have 117 grams of table salt (NaCl). How
many particles of salt are present?
First, calculate the molar mass (using the average atomic
masses on the Periodic Table)
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Second, convert grams to moles
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1 Na @ 23g = 23g
1 Cl @ 23.5g = 35.5g
23g + 35.5g = 58.5g
117g NaCl x 1 mole NaCl/58.5g NaCl = 2 moles NaCl (the grams
cancel and you are left with moles)
Third, convert moles to particles (using Avogadro's Number)
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2 mole NaCl x 6.02x10^23 particles NaCl/1 mole NaCl =
1.2x10^24 particles NaCl
Now You Try!
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If you were given a 78g sample of LiF,
how many moles would be present in
the sample? Use the Periodic Table.
A. 1 mole
B. 2 moles
C. 3 moles
D. 4 moles
Calculating Molar Masses
Using the Periodic Table
•You can find the molar mass of an element by
looking at its atomic mass. Here it is located
directly under the element symbol and is
107.87.
•To find the atomic mass for a compound you
just have to count the number of each element
and find the atomic mass for each then add
them together.
•For example, AgO3 is
•1 Ag @ 107.87g
•3 O @ 16g = 16x3 = 48g
•107.87g + 48g = 155.87g
•So, there are 155.87g in one mole of AgO3
Not Quite
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Review the example problem and try again.
Correct!!!
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Great Job!
Another Example Problem
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A.
B.
C.
D.
How many moles are in 12 grams of
NH3?
1.0
2.5
.71
1.8
Need the Periodic Table?
Incorrect
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Please try again.
Yup!!!
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Good Answer. Now try to convert
moles to particles.
Try This One
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How many atoms are present in 2.5
moles of pure sodium?
A. 1.5x10^24
B. 1.2x10^23
C. 57.5
D. 135.8
Nope…
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Try Again!
You’re Right!!!
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Good Work!
Final Assessment
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A.
B.
C.
D.
How many particles (molecules) of
glucose (C6H12O6) are present in a 270
gram sample?
1.5
9.03x10^23
6.02x10^23
2
Not Quite
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Remember it’s a two step process. You
have to convert grams to moles and
then moles to particles.
Try Again
Great Job!
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You have learned about the mole and
mole conversions!