Transcript 1 mole

Section 3.6—Counting
Molecules
Objectives
•Define a mole and Avogadro’s number
•Define and calculate molar mass
•Define molecular and atomic mass as mass for 1 mole
of particles
•Perform calculations between numbers of moles,
particles, and masses
So the number of molecules affects pressure of an
airbag…how do we “count” molecules?
What is a mole?
Mole – SI unit for counting
The only acceptable abbreviation for “mole” is
“mol”…not “m”!!
You have had experience with counting units before:
Dozen = counting unit that means “12”
A dozen eggs is 12 eggs.
Pair = counting unit that means “2”
A pair of mittens is 2 mittens.
The Mole
Since atoms and molecules are extremely small, even
if we have a small sample, the number of molecules
would be overwhelming.
For example, one drop of water contains about 5 x 1020
molecules.
500,000,000,000,000,000,000 molecules!!
These huge numbers are impractical!
Using the “mole” counting unit, it becomes more
manageable. 1 drop of water is about 8 x 10-4 (0.0008)
moles.
The Mole
1 mole of anything = 6.02  1023 of those things
(This number is called Avogadro’s number)
“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
Converting Between Moles & Molecules
Remember: 1 mole = 6.02 x 1023 particles
Use dimensional analysis to go from moles to
particles:
3.24 mol Fe x 6.02 x 1023 atoms =
1 mole
Use dimensional analysis to go from particles
to moles:
9.56 atoms Fe x
1 mole
=
6.02 x 1023 atoms
Practice #1: Molecules & Moles
Example:
How many
molecules
of water
are in 1.25
moles?
Practice #1: Molecules & Moles
1 mol = 6.021023 molecules
Example:
How many
molecules
of water
are in 1.25
moles?
1.25 mol
H2O
6.02  1023
1
Molecules
H2O
mol H2O
7.521023 molecules H2O
= _______
Practice #2
Example:
How many
moles are
equal to
2.8 × 1022
molecules
Practice #2
1 mol = 6.021023 molecules
Example:
How many
moles are
equal to
2.8 × 1022
molecules
2.8 × 1022 molecules
1
mole
6.02  1023 molecules
0.047
= _______
moles
How is a mole related to mass?
Molar Mass
Molar Mass – The mass for one mole
of atoms or molecules.
Unit for molar mass: g/mole or g/mol
For Elements
Mass of 1 mole =
the atomic mass of the element in grams
Recall: Atomic mass is found on the periodic table.
In THIS CLASS, we will round the atomic mass to the
nearest 0.1 g
Examples
Mass
Element
1 mole of carbon atoms
12.0 g
1 mole of oxygen atoms
16.0 g
1 mole of hydrogen
atoms
1.0 g
Practice
1. Determine the molar mass of helium.
2. Determine the molar mass of lead.
3. What is the mass of 1 mole of chlorine
atoms?
Molar Mass for Compounds
Mass of 1 mole =
*SUM of the atomic masses of all
elements in the compound, in
grams
*The sum of the atomic masses of all the
elements in a compound is also called the
formula mass or the gram formula mass.
Practice: Calculate the Molar Mass of CaCl2
1
Count the number of each type of atom
1 Ca and 2 Cl
2
Find the mass of each atom on the periodic table
Ca = 40.1 and Cl = 35.5
3
Multiple the # of atoms  mass for each atom
1 x 40.1 = 40.1 for Ca
4
2 x 35.5 = 71.0 for Cl
Find the sum of all the masses
40.1 + 71.0 = 111.1 g/mol
Example 1: Molar Mass
Example:
Find the
molar
mass for
CaBr2
Example 1: Molar Mass
1
Example:
Find the
molar
mass for
CaBr2
Count the number of each type of atom
Ca
1
Br
2
Example 1: Molar Mass
2
Example:
Find the
molar
mass for
CaBr2
Find the molar mass of each atom on the periodic table
Ca
1
40.1 g/mole
Br
2
79.9 g/mole
Example 1: Molar Mass
3
Example:
Find the
molar
mass for
CaBr2
Multiple the # of atoms  molar mass for each atom
Ca
1  40.1 g/mole
=
40.1 g/mole
Br
2  79.9 g/mole
=
159.8 g/mole
Example 1: Molar Mass
4
Example:
Find the
molar
mass for
CaBr2
Find the sum of all the masses
Ca
1  40.1 g/mole
=
40.1 g/mole
Br
2  79.9 g/mole
=
+ 159.8 g/mole
199.9 g/mole
1 mole of CaBr2 molecules would have a mass of 199.9 g
Example 2: Molar Mass
Be sure to distribute the subscript outside the
parenthesis to each element inside the parenthesis.
Example:
Find the
molar
mass for
Sr(NO3)2
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  87.6 g/mole
=
87.6 g/mole
N
2  14.0 g/mole
=
28.0 g/mole
O
6  16.0 g/mole
=
+ 96.0 g/mole
211.6 g/mole
1 mole of Sr(NO3)2 molecules would have a mass of 211.6 g
Let’s Practice #1
Example:
Find the
molar
mass for
Al(OH)3
Let’s Practice #1
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  27.0 g/mole
=
27.0 g/mole
O
3  16.0 g/mole
=
48.0 g/mole
H
3  1.0 g/mole
=
+ 3.0 g/mole
78.0 g/mole
1 mole of Al(OH)3 molecules would have a mass of 78.0 g
Conversions Between
Moles & Mass
Example: Moles to Grams
Example:
How many
grams are
in 1.25
moles of
water?
Example: Moles to Grams
First determine the given quantity and the unknown
one!
Next determine the molar mass for the compound.
Example:
How many
grams are
in 1.25
moles of
water?
H 2  1.0 g/mole
O 1  16.0 g/mole
2.0 g/mole
=
= + 16.0 g/mole
18.0 g/mole
Finally, use dimensional analysis to get the answer!
1.25 mol H2O
18.0
g H2O
1
mol H2O
22.5
= _______
g H2O
Example: Grams to Moles
Determine the number of moles in 58.6 g of
Li(OH)2
1.58.6 g Li(OH)2
2.Li
1 x 6.9
O 2 x 16.0
H 2 x 1.0
= ___ mol
= 6.9 g/mol
= 32.0 g/mol
= 2.0 g/mol
40.9 g/mol
3. 58.6 g Li(OH)2 x 1 mole = 1.43 mol
40.9 g
Practice
1. Determine the number of moles in 28.4 g of
AgNO3.
2. What is the mass of 3.6 mol ZnO?
3. Determine the number of moles in 15.7 g of
CO2.
4. What is the mass of 89.0 g of N2?
Converting From Particles to Mass
We have learned how to convert from the
number of particles to moles and vice versa.
We use 1 mol = 6.02 x 1023 as the conversion
factor.
We have learned how to convert from number
of moles to a mass and vice versa. We use
1 mol = molar mass (g) as the conversion
factor.
Converting From Particles to Mass
Number
of
Particles
Mass
1 mol =
6.02 x 1023
particles
1 mol =
molar mass
(g/mol)
Mole
We can convert from number of particles
to mass in 2 separate steps.
Example: Grams to Molecules
Example:
How many
molecules
are in
25.5 g
NaCl?
Example: Grams to Molecules
Example:
How many
molecules
are in
25.5 g
NaCl?
25.5 g NaCl
Na 1  23.0 g/mole
Cl 1  35.5 g/mole
= 23.0 g/mole
= + 35.5 g/mole
58.5 g/mole
1 mol = 6.021023 molecules
1
58.5
mol NaCl
g NaCl
= _________ molecules NaCl
Example: Grams to Molecules
Example:
How many
molecules
are in
25.5 g
NaCl?
Na 1  23.0 g/mole
Cl 1  35.5 g/mole
= 23.0 g/mole
= + 35.5 g/mole
58.5 g/mole
1 mol = 6.021023 molecules
0.436 mol NaCl
x
6.021023 molecules NaCl
1
mol NaCl
2.62  1023 molecules NaCl
= _________
Example: Molecules to Grams
Example:
How many
grams is a
sample of
2.75 × 1024
molecules of
SrCl2?
Let’s Practice #4
Example:
How many
grams is a
sample of
2.75 × 1024
molecules of
SrCl2?
2.75 × 1024 molecules
SrCl2
Sr 1  87.6 g/mole
Cl 2  35.5 g/mole
= 87.6 g/mole
= + 71.0 g/mole
158.6 g/mole
1 mol = 6.021023 molecules
1
mol SrCl2
6.02 × 1023 molecules
SrCl2
= _____ g SrCl2
Let’s Practice #4
Example:
How many
grams is a
sample of
2.75 × 1024
molecules of
SrCl2?
Sr 1  87.6 g/mole
Cl 2  35.5 g/mole
= 87.6 g/mole
= + 71.0 g/mole
158.6 g/mole
1 mol = 6.021023 molecules
4.57 mol SrCl2
158.6
1
g SrCl2
mol SrCl2
724
= _________
g SrCl2