Transcript The MOLE - Fort Bend ISD

Moles
•An Introduction
The MOLE
•The term “mole” is
used to count
 Atoms of an element
 Molecules of a
molecular compound
 Formula units of an
ionic compound
•One mole is 6.02x1023
of anything
Avogadro’s Number
•Amadeo Avogadro
 Italian physics professor
 Hypothesized “equal
volumes of different gases
contain equal numbers of
atoms”
•Scientists later expanded his
hypothesis for all matter – a
molar mass of any substance
has the same number of
particles
A Mole is a BIG Number
•A dozen eggs
makes a large
omelet
•A mole of eggs
would fill all of
Earth’s oceans 30
million times
A Mole is a BIG Number
•It would take 12
billion chickens
laying 12 eggs per
day about 12 billion
years to lay 1 mole
of eggs
How Many in a Mole?
•A mole is 6.02x1023 items
•That is:
602,000,000,000,000,000,000,000
602 sextillion!
So why would we ever use such a big number?
Counting Atoms and Molecules
•Atoms and molecules are
very tiny – it takes a LOT
of them to make even a
single milliliter!
 For example, one
milliliter of water would
have:
• 3.34x1022 atoms of oxygen
• 6.68x1022 atoms of
hydrogen
Counting Atoms and Molecules
 Instead of
counting …illions
and …illions it’s
much easier to
count in moles
Elemental Molar Masses
• For any element, the
molar mass is equal to
its average atomic mass.
 Found on the periodic
table
 Measured in grams per
mole (g/mol)
Diatomic Elements
• Most elements are listed as single
atoms when in the elemental form,
but seven of them are not. You need
to know which elements are
diatomic!
 Hydrogen, Nitrogen, Oxygen, Fluorine,
Chlorine, Bromine and Iodine!
Diatomic Elements
• Whenever one of these elements is by
itself it will always be in twos!
 Example: N2 is nitrogen gas
• This does NOT affect these elements
when they are in a compound, only
when by themselves!
Mole Calculations
• Use dimensional analysis to solve
mole problems.
• Points to remember:
 Always go to moles first!
 Write your units at every step!
Example 1
•How many moles
are in 24.6 g of
1 mol Ne
24.6 g Ne 

neon?
20.180g Ne
•Neon is 20.180
g/mol
24.6 mol Ne
 1.22 mol Ne
20.180
Example 2
•What is the mass
of 2.50 moles of
2.016 g H 2
2.50 mol H 2 

hydrogen gas?
mol H 2
•Hydrogen is
diatomic, so it is H2
•Molar mass is 2.016
g/mol
2.50  2.016 g H2  5.04 g H2
Example 3
•How many atoms are in 3.95
moles of beryllium?
6.02 10 atoms Be
3.95 mol Be 

mol Be
23
3.95  6.02 10 atoms Be  2.38 10 atoms Be
23
23
Example 4
•How many moles are in
5.15x1023 atoms of sulfur?
mol S
5.15 10 atoms S 

23
6.02 10 atoms S
23
5.15 10 mol S

0
.
855
mol
S
23
6.02 10
23
Example 5
•What is the mass of 2.00x1024 atoms
iron?
mol Fe
55.845 g Fe
2.00 10 atoms Fe 


23
6.02 10 atoms Fe mol Fe
24
2.00 10  55.845g Fe  186 g Fe
24
6.02 10
23
Example 6
•How many atoms are in 15.4 g
lithium?
mol Li 6.02 10 atoms Li
15.4 g Li 


6.941 g Li
mol Li
23
15.4  6.02 1023 atoms Li  1.34 1024 atoms Li
6.941