Transcript Mole Power Point

The Mole
I. Molar
Conversions
I
II
III
IV
What is the Mole?
A counting number (like a dozen or a pair)
•
Avogadro’s number 6.02  1023
•
1 mole = 6.02  1023 things. (things can be
atoms, molecules, formula units)
A
large amount!!!!
A. What is the Mole?
1 mole of hockey pucks would
equal the mass of the moon!
1 mole of basketballs would fill a
bag the size of the earth!
1 mole of pennies would cover the
Earth 1/4 mile deep!
Example
n
How many molecules are in
2.50 moles of C12H22O11?
6.02  1023
2.50 mol molecules
1 mol
= 1.51  1024
molecules
C12H22O11
Mole- Volume
n
n
At the same temperature:
 Equal volumes of gases contain
equal numbers of moles
STP
 Standard temperature and pressure
 1 mole of any gas at STP has a
volume of :
22.4 L
Example
n
How many moles of neon are in
44.8L of neon at STP?
44.8 L
1 mol
22.4 L
= 2 mol
Molar Mass
How much do I
weigh?? 
Molar Mass
n
Mass of 1 mole (6.02 X 1023 atoms or
molecules) of an element or
compound.
n
Atomic mass tells the...
 atomic mass units per atom (amu)
 grams per mole (g/mol)
n
Round to 2 decimal places when
Molar Mass Examples
This is easy! Just look at the periodic
table!
•
Phosphorus
30.97 g/mol
•
Aluminum
26.98 g/mol
•
Helium
•
Silver
4.00 g/mol
107.87 g/mol
Molar Mass Examples
WATER:
 H2O
H → 2 x 1.01 g/mol = 2.02 g/mol
O → 1 x 16.0 g/mol = 16.0 g/mol
 Ca(OH)2
18.02 g/mol
Ca 40.08 + O2(16) + H 2(1.01) = 74.10 g/mol
Molar Mass
n
sodium bicarbonate
 NaHCO3
 84.01 g/mol
n
sucrose
 C12H22O11
 342.34 g/mol
Example
n
How many moles of carbon are
in 26 g of carbon?
26 g C 1 mol C
12.01 g C
= 2.2 mol C
Examples
n
Find the mass of 2.1  1024
molecules of NaHCO3.
2.1  1024
molecules
1 mol
84.01 g
6.02  1023 1 mol
molecules
= 290 g NaHCO3
A. Percentage Composition
n
the percentage by mass of each
element in a compound
mass of element
% composition 
 100
total mass
A. Percentage Composition
n
Find the % composition of Cu2S.
%Cu =
%S =
127.10 g Cu
 100 =
159.17 g Cu2S
79.852% Cu
32.07 g S
159.17 g Cu2S
 100 =
20.15% S
A. Percentage Composition
Find the percentage composition
of a sample that is 28 g Fe and
8.0 g O.
28 g
 100 = 78% Fe
%Fe =
36 g
n
%O =
8.0 g
36 g
 100 = 22% O
A. Percentage Composition
n
How many grams of copper are in
a 38.0-gram sample of Cu2S?
Cu2S is 79.852% Cu
(38.0 g Cu2S)(0.79852) = 30.3 g Cu
Empirical/Molecular
Formulas
The Mole
I
II
III
IV
B. Empirical Formula
n
Smallest whole number ratio of
atoms in a compound
C2H6
reduce subscripts
CH3
Empirical Formula
1.
Find mass (or %) of each
element. (may be given)
2. Find moles of each element. (g to
moles)
3. Divide moles by the smallest # to
find subscripts.
4. When necessary, multiply
subscripts by 2, 3, or 4 to get
Empirical Formula
n
Find the empirical formula for a
sample of 25.9% N and 74.1% O.
25.9 g 1 mol
= 1.85 mol N
=1N
1.85 mol
14.01 g
74.1 g 1 mol
= 4.63 mol O
= 2.5 O
16.00 g
1.85 mol
Empirical Formula
N1O2.5
Need to make the subscripts whole
numbers  multiply by 2
N2O5
Examples
n
n
An organic compound is found to
contain 92.25% carbon and 7.75%
hydrogen. Determine the
empirical formula.
 Empirical Formula: CH
What is the empirical formula of a
compound that contains 53.73%
Fe and 46.27% S?
 Empirical Formula: Fe2S3
Molecular Formula
n “True Formula” - the actual number
of atoms in a compound
empirical
formula
CH3
?
molecular
formula
C2H6
C. Molecular Formula
1. Find the empirical formula.
2. Find the empirical formula mass.
3. Divide the molecular mass by the
empirical mass.
4. Multiply each subscript by the
answer from step 3.
MF mass
n
EF mass
EF n
Molecular Formula
n
The empirical formula for ethylene
is CH2. Find the molecular formula
if the molecular mass is 28.1
g/mol?
empirical mass = 14.03 g/mol
28.1 g/mol
14.03 g/mol
= 2.00
(CH2)2  C2H4