Molar Relationships
Names associated with an amount
Can you think of any more?????
The Mole…..
The mole (mol) is the amount of a
substance that
contains as many elementary
entities as there
are atoms in exactly 12.00 grams
of 12C
1 mol = NA = 6.0221367 x 1023
Avogadro’s number (NA)
What is the mass of one mole of:
S
C
Hg
Cu
Fe
3.2
Molar Mass
 The Mass of 1 mole (in grams)
 Equal to the numerical value of the average
atomic mass (get from periodic table)
1 mole of C atoms
=
1 mole of Cu atoms
=
1 mole of S atoms
=
1mole of Hg atoms
1 mole of Fe atoms
=
=
Learning Check!
Find the molar mass
(usually we round to the tenths place)
A. 1 mole of Br atoms = 79.9 g/mole
B. 1 mole of Sn atoms = 118.7 g/mole
Molecular mass (or molecular weight) is the sum of
the atomic masses (in amu) in a molecule.
1S
SO2
2O
SO2
32.07 amu
+ 2 x 16.00 amu
64.07 amu
For any molecule
molecular mass (amu) = molar mass (grams)
1 molecule SO2 = 64.07 amu
1 mole SO2 = 64.07 g SO2
Let’s try some more……………..
3.3
Molar Mass of Molecules and
Compounds
Mass in grams of 1 mole equal numerically to
the sum of the atomic masses
1 mole of CaCl2
= 111.1 g/mol
1 mole Ca x 40.1 g/mol
+ 2 moles Cl x 35.5 g/mol
Practice with this one:
= 111.1 g/mol CaCl2
1 mole of N2O4
=
Learning Check!
A. Molar Mass of K2O = ? Grams/mole
B. Molar Mass of antacid Al(OH)3 = ?
Grams/mole
Learning Check
Prozac, C17H18F3NO, is a widely used
antidepressant that inhibits the uptake of
serotonin by the brain. Find its molar mass.
So, if one mole = the formula mass how do we
calculate….
 The mass of 05 mol of Calcium Carbonate
 The mass of 2.25 mol of Sodium Chloride
How many moles are there in?
 100 g of Magnesium Hydroxide ?
 64 g of Oxygen ?
Converting to # of atoms or molecules
 How many atoms are in 3.00 moles of Iron?
 How many atoms are in 0.25 moles of Water?
Molar Mass
The molar mass of a compound is found by adding
Together the molar masses of all of its elements, taking
Into account the number of moles of each element present.
Homework: pg 157 # 5-11
Factor-Label Method (also called… dimensional
analysis)
 Use fractions that include numbers and units to
convert from one item to another.
 All fractions must have a valued of “1”
 Example problem: How many seconds are there in
one year?
Types of Mole Conversion Problems:
 Grams to Moles
---
Moles to Grams
 Example Problem:
 How many Moles are in 58 g of NaHCO3?
 How many grams are in 3.75 Moles of Water?
Moles
Particles (atoms,ions,molecules)
How many atoms are in .75 moles of Oxygen Gas?
How many moles are in 2.709 x 1025 molecules of Calcium
Hydroxide?
How many hydroxide ions are there in 4.5 Moles of Calcium
Hydroxide?
Percent Composition
• Percent Composition –
the percentage by mass of
each element in a compound
Part
_______
Percent =
x 100%
Whole
Percent composition Mass of element in 1 mol
x 100%
of a compound or = _________________
Mass
___ of 1 mol
molecule
Percent Composition
Example: What is the percent composition of
Potassium Permanganate (KMnO4)?
Molar Mass of KMnO4
K = 1(39.1) = 39.1
Mn = 1(54.9) = 54.9
O = 4(16.0) = 64.0
MM = 158 g
Percent Composition
Example: What is the percent composition of
Potassium Permanganate (KMnO4)?
Molar Mass of KMnO4 = 158 g
%
K
39.1 g K
158 g
54.9 g Mn
% Mn 158 g
K = 1(39.10) = 39.1
Mn = 1(54.94) = 54.9
O = 4(16.00) = 64.0
MM = 158
64.0 g O
%O
158 g
x 100 = 24.7 %
x 100 = 34.8 %
x 100 = 40.5 %
Percent Composition
Determine the percentage composition of sodium carbonate
(Na2CO3)?
Molar Mass
Na = 2(23.00) = 46.0
C = 1(12.01) = 12.0
O = 3(16.00) = 48.0
MM= 106 g
Percent Composition
46.0 g
% Na = 106 g
12.0 g
% C = 106 g
48.0 g
% O = 106 g
x 100% = 43.4 %
x 100% = 11.3 %
x 100% = 45.3 %
Hydrates
Hydrated salt – salt that has water molecules trapped
within the crystal lattice
Examples: CuSO4•5H2O , CuCl2•2H2O
Anhydrous salt – salt without water molecules
Examples: CuCl2
Can calculate the percentage of water in a
hydrated salt.
Hydrated Compounds: Chemicals that
usually have water associated with them.
 How they are written:
 BaCl2. 2H2O – Barium
Chloride dihydrate
 CuSO4.5H2O – Copper Sulfate pentahydrate
 NaCO3.10H2O-__________________
Percent Composition
If 145 grams of copper (II) sulfate pentahydrate is completely
dehydrated, how many grams of anhydrous copper sulfate will
remain?
CuSO4 . 5 H2O
1. Molar Mass
Cu = 1 x 63.55 = 63.55 g
S = 1 x 32.06 = 32.06 g
O = 4 x 16.00 = 64.00 g
MM = 159.61 g
H = 2 x 1.01 = 2.02 g
O = 1 x 16.00 = 16.00 g
MM = 18.02 g
Mass of 5 moles of H2O =
5 x 18.02 g = 90.1 g
Total Molar mass =
159.6 g + 90.1 g = 249.7 g
2. % CuSO4
159.6 g X 100 = 63.92 %
249.7 g
3. Grams anhydrous CuSO4
0.6392 x 145 =
92.7 g
Calculate the Molar Mass of Hydrates- ZnSO4.7H2O
 Na2CO3.10H2O
Formulas
Percent composition allow you to calculate the simplest
ratio among the atoms found in compound.
Empirical Formula – formula of a compound that expresses
lowest whole number ratio of atoms.
Molecular Formula – actual formula of a compound showing
the number of atoms present
Examples:
C4H10 - molecular
C2H5 - empirical
C6H12O6 - molecular
CH2O
- empirical
Determining Empirical Formula
PERCENT
Grams in 100g
sample
C
40 %
40 g
H
6.71%
6.71 g
O
53.3%
53.3 g
Moles
Mole
Ratio
Empirical
Formula
Try this one: An oxide of aluminum is formed
by the reaction of 4.151 g of aluminum with 3.692g
of oxygen. Calculate the empirical formula.
E
L
E
me
nts
PERCENT
Grams in 100g
sample
Moles
Mole
Ratio
Empirical
Formula
A 4.550 g sample of cobalt reacts with 5.475 g chlorine
to form a binary compound. Determine the empirical
formula for this compound.
E
L
E
me
nts
PERCENT
Grams in 100g
sample
Moles
Mole
Ratio
Empirical
Formula