Mole
A MOLE IS JUST A NUMBER
6 . 0 2 X 1 0 23
Mole Map
Molar Density
 Density is Mass/Volume
 Molar density = Mass of one mole

Volume of one mole
= Molar Mass
22.4L
Argon= 39.95 g = 1.78g/l
22.4 l
Gas Density
 http://www.youtube.com/watch?v=w7G4o2alLww&
feature=related
 Mole Density and Molar Mass of a Gas Experiment
 http://www.youtube.com/watch?v=D0CzquuOrxM
Percent Composition
 When the grams are not given, use the molar mass
 Molar mass of each element X 100
Molar mass of compound
Example: H2SO4
1.) H—2(1.01)=2.02
 S—1(32.06)=32.06
 O—4(16.00)=64.00
2). Get total mass
 2.02 + 32.06 + 64.00= 98.08 (this is bottom #)
3). H 2.02/98.08 X 100= 2.06%
 S 32.06/98.08 X 100= 32.65%
 O 64.00/98.08 X 100= 65.25%
Percent Comp by molar mass
 http://www.youtube.com/watch?v=JmDd_nJaP3o&
feature=related
When mass is given, use mass as part over whole.
 Grams element/grams compound X 100
 Example: if 64 g of Mg is combined with 32 g oxygen,




what is the percent composition?
64
X 100= 66.7 %
64 + 32
32
X 100= 33.3%
64 + 32
% Comp by mass
 http://www.youtube.com/watch?v=DB2YCK2p56o
Empirical vs. Molecular Formulas
Empirical Formula
 Consists of the symbols
and the subscripts
showing the smallest
whole number ratio of
atoms.
 Subscripts are reduced.
 May not be the actual
formula.
 Examples: CO, CO3,
N3P
Molecular Formula
 The actual formula.
 You can reduce the
subscripts.
 Examples: C2O2, C2O6,
N9P3
How do you calculate empirical formulas?
 1. Change the % sign into a g. (g for grams)
 2. Divide mass by molecular weight(convert grams
into moles)
 3. Divide by the smallest.
 4. If necessary, multiply to make whole numbers.
 5. These are your SUBSCRIPTS.
Example of empirical formulas.
 Find the empirical formula of a compound found to
contain 63.52% Fe and 36.48% S.
 63.52 g Fe
=
36.48 g S =
55.85 g
32.07 g
Fe1S1
Example #2
 Find the empirical formula of a compound found to
contain 26.56% K, 35.41% Cr, and the remainder O.
 26.56 g K
 35.41 g Cr
 38.03 g O
Empirical to Molecular
 X(empirical formula) = molecular formula
 X = molecular weight of molecular formula




molecular weight of empirical formula
Example: The empirical formula of a compound of P and
O was found to be P2O5. The molar mass of the
compound is 283.89 g/mol. What is the molecular
formula?
1. Find the molecular weight of the empirical formula.
2. Divide molecular/empirical.
3. Multiply x by empirical formula.
Example
 http://www.youtube.com/watch?v=LPN-3d0FOMU
 Determine the molecular formula for a compound
that is 40.0% C, 6.6% H, and 53.4 % O. The molar
mass is 120 g.
 Determine the molecular formula of a compound
with an empirical formula of CH and a formula mass
of 78.110 amu.
Practice
 1. Find the percent composition of Mg(OH)2.
 2. Find the percent composition of a compound that
contains 1.94g C, 0.48g H, and 2.58g S in a 5.0g
sample.
 3.Determine the empirical formula of a compound
containing 1.723gC, 0.289gH, and 0.459gO.
 4. Find the molecular formula of a compound that
contains 30.45gN and 69.55gO. The molar mass is
92.02g/mol.