Transcript Unit 11: The Mole

FLASHBACK
In your notes … answer the following question to
the best of your ability:
1.) How many atoms would there be in one mole?
2.) What would be the mass of one mole of
Carbon atoms?
3.) What would be the mass of 2 moles of H2O?
THE MOLE
BY: MS. BUROKER
WHAT IS THE MOLE?
The mole is the SI base unit used to
measure the amount of a substance.
* commonly abbreviated mol
The mole can be defined as the
number equal to the number of
carbon atoms in 12.01 grams of
carbon.
AVOGADRO’S NUMBER
One mole of something consists of 6.022 x 1023 units of that
substance.
1 mol = 6.022 x 1023 particles
Molecules
Atoms
Formula Units
(Ionic Compounds)
1 mole of any element has a mass in grams that is
equal to its average atomic mass
Silver (Ag)
Lead (Pb)
Average atomic
mass of this
element
107.9 amu
207.2 amu
Mass of this
sample
107.9 g
207.2 g
Number of atoms
in this sample
6.022 x 1023
atoms
6.022 x 1023
atoms
MOLAR MASS
The molar mass of an element is the
mass in grams of one mole of any pure
substance.
The molar mass of a compound or
molecule is equal to the sum of the mass
(in grams) of the elements involved.
EXAMPLE:
CHCl3
C: 12.01g/mol
H: 1.01g/mol
Cl: 35.45g/mol x 3= 106.35g
MOLE RELATIONSHIP AND
COMPOUNDS
A chemical formulas tell us the
number of atoms that make the
compound … but, it can also tell us
something about the number of moles
of atoms in the compound!
For example: CaCl2
1 calcium atom
2 chlorine atoms
In 1mol of CaCl2,
there is 1mol of
calcium
In 1mol of CaCl2,
there are 2moles of
chlorine
LET’S PRACTICE!!
Determine the number of moles of
chloride ions in 2.50mol ZnCl2
5.00mol Cl-
Calculate the number of moles of each
element in 1.25mol glucose (C6H12O6)
7.50mol C
15.0mol H
7.5mol O
SOME VOCABULARY …
Percent Composition: The percent by mass of
each element in a compound.
Empirical Formula: The formula with the
smallest whole number ratio of the
elements.
Molecular Formula: The formula which
specifies the actual number of atoms of
each element in one molecule or formula
unit.
PERCENT COMPOSITION
Mass of element X 100 = Percent by
Mass
Mass of compound
Examples:
Sodium hydrogen carbonate, also called baking
soda, is an active ingredient in some antacids
used for the relief of indigestion. Determine
the percent composition of sodium hydrogen
carbonate.
EMPIRICAL FORMULAS
Empirical formulas may or may not
be the same as the molecular
formula …
Example: Hydrogen peroxide
empirical formula: HO
molecular formula: H2O2
HOW DO I FIND THE EMPIRICAL
FORMULA?
1.)Find the number of moles of each element.
* If given percent composition- assume
100.0g
2.) Calculate the simplest ratio of moles of
the elements by dividing each number of
moles by the smallest whole number ratio.
* If the number are not whole, then
multiply by the smallest number that will
produce a ratio of whole numbers.
MOLECULAR FORMULAS
Experimentally determined molar mass
=n
Mass of Empirical Formula
Multiply the numbers in the
empirical formula by the value
of “n”
Molecular formula = (empirical formula) n