Focusing Task
(White Board)
• How many protons, neutrons and
electrons are in an atom of calcium?
• What is the average atomic mass of
phosphorus?
• What is the difference between the mass
number of an atom and its average atomic
mass?
Moles & Molar Mass
Chemistry
Unit 6: Chemical Quantities
Lecture 6.1
Objectives
• Explain how the quantity “mole” is defined
• State the number of particles contained in
the quantity “mole”
• Determine the molar mass of a molecule
from its chemical formula and atomic
masses
The Mole
• A word that stands for a number of items
like:
– Pair
– Dozen
– Quadruplet
• Could stand for any items
How the Mole is Defined
• One mole is:
The number of atoms in a 12 gram sample
of the Carbon-12 isotope
How Many IS a Mole?
• 1 mol = 6.022 x 1023
• 602,000,000,000,000,000,000,000
Why such a big number?
Because atoms are so VERY SMALL!!
Molar Mass
Definition: the mass of one mole of
molecules or formula units
Example: What is the molar mass of Ca(OH)2?
Ca: 1 x 40.08 g/mol =
O: 2 x 16.00 g/mol =
H: 2 x 1.01 g/mol =
40.08 g/mol
32.00 g/mol
2.02 g/mol
74.10 g/mol
Determining Molar Mass
1. Determine which atoms, and how many
of each are contained within the
chemical formula
2. Multiply the number of each type of atom
in the chemical formula by the molar
(atomic) mass of each
3. Determine the sum of the products in #2
above.
Counting Atoms
• The subscript following an atomic symbol
tells you how many
• If there are parentheses, multiply the
subscript inside the parentheses by the
subscript outside the parentheses
• If the atom is listed more than once in the
formula, add them all together.
Practice Counting Atoms
• CH4
• Cu3(PO4)2
• CH3COOH
Practice
Calculate the molar masses of the following
chemicals: (show your work!)
• FeO
• NH4Cl
• Cu3(PO4)2
Quick Quiz
1.
How did scientists decide how many particles a “mole”
would represent?
A mole is the number of atoms found in a 12 g sample of carbon-12
2.
How many particles IS a “mole”?
A mole is equal to 6.022 x 1023 particles (items)
3.
How do you determine the molar mass of a chemical?
Multiply the number of each atom in the chemical formula by its atomic
mass, then add these together.
4.
What is the molar mass of H2CO3?
62.03 g/mol
5.
What is the molar mass of Sn(C2H3O2)4?
354.91 g/mol
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questions now