Formula Weight & Molecular Weight
• The FORMULA WEIGHT of a compound
equals the SUM of the atomic masses of the
atoms in a formula.
• If the formula is a molecular formula, the
formula weight is also called the MOLECULAR
WEIGHT.
The MOLE
• Amount of substance that
contains an Avogadro’s
number (6.02 x 10 23)of
formula units.
The MOLE
• The mass of 1 mole of atoms,
molecules or ions = the formula
weight of that element or
compound in grams. Ex. Mass of 1
mole of water is 18 grams so molar
mass of water is 18 grams/mole.
Formula for Mole
Mole = mass of element
formula weight of
element
Sample Mole Calculations
1 mole of C = 12.011 grams
»
12.011 gm/mol
• 0.5 mole of C = 6.055 grams
»
12.011 gm/mol
Avogadro’s Number
• Way of counting atoms
• Avogadro’s number
23
= 6.02 x 10
Point to Remember
One mole of anything is 6.02
23
x 10 units of that
substance.
And……..
• 1 mole of C has the same
number of atoms as one mole
of any element
Formula Weight & Molecular Weight
• The FORMULA WEIGHT of a compound
equals the SUM of the atomic masses of the
atoms in a formula.
• If the formula is a molecular formula, the
formula weight is also called the MOLECULAR
WEIGHT.
Summary
• Avogadro’s Number gives the
number of particles or atoms in a
given number of moles
• 1 mole of anything = 6.02 x 10
atoms or particles
23
Sample Problem 2
• Compute the number of
atoms and moles of atoms in
a 10.0 gram sample of
aluminum.
Solution
• PART I:
• Formula for Mole:
–Mole = mass of element
atomic mass of element
Solution (cont.)
• Part II:
atoms
To determine # of
• # atoms = moles x Avogadro’s
number
Problem # 2
• A diamond contains 5.0 x 1021
atoms of carbon. How many
moles of carbon and how
many grams of carbon are in
this diamond?
Molar Mass
• Often referred to as molecular mass
–Unit = gm/mole
• Definition:
–mass in grams of 1 mole of the
compound
Example Problem
• Determine the Molar Mass of
C6H12O6
Solution
• Mass of 6 mole C = 6 x 12.01 = 72.06 g
• Mass of 12 mole H = 12 x 1.008 = 12.096 g
• Mass of 6 mole O = 6 x 16
= 96.00 g
• Mass of 1 mole C6H12O6
180.16 g
=
Problem #3
• What is the molar mass of
(NH4)3(PO4)?
Molar Mass
• Often referred to as molecular mass
–Unit = gm/mole
• Definition:
–mass in grams of 1 mole of the
compound
Sample Problem
•
•
•
•
•
•
•
•
•
•
Given 75.99 grams of (NH4)3(PO4), determine the ff:
1. Molar mass of the compound
2. # of moles of the compound
3. # of molecules of the compound
4. # of moles of N
5. # of moles of H
6. # of moles of O
7. # of atoms of N
8. # of atoms of H
9. # of atoms of O