Download The Mole - Ms. Perez`s Science

THE MOLE: A SHORTCUT
FOR CHEMISTS
Source: http://en.wikipedia.org/wiki/Mole_(animal)
S-C-8-1_The Mole Presentation
The Mole
•The mole is a
counting unit for
chemists, the
same way a baker
uses a dozen.
•1 dozen = 12
objects
The Mole
• mole = 6.02 × 1023 objects
=
602,000,000,000,000,00
0,000,000 objects
• That’s almost a trillion
trillion!
• 6.02 × 1023 is called
Avogadro’s number.
• “Mole” in writing; “mol”
in calculations.
Representative Particles
•Moles can be
used to count
“representative
particles:”
atoms,
molecules, ions,
and formula
units.
Representative Particles
• The representative
particle of an ionic
compound is the formula
unit.
• The representative
particle of a covalent
compound is the
molecule.
• The representative
particle of an element is
the atom.
Atomic Masses
• What do the atomic masses
on the periodic table
represent?
• Carbon has an atomic mass
of 12; this means a carbon
atom weighs 12 atomic
mass units (amu).
• The actual mass of an atom
of carbon is only
2 x 10-23 grams.
• Practice: What is the atomic
mass of one molecule of
CO2?
12.01 + 16.00 + 16.00 = 44.01
Formula Weight
• Formula weight: The weight of a
molecule or an ionic compound.
• Molecule: CO2
12.01 + 16.00 + 16.00 = 44.01 amu
For molecules, formula weight is
also called the “molecular
weight.”
• Ionic compound: NaCl
22.99 + 35.45 = 58.44 amu
Molar Mass
• Molar mass = the mass of one mole.
• For atoms, molar mass is the same as atomic mass.
• The molar mass of a compound allows you to
convert between the amount of the element
(moles) and its mass (grams).
• If you want to convert from amount (moles) to mass
(grams): # of moles
Formula weight
Mass (in grams)
×
1 mol
=
• If you want to convert from mass (grams) to
amount (moles):
mass (grams)
×
1 mol
formula weight
=
# of moles
Molar Mass Examples
• 1 mol N = 14.01 g N
• Written as 14.01 g/mol
• Calculate the following molar masses:
•Br
•CaF2
•NO2
•NaCl
Molar Mass Examples: Solutions
Calculate the following molar masses:
• Br
79.90
• CaF2
40.08 + 19.00(2) = 78.08 g/mol
• NO2
14.01 + 16.00(2) = 46.01 g/mol
• NaCl
22.99 + 35.45 = 58.44 g/mol
Conversion Factors:
Mole-Mass Problems
• The red portions in the examples above are the
conversion factors.
• Conversion factor: A ratio equal to one that
expresses the same quality in two different ways.
• Another example: To find the number of eggs in 3
dozen:
3 dozen x 12 eggs/dozen = # of eggs
Mole-Mass Problems
1. What is the mass of 0.50 mol HCl?
2. What is the mass of 2 mol Zn?
3. How many moles are in 1.5 g of Cu?
4. How many moles are in 50 g H2SO4?
Mole-Mass Answers
1. What is the mass of 0.50 mol HCl?
0.50 mol × 36.46 g/mol = 18.23 g HCl
2. What is the mass of 2 mol Zn?
2 mol × 65.41 g/mol = 130.82 g
3. How many moles are in 1.5 g of Cu?
1.5 g × 1 mol/63.55 g = 0.02 mol
4. How many moles are in 50 g H2SO4?
50 g × 1 mol/98.09 g = 0.51 mol