February 24, 2014
• Chemical Formulas
• The Mole
• One-Step Molar Conversions
Materials
• Calculator
• Periodic Table
• A good attitude about math
Chemical Formulas
• Covalent:
C8H18
– Octane
– # Carbon: 8
– # Hydrogen: 18
• Ionic:
–
–
–
–
Al2(SO4)3
Aluminum Sulfate
# Aluminum: 2
# Sulfur: 3
# Oxygen: 12
• (4 O’s in each sulfate, 3 sulfates in the compound, 3 x 4 = 12)
Formula Mass
• The mass of one molecule, formula unit, or
ion.
• Calculate by adding atomic masses together
from the periodic table.
• Units: amu (atomic mass unit)
Example: HCl
• Mass H + Mass Cl
• 1.0079 + 35.453 = 36.4069 amu
Example: NH4NO3
• Mass N + 4(Mass H) + Mass N + 3(Mass O)
• 14.007 + 4(1.0079) + 14.007 + 3(15.999) =
• 80.0426 amu
• OR
• 2(Mass N) + 4(Mass H) + 3(Mass O)
• 2(14.007) + 4(1.0079) + 3(15.999) =
• 80.0426 amu
Example: PO43• Mass P + 4(Mass O)
• 30.974 + 4(15.999) = 94.97 amu
• The charge does not affect the mass because
the mass of an electron is so very small that it
is negligible (able to be ignored).
And now: MOLES
The Mole
• 1 mole = 6.02 × 1023 particles
Avogadro’s number
• It is the number of atoms in exactly 12.0 g of
carbon-12
• It is used the same way as:
– A dozen (12)
– A pair (2)
– A score (20)
How did they come up with
6.02 x 1023 anyway?
• If you divide the charge on a mole of electrons
by the charge on a single electron you obtain a
value of Avogadro’s number of 6.02214154 x
1023 particles per mole.
Chemical Formulas
• Covalent:
–
–
–
–
Octane
Moles Octane: 1
Moles Carbon: 8
Moles Hydrogen: 18
• Ionic:
–
–
–
–
–
C8H18
Al2(SO4)3
Aluminum Sulfate
Moles aluminum sulfate: 1
Moles Aluminum: 2
Moles Sulfur: 3
Moles Oxygen: 12
Molar Mass
• Mass of one mole (6.022 × 1023) of any
molecule, formula unit, or ion.
• Calculate by adding atomic masses together
from the periodic table.
• Units: g/mol
Example: H2SO4
• 2(Mass H) + Mass S + 4(Mass O)
• 2(1.0079) + 32.066 + 4(15.999)
• 98.0178 g/mol
Example: Ca(NO3)2
• Mass Ca + 2(Mass N) + 6(Mass O)
• 40.078 + 2(14.007) + 6(15.999) =
• 164.086 g/mol
• OR
• Mass Ca + 2((Mass N) + 3(Mass O))
• 40.078 + 2((14.007) + 3(15.999)) =
• 164.086 g/mol
Molar Conversions
Mass in
grams
Divide by the
molar mass
Multiply by the
molar mass
Amount in
moles
Example: How many moles are in 2.0 g
calcium chloride?
• Start with: g
• End with: moles
• Math: divide by molar mass
• Molar mass of calcium chloride, CaCl2
• 40.078 + 2(35.453) = 110.984 g/mol
• 2.0 g CaCl2 = 0.018 mol
110.984 g/mol
Example: How many grams are in 1.5
mol potassium iodide?
• Start with: moles
• End with: g
• Math: multiply by molar mass
• Molar mass of potassium iodide, KI
• 39.098 + 126.90 = 165.998 g/mol
• 1.5 mol x 165.998 g/mol = 248.997 g
Molar Conversions
Amount in
moles
Multiply by
Avogadro’s #
Divide by
Avogadro’s #
Number of
particles
•
•
•
•
Formula unit
Molecule
Ion
Atom
Example: How many formula units are
in 6.0 mol calcium bromide?
• Start with: mol
• End with: formula units (particles)
• Math: multiply by Avogadro’s number
• 6.0 mol x 6.02 x 1023 =3.612 x 1024 f. units
• Calculator Help: Use the EE button
• EE = x 10
• 6.02 x 1023 = 6.02EE23
Example: How many moles are in 5.0 ×
1022 molecules H2?
• Start with: molecules (particles)
• End with: moles
• Math: divide by Avogadro’s number
• 5.0 x 1022 molecules
= 0.083 mol
• 6.02 x 1023 molecules/mol
• Calculator Help: Use the EE button
• 6.02 x 1023 = 6.02EE23