The Mole: Avogadro’s number
How much is:
• A dozen?
• A century?
• A mole?
Can you count a mole of pennies?
• If you could count 5 per second, it would take
you
• 6.02 x 10 23 ÷ 5 pennies/second ÷ 60
sec/min ÷ 60 min/hr ÷ 24hrs/day ÷ 365
days/yr =
Can you spend a mole of dollars?
• If you could spend $1,000,000 every second it
would take you
• 6.02 x 10 23 ÷ $1,000,000/sec ÷ 60 sec/min
÷ 60 min/hr ÷ 24hrs/day ÷ 365 days/yr =
When measuring amounts, you can count
or you can mass them.
If I want 2 dozen baseballs, I can count
Or I can mass
of baseballs.
baseballs
Since we can’t count a mole of atoms,
we MUST mass chemicals to measure
moles
6.02 x 10 23 atoms of sulfur
32.07 grams of sulfur
6.02 x 10 23 atoms of carbon
12.01 grams of carbon
How do we measure moles?

mole = number of particles equal to the
number of atoms in 12 g of C-12



1 atom of C-12 weighs exactly
1 mole of C-12 weighs exactly
The number of particles in 1 mole is called
____________ Number = 6.0221421 x 1023

1 mole of C atoms weighs
atoms

and has
the average mass of a C atom is 12.01 amu
How do we measure moles?
• The atomic mass on your periodic table is the
mass of a mole of atoms of that element.
• What is the mass of a mole of copper atoms?
• So, to count 6.02 x 1023 copper atoms, we
mass out
on the scale.
Mole and Mass Relationships
Substance Pieces in 1 mole
Weight of 1 mole
hydrogen
6.022 x 1023 atoms
1.008 g
carbon
6.022 x 1023 atoms
12.01 g
oxygen
6.022 x 1023 atoms
16.00 g
sulfur
6.022 x 1023 atoms
32.06 g
calcium
6.022 x 1023 atoms
40.08 g
chlorine
6.022 x 1023 atoms
35.45 g
copper
6.022 x 1023 atoms
63.55 g
1 mole
Sulfur
32.06 g
1 mole
Carbon
12.01 g
Find the mass of:
• A mole of silicon atoms
• 6.02 x 1023 atoms of nitrogen
• 6.02 x 1023 atoms of sodium
• 2 moles of sodium atoms
How many atoms are in:
• A mole of silicon
• 14.01 g of nitrogen
• 2 moles of sodium
• 45.98 g of sodium
How many things are in:
• A mole of footballs
• A mole of water
• 2 moles of pencils
• ½ mole of lead
Molar mass is the mass of one mole of
a substance
• To find the molar mass of an element, look on
the periodic table.
• To find the molar mass of a compound,
add all the masses of its elements
Chemical Formulas as Conversion
Factors
• 1 spider  legs
• 1 chair  legs
• 1 H2O molecule  H atoms & O atom
Molar Mass of Compounds
• the relative weights of molecules can be
calculated from atomic weights
Formula Mass = 1 molecule of H2O
• since 1 mole of H2O contains 2 moles of H and 1
mole of O
Molar Mass = 1 mole H2O
Find the molar mass of:
•
•
•
•
•
•
•
•
•
Ammonium phosphate
NH4+
PO43(NH4)3PO4
=
=
Carbon dioxide
CO2
=
=
Find the molar mass of:
•
•
•
•
•
•
Hydrogen gas
H2
=
Elemental hydrogen
H
=
Find the molar mass of:
•
•
•
•
•
•
•
•
Iron
Fe
=
Iron (III) hydroxide
Fe3+
OHFe(OH)3
=
=
Converting to and from moles.
• To convert between moles and particles,
simply multiply or divide by Avogadro’s
number.
• 2 mol x (6.02 x 1023 particles/mol) = 1.20 x 1024 particles
• 3.1 x 1024 particles x (1 mol/ 6.02 x 1023 particles) = 5.0 mol
Remember unit
factors?
Converting to and from moles.
• Converting between moles and mass requires
the molar mass of the substance from the
periodic table.
• Element: Ag =
g/mol
• Ionic compound: CaCl2 =
g/mol
• Covalent compound: NO2 =
g/mol
• Always keep at least two decimal place on all
values taken from the periodic table.
Converting to and from moles.
• To convert from moles to grams, multiply
by molar mass:
0.500 mol H2O x (18.0g/mol) =
9.00g H2O
• To convert from grams to moles, divide by
molar mass:
54g H2O x (1mol/18.0g) =
3.0 mol H2O
Converting to and from moles.
• For gases, use the fact that at STP, 1 mol of
any gas has a volume of
Liters.
• What is STP?
• Standard Temperature =
K or °C
• Standard Pressure = atmosphere =
–
mm Hg (barometric) =
kPa.
Converting to and from moles.
• To go from moles to volume, multiply by
22.4L.
• 3.00 mol x (22.4L/mol) =
of gas
• To go from volume to moles, divide by 22.4L
• 44.8L x (1mol/22.4L) =
moles of gas
Converting to and from moles.
• A convenient tool for making these
conversions is called a “mole map.”
• With the mole at the center, we can put all of
the aforementioned calculations together into
one simple picture.
The Mole Map
Gas
Volume
@ STP
#
Particles
Mole
Mass
Percent Composition
•
Percentage of each element in a compound
– By mass
•
Can be determined from
1. the
of the compound
2. the experimental mass analysis of the compound
3. the total mass of
•
The percentages may not always total to 100% due to
part
Percentage 
 100%
whole
What percentage of water is Oxygen?
1. Formula of the compound
2. Mass of the compound
3. Mass of each element
Mass Percent as a
Conversion Factor
• the mass percent tells you the mass of a
constituent element in 100 g of the
compound
– the fact that NaCl is 39% Na by mass means that
100 g of NaCl contains 39 g Na
• this can be used as a conversion factor
– 100. g NaCl  39.0 g Na
39 g Na
g NaCl 
 g Na
100 g NaCl
100 g NaCl
g Na 
 g NaCl
39 g Na
Empirical Formulas
• The simplest, whole-number ratio of atoms in a
molecule is called the
– can be determined from percent composition or
combining masses
• The Molecular Formula is a multiple of the
Empirical Formula
100g
%A
mass A (g)
100g
%B
mass B (g)
MMA
MMB
moles A
moles A
moles B
moles B
Empirical Formulas
Hydrogen Peroxide
Molecular Formula = H2O2
Empirical Formula = HO
Benzene
Molecular Formula =
Empirical Formula =
Glucose
Molecular Formula =
Empirical Formula =
All these molecules have the same Empirical
Formula. How are the molecules different?
Name
Molecular
Formula
glyceraldehyde
C3H6O3
Empirical
Formula
CH2O
erythrose
C4H8O4
CH2O
arabinose
C5H10O5
CH2O
glucose
C6H12O6
CH2O
Molecular Formulas
• The molecular formula is a multiple of
• To determine the molecular formula you
need to know
and the
of the compound
What is the molecular formula for ethane if it has a
molar mass of 30.0 g/mol?
CH3=
g/mol
ratio 
Molecular formula =

Determine the Molecular Formula of Cadinene if it
has a molar mass of
204 g and an empirical formula of C5H8
Ask a chemist, they always have
Solutions
Solutes and Solvents
• Solution:
• Solute:
• Solvent:
– (usually found in the largest amounts)
– If the solvent is water, then it is called an
Solubility
• Why does sugar “disappear” in your iced
tea?
• How do fish breathe underwater?
• Why does soda go flat faster when left out
than when it is refrigerated?
• It is all based on solubility!
Solubility
• Example: iced tea
– Solute
– Solvent
States and Solutions
• Solutions can be any state of matter
– Solid-solid:
– Solid-liquid:
– Liquid-liquid:
– Liquid-gas:
– Gas-gas:
How Things Dissolve
• Need to find/ create “__________” in
water for the dissolving substance to move
• Get _______________ between water
molecules and molecules of the solute
Why some coffee is so strong it can
“Put hair on your chest.”
• “Strong’ coffee has more
coffee dissolved in a given
amount (say 1 pot) than
“weak” coffee.
– Strong coffee =
concentrated
– Weak coffee = dilute
• Concentration:
Molarity (M)
• Most common way to express concentration
• Molarity is the number of ____________ of solute
dissolved in each __________of solution
• Formula
M = moles of solute
liters of solution
• Dependent on _______________
• The higher the molarity the stronger the
concentration
Practice Problems
1. What is the molarity when 6.0 moles of
glucose is dissolved in water to make 3.0 L of
solution.
2. How many moles of sodium chloride are
there in 500 mL of 4.0 M solution?
3. What is the volume of 3.0 M solution that
contains 15 moles of glucose?
How does something so strong
become so weak?
• The answer is dilution.
• The more dilute something is, the lower the
concentration (it’s weaker).
• To accomplish this, add more solvent
• How do we know how much to add?
M 1 V1 = M 2 V2
–Typically start with a highly concentrated solution
and dilute down to what you need
Figure 15.8: Process of making 500 mL of a 1.00 M acetic acid
solution.
End of Chapter