Unit 5
The Mole
S
The Mole
S  We are familiar with using a specific term to
represent a number of items in a group.
S  1 dozen = 12 units of something
S  1 case of Cokes = 24 Cokes
S  In chemistry we use the term MOLE to indicate a
collection of particles that = 6.02 x 1023
S  6.02 x 1023 is referred to as Avogadro’s number
S  1 mole of an element has 6.02 x 1023 particles
Avogadro’s Number
S  To help you better visualize the enormous size of
Avogadro's number, 6.02 x 1023, consider the following
analogies:
S  If we had 1 mole of rice grains, all the land area of the
earth would be covered with rice to a depth of about 75
meters! (246 ft)
S  One mole of rice grains is more grains than the number of
all grains grown since the beginning of time.
S  One mole of marshmallows (standard 1 in3 size) would
cover the United States to a depth of 650 miles.
Avagadro’s Number
S  If the Mount St. Helens eruption had released a
mole of particles the size of sand grains, the
entire state of Washington would have been
buried to a depth equal to the height of a 10-story
building.
S  A mole of basketballs would just about fit
perfectly into a ball bag the size of the earth.
The Mole
S  1 mole of Aluminum = 6.02 x 1023 atoms
S  1 mole of Sulfur = 6.02 x 1023 atoms
S  1 mole of Water (H2O) = 6.02 x 1023 molecules of H2O
S  1 mole of NaCl = 6.02 x 1023 molecules of NaCl
The Mole
S  We can use Avogadro’s number to convert between the number of
moles of a substance and the number of particles it contains.
S  If you have 4.00 moles of Sulfur (S), how many particles of S do
you have?
S  4.00 moles S x 6.02 x 1023 S atoms = 2.41 x 1024 S atoms
1 mole S atoms
S  If you have 3.01 x 1024 molecules of CO2 how many moles of CO2
do you have?
S  3.01 x 1024 CO2 molecules x
1 mole CO2
= 5.00 moles CO2
6.02 x 1023 CO2 molecules
The Mole
S  In a chemical formula the subscript numbers indicate the
number of atoms of each type of element.
S  Aspirin’s chemical formula is C9H8O4
S  In a molecule of aspirin there would be 9 Carbon atoms, 8
Hydrogen atoms, and 4 Oxygen atoms.
S  These number also indicate the number of moles of each
element.
S  Using this information, you can calculate the number actual
moles of each element.
Calculating Actual Moles of an
Element in a Compound
S  For 1.50 moles of aspirin, C9H8O4, how many moles of
Carbon, Hydrogen & Oxygen are present?
S  Carbon: 1.50 moles C9H8O4 x 9 moles C = 13.5 moles C
1 mole C9H8O4
S  Hydrogen:1.50 moles C9H8O4 x 8 moles H = 12 moles H
1 mole C9H8O4
S  Oxygen: 1.50 moles C9H8O4 x 4 moles O = 6 moles O
1 mole C9H8O4
S  How many moles of aspirin contain 0.480 moles of O
atoms?
Molar Mass
S  For any element, the quantity called MOLAR MASS is the
quantity in grams that equals the atomic mass of that
element.
S  Atomic mass of C = 12.01
S  Atomic mass of Ag = 107.9
S  Atomic mass of S = 32.07
12.01 g C = 1 mole C
107.9 g Ag = 1 mole C
32.07 g S = 1 mole S
Molar Mass of a Compound
S  Molar mass of a compound is the sum of the molar mass of
each element multiplied by the number of atoms in the
compound.
S  Atomic mass SO3 = Mass of S + 3 (Mass of O)
= 32.07 g + 3 (16.0 g) = 80.1 g = 1 mole SO3
S  Atomic mass NaCl = Mass of Na + Mass of Cl
= 22.99 g + 35.45 g = 58.44 g = 1 mole NaCl
Calculations Using Molar Mass
S  You can use the molar mass to change from moles of a
substance to grams or from grams to moles.
S  If a piece of jewelry requires 0.750 moles Ag, how many
grams of silver are needed?
S  1 mole Ag = 107.9 g of Ag
S  0.750 moles Ag x 107.9 g Ag = 80.93 g Ag
1 mole Ag
Calculations Using Molar Mass
S  A box of salt contains 737 g NaCl. How many moles of
NaCl are present in that box?
S  1 mole NaCl = 58.44 g NaCl
S  737 g NaCl x 1 mole NaCl = 12.6 mole NaCl
58.44 g NaCl
Physical vs. Chemical Changes
S  What type of change did we see when water boiled?
S  Physical Change
S  Altered the appearance but not the formula
S  If physical change only changes appearance (physical
properties), what other changes can happen?
S  Chemical change
S  Substances are changed on a molecular level to create new
substances
S  Example: Our reaction to produce “elephant toothpaste”
Chemical Reactions
S  Chemical reactions produce chemical change.
S  Bonds between elements are broken and new bonds are formed.
S  Example: Alka Seltzer in Water:
S  NaHCO3 (Sodium Hydrogen Carbonate) and C6H8O7 (Citric
Acid) react to form CO2 and other products.
S  Evidence of chemical reactions:
S  Change in color
S  Formation of a gas (bubbles)
S  Formation of a solid (precipitate)
S  Heat (or a flame) produced or heat absorbed
Chemical Equations
S  Chemical equations are like a recipe that tells us the
materials we need and what will be produced.
S  If you were going to make a cake:
S  Flour + Eggs + Sugar + Milk
Cake
S  A simple chemical equation is similar. If you burn charcoal
in a BBQ pit:
S  C (s) + O2 (g)
CO2 (g)
S  C & O are called reactants
S  CO2 is product
S  Abbreviations in parenthesis represent the physical state
Chemical Equations
S  Every chemical equation must be BALANCED meaning
the number of atoms of reactants must equal the number of
atoms of products.
S  H2 (g) + O2 (g)
H2O (g)
S  Products: 2 atoms H, 2 atoms O
S  Reactants: 2 atoms H, 1 atom O
S  Is this balanced?
S  Balanced Equation:
2H2 (g) + O2 (g)
2H2O (g)
S  Coefficients are placed in front of the formulas
S  These multiply the formula by the number of the coefficient.
Types of Reactions
S  Most reactions fit into 4 general reaction types:
S  1. Combination Reactions- two or more elements combine
to form one product.
S  S (s) + O (g)
SO2 (g)
S  2. Decomposition Reactions- a reactant splits into two or
more simpler products.
S  2HgO (s)
2Hg (l) + O2 (g)
Types of Reactions
S  3. Replacement Reactions – elements in a compound are
replaced by other elements.
S  Two Types:
S  Single Replacement – a reacting element switches places with
an element in the other reacting compound
S  A + BC
AC + B
S  Zn (s) + 2HCl (aq)
ZnCl2 (aq) + H2 (g)
S  Double Replacement – the positive ions in the reacting
compounds switch places.
S  AB + CD
AD + CB
S  BaCl2 (aq) + Na2SO4 (aq)
BaSO4 (s) + 2NaCl (aq)