CHEMISTRY
Matter and Change
CHAPTER
10
Table Of Contents
Section 10.1 Measuring Matter
Section 10.2 Mass and the Mole
Section 10.3 Moles of Compounds
Chapter 10: The Mole
Section 10.4 Empirical and Molecular Formulas
Section 10.5 Formulas of Hydrates
Click a hyperlink to view the corresponding slides.
SECTION
10.1
Measuring Matter
• Explain how a mole is
used to indirectly count
the number of particles of
matter.
• Relate the mole to a
common everyday
counting unit.
• Convert between moles
and number of
representative particles.
molecule: two or more
atoms that covalently
bond together to form a
unit
SECTION
Measuring Matter
Counting Particles
• Chemists need a convenient method for accurately
counting the number of atoms, molecules, or formula
units of a substance.
• The mole is the SI base unit used to measure the
amount of a substance.
mole
Avogadro’s number
Chemists use the mole to count atoms,
molecules, ions, and formula units.
10.1
SECTION
10.1
Exit
Measuring Matter
• 1 mole is the amount of atoms in 12 g of pure carbon12, or 6.02  1023 representative particles, which is
any kind of particle – an atom, a molecule, a formula
unit, an electron, an ion, etc.
• The number is called Avogadro’s number.
SECTION
10.1
Measuring Matter
Converting Between Moles and Particles
Converting Between Moles and Particles
• Conversion factors must be used.
(cont.)
• Moles to particles
• Particles to moles
• Use the inverse of Avogadro’s number as the
conversion factor.
Number of molecules in 3.50 mol of sucrose
1
SECTION
Mass and the Mole
10.2
• Relate the mass of an atom conversion factor: a
to the mass of a mole of
ratio of equivalent
atoms.
values used to express
the same quantity in
• Convert between number
different units
of moles and the mass of
an element.
• Convert between number
of moles and number of
atoms of an element.
molar mass
SECTION
10.2
Mass and the Mole
The Mass of a Mole
• 1 mol of copper (6.02 x 1023 atoms of
copper) and 1 mol of carbon (6.02 x 1023
atoms of carbon) have different masses.
• One copper atom has a different mass than 1
carbon atom.
A mole always contains the same number
of particles; however, moles of different
substances have different masses.
SECTION
10.2
Mass and the Mole
SECTION
10.2
Mass and the Mole
The Mass of a Mole (cont.)
Using Molar Mass
• Molar mass is the mass in grams of one
mole of any pure substance.
• Moles to mass
• The molar mass of any element is
numerically equivalent to its atomic mass and
has the units g/mol.
3.00 moles of copper has a mass of 191 g.
SECTION
10.2
Mass and the Mole
SECTION
10.2
Mass and the Mole
Using Molar Mass (cont.)
Using Molar Mass (cont.)
• Convert mass to moles with the inverse
molar mass conversion factor.
• This figure shows the steps to complete
conversions between mass and atoms.
• Convert moles to atoms with Avogadro’s
number as the conversion factor.
2
SECTION
10.3
Moles of Compounds
SECTION
10.3
Moles of Compounds
The molar mass of a compound can be
calculated from its chemical formula
and can be used to convert from mass
to moles of that compound.
• Recognize the mole relationships shown by a
chemical formula.
• Calculate the molar mass of a compound.
• Convert between the number of moles and mass of
a compound.
• Apply conversion factors to determine the number of
atoms or ions in a known mass of a compound.
representative particle: an atom, molecule, formula
unit, or ion
SECTION
10.3
Moles of Compounds
SECTION
10.3
Moles of Compounds
Chemical Formulas and the Mole
The Molar Mass of Compounds
• Chemical formulas indicate the numbers
and types of atoms contained in one unit of
the compound.
• The molar mass of a compound equals the
molar mass of each element, multiplied by
the moles of that element in the chemical
formula, added together.
• One mole of CCl2F2 contains one mole of C
atoms, two moles of Cl atoms, and two moles
of F atoms.
SECTION
10.3
Moles of Compounds
Converting Moles of a Compound to Mass
• For elements, the conversion factor is the
molar mass of the compound.
• The procedure is the same for compounds,
except that you must first calculate the molar
mass of the compound.
• The molar mass of a compound
demonstrates the law of conservation of
mass.
SECTION
10.3
Moles of Compounds
Converting the Mass of a Compound to
Moles
• The conversion factor is the inverse of the
molar mass of the compound.
3
SECTION
10.3
Moles of Compounds
SECTION
10.3
Moles of Compounds
Converting the Mass of a Compound to
Number of Particles
Converting the Mass of a Compound to
Number of Particles (cont.)
• Convert mass to moles of compound with
the inverse of molar mass.
• This figure summarizes the conversions
between mass, moles, and particles.
• Convert moles to particles with Avogadro’s
number.
SECTION
10.4
Empirical and Molecular Formulas
• Explain what is meant by
the percent composition
of a compound.
• Determine the
empirical and molecular
formulas for a
compound from mass
percent and actual
mass data.
percent by mass: the
ratio of the mass of each
element to the total
mass of the compound
expressed as a percent
SECTION
10.4
Empirical and Molecular Formulas
Percent Composition
• The percent by mass of any element in a
compound can be found by dividing the
mass of the element by the mass of the
compound and multiplying by 100.
percent composition
empirical formula
molecular formula
A molecular formula of a compound is
a whole-number multiple of its
empirical formula.
SECTION
10.4
Empirical and Molecular Formulas
SECTION
10.4
Empirical and Molecular Formulas
Percent Composition (cont.)
Empirical Formula
• The percent by mass of each element in a
compound is the percent composition of
a compound.
• The empirical formula for a compound is the
smallest whole-number mole ratio of the elements.
• You can calculate the empirical formula from percent
by mass by assuming you have 100.00 g of the
compound. Then, convert the mass of each element
to moles.
• Percent composition of a compound can also
be determined from its chemical formula.
• The empirical formula may or may not be the same
as the molecular formula.
Molecular formula of hydrogen peroxide = H2O2
Empirical formula of hydrogen peroxide = HO
4
SECTION
10.4
Empirical and Molecular Formulas
SECTION
10.5
Formulas of Hydrates
Molecular Formula
• The molecular formula specifies the actual
number of atoms of each element in one
molecule or formula unit of the substance.
• Explain what a hydrate
is and relate the name of
the hydrate to its
composition.
• Molecular formula is always a whole-number
multiple of the empirical formula.
• Determine the formula
of a hydrate from
laboratory data.
crystal lattice: a threedimensional geometric
arrangement of particles
hydrate
Hydrates are solid ionic compounds in
which water molecules are trapped.
SECTION
10.5
Formulas of Hydrates
SECTION
10.5
Formulas of Hydrates
Naming Hydrates
Analyzing a Hydrate
• A hydrate is a compound that has a
specific number of water molecules bound
to its atoms.
• When heated, water molecules are
released from a hydrate leaving an
anhydrous compound.
• The number of water molecules associated
with each formula unit of the compound is
written following a dot.
• To determine the formula of a hydrate, find
the number of moles of water associated with
1 mole of hydrate.
• Sodium carbonate decahydrate =
Na2CO3 • 10H2O
SECTION
10.5
Formulas of Hydrates
SECTION
10.5
Formulas of Hydrates
Analyzing a Hydrate (cont.)
Use of Hydrates
• Weigh hydrate.
• Anhydrous forms of hydrates are often
used to absorb water, particularly during
shipment of electronic and optical
equipment.
• Heat to drive off the water.
• Weigh the anhydrous compound.
• Subtract and convert the difference to moles.
• The ratio of moles of water to moles of
anhydrous compound is the coefficient for
water in the hydrate.
• In chemistry labs, anhydrous forms of
hydrates are used to remove moisture from
the air and keep other substances dry.
5