Section 7.1
The Mole: A Measurement of
Matter
Chapter 7
Chemical Quantities
„ OBJECTIVES:
–Describe how Avogadro’s
number is related to a mole of
any substance.
–Calculate the mass of a mole of
any substance.
Adapted from notes by Stephen Cotton
What is a Mole?
„ Chemists
Representative particles
„ The
smallest piece of a substance.
–Molecular compound =
–Ionic compound =
–Element =
typically measure:
–mass in
–volume in
–Representative particles in
.
Moles (abbreviated: mol)
„ Defined
as the number of C
atoms in exactly
grams of
C-12.
„ 1 mol =
particles =
Avogadro’s Number
„
How many?
Eggs in a dozen?
Doughnuts in a baker’s dozen?
„ Sheets of paper in a ream?
„ Pencils in a gross?
„ Eggs in a mole?
„ Doughnuts in a mole?
„ Sheets of paper in a mole?
„ Pencils in mole?
„
„
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Examples
„
Example
How many oxygen atoms in the
following?
– CaCO3
– Al2(SO4)3
„ How
many molecules of CO2 are
there in 4.56 moles of CO2?
Gram Atomic Mass
OR
Gram Formula Mass
OR
Molar Mass
Example
„ How
many atoms of carbon are
there in 1.23 moles of C6H12O6?
„
„
„
„
1 mol C =
1 mol H =
1 mol CO2 =
CO2
1 mol NaCl =
Examples
„ What
is the gram atomic mass of sodium?
„ What
is the gram formula mass of CH4?
„ What
is the molar mass of oxygen gas?
gC=
gH=
g CO2 =
g NaCl =
atoms C
atoms H
molecules
f.u. NaCl
Example
„ What
is the mass of 2.34 moles of C?
„ What
is the molar mass of calcium
nitrate?
2
Example
„ How
many moles of magnesium
is 24.31 g of Mg?
Section 7.2
Mole-Mass and Mole-Volume
Relationships
„
OBJECTIVES:
– Use the molar mass to convert
between mass and moles of a
substance.
– Use the mole to convert among
measurements of mass, volume,
and number of particles.
How big of a container would it
take to…
„
contain 1 mole of rice grains?
„
contain 1 mole of rain drops?
„
contain 1 mole of water molecules?
GO FOR
THE
Example
„ How
many molecules is 6.8 g of
CH4?
Example
„ 49
molecules of C6H12O6 weighs
how much?
3
Gases
to
are compressible so
can change.
„ Temperature and
volume.
Standard Temperature and
Pressure (STP)
„ Difficult
„ 0ºC
„ Gases
affect
and
pressure
„ At STP 1 mole of any gas
occupies
„.
= (22.4 L/mol)
Example
„ What
is the volume of 4.59 moles
of CO2 gas at STP?
Section 7.3
Percent Composition and
Chemical Formulas
„
OBJECTIVES:
– Calculate the percent composition
of a substance from its chemical
formula or experimental data.
– Derive the empirical formula and
the molecular formula of a
compound from experimental data.
Example
„ What
is the molar mass of a gas
with a density of 1.964 g/L at
STP?
Calculating Percent Composition of
a Compound
„ Like
all percent problems:
Part
x
Whole
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Example
Example
„ Calculate
the percent
composition of C2H4?
„ Calculate
the percent
composition of a compound that
is 29.0 g of Ag with 4.30 g of S.
Empirical Formula
„ Lowest
Example
of
elements in a compound.
„ Molecular formula = the
ratio
of elements in a compound.
„ The two
be the same.
„ Ex: C2H4 is a molecular formula
„.
is the empirical formula
„
Caffeine is 49.48% C, 5.15% H,
28.87% N and 16.49% O. What is its
empirical formula? Caffeine has a
molar mass of 194 g, what is its
molecular formula?
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