Chapter 10.1 The Mole: A
Measurement of Matter
• The measurement of the amount of
something is done by one of three different
methods: by count, by mass, or by volume.
• Ex. Soda, grapes, gas
• Practice problem 1 & 2 pg 289
• Ex. 1 dozen = 12
Chapter 10 10.1 The Mole: A
Measurement of Matter
• Chemist use a unit that is a specified unit of particles.
This unit is called the mole.
• Ex. 1 dozen = 12
• 1 mole = 6.02 x 1023 representative particles
• Avagadro’s number is 6.02 x 1023
• A mole of any substance contains Avogadro’s number
of representative particles, or 6.02 x 1023
representative particles.
• Representative particles- refers to what is
present in a substance; usually atoms,
molecules, or formula units
• When dealing with compounds representative
particles are molecules.
• When dealing with elements representative
particles are atoms.
Converting number of particles to
moles:
• moles = representative particles X
___ _ 1 mole_________
6.02 x 1023 representative particles
Converting moles to number of
particles
• representative particles = moles x
6.02 X 1023 representative particles
1 mole
• Remember the atomic mass of an element is
expressed in atomic mass units (amu)
• Therefore 100 carbon atoms are 12 times heavier than
100 hydrogen atoms
• The atomic mass of an element expressed in grams is
the mass of a mole of the element.
• Molar mass- The mass of a mole of an element.
• Ex. Sulfur 32.06 amu Molar Mass = 32.1g
The mass of a mole of a compound
• To find the mass of a mole of a compound you
must know the formula of the compound.
• To calculate the molar mass of a compound,
find the number of grams of each element in
one mole of a compound. Then add the
masses of the elements in the compound.
• Ex. C6 H 1206
Chapter 10- 10.2 Mole-Mass and
Mole Volume Relationships
• Use the molar mass of an element or
compound to convert between the mass of a
substance and the mole of a substance.
•
• or
•
Mass(grams) = Number of moles x mass(grams)
1 mole
Moles = mass(grams) x 1 mole
Mass(grams)
The Mole Volume Relationship
• Avagadro’s hypothesis - states the equal volumes of gases
at the same temperature and pressure contain equal
number of particles.
• Standard Temperature and Pressure (STP) - a temperature
of 0 degrees Celsius, and pressure of 101.3 kPa, or 1
atmosphere (atm)
• At STP, 1 mol or 6.02 x 1023 representative particles, of any
gas occupies a volume of 22.4 L.
• Molar volume of a gas is the quantity 22.4 L.
Calculating Volume at STP
• Volume of gas = moles of gas x 22.4 L
1 mol
• Calculating Molar mass from Density
•
Grams =
Mole
Grams x 22.4 L
L
1 mole
10.3 Percent Composition and
Chemical Formulas
• Percent composition- The relative amount of the elements
in a compound
• The percent by mass of an element in a compound, is the
number of grams of the element divided by the mass in
grams of the compound, multiplied by 100%
•
% mass of element = mass of element
mass of compound
X
100
Percent Composition from the
Chemical Formula
• % mass = mass of element in 1 mol compound X 100%
Molar mass of compound
Empirical Formula
• Empirical formula- gives the lowest whole
number ratio of the atoms of the elements in
a compound.
• The empirical formula of a compound shows
the smallest whole number ratio of the atoms
in a compound.
• Ex. Sample problem pg. 310
Molecular Formulas
• The molecular formula of a compound is
either the same as its experimentally
determined empirical formula, or it is a simple
whole number multiple of its empirical
formula.
• Once the empirical formula is known, you can
determine its molecular formula but you have
to know the compounds molar mass
• Sample problem pg.312