Chapter 10 Notes
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Transcript Chapter 10 Notes
10-1 Notes
The Mole – A measurement of matter
Measuring Matter
Chemistry is a quantitative science
We will be analyzing the composition of
samples of matter and perform chemical
calculations that relate quantities of reactants
in a chemical reaction to the quantities of
products
Ex: How many grams of H2 and N2 must be
combined to make 200 grams of fertilizer (NH3)?
1st we must find a way to measure the
amount of matter we have.
By counting how much matter, finding the
mass, or finding the volume of matter
What is a Mole?
Review: Matter is composed of atoms,
molecules, and ions
Particles that are much to small to count
We use a unit called a mole (mol) to count
particles of matter
A mole of a substance is 6.02 x 1023
representative particles of that substance
Known as Avogadro’s Constant
see table 10.1
Ex. 1 mole of Na = 6.02 x 1023 atoms of Na
Mole Conversions
How many moles of Mg are in 1.25 x 1023
atoms of Mg?
Use this conversion: 1 mol = 6.02 x 1023
Answer: 0.208 mol Mg
Practice Problem # 3
How many atoms are in 2.12 mol of
propane?
Conversion – moles molecules atoms
Answer: 1.40 x 1025 atoms
Practice Problem #5
The Mass of a Mole
Review: The atomic mass of an element is
expressed in atomic mass units (amu).
The atomic masses are relative values based
on the most common isotope of carbon.
The atomic mass of C is 12 amu which is 12
times heavier then H (mass of 1 amu)
Results in a constant 12:1 ratio
Therefore, 12 grams of C and 1 gram of H
must contain the same number of atoms
The Mass of a Mole
The atomic mass of an element expressed
in grams is the mass of a mole of the
element
Ex. The molar mass of Carbon is 12
grams
Because 1 mole of any element contains
6.02 x 1023 atoms, the number of atoms
in 12 grams of Carbon = the number of
atoms in 16 grams of Oxygen
Molar Mass is the mass of 1 mol of atoms
of any element
The Mass of a Mole
Step 1: Determine the formula for the
compound
Step 2: Find the number of grams of each
element in one mole of the compound
Step 3: Add the masses of the elements in
the compound
This method is used for any type of
compound
The Mass of a Mole
Find the mass of 1 mol of Sulfur trioxide
SO3 = 1 sulfur atom and 3 oxygen atoms
1 atom sulfur x 32.1 amu = 32.1 amu
3 atoms oxygen x 16.0 amu (per oxygen) =
48.0 amu
32.1 amu + 48.0 amu = 80.1 amu for Sulfur
trioxide
Substitute grams for amu.
1 mol of SO3 has a mass of 80.1 grams
Practice Problem # 7
10-2 Notes
Mole-Mass and Mole-Volume Relationships
Mole-Mass Relationship
Use the molar mass of an element or
compound to convert between the mass
of a substance and the moles of that
substance.
Mass (grams) = number of moles x
(mass / 1 mole)
Ex. The molar mass of NaCl is 58.5 grams.
What is the molar mass of 3 moles of NaCl?
3.00 mol NaCl x 58.5g/1 mol = 176 g
Sample problem 10.5
Mole-Mass Relationship
Suppose in the lab you were able to obtain
10.0 grams of Na2SO4.
How many moles is this?
moles = mass x (1mol/mass)
moles of Na2SO4 = 10.0 grams x (1 mol/142.1 g)
moles of Na2SO4 = 7.04 x 10-2
Sample problem 10.6
Mole-Volume Relationship
The volumes of one mole of different solid
and liquid substances are not the same
fig. 10.7 on page 295
The volumes of gases are much more
predictable
In 1811 Avogadro stated that equal
volumes of gases at the same temperature
and pressure contain equal number of
particles
Even though the particles that make up
different gases are not the same size, they
take up relatively the same space
Mole-Volume Relationship
The volume of a gas will vary depending on the
temperature or the pressure
Increase in pressure = decrease in volume
The volume of a gas is usually measured at
standard temperature and pressure (STP)
STP is at O oC and at a pressure of 101.3 kPa
or 1 atmosphere (atm)
At STP 1 mol of any gas occupies a volume of
22.4 L
This is referred to as molar volume
Mole-Volume Relationship
To calculate volume of a gas at STP:
Volume of gas = moles of gas x (22.4 L/1
mol)
Determine the volume (Liters) of 0.60 mol SO2 at
STP
You can also calculate molar mass from
Density.
The density of a gas at STP is 22.4L/mol
Molar mass = density @ STP x molar
volume @ STP
Determine the mass of a compound that has
a density of 1.964 g/L at STP
10-3 Notes
Percent Composition
and Chemical Formulas
Percent Composition
The % composition of a compound consists of a
% value for each different element in the
compound
% composition from mass data
The % mass of an element is the # of grams of the
element divided by the mass in grams of the
compound, multiplied by 100
% mass of element =
mass of element
x 100
mass of compound
Sample problem 10.9
Percent Composition
% Composition from the Chemical Formula
% mass =
Mass of element in 1 mol compound
Molar mass of compound
Sample Problem 10.10
x 100
% Composition as a Conversion
Factor
You can use % comp. to calculate the
number of grams of any element in a specific
mass of a compound
Multiply the mass of the compound by a
conversion factor based on the % comp of
the element in the compound.
Sample problem:
In 10.10 we found in propane, the % comp of
Carbon was 81.8%. What would the mass of
Carbon be in an 82.0 g sample?
Empirical Formulas
The % comp. of any compound is the data we use to
calculate the basic ratio of elements contained in a
compound
The basic ratio that gives the lowest whole-number
ratio of the atoms of the elements in a compound is
called the empirical formula
An empirical formula may or may not be the same as
a molecular formula
Example: The molecular formula for hydrogen peroxide
is H2O2 the empirical formula is HO
Sample problem 10.11
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
To find the molecular formula you must
first know the molar mass of the
compound.
Sample Problem 10.12