Counting
One dozen = 12 things
We use a dozen to make it easier to
count the amount of substances.
CH. 8.2 Moles
the SI base unit that
describes the amount of
a substance.
Mole is abbreviated mol
Happy Mole Day
So what does a Mole equal?
Avogodro’s constant is the amount of
particles in one mole of a substance.
He found that 6.02x1023 is the amount
particles are always found in 22.4 L.
This amount is exactly equal the
amount of 1.0 mole.
Moles
Used by chemist when
counting large numbers of
tiny particles such as atoms
One mole of anything will
equal the same amount of
particles.
Moles and Mass
Can you have the same
amount of different things?
Do they have to have the
same mass?
Ex. 12 eggs and 12 donuts
Molar Mass
The mass in grams of 1
mol of any substance.
Using the periodic chart
you can determine the
molar mass of any
element or compound.
g/ 1 mole
6.02 x 1023
Percent Composition
A measurement that measures
the amount of each element in
the total compound.
2%
22%
76%
HNO3
Hydrogen
Nitrogen
Oxygen
Calculating Empirical Formula
A compound is made from 30.5% nitrogen and 69.5%
oxygen. What is the empirical formula?
Assume you have a 100 gram sample
30.5 g N/ 14 gram per mole = 2.2 moles N
69.5 g O/ 16 grams per mole = 4.3 mole O
2.2 mole N/ 2.2 = 1 mole N
4.3 mole O/2.2 = 2 mole O
Formula is NO2
Determining Molecular Formula
The empirical formula is nitrogen dioxide.
Its molar mass is 92 g/mole. What is the
molecular mass?
Molar mass of NO2 is 46 g/ mole.
92g / 46g = 2
NO2 x 2 = N2O4
Molar Mass Calculations
Chemists must use mole
calculations in order to prepare
reactions.
They act as recipes for
chemists.
EXAMPLE PROBLEM #1
How many grams of
Calcium fluoride must a
chemist prepare if the
reaction requires 4.0 moles
of calcium fluoride?
Solution
The molar mass of CaF2 is
78 g/1 mol.
4.0 moles x 78 grams = 310 g
1 mole
Example Problem #2
How many moles were
produced if your reaction
yielded 92.0 grams of
sodium sulfate?
Solution
MM of Na2(SO4) is 142 g/1 mole
92.0 g x 1 mole = 0.648 moles
142 g
Example Problem #3
How many molecules were
produced if your reaction
yielded 12.0 grams of
Carbon monoxide?
Solution
MM of CO is 28 g/1 mole
12.0 g CO x 1 mole CO x 6.02x1023molecules CO
28 g CO
1mole CO
= 2.58x1023 molecules CO
Example Problem #4
How many liters are in
6.5 moles of fluorine gas?
6.5 mole F2 x 22.4 L___
1mole F2
= 150 liters of
F2
Ch 9.1 Chemical Reactions
• When substances undergo
chemical changes, they
form new substances.
• Atoms are rearranged,
because bonds are broken
and reformed
Chemical Reactions
• Signs are:
1. evolution of heat and light
2. color change
3. gases emitted
4. a precipitate forms (solid
residue)
Equation Make-up
•Reactants
substances that
will undergo a
chemical change.
(Left side)
Reaction Make-up
•Products
substances that
are formed as a
result of a
chemical change.
(Right side)
Recipes:
• 1 cup batter +1/2 cup water + 2 eggs → 4 pancake
Reactants
Products
6CO2 +6H2O→C6H12O6 + 6O2
Balancing
• All equations must have the
same type and number of atoms
on each side of the equation.
• Law of Conservation of Mass
• Tells you the amounts
Rule to Balancing
• Can only change coefficients
and never subscripts.
• Always balance H and O last if
water is in the equation.
• Balance the polyatomic ions
first if present
Mole Ratios
• Coefficients show the amount of
moles of each substance.
• Mole ratio is the smallest
relative number of moles of the
substance involved in a
reaction.
• 2H2 + O2 → 2H2O = 2:1:2
Writing Equations
•
•
•
•
Phase identification
S, l, g, v, aq
All ionic compounds are solids
Solutions and acids are mixed
with water, so are considered
aqueous.
Reaction Types
• 5 types of reactions
1. Synthesis Reaction
•A reaction when two
substances form at
least one new, more
complex compound.
Synthesis Reaction
•two or more
reactants = one
product
Synthesis Reaction
•
EXAMPLE:
A
2Fe
+
B→A B
+ O2 →2FeO
2. Decomposition Reaction
•A reaction in which
one compound breaks
into at least two
products.
Decomposition Reaction
•one reactant = two
or more products
Decomposition Reaction
EXAMPLE:
AB → A
+
B
2 NI3 → N2 + 3I2
3. Combustion reaction
•Reaction in which an
organic compound
and oxygen burn.
•Oxygen always is a
reactant
Combustion reaction
•CO or CO2 will
always be a product
• H2O will always be a
product
Combustion reaction
C2H50H + 3O2
→
2CO2 + 3H2O
4. Single displacement Reaction
•A reaction in which
atoms of one element
take the place of
atoms of another
compound.
Single displacement Reaction
• Example
X A + B→B A +
X
3CuCl2 + 2Al
→
2AlCl3 + 3Cu
5. Double Replacement Reaction
(Precipitation Reaction)
• A reaction in which the apparent
exchange of ions between two
compound solutions.
• Product will be an aqueous
solution and insoluble precipitate
Double replacement
reaction
AX + BY → AY + BX
Pb(NO3)2 +K2(CrO4)
→
Pb(CrO4) + 2K(NO3)