Post on 01-Feb-2022
transcript
Chapter Warm Up
1. If you had 144 eggs, how many dozen eggs
would you have?
2. If you baked 6.5 dozen cookies, how many
cookies did you bake?
3. If a recipe called for 2.5 cups of flour to
make 3 dozen cookies, how much flour
would you need to make 13.25 dozen
cookies?
Chemical Quantities
Equations --- A Second Look
What do the coefficients tell us?
How many atoms or molecules are involved in the
reaction
BUT….
Atoms and molecules are microscopic
Can’t see them, so can’t count them
So…..
How to count?
Come up with a new quantity– amount of substance
Whose unit is
THE MOLE!!!!(not an adorable furry creature)
(not a skin growth)
A UNIT
The Mole
Quantity:Amount of substance (n)
Symbol: n
Unit: Mole(mol)
1 mole of anything = 6.02 x 1023 of that thing
6.02 x 1023 known as Avogadro’s Number (NA)
Like a dozen is 12 of anything, a mole is
6.02 X 1023 of anything
Examples
1) How many moles of apples are in 3.25 x 1056
apples?
3.25 x 1056 apples 1 mole apples = 5.40 x 1032 moles apples
6.02 x 1023 apples
2) How many apples are in 7.50 moles of
apples?
7.50 moles apples 6.02 x 1023 apples = 4.52 x 1024 apples
1 mole apples
Practice
1) The population of the Earth is about 7.10 x
109 people. How many moles of people is
this?
1.18 x 10-14 moles people
2) The United States has a population of about
5.25 x 10-16 moles of people. How many
people is this?
3.16 x 108 people
Being Practical
How do we actually count/measure this stuff?
We can’t count it, so we must find another way
to measure it
We can measure mass, so how do we compare #
of atoms or molecules to mass or the numbers
of moles of atoms or molecules to mass?
Need to know the mass of 1 mole of the element
or compound
For elements(atoms)
Called the average atomic mass
From PT
We know it in amu’s
It’s the same value in grams/mole
For compounds known as formula weight(FW)
or molar mass(MM)
Sum of masses of all atoms in compound
Expressed in grams/mole (g/mol)
Examples
1) What is the molar mass of NaCl?
22.990 g/mol + 35.453 g/mol = 58.443g NaCl/ 1
mol NaCl
2) What is the molar mass of Cu3(PO4)2?
3(63.546g/mol) + 2(30.974g/mol) + 8(15.999g/mol)
= 190.638 g/mol +61.948 g/mol + 127.992 g/mol
= 380.578 g Cu3(PO4)2 / 1 mol Cu3(PO4)2
Practice
Calculate the molar mass of the following.
1) CdS
144.48g CdS/1 mole CdS
2) (NH4)3PO4
149.12 g (NH4)3PO4/ 1 mole (NH4)3PO4
Chemical Calculations --
Stoichiometry
Calculating how much of a product can be made
from a given amount of reactant or how much
of a reactant is needed to form a certain
amount of a product
Based on balanced chemical equations
Coefficients represent atom (molecules) of a
substance or moles of a substance
2Al(s) + 3I2(s) → 2AlI3(s)
Means 2 atoms of aluminum react with 3 molecules of
iodine to form 2 molecules of aluminum iodide
Means 2 moles of aluminum react with 3 moles of
iodine to form 2 moles of aluminum iodide
DOES NOT MEAN 2 grams of aluminum react with 3
grams of iodine to form 2 grams of aluminum iodide
CalculationsFollow patterns or “road maps” from have to want
moles A to moles B (have moles A want moles B)
One step
Road Map
moles A → moles B
Use mole ratio (mole bridge)
Allows us to go from one substance to another
Fraction made with coefficients from balanced chemical
equation
Want/have
Example
The reaction of aluminum and iodine to produce
aluminum iodide is 2Al(s) + 3I2(s) → 2AlI3(s).
1) How many moles of AlI3 can be produced
from 5.75 moles of Al?
5.75 moles AlI3
mass of A to mass of B (have mass A want mass B)
Multiple steps
Remember—chemical equations are not written
in terms of mass
Must go from mass to moles to use the chemical
equation
Road Map
mass A → moles A → moles B→ mass B
mass → moles uses average atomic mass(element) or
molar mass(compound or diatomic)
moles A → moles B uses mole ratio
Examples
In the reaction 2Al(s) + 3I2(s) → 2AlI3(s),
How many grams of AlI3 can be produced from
165g Al?
2.49 x 103 g AlI3