Chapter 8- The Mole
How is the mole concept related to chemical formulas?
S
The “Mole”
We are not talking about this
mole…..
The “Mole”
……and we are not talking
about this kind of mole……
The “Mole”
WE ARE TALKING ABOUT
THIS KIND OF MOLE!!
What is a mole?
S The amount of a substance
S Tells us how much of “stuff ” is in a given amount
S Avogadro's mole:
S 1 mole= 6.02 x 1023 atom, ions, or molecules
S 1 mole of carbon = 12.01 g
Volume
Island
(# moles) x (6.02x1023 atoms)
Atom
Island
Mole Island
(# atoms) / (6.02x1023 atoms)
(molar mass) / (# moles)
Mass Island
(g)
(# moles) / (molar mass)
Practice problems
1.
Determine the mass in grams, of 3.50 mole of copper
2.
How many atoms of O2 are there in 2.86 moles?
3.
How many atoms are in 28.09 g of silicon?
4.
Determine the number of moles in the following elements:
a.
b.
c.
d.
0.345 g chlorine
184.2 g of sodium
0.320 g copper
282.4 g of iron
Practice Problem Answers
1.
0.05508 grams
2.
1.72 x 1024 atoms
3.
6.02 x 1023 atoms
a.
b.
c.
d.
0.00973 moles of chlorine
8.010 moles of sodium
0.005035 moles of copper
5.057 moles of iron
Relative Atomic Mass and the
Periodic Table
S Proton 1.007276 amu
S Neutron 1.008665 amu
S Electron 0.0005488 amu
Relative Atomic Mass and the
Periodic Table
S Sodium: 11 protons (1.007276) = 11.080036 amu
11 electrons (0.0005488) = 0.0060368 amu
12 neutrons (1.008665) = 12.10398 amu
Total mass = 23.190… amu
S Why is this different from the periodic table??
S Take into account, isotopes
S Periodic table displays *relative atomic mass*
S Atomic masses will never be whole numbers
Calculating Relative Atomic
Mass
S The mass of copper-63 atom is 62.94 amu and that of a
copper-65 atom is 64.93 amu. Using this data and the
abundance of these two isotopes, determine the average
atomic mass of native copper. The abundance of copper-63
is 69.17%. The abundance of copper-65 is 30.83%.
Answer
(62.94 x 0.6917) + (64.93 x 0.3083) = 63.55 amu
copper-63
copper-65
Calculating Relative Atomic
Mass
S Calculate the average atomic mass for silicon if 92.21% of
its atoms have a mass of 27.98 amu, 4.70% have a mass of
28.98 amu, and 3.09% have a mass of 29.97 amu.
Answer
(27.98 x 0.9221) + (28.98 x 0.047) + (29.97 x 0.0309) = 28.09 amu
How is the mole concept related
to chemical formulas?
1. Chemical Formulas reveal composition
S Shows the ratio between elements
NH4….. 1 mole of NH4 = 4 moles of H and 1 mole of N
S H2O……. 1 mole of H2O = 2 moles of H and 1 mole of O
S
How is the mole concept related
to chemical formulas?
2. Can calculate molar mass of compounds
S
NH4 :
S
H2 O :
1 N= 1(14.00 amu)
4 H= 4(1.01 amu)
Atomic mass = 18.04 g/mol
2 H = 2(1.01)
1 O = 1(16.00)
Atomic mass = 18.02
More formulas….
S What is the molar mass of zinc chloride?
136.315 g/mole
S What is the molar mass of barium nitrate?
261.37 g/mole
Percentage Composition
S Percentage composition describes the percentage by mass of
each element in a compound
1.
Find the molar mass of the compound.
2.
Divide the mass of the element of interest by the molar
mass of the compound
3.
Multiply by 100 to get the percent
Percentage Composition
S Example 1: What is the percent composition of oxygen in
water?
S H2O: Molar mass = 2(1.01) + 1(16.00)
Molar mass = 18.02 g/mole
Percent composition of oxygen:
(16.00/18.02) x 100 = 88.79%
Percentage Composition
S Example 2: What is the percentage composition of
potassium in potassium chlorate?
(39.09/122.55) x 100 = 31.89%
Extra Credit Opportunity!!
Create your own “mole”
Requirements:
1.
Must create a stuffed animal
2.
Write a 1 page (no double space) on how your mole character relates
to Avogadro's number. Aka the story about your mole character.
3.
A small index card description of your mole with its name on it
Can earn up to 20 points extra credit!!!! The more creative it is, the more
points you will earn!!