1. No category

The Mole Concept
Introduction
Number of Particles, Moles, and Mass
Dimensional Analysis
• starting with one unit of measurement and
ending up with a different one
• “cancel out” what you don’t want
• use conversion factors (fraction that equals one)
•
•
the numerator will contain the unit you want
the denominator will contain the unit you are trying
to get rid of
• try to predict a “ball park answer” if possible so
you might recognize a wrong answer
• sometimes they can be done in one step
• example: 23,532 seconds = ? minutes
23,532 sec. X 1 min.
1
60 sec.
392.20 min.
• sometimes they take multiple steps
• example: 23,532 seconds = ? hours
23,532 sec. X 1 min. X 1 hour =
1
60 sec.
60 min.
6.5367 hours
• but if you don’t know the conversion
factor(s), the problem becomes impossible
• example: 750 ml = ? fl oz
750 ml X 1 fl oz
1
29.6 ml
25.3 fl oz
How many minutes are in 2.5 hours?
Initial unit
2.5 hr
Conversion
factor
2.5 hr x 60 min
1 hr
cancel
Final
unit
= 150 min
Answer (2 SF)
LecturePLUS Timberlake
How many seconds are in 1.4 days?
What is wrong with the following setup?
1.4 day
x 1 day
24 hr
x
60 min
1 hr
x 60 sec
1 min
How many seconds are in 1.4 days?
1.4 day
x 1 day
24 hr
x
60 min
1 hr
Units would be = day2(sec)/hr2
Not the final unit needed
x 60 sec
1 min
Measuring Matter
• By counting
 simply
a number or moles
• By determining the mass
 grams
• By determining the volume
 liters
Not these!
The Mole
Not this!
Counting particles
simply a number or moles
• the mole is a unit used in chemistry
to represent a large number of
particles such as…
•
•
•
•
•
atoms (Ne, Ar…)
molecules (H2O, CO2…)
ionic compounds (NaCl, MgCl2…)
ions (Mg2+, Cl1-…)
similar to a dozen, except instead of 12,
it’s 602 billion trillion
• 6.02 x 1023 or 602,214,199,000,000,000,000,000
• known as Avogadro’s number
 1 dozen cookies = 12 cookies
 1 mole of cookies = 6.02 X 1023 cookies
 1 dozen cars = 12 cars
 1 mole of cars = 6.02 X 1023 cars
 1 dozen Al atoms = 12 Al atoms
 1 mole of Al atoms = 6.02 X 1023 atoms
Note that the NUMBER is always the same,
but the MASS would be very different!
Mole is abbreviated mol (gee, that’s a lot
quicker to write, huh?)
 1 mole C
 6.02
x 1023 C atoms
 1 mole water
 6.02
x 1023 H2O molecules
 1 mole NaCl
x 1023 NaCl ionic compounds
(formula units)
 6.02
• 6.02 x 1023 Na+ ions
• 6.02 x 1023 Cl– ions
Note that a particle could be an
atom OR a compound OR a
molecule!
 for counting in chemistry, the conversion
factor will be:

1 mole
6.02 x 1023 particles
OR

6.02 x 1023 particles
1 mole
Number of particles to moles
• How many moles in 5.68 x 1025 fluorine
molecules?
5.68 x 1025 F2 molecules
1
x _____1 mole____
6.02 x 1023 molecules
= 94.4 mol F2
• How many moles of water in 7.77x1024
molecules of water?
• 7.77 x 1024 molecules H2O x
1mole
6.02x1023 molecules
•
= 12.9 moles H2O
Number of moles to particles
• How many atoms in 5.59 moles of He?
5.59 moles He
1
x 6.02 x 1023 atoms
1 mole
= 3.36 x 1024 atoms
• How many atoms in 2.98 moles of H20 molecules?
2.98 moles x 6.02 x 1023 molecules H2O x
3 atoms
1
1 mole
1 molecule H2O
= 5.38 x 1024 atoms
Measuring mass
in grams
molar mass
•
•
this is how many grams you would have in
a mole of a substance
simply change atomic mass from the
periodic table for the element/molecule/
compound to grams
• oxygen’s atomic mass is 16.00 amu
 therefore 1 mole of oxygen has a molar
mass is 16.00 g/mol
• sugar’s (C6H12O6) atomic mass is 180.0 amu
• carbon: 12.00(6) = 72.00
• hydrogen: 1.00(12) = 12.00
• oxygen: 16.00(6) = 96.00
• therefore 1 mole of sugar has a molar
mass of 180.00 g/mol
 Calculate the Molar Mass of Na3PO4.
Atom
Na
P
O
#
3
1
4
Atomic Mass
X 23.0
X 31.0
X 16.0
Total
=
=
=
=
Total
69.0
31.0
64.0
164.0
Therefore the molar mass is 164.0 g mol-1
• Give the molar mass (mass of one
mole):
• Fe → 55.9 g/mol
• C2H6 → 30.1 g/mol
• Fe(OH)2 → 89.9 g/mol
• C12H22O11 → 342.3 g/mol
• CuSO4 · 5 H2O → 238 g/mol
Converting Moles to Grams and
Grams to Moles
 conversion factor will be:


1 mole
molar mass
OR
molar mass__
1 mole
Number of moles to mass(g)
• Find the mass (in grams) of 1.93 moles of MgO?
1.93 mol MgO
1
x
40.3 g MgO
1 mol MgO
= 77.8 g MgO
Mass(g) to moles
• Find the number of moles in 23.5 g of MgO?
23.5 g MgO
1
x
1 mole MgO
40.3 g MgO
= 0.583 mol MgO
Number of grams to moles to particles
• Find the number of particles in 13.9 g of MgO?
13.9 g MgO x
1
1 mole MgO_ x _6.02 X 1023 particles MgO
40.3 g MgO
1 mole MgO
= 2.07 X 1023 particles of MgO
here it is again
combining two
conversion factors
1 mole MgO_ x _6.02 X 1023 particles MgO
40.3 g MgO
1 mole MgO
6.02 X 1023 particles MgO
40.3 g MgO molar mass (g)
same thing but be
careful if you do this!
 What is the mass of 2.55 × 1023 atoms of lead?
2.55 × 1023 atoms Pb ×
1 mol Pb
207.2 g Pb
×
23
1 mole Pb
6.02×10 atoms Pb
= 87.8 g Pb
How many atoms in 22 grams of copper?
The Mole Road Map
Mass
“Stuff”
6.022 x 1023
mole
mole
g
Stuff:
g
mole
Mole
•Atoms
•Molecules
mole .
6.022 x 10
•Particles
•Electrons
22.7 L
•Ions
mole
For Gases only: •Formula Un
@ STP
(Standard Temp &
Pressure)
(0 oC (273 K) & 1
23
mole .
22.7 L
Volume