Download Sec. 10.3 - Midland Park School District

Ch. 10: The Mole
*Part of Sec. 13.2: Avogadro’s
Principle (pages 452-453)
Sec. 10.3: Moles of Compounds
(pages 333 – 334 & 338 - 339)
Moles of Compounds
Avogadro’s Principle
Relate numbers of particles and
volumes by using Avogadro’s principle.
Recognize the mole relationships shown
by a chemical formula.
Determine the number of atoms or ions
in a mass of a compound.
Avogadros’ Principle
O
O
C
O
The particles making up
different gases can vary
greatly in size.
O
Avogadros’ Principle
Yet, the particles in all
gases are far enough
away from each other
that their size has no
effect on the amount of
space (volume) a sample
occupies.
All gases are mostly
empty space.
Avogadros’ Principle
That means, at the same temperature
and pressure, 1000 oxygen molecules
will occupy the same space as 1000
carbon dioxide molecules. They both
occupy the same space as 1000 helium
atoms.
This is Avogadro’s Principle.
Avogadros’ Principle
Avogadro’s Principle states that equal
volumes of gases at the same
temperature and pressure contain
equal numbers of particles.
Further, one mole (or 6.02 x 1023
particles) of a gas (no matter what it is)
will always have the same volume.
Molar Volume
The molar volume of a gas is the
volume occupied by one mole of a gas
at STP.
STP stands for standard temperature
and pressure: 0o C and 1 atm. pressure.
Avogadro showed that 1 mole of any
gas will occupy a volume of 22.4 liters
at STP.
Molar Volume
OR 1 mole of any gas will occupy 22.4 L of space.
Mole/Volume Conversions
Calculate the volume that 0.881 mol of
helium will occupy at STP.
0.881 mol x 22.4 L = 19.7 L
1 mole
Determine the volume of a container
that holds 2.4 mol of gas at STP.
How many moles of nitrogen gas will be
contained in a 2 L flask at STP?
Molar Volume
Now it is possible to relate moles, mass,
# of particles and volume for all gases.
1 mole
= 6.02 x 1023 particles
= atomic or formula mass in grams
= 22.4 L
MASS
Use: 1 mole = atomic
mass in grams
PARTICLES
MOLES
Use: 1 mole = 6.02
x 1023 particles
Use: 1 mole = 22.4 L
VOLUME
Mass/Volume Conversions
Calculate the volume that 50 g of
methane (CH4) will occupy at STP.
50 g x 1 mole = 3.1 mol x 22.4 L = 69 L
16 g
1 mol
What volume will 0.416 g of krypton
gas occupy at STP?
How many grams of carbon dioxide gas
are in a 1.0 L balloon?
Chemical Formulas & the Mole
The formula CCl2F2 (freon) indicates that 1
molecule of CCl2F2 contains 1 C atom, 2 Cl
atoms, and 2 F atoms.
What if we multiply all the numbers in this
expression by 6.02 x 1023?***
This means, 1 mole of CCl2F2 will contain 1
mole of C atoms, 2 moles of Cl atoms, and 2
moles of F atoms.
These equivalencies that we find in the
formula can be written as conversion factors.
They are . .
How many moles of fluorine atoms are in 5.5
moles of freon?
Chemical Formulas & the Mole
5.5 moles CCl2F2 x 2 moles F atoms
1 mole CCl2F2
= 11.0 moles F atoms
Chemical Formulas & the Mole
Conversion factors can be determined
for any element or ion from the formula
of a compound.
In the conversion factor, the subscript
for an element or ion in the formula is
the number of moles of that element or
ion in one mole of the compound.
Practice Problems
1. 1 mole Al2(SO4)3 contains:
_____ mol Al+3 ions
_____ mol SO4-2 ions
_____ mol O atoms
2. 4.5 mol Ca3(PO4)2 contains:
_____ mol Ca+2 ions
_____ mol PO4-3 ions
_____ mol O atoms
More Practice Problems
Determine the moles of aluminum ions
(Al+3) in 1.25 moles of aluminum oxide
(Al2O3).
How many moles of oxygen atoms are
present in 5.0 mol diphosphorus
pentoxide (P2O5)?
Determine the number of moles of
oxygen atoms in 0.34 mol of oxygen
gas (O2).
Converting Mass to # of Particles
Remember:
# of Particles
Mass
Converting Mass to # of Particles
Now, in addition to the conversions
pictured, you can determine the # of
atoms or ions in a compound by using a
conversion factor that is written from
the formula of a compound.
Converting Mass to # of Particles
A sample of silver chromate (Ag2CrO4)
has a mass of 25.8 g. How many Ag+
ions are present?
Step 1: mass given to moles compound
25.8 g Ag2CrO4 x 1 mole = 0.0778 mol Ag2CrO4
331.8 g
Converting Mass to # of Particles
Step 2: moles compound to moles particles
0.0778 mol Ag2CrO4 x 2 moles Ag+ = 0.156 moles Ag+
1 mol Ag2CrO4
Step 3: moles particles to # of particles
0.156 moles Ag+ x 6.02 x 1023 Ag+ ions
1 mole Ag+
= 9.39 x 1022 Ag+ ions
Practice Problems
A sample of aluminum chloride has a mass of
35.6 g. How many Cl- ions are present in the
sample?
How many moles of calcium ions are present
in 1 g of CaCO3? How many calcium ions are
present?
What mass of sodium chloride (NaCl)
contains 4.59 x 1024 Cl- ions?
A sample of Pb(NO3)2 has 8.2 x 1025 formula
units. How many nitrate ions does it contain?