Stoichiometry & the Mole
Part 1
The Mole
Dimensional Analysis Review
• How many seconds are in 5.0 hours?
Stoichiometry
• Stoichiometry is just a long word for
changing units in chemistry
• If you can do Dimensional Analysis, you can
do stoichiometry
The Mole
• Chemists need a convenient method for
counting accurately the number of atoms,
molecules, or formula units in a sample of a
substance.
• The mole, commonly abbreviated mol, is the
SI base unit used to measure the amount of a
substance.
The Mole
• A mole of anything contains 6.0221367 x 1023
particles.
• A particle may be atoms, molecules, formula
units, electrons, or ions.
• In this class, Avogadro’s number will be
rounded to four significant figures— 6.022 x
1023.
Just How Big is a Mole?
• Enough soft drink cans to cover the
surface of the earth to a depth of
over 200 miles.
• If you had Avogadro's number of
unpopped popcorn kernels, and
spread them across the United
States of America, the country would
be covered in popcorn to a depth of
over 9 miles.
• If we were able to count atoms at the
rate of 10 million per second, it
would take about 2 billion years to
count the atoms in one mole.
A Mole of Particles
Contains 6.02 x 1023 particles
1 mole C
= 6.02 x 1023 C atoms
1 mole H2O = 6.02 x 1023 H2O molecules
1 mole NaCl = 6.02 x 1023 NaCl “molecules”
(technically, ionics are compounds not
molecules so they are called formula units)
6.02 x 1023 Na+ ions and
6.02 x 1023 Cl– ions
Conversion Factor #1
Atoms or
Molecules
Mole Map
1 mole
6.02 X 1023 particles
6.02 X 1023 particles
1 mole
Moles
Mole –Particle Calculations
• Calculate the number of atoms in 3.50 moles
of copper
Mole –Particle Calculations
• How many moles of MgO are in 9.72 x 10 23
formula units of MgO?
Mole – Mass Relationship
• The mass in grams of one mole of any pure
substance is called its molar mass.
• The molar mass of any element is numerically
equal to its atomic mass and has the units
g/mol.
Molar Mass of Compounds
• The molar mass (MM) of a compound is determined
by adding up all the atomic masses for the molecule
(or compound)
– Ex. Molar mass of CaCl2
20
Ca
40.08
17
Cl
35.45
Practice
• Calculate the Molar Mass of calcium
phosphate
– Formula =
Ca3(PO4)2
– Masses elements:
– Molar Mass =
Calculating Molecular Mass
• What is the molar mass of (C3H5)2S?
• What is the molar mass of BeC2O42H2O?
Conversion Factor # 2
1 mole
Molar mass (g)
The molar mass comes from
the periodic table!
Mole – Mass Calculations
• What is the mass of 4.21 moles of iron (III)
oxide?
Mole – Mass Calculations
• How many moles of Ca(OH)2 are in 325
grams?
Learning Check!
The artificial sweetener aspartame
(Nutra-Sweet) formula C14H18N2O5 is
used to sweeten diet foods, coffee and
soft drinks. How many moles of
aspartame are present in 225 g of
aspartame?
Atoms or
Molecules
Mole Map
Molar Mass
1 mole
Mass
(grams)
1 mole
6.02 X 1023 particles
6.02 X 1023 particles
1 mole
1 Mole
Molar Mass
Moles
Calculations
molar mass
Grams
Avogadro’s number
Moles
particles
Everything must go through
Moles!!!
Mass – Particle Conversions
• How many atoms of gold are in 25.0 g of gold?
Mole-Liters
STP
Temperature = 298 K
Pressure = 1 atm
At standard temperature and pressure (STP),
one mole of gas (no matter what the gas is)
occupies 22.4 liters of space.
Conversion Factor #3
1 mole
22.4 Liters
This is ONLY true at STP
Atoms or
Molecules
Mole Map
Mass
(grams)
Molar Mass
1 mole
1 mole
6.02 X 1023 particles
1 Mole
Molar Mass
6.02 X 1023 particles
1 mole
Moles
22.4 Liters
1 mole
1 Mole
22.4 Liters
Liters of GAS
(at STP)
Mole – Liter Calculations
• What is the volume of 4.21 moles of carbon
dioxide gas at STP?
Atoms or
Molecules
Mole Map
6.022 X 1023
Mass
(grams)
Molar Mass
22.4
Multiply with the
arrows
Divide against the
arrows
Liters (at STP)
Mixed Practice
Calculate the molar mass of the following
1. C3H5N3O3
2. Al(NO3)3
3.
SO2
Mixed Practice
Calculate the mass in grams of each of
the following
4. 5.49 mol of KI
5. 0.354 mol of Fe3(Fe(CN)6)2
6. 1.50 mol of Ca(NO3)2.3 H2O
Mixed Practice
Calculate the number of moles in
each of the following:
7.
10.0 g of Na2S
8.
50.0 g of C16H18N2O4S
9.
84.2 g of K2SO4
Calculate the number of atoms,
molecules, or ions for each of the
following
10.
3.34 mole of CO2, number of
molecules
11. 68.0 g of H2S, number of molecules
12.
0.125 mole of Mg+2, number of
ions
• Calculate the number of grams in each
of the following:
13. 1.50 X 1023 ions of Na+
14. 3.01 X 1023 atoms of S
15.
2.41 X 1024 molecules of H2O
Practice Problems (Calculator Free)
1. A balloon is filled with 1.0 mole of CO2 at STP.
1. What is the balloon’s mass?
2. What is the balloon’s volume?
3. How many molecules are in the balloon?
Practice Problem #2 (Calc. Free)
• A student measures out 0.250 moles of
Radon, how many atoms of radon did the
student measure out?
Practice Problem #3 (Calc. Free)
• The mass of 1.204 X 1024 atoms of hydrogen
gas is equal to ____________.
Practice Problem #4 (Calc. Free)
• The mass of 3.01 X 1023 molecules of gas is
18.0 grams. What volume does 12.0 grams of
the gas occupy at STP?
Practice Problem #5
Who am I?
1. A 22 gram sample of
me contains 6.02 x
1023 atoms of oxygen
2. 0.25 moles of me
weighs 10.0 grams.
A.
B.
C.
D.
E.
C12H22O11
Calcium sulfate
Carbon Dioxide
Water
Sodium hydroxide
Additions to the Mole Map
Liters of a liquid
The number of moles in a
liter of liquid can be
found if the MOLARITY
of the solution is
known.
Molarity = mole
Liters
To go from liters to moles,
multiply by this
molarity.
To go from moles to liters,
divide by this molarity.
Atoms or
Molecules
Mole Map
Mass
(grams)
Molar Mass
1 mole
1 mole
6.02 X 1023 particles
6.02 X 1023 particles
1 mole
Molarity
1
1 Mole
Molar Mass
Moles
22.4 Liters
1 mole
1
1 Mole
22.4 Liters
Molarity
Liters of liquid
Liters of GAS
(at STP)
Additions to the mole map
Gases not at STP (0 C and 1 atm)
The equation PV=nRT is used
P= pressure in atm
V= volume in L
N= moles of gas
R=8.314 J/mol*K
T=Temperature in Kelvin
Part II
Percent Composition, Empirical and
Molecular Formula
Calculating Percentage Composition
Calculate the percentage composition of
barium sulfate.
Step 1: Determine the molar mass of the compound.
Step 2: Divide the mass of the element in the
compound by the total molar mass, then multiply by
100%.
Practice Problem
• Find the percent composition of sodium
nitrate.
Practice Problem (Calc. Free)
What is the percent oxygen in potassium
chlorate (molar mass 123 g/mol)?
You try!
• Determine the percent composition of
NaCl.
• Determine the percent composition of
water.
Formulas
Empirical formula: the lowest whole
number ratio of atoms in a
compound.
Molecular formula: the true
number of atoms of each element
in the formula of a compound.
 molecular formula = C6H6
 empirical formula = CH
Formulas
(continued)
Formulas for ionic compounds are ALWAYS
empirical (lowest whole number ratio).
Examples:
NaCl
MgCl2
Al2(SO4)3
K2CO3
Formulas
(continued)
Formulas for molecular compounds MIGHT
be empirical (lowest whole number ratio).
Molecular:
H2O
C6H12O6
C12H22O11
Empirical:
H2O
CH2O
C12H22O11
Practice Problem
Which of the following are NOT empirical
formulas?
I. K2CO3
II.C6H12O6 (glucose)
III.H2O (water)
IV.C2H4
Empirical Formula Determination
1. If given percentages (%) convert these
to grams by assuming a 100g sample.
2. Convert grams to moles.
3. Divide each value of moles by the
smallest of the values.
4. If the resulting answers contain
numbers other than whole numbers,
you will have to multiply them all by
the same # to get whole #s.
Empirical Formula Determination
Practice Problem
Adipic acid contains 49.32% C, 43.84% O,
and 6.85% H by mass. What is the
empirical formula of adipic acid?
Practice Problem
A compound is found to contain 36.48%
Na, 25.41% S, and 38.11% O. Find its
empirical formula.
Practice Problem
Analysis of a 10.150 g sample of a
compound known to contain only
phosphorus and oxygen indicates a
phosphorus content of 4.433 g. What is
the empirical formula of this compound?
Practice Problem (Calc. Free)
A sample is analyzed and found to contain
24.0 grams C, 4.0 g H and 32.0 g O.
What is the empirical formula?
Finding the Molecular Formula
The empirical formula for adipic acid is
C3H5O2. The molar mass of adipic acid is
146 g/mol. What is the molecular formula
of adipic acid?
Step 1: Find the molar mass of the
empirical formula.
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
Finding the Molecular Formula
The empirical formula for adipic acid is
C3H5O2. The molar mass of adipic acid is
146 g/mol. What is the molecular formula
of adipic acid?
Step 2: Divide the molar mass of the
compound by the molar mass
given by the empirical formula.
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
146
2
73
Finding the Molecular Formula
The empirical formula for adipic acid is
C3H5O2. The molar mass of adipic acid is
146 g/mol. What is the molecular formula
of adipic acid?
3. Multiply the empirical formula by this
number to get the molecular formula.
3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g
146
2
73
(C3H5O2) x 2
=
C6H10O4
Practice Problem
What is the molecular formula of a
compound that has an empirical formula
of CH2 and a molar mass of 28 g/mol?
Practice Problem
A compound is 81.06% boron and 18.94%
hydrogen. The molar mass was
experimentally determined to be 54
g/mol. What is the molecular formula
for the compound?