### The Mole

```The Mole
Mr. Solsman
Chapter 10
Goals
• Explain how a mole is used to indirectly count
the number of particles of matter.
• Relate the mole to a common everyday
counting unit.
• Convert between moles and number of
representative particles
Counting Particles
• Chemists need a convenient method for
accurately counting the number of atoms,
molecules, or formula units of a substance.
• The mole is the SI base unit used to measure
the amount of a substance.
• 1 mole is the amount of atoms in 12 g of pure
carbon-12, or 6.02  1023 atoms.
• The number is called Avogadro’s number.
Conversion factors must be used
• Moles to particles
Number of molecules in 3.50 mol
of sucrose
• Particles to moles
• 1. How many zinc atoms are there in 2.50
mole of Zn?
• 2. Calculate the number of molecules in 11.5
mol of water.
• 3. How many formula units of silver nitrate
are in 3.25 moles of silver nitrate?
• 4. How many moles contain each of the
following?
• 5.75 x 1024 atoms of Al
• 2.50 x 1020 atoms of Fe
The Mass of a Mole
• 1 mol of copper and 1 mol of carbon have
different masses.
• One copper atom has a different mass than 1
carbon atom.
• Molar mass is the mass in grams of one mole
of any pure substance.
• The molar mass of any element is numerically
equivalent to its atomic mass and has the
units g/mol.
Using Molar Mass
3.00 moles of copper has a mass of 191 g.
• 1. Determine the mass of each of the
following:
• 3.57 mol Al
• 42.6 mol Si
• 2. Convert the moles given to mass in grams:
• 3.45 x 102 mol Co
• 2.45 x 10-2 mol Zn
• 3. Convert each mass to moles:
• 300.0 g S
• 1.00 kg Cr
• 0.120 kg Ti
Moles of Compounds
• The molar mass of a compound can be
calculated from its chemical formula and can
be used to convert from mass to moles of that
compound.
• Chemical formulas indicate the numbers and
types of atoms contained in one unit of the
compound.
• One mole of CCl2F2 contains one mole of C
atoms, two moles of Cl atoms, and two moles
of F atoms.
The Molar Mass of Compounds
• The molar mass of a compound equals the
molar mass of each element, multiplied by the
moles of that element in the chemical
• The molar mass of a compound demonstrates
the law of conservation of mass.
• 1. Find the molar mass of NaOH
• 2. CaCl2
• 3. KC2H3O2
• 4. Sr(NO3)2
• 5. Determine the number of moles present:
• 22.6 g AgNO3
• 6.50 g ZnSO4
• 35.0 g HCl
• 25.4 mg PbCl4
• 6. Ethanol (C2H5 OH) is often blended with
gasoline. A lab sample of ethanol has a mass
of 45.6 grams.
• A. How many moles of ethanol are present?
• B. How many moles of carbon atoms are
present?
• C. How many carbon atoms are present?
•
Percent Composition
• The percent by mass of any element in a
compound can be found by dividing the mass
of the element by the mass of the compound
and multiplying by 100.
• What is the percent by mass of oxygen in 36.0
grams of water if it contains 16 grams of
oxygen?
• The percent by mass of each element in a
compound is the percent composition of a
compound.
• Sodium hydrogen carbonate (NaHCO3 ) also
called baking soda is an active ingredient in
antacids. Determine the percent composition
of the compound.
• Sucrose commonly called table sugar, has the
formula C12 H22 O11. Find the percent
composition.
Empirical Formula
• The empirical formula for a compound is the
smallest whole-number mole ratio of the
elements. You can calculate the empirical formula
from percent by mass by assuming you have
100.00 g of the compound. Then, convert the
mass of each element to moles.
• The empirical formula may or may not be the
same as the molecular formula.
Molecular formula of hydrogen peroxide = H2O2
Empirical formula of hydrogen peroxide = HO
The molecular formula specifies the actual
number of atoms of each element in one
molecule or formula unit of the substance.
A molecular formula is always a whole-number
multiple of the empirical formula.
• Propane is a hydrocarbon composed of only
carbon and hydrogen. If a sample is 81.82%
carbon and 18.18% hydrogen, what is its
empirical formula?
• Methyl acetate is a solvent used in paints, etc.
Determine the empirical formula for a sample
that has the following analysis:
• 48.64% carbon, 8.16% hydrogen, and 43.20%
oxygen.
• Aspirin is the world’s most often used
medication. The chemical analysis of aspirin
indicates that the molecule is 60.00% carbon,
4.44% hydrogen, and 35.56% oxygen. What is
its empirical formula?
• A sample of the mineral ilmenite contains 5.41
g of iron, 4.64 g Titanium, and 4.65 g oxygen.
Determine its empirical fomula.
• A compound was found to contain 49.98 g of
carbon and 10.47 g of hydrogen. The molar
mass of the compound is 58.12 g/mol. Find
the molecular formula.
• A chemical analysis of Vitamin D yielded data
that gave 84.31% carbon, 11.53% hydrogen,
and 4.16% oxygen. The molar mass was found
to be 384 g/mol. What is its empirical and
molecular and empirical formulas?
Naming Hydrates
• A hydrate is a compound that has a specific
number of water molecules bound to its
atoms.
• The number of water molecules associated
with each formula unit of the compound is
written following a dot.
• Sodium carbonate decahydrate =
Na2CO3 • 10H2O
• When heated, water molecules are released
from a hydrate leaving an anhydrous
compound.
• To determine the formula of a hydrate, find
the number of moles of water associated with
1 mole of hydrate.
•
•
•
•
•
Weigh hydrate.
Heat to drive off the water.
Weigh the anhydrous compound.
Subtract and convert the difference to moles.
The ratio of moles of water to moles of
anhydrous compound is the coefficient for
water in the hydrate.
• An 11.75 gram sample of a common hydrate
of cobalt(II) chloride is heated. After heating,
0.0712 mol of anhydrous cobalt chloride
remains. What is the formula and name of
the hydrate?
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