Transcript Chemistry: Matter and Change

Chapter 10
The Mole
Honors Chemistry
December
Mrs. Warren
Counting Units
• Pair of Gloves
• Dozen of
Donuts/Roses
• Gross of Pencils
• Ream of Paper
• The numbers of the
units described to the
left are always
constant.
• Why do we use these
words?
– Convenience!
Counting Particles
• The mole is the SI base unit used to measure the
amount of a substance.
• 1 mole of anything = 6.02 x 1023 representative
particles.
• 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.
• Named after Amedeo Avogadro (Italian
Physicist and lawyer)
Converting Between Moles and Particles
• Conversion factors must be used.
• Moles to particles
Number of molecules in 3.50 mol of sucrose
Converting Between Moles and Particles (cont.)
• Particles to moles
• Use the inverse of Avogadro’s number as the
conversion factor.
Mole Calculations
• How many sodium atoms are in 0.120 mol Na?
– Step 1: we want atoms of Na
– Step 2: we have 0.120 mol Na
– Step 3: 1 mole Na = 6.02 × 1023 atoms Na
6.02 × 1023 atoms Na
= 7.22 × 1022 atoms
0.120 mol Na ×
1 mol Na
Na
Mole Calculations I
• How many moles of potassium are in 1.25 × 1021
atoms K?
– Step 1: we want moles K
– Step 2: we have 1.25 × 1021 atoms K
– Step 3: 1 mole K = 6.02 × 1023 atoms K
1.25 ×
1021
1 mol K
-3
atoms K ×
=
2.08
×
10
6.02 × 1023 atoms KmolK
Practice Mole Calculations
• How many moles of potassium are in 1.25 ×
1021 atoms K?
• Determine the number of Zinc atoms in 2.50
mol of Zn.
• Calculate the number of molecules in 11.5 mol
of water (H2O).
• How many formula units of Ag(NO3) are there
in 3.25 mol of silver nitrate?
Practice Mole Calculations
• Challenge: Identify the representative
particle for each (is it a formula unit,
molecule, atom, etc.) and convert the
given number of representative particles to
moles:
– 3.75 x 1024 CO2
– 3.58 x 1023 ZnCl
The Mass of a Mole
• 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.
55.845 g/mol
Using Molar Mass
• How do we calculate Molar Mass?
Convert 3 moles of Cu to grams of Cu.
3.00 moles of copper has a mass of 191 g.
Molar Mass Calculations
• Calculate the mass in grams of 0.0450 mol
of Chromium.
• How many moles of Calcium are in 525
grams of Ca?
• Determine the mass in grams of each:
– 3.57 mol Al
– 42.6 mol Si
• Determine the number of moles in each:
– 25.5 g Ag
– 300.0 g S
Converting Between Mass and Atoms
• How many atoms of gold are in a U.S.
Eagle, a gold alloy coin with a mass of
31.1 g Au
• A party balloon contains 5.50 x 1022 atoms
of Helium gas. What is the mass, in grams,
of He?
Try on your Own…
• How many atoms are in each of the
following?
– 55.2 g Li
– 0.230 g Pb
• What is the mass in grams of each of the
following?
– 6.02 x 1024 atoms Bi
– 1.5 x 1015 atoms U
Chemical Formulas and the Mole
• 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.
• [Remember that the chemical formula not
only represents an individual molecule of
CCl2F2, it also represents a mole of the
compound.]
• Other Examples…
Try on your Own…
• Calculate the number of moles of each
element in 1.25 mol C6H12O6.
• Determine the number of moles of sulfate
ions present in 3.00 mol of Fe2(SO4) 3.
Molar Mass of Compounds
•
•
•
•
•
Potassium Chromate
Sodium Hydroxide
Carbon Tetrachloride
Strontium Nitrate
Calcium Chloride
Converting Moles of a Compound to Mass
• What is the mass of 2.50 mol of (C3H5) 2S?
• What is the mass of 3.25 mol of H2SO4?
Let’s Flip it! 
• Calculate the number of moles present in
each compound:
– 22.6 g AgNO3
– 35.0 g HCl
– 2.50 kg Fe2O3
– 25.4 mg PbCl4
More Challenging…
• Converting the Mass of a Compound to
Number of Particles
– A sample of Aluminum Chloride has a mass
of 35.6 grams.
• How many aluminum ions are present?
• How many chloride ions are present?
• What is the mass in grams of one formula unit of
aluminum chloride?
More Practice….
• A sample of sodium sulfite has a mass of
2.25 grams.
– How many sodium ions are present?
– How many sulfite ions are present?
– What is the mass in grams of one formula unit
of sodium sulfite?
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.
•The percent by mass of all of the elements
of a compound must always add up to 100.
Percent Composition (cont.)
• The percent by mass of each element in a
compound is the percent composition of
a compound.
• Percent composition of a compound can also
be determined from its chemical formula.
Percent Composition Example
• Determine the percent composition of
Na(HCO3).
• What is the percent composition of
H3(PO4)?
• Sodium Sulfate is used in most detergents:
– Write the chemical formula and determine if it is
ionic or molecular
– Calculate the percent by mass of each element
in sodium sulfate.
Empirical Formula
• The empirical formula for a compound is
the smallest whole-number mole ratio of
the elements.
• 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
Empirical Formula Calculations
• Determine the empirical formula for methyl
acetate, which has the following chemical
analysis: 48.64% carbon, 8.16%
hydrogen, and 43.20% oxygen.
Section 10.4 Assessment
What is the empirical formula for the
compound C6H12O6?
A. CHO
B. C2H3O2
D
A
0%
C
D. CH3O
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. CH2O
Section 10.4 Assessment
Which is the empirical formula for
hydrogen peroxide?
A. H2O2
B. H2O
D
A
0%
C
D. none of the above
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. HO
Molecular Formula
• The molecular formula specifies the
actual number of atoms of each element in
one molecule or formula unit of the
substance.
• Molecular formula is always a whole-number
multiple of the empirical formula.
Molecular Formula Practice…
• The molar mass of acetylene is 26.04
g/mol, and the mass of the empirical
formula (CH) is 13.02 g/mol. How can we
find the molecular formula?
Molecular Formula and Empirical Formula
Relationship
• Succinic Acid is composed of 40.68% carbon, 5.08%
hydrogen, and 54.24% oxygen and has a molar mass of
118.1 g/mol. Determine the empirical formula and
molecular formula for succinic acid.