Section 1: Measuring Matter
Chemists use the mole to count atoms, molecules, ions, and
formula units.
K
What I Know
W
What I Want to Find Out
L
What I Learned
• 8(A) Define and use the concept of a mole.
• 8(B) Use the mole concept to calculate the number of atoms, ions, or
molecules in a sample of material.
• 2(G) Express and manipulate chemical quantities using scientific
conventions and mathematical procedures, including dimensional
analysis, scientific notation, and significant figures.
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Measuring Matter
Essential Questions
• How is a mole used to indirectly count the number of particles
of matter?
• What is a common everyday counting unit to which the mole
can be related?
• How can moles be converted to number of representative
particles and vice versa?
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Measuring Matter
Vocabulary
Review
New
• Molecule: forms when two or
• Mole: the SI Unit used to
more atoms covalently bond and
measure the amount of a
is lower in potential energy than
substance
its constituent atoms
• Ex. The number of carbon
• Atomic mass: the weighted
atoms in exactly 12 g of pure
average mass of the isotopes of
carbon
that element
• Amount 6.02 x 1023
• Avogadro’s number: 6.02 X 1023
• Atomic mass Unit (amu): one
twelfth the mass of a carbon-12
atom
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Measuring Matter
Practice Review
• Write the following in scientific notation
– 0.00582
– 24,367
– 400
• Circle the significant figures in the number
below
– 75,600,000
– 0.00033
– 3.140
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 representative
particles, which is any kind of particle – an atom, a
molecule, a formula unit, an electron, an ion, etc.
The number is called Avogadro’s number.
Mole- SI based unit used to measure the quantity of
matter
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Measuring Matter
Avogadro's Number
List common counting units and their
values
•
•
•
•
Dozen –
PairGrossReam -
Why the need for a new counting
number
• A convenient method for accurately counting
atoms, molecules, or formula units in a
sample of a substance.
• Atoms are so small and there are so many of
them that it is impossible to count them
directly.
What can be measured using a mole
• atom
Molecule
• Formula unit
Converting Between Moles and Particles
Conversion factors must be used.
Moles to particles:
•
Number of molecules in 3.50 mol of sucrose:
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Measuring Matter
Converting Between Moles and Particles
Particles to moles
Use the inverse of Avogadro’s number as the conversion factor.
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Measuring Matter
PARTICLES-TO-MOLES CONVERSION
KNOWN
Use with Example Problem 1.
Problem
Zinc (Zn) is used as a corrosion-resistant
coating on iron and steel. It is also an
essential trace element in your diet.
Calculate the number of moles of zinc
that contain 4.50 × 1024 atoms.
Number of atoms = 4.50 × 1024 atoms Zn
1 mol Zn = 6.02 × 1023 atoms Zn
UNKNOWN
Moles Zn = ? mol
SOLVE FOR THE UNKNOWN
Response
ANALYZE THE PROBLEM
You are given the number of atoms of zinc
and must find the equivalent number of
moles. If you compare 4.50 × 1024 atoms Zn
with 6.02 × 1023, the number of atoms in 1
mol, you can predict that the answer should
be less than 10 mol.
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Use a conversion factor—the inverse of
Avogadro’s number—that relates moles to
atoms.
•
Apply the conversion factor.
1 mol
number of atoms =
6.02 × 1023 atoms
= number of moles
Measuring Matter
PARTICLES-TO-MOLES CONVERSION
SOLVE FOR THE UNKNOWN
EVALUATE THE ANSWER
•
Both the number of Zn atoms and
Avogadro’s number have three significant
figures. Therefore, the answer is
expressed correctly with three digits. The
answer is less than 10 mol, as predicted,
and has the correct unit, moles.
Substitute the number of Zn atoms = 4.50
× 1024. Multiply and divide numbers and
units.
1 mol Zn
4.50 × 1024 atoms Zn =
6.02 × 1023 atoms Zn
= 7.48 mol Zn
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Measuring Matter
Conversion Practice
• Calculate the number of molecules in 11.5 mol
of water.
Conversion Practice
• Silver Nitrate is used to make several different
silver halides used in photographic films. How
many formula units of silver nitrate are there
in 3.25 mol of silver nitrate?
Review
Essential Questions
• How is a mole used to indirectly count the number of particles of
matter?
• What is a common everyday counting unit to which the mole can be
related?
• How can moles be converted to number of representative particles
and vice versa?
Vocabulary
• mole
• Avogadro’s number
Copyright © McGraw-Hill Education
Measuring Matter