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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
• mole
• Avogadro’s number
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Measuring Matter
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.
Copyright © McGraw-Hill Education
Measuring Matter
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.
Copyright © McGraw-Hill Education
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.
Copyright © McGraw-Hill Education
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
Copyright © McGraw-Hill Education
Measuring Matter
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