1. 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

2. 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

3. 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

4. Vocabulary Review New molecule mole Avogadro’s number Measuring Matter
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5. 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.
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Measuring Matter

6. 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

7. 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

8. Particles-to-Moles Conversion
KNOWN
Number of atoms = 4.50 × 1024 atoms Zn
1 mol Zn = 6.02 × 1023 atoms Zn
UNKNOWN
Moles Zn = ? mol
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.
SOLVE FOR THE UNKNOWN
Use a conversion factor—the inverse of Avogadro’s number—that relates moles to atoms.
Apply the conversion factor.
number of atoms = 1 mol 6.02 × atoms =number of moles
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.
Measuring Matter
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9. Particles-to-Moles Conversion
SOLVE FOR THE UNKNOWN
Substitute the number of Zn atoms = 4.50 × Multiply and divide numbers and units.
4.50 × 1024 atoms Zn = 1 mol Zn 6.02 × atoms Zn =7.48 mol Zn
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.
Measuring Matter
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10. Review Essential Questions Vocabulary
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
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Measuring Matter