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**Tuesday, April 5th: “A” Day Wednesday, April 6th: “B” Day Agenda**

PSAE Practice Test #3 Begin Chapter 7: “The Mole and Chemical Composition” In-Class Assignments: Practice pg. 228: #1-4 Practice pg. 229: #1-4 Concept Review: “Avogadro’s Number and Molar Conversions”: #1-5

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**Begin Section 7.1: “Avogadro’s Number and Molar Conversions”**

Atoms, ions, and molecules are very small, so even tiny samples have huge numbers of particles. Scientists use the mole to make counting such large numbers easier. Mole: the SI unit for amount; the number of atoms in exactly 12 grams of carbon-12.

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**Avogadro’s Number & the Mole**

The number of particles in a mole is called Avogadro’s Number. Avogadro’s number is 1023; the number of atoms or molecules in 1 mole

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**The Mole is a Counting Unit**

The mole is used to count out a given number of particles, whether they are atoms, molecules, formula units, ions, or electrons. The mole is just one kind of counting unit: 1 dozen = 12 objects 1 roll = 50 pennies 1 hour = 3,600 seconds 1 pair = 2 1 mole = 1023 particles

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**Conversion Factors The definition of one mole is:**

6.022 1023 particles = 1 mol Using this definition, we get 2 conversion factors: 6.022 X 1023 particles = 1 1 mol _____1 mol________ = 1 6.022 X 1023 particles

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**Choose the Conversion Factor that Cancels the Known Units**

**Because a conversion factor is equal to 1, it can multiply any quantity without changing the value. Only the units are changed. ** When solving conversion problems, the unit that you’re trying to get rid of goes on the bottom of the fraction.

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**Converting Between Amount in Moles and Number of Particles**

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**Find the number of molecules in 2.5 mol of sulfur dioxide, SO2.**

Sample Problem A, pg 228 Converting Between Amount in Moles to Number of Particles Find the number of molecules in 2.5 mol of sulfur dioxide, SO2. Known: 2.5 moles of SO2 Unknown: # of molecules of SO2 Conversion factor: X 1023 molecules SO2 1 mole SO2 Start with what you know, mult. by conversion factor: 2.5 mol SO2 X X 1023 molecules SO2 = 1.5 X mole SO molecules SO2

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Additional Practice How many particles are there in 2.45 X 10-6 mol of nickel, Ni (II) selenide, NiSe? Known: X 10-6 moles NiSe Unknown: # of particles of NiSe Conversion factor: X 1023 particles NiSe 1 mol NiSe Start with what you know, mult. by conversion factor: 2.45 X mol NiSe X X 1023 particles NiSe = mole NiSe 1.48 X 1018 particles NiSe

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**We can go the other way too and convert number of particles to amount in moles…**

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**Sample Problem B, pg. 229 Converting Number of Particles to Amount in Moles**

A sample contains 3.01 X 1023 molecules of sulfur dioxide, SO2. Determine the amount in moles. Known: X 1023 molecules of SO2 Unknown: moles of SO2 Conversion factor: ____1 mole SO2_____ 6.022 X 1023 molecules SO2 Start with what you know, mult. by conversion factor: 3.01 X 1023 molecules SO2 X __1 mole SO2______ = moles SO2

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Additional Practice How many moles are equivalent to 7.95 X 1024 copper (II) chloride, CuCl2, formula units? Known: X 1024 CuCl2 formula units Unknown: # of moles of CuCl2 formula units Conversion factor: _____1 mole CuCl2__ 6.022 X 1023 formula units CuCl2 Start with what you know, mult. by conversion factor: 7.95 X form. unit CuCl2 X ____1 mole_CuCl2___ 6.022 X 1023 form. unit CuCl2 = 13.2 mol CuCl2

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**In-Class Assignments You must SHOW WORK!**

Practice pg. 228: #1-4 Practice pg. 229: #1-4 Concept Review: Avogadro’s Number and Molar Conversions”: #1-5

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1 Chapter 5 Chemical Reactions and Quantities 5.5 The Mole Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings.

1 Chapter 5 Chemical Reactions and Quantities 5.5 The Mole Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings.

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