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Tuesday, April 5 th : “A” Day Wednesday, April 6 th : “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 6.022 10 23 ; 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 = 6.022 10 23 particles

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Conversion Factors The definition of one mole is: 6.022 10 23 particles = 1 mol Using this definition, we get 2 conversion factors: 6.022 X 10 23 particles = 1 1 mol _____1 mol________ = 1 6.022 X 10 23 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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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, SO 2. Known: 2.5 moles of SO 2 Unknown: # of molecules of SO 2 Conversion factor: 6.022 X 10 23 molecules SO 2 1 mole SO 2 Start with what you know, mult. by conversion factor: 2.5 mol SO 2 X 6.022 X 10 23 molecules SO 2 = 1.5 X10 24 1 mole SO 2 molecules SO 2

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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: 2.45 X 10 -6 moles NiSe Unknown: # of particles of NiSe Conversion factor: 6.022 X 10 23 particles NiSe 1 mol NiSe Start with what you know, mult. by conversion factor: 2.45 X 10 -6 mol NiSe X 6.022 X 10 23 particles NiSe = 1 mole NiSe 1.48 X 10 18 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 10 23 molecules of sulfur dioxide, SO 2. Determine the amount in moles. Known: 3.01 X 10 23 molecules of SO 2 Unknown: moles of SO 2 Conversion factor: ____1 mole SO 2 _____ 6.022 X 10 23 molecules SO 2 Start with what you know, mult. by conversion factor: 3.01 X 10 23 molecules SO 2 X __1 mole SO 2 ______ 6.022 X 10 23 molecules SO 2 = 0.500 moles SO 2

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Additional Practice How many moles are equivalent to 7.95 X 10 24 copper (II) chloride, CuCl 2, formula units? Known: 7.95 X 10 24 CuCl 2 formula units Unknown: # of moles of CuCl 2 formula units Conversion factor: _____1 mole CuCl 2 __ 6.022 X 10 23 formula units CuCl 2 Start with what you know, mult. by conversion factor: 7.95 X 10 24 form. unit CuCl 2 X ____1 mole_CuCl 2 ___ 6.022 X 10 23 form. unit CuCl 2 = 13.2 mol CuCl 2

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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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