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

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.

Avogadro’s Number & the Mole The number of particles in a mole is called Avogadro’s Number. Avogadro’s number is 6.022  1023; the number of atoms or molecules in 1 mole

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  1023 particles

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

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.

Converting Between Amount in Moles and Number of Particles

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: 6.022 X 1023 molecules SO2 1 mole SO2 Start with what you know, mult. by conversion factor: 2.5 mol SO2 X 6.022 X 1023 molecules SO2 = 1.5 X1024 1 mole SO2 molecules SO2

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 1023 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 1023 particles NiSe = 1 mole NiSe 1.48 X 1018 particles NiSe

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

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: 3.01 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______ = 0.500 moles SO2

Additional Practice How many moles are equivalent to 7.95 X 1024 copper (II) chloride, CuCl2, formula units? Known: 7.95 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 1024 form. unit CuCl2 X ____1 mole_CuCl2___ 6.022 X 1023 form. unit CuCl2 = 13.2 mol CuCl2

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