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

AgendaPSAE Practice Test #3Begin Chapter 7: “The Mole and Chemical

Composition”In-Class Assignments:

Practice pg. 228: #1-4Practice pg. 229: #1-4Concept Review: “Avogadro’sNumber 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 UnitThe 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 objects1 roll = 50 pennies 1 hour = 3,600 seconds1 pair = 2 1 mole = 6.022 1023 particles

Conversion FactorsThe 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________ = 16.022 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

Sample Problem A, pg 228Converting Between Amount in Moles to Number of

ParticlesFind 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 PracticeHow many particles are there in 2.45 X 10-6 mol of nickel,

Ni (II) selenide, NiSe?Known: 2.45 X 10-6 moles NiSeUnknown: # of particles of NiSeConversion factor: 6.022 X 1023 particles NiSe

1 mol NiSeStart 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. 229Converting 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______

6.022 X 1023 molecules 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 AssignmentsYou must SHOW WORK!

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

Molar Conversions”: #1-5