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Section 3.3Section 3.3The Mole: A Measurement of The Mole: A Measurement of

MatterMatter OBJECTIVES:OBJECTIVES:

–Describe how Avogadro’s Describe how Avogadro’s number is related to a mole of number is related to a mole of any substance.any substance.

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Section 3.3Section 3.3The Mole: A Measurement of The Mole: A Measurement of

MatterMatter OBJECTIVES:OBJECTIVES:

–Calculate the mass of a mole of Calculate the mass of a mole of any substance.any substance.

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What is a Mole?What is a Mole?

You can measure You can measure massmass, , or or volumevolume,, or you can or you can count piecescount pieces.. We measure mass in We measure mass in gramsgrams.. We measure volume in We measure volume in litersliters.. We count pieces inWe count pieces in MOLESMOLES..

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Moles (abbreviated: mol)Moles (abbreviated: mol) Defined as the number of carbon Defined as the number of carbon

atoms in exactly 12 grams of atoms in exactly 12 grams of carbon-12.carbon-12.

1 mole is 6.02 x 101 mole is 6.02 x 102323 particles. particles. Treat it like a very large dozenTreat it like a very large dozen 6.02 x 106.02 x 102323 is called is called Avogadro’s Avogadro’s

number.number.

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Representative particlesRepresentative particles The smallest pieces of a substance.The smallest pieces of a substance.

–For a molecular compound: it is For a molecular compound: it is the molecule.the molecule.

–For an ionic compound: it is the For an ionic compound: it is the formula unit.formula unit.

–For an element: it is the atom.For an element: it is the atom.

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Types of questionsTypes of questions How many molecules of COHow many molecules of CO22 are are

there in 4.56 moles of COthere in 4.56 moles of CO22 ? ? How many moles of water is 5.87 x How many moles of water is 5.87 x

10102222 molecules? molecules? How many atoms of carbon are How many atoms of carbon are

there in 1.23 moles of Cthere in 1.23 moles of C66HH1212OO66 ? ? How many moles is 7.78 x 10How many moles is 7.78 x 102424

formula units of MgClformula units of MgCl22??

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Measuring MolesMeasuring Moles Remember relative atomic mass?Remember relative atomic mass? The amu was one twelfth the mass The amu was one twelfth the mass

of a carbon-12 atom.of a carbon-12 atom. Since the mole is the number of Since the mole is the number of

atoms in 12 grams of carbon-12,atoms in 12 grams of carbon-12, the decimal number on the periodic the decimal number on the periodic

table is also the mass of 1 mole of table is also the mass of 1 mole of those atoms in grams.those atoms in grams.

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Gram Atomic Mass (gam)Gram Atomic Mass (gam) Equals the mass of 1 mole of an Equals the mass of 1 mole of an

element in gramselement in grams 12 grams of C has the same number 12 grams of C has the same number

of pieces as 1 gram of H and 56 of pieces as 1 gram of H and 56 grams of iron.grams of iron.

We can write this as We can write this as 12 g C = 1 mole C 12 g C = 1 mole C

We can count things by weighing We can count things by weighing them.them.

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ExamplesExamples How much would 2.34 moles of How much would 2.34 moles of

carbon weigh?carbon weigh? How many moles of magnesium is How many moles of magnesium is

24 g of Mg?24 g of Mg? How many atoms of lithium is 1.00 How many atoms of lithium is 1.00

g of Li?g of Li? How much would 3.45 x 10How much would 3.45 x 102222 atoms atoms

of U weigh?of U weigh?

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What about compounds?What about compounds? in 1 mole of Hin 1 mole of H22O molecules there are O molecules there are

two moles of H atoms and 1 mole of O two moles of H atoms and 1 mole of O atomsatoms

To find the mass of one mole of a To find the mass of one mole of a compound compound –determine the moles of the elements determine the moles of the elements

they havethey have–Find out how much they would weighFind out how much they would weigh–add them upadd them up

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What about compounds?What about compounds? What is the mass of one mole of CHWhat is the mass of one mole of CH44??

1 mole of C = 12 g1 mole of C = 12 g

4 mole of H x 1 g = 4 g4 mole of H x 1 g = 4 g

1 mole CH1 mole CH44 = 12 + 4 = 16 g = 12 + 4 = 16 g The The Gram Molecular Mass (gmm) Gram Molecular Mass (gmm) of of

CHCH44 is 16 g is 16 g

– this is the mass of one mole of a this is the mass of one mole of a molecular compound.molecular compound.

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Gram Formula Mass (gfm)Gram Formula Mass (gfm) The mass of one mole of an ionic The mass of one mole of an ionic

compound.compound. Calculated the same way as gmm.Calculated the same way as gmm. What is the GFM of FeWhat is the GFM of Fe22OO33??

2 moles of Fe x 56 g = 112 g2 moles of Fe x 56 g = 112 g

3 moles of O x 16 g = 48 g3 moles of O x 16 g = 48 g

The GFM = 112 g + 48 g = 160 gThe GFM = 112 g + 48 g = 160 g

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Section 3.3Section 3.3Mole-Mass and Mole-Volume Mole-Mass and Mole-Volume

RelationshipsRelationships OBJECTIVES:OBJECTIVES:

–Use the molar mass to convert Use the molar mass to convert between mass and moles of a between mass and moles of a substance.substance.

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Section 3.3Section 3.3Mole-Mass and Mole-Volume Mole-Mass and Mole-Volume

RelationshipsRelationships OBJECTIVES:OBJECTIVES:

–Use the mole to convert among Use the mole to convert among measurements of mass, measurements of mass, volume, and number of volume, and number of particles.particles.

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Molar MassMolar Mass Molar massMolar mass is the generic term for is the generic term for

the mass of one mole of any the mass of one mole of any substance (in grams) substance (in grams)

The same as: 1) gram molecular The same as: 1) gram molecular mass, 2) gram formula mass, and 3) mass, 2) gram formula mass, and 3) gram atomic mass- just a much gram atomic mass- just a much broader term.broader term.

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ExamplesExamples Calculate the molar mass of the Calculate the molar mass of the

following and tell what type it is:following and tell what type it is: NaNa22SS

NN22OO44

CC Ca(NOCa(NO33))22

CC66HH1212OO66

(NH(NH44))33POPO44

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Molar MassMolar Mass The number of grams of 1 mole The number of grams of 1 mole

of atoms, ions, or molecules.of atoms, ions, or molecules. We can make conversion factors We can make conversion factors

from these.from these.

–To change grams of a To change grams of a compound to moles of a compound to moles of a compound.compound.

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g mole

g

need to change grams to moles

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g mole

g

need to change grams to moles for NaOH

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g mole

g

need to change grams to moles for NaOH 1mole Na = 23 g 1 mol O = 16 g 1 mole of H = 1 g

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g mole

g

need to change grams to moles for NaOH 1mole Na = 23 g 1 mol O = 16 g 1 mole of H = 1 g 1 mole NaOH = 40 g

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g 1 mole

40.00 g

need to change grams to moles for NaOH 1mole Na = 23 g 1 mol O = 16 g 1 mole of H = 1 g 1 mole NaOH = 40 g

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For exampleFor example

How many moles is 5.69 g of NaOH?How many moles is 5.69 g of NaOH?

5 69. g 1 mole

40.00 = 0.142 mol NaOH

g

need to change grams to moles for NaOH 1mole Na = 23 g 1 mol O = 16 g 1 mole of H = 1 g 1 mole NaOH = 40 g

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ExamplesExamples How many moles is 4.56 g of COHow many moles is 4.56 g of CO22?? How many grams is 9.87 moles of How many grams is 9.87 moles of

HH22O?O? How many molecules is 6.8 g of How many molecules is 6.8 g of

CHCH44??

49 molecules of C49 molecules of C66HH1212OO66 weighs weighs

how much?how much?

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GasesGases Many of the chemicals we deal with Many of the chemicals we deal with

are gases.are gases.–They are difficult to They are difficult to weighweigh..

Need to know how many moles of gas Need to know how many moles of gas we have.we have.

Two things effect the volume of a gasTwo things effect the volume of a gas–Temperature and pressureTemperature and pressure

We need to compare them at the same We need to compare them at the same temperature and pressure.temperature and pressure.

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Standard Temperature and Standard Temperature and PressurePressure

0ºC and 1 atm pressure0ºC and 1 atm pressure abbreviated abbreviated STPSTP At STP 1 mole of gas occupies At STP 1 mole of gas occupies

22.4 L22.4 L Called the Called the molar volumemolar volume 1 mole = 22.4 L of any gas at STP1 mole = 22.4 L of any gas at STP

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ExamplesExamples What is the volume of 4.59 mole What is the volume of 4.59 mole

of COof CO22 gas at STP? gas at STP?

How many moles is 5.67 L of OHow many moles is 5.67 L of O2 2

at STP?at STP? What is the volume of 8.8 g of What is the volume of 8.8 g of

CHCH44 gas at STP? gas at STP?

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Density of a gasDensity of a gas D = m / VD = m / V–for a gas the units will be g / Lfor a gas the units will be g / L

We can determine the density of any We can determine the density of any gas at STP if we know its formula.gas at STP if we know its formula.

To find the density we need the mass To find the density we need the mass and the volume.and the volume.

If you assume you have 1 mole, then If you assume you have 1 mole, then the mass is the molar mass (from PT)the mass is the molar mass (from PT)

At STP the volume is 22.4 L.At STP the volume is 22.4 L.

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ExamplesExamples Find the density of COFind the density of CO2 2 at STP.at STP.

Find the density of CHFind the density of CH44 at STP. at STP.

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The other wayThe other way Given the density, we can find the molar Given the density, we can find the molar

mass of the gas.mass of the gas. Again, pretend you have 1 mole at STP, Again, pretend you have 1 mole at STP,

so V = 22.4 L.so V = 22.4 L. m = D x Vm = D x V m is the mass of 1 mole, since you have m is the mass of 1 mole, since you have

22.4 L of the stuff.22.4 L of the stuff. What is the molar mass of a gas with a What is the molar mass of a gas with a

density of 1.964 g/L?density of 1.964 g/L? 2.86 g/L?2.86 g/L?

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SummarySummary These four items are all equal:These four items are all equal:

a) 1 molea) 1 mole

b) molar mass (in grams)b) molar mass (in grams)

c) 6.02 x 10c) 6.02 x 102323 representative representative particlesparticles

d) 22.4 L at STPd) 22.4 L at STP

Thus, we can make conversion Thus, we can make conversion factors from them.factors from them.