Ch. 11Ch. 11

TheThe MoleMole

11.1 Measuring Matter11.1 Measuring Matter Mole-Mole- SI base unit used to SI base unit used to

measure the amount of a measure the amount of a substancesubstance

Equal to the number of Equal to the number of representative particles (carbon representative particles (carbon atoms) in exactly 12 grams of atoms) in exactly 12 grams of carbon-12carbon-12

Representative particle :Representative particle : Elements –atomElements –atom Covalent –moleculesCovalent –molecules Ionic - formula unitsIonic - formula units

Avogadro’s NumberAvogadro’s Number Avogadro’s NumberAvogadro’s Number

= 6.022 X 10= 6.022 X 102323 Is a very large Is a very large

number because it is number because it is used to count used to count extremely small extremely small particles. particles.

Conversion of a Mole Conversion of a Mole to a Particleto a Particle

1 mole = 6.02 x 101 mole = 6.02 x 102323

# of moles x 6.02 x 10# of moles x 6.02 x 1023 23

representative particles = # of representative particles = # of representative particlesrepresentative particles

Ex: How many molecules are Ex: How many molecules are in 3.5 moles of sucrose?in 3.5 moles of sucrose?

3.5 moles sucrose x 3.5 moles sucrose x 6.02 x 106.02 x 1023 23 moleculesmolecules = = 1 mole 1 mole sucrosesucrose

= 2.11 x 10= 2.11 x 102424 molecules of sucrose molecules of sucrose

Conversion of a Particle Conversion of a Particle to a Moleto a Mole Reverse conversion factor to Reverse conversion factor to

solve for # of molessolve for # of moles Ex: How many moles are in 4.50 x Ex: How many moles are in 4.50 x

10102424 atoms of zinc? atoms of zinc? 4.50 x 104.50 x 1024 24 atoms Zn x atoms Zn x 1 mol Zn1 mol Zn

6.02 x 106.02 x 1023 23 atoms Znatoms Zn

= 7.48 mol Zn= 7.48 mol Zn

STOP! YOUR TURN!STOP! YOUR TURN!

Practice Problems 11.1Practice Problems 11.1

11.2 Mass and the Mole11.2 Mass and the Mole

Just as a dozen bricks and a Just as a dozen bricks and a dozen feathers don’t have the dozen feathers don’t have the same mass, moles of different same mass, moles of different substances also have different substances also have different masses.masses.

Molar mass-Molar mass- mass in grams of mass in grams of one mole of any pure substanceone mole of any pure substance

The molar mass of any element The molar mass of any element is numerically equal to its atomic is numerically equal to its atomic mass and has the units g/molmass and has the units g/mol

Using Molar MassUsing Molar Mass

Ex: What is the mass in grams of Ex: What is the mass in grams of 0.0450 moles of chromium?0.0450 moles of chromium?

Moles Cr x Moles Cr x grams Crgrams Cr = grams Cr = grams Cr

1 mole Cr1 mole Cr 0.0450 mol Cr x 0.0450 mol Cr x 52.00 g Cr52.00 g Cr = 2.34 g Cr = 2.34 g Cr

1 mol Cr1 mol Cr

Mols MassMols Mass

ParticlesParticles

(atoms, molecules, formula unit)(atoms, molecules, formula unit)

Converting Mass to Converting Mass to Atoms and Atoms to MassAtoms and Atoms to Mass

Ex: How many atoms of gold are in a Ex: How many atoms of gold are in a pure nugget having a mass of 25.0 g?pure nugget having a mass of 25.0 g?

Known:Known: Mass = 25.0 g AuMass = 25.0 g Au Molar mass Au = 196.97 g/mol AuMolar mass Au = 196.97 g/mol Au

Unknown:Unknown: Number of atoms = ? Atoms AuNumber of atoms = ? Atoms Au

Mass Au x Mass Au x 1 mole Au1 mole Au = moles Au = moles Au

# g Au# g Au 25.0 g Au x 25.0 g Au x 1 mol Au 1 mol Au = ? mol = ? mol

AuAu

196.67 g Au196.67 g Au

= 0.127 mol Au= 0.127 mol Au

Half way there!!Half way there!!

Moles Au x Moles Au x 6.02 x 106.02 x 102323 atoms Au atoms Au = = 1 mole Au1 mole Au

0.127 mol Au x 0.127 mol Au x 6.02 x 106.02 x 102323 atoms Au atoms Au 1 mol Au1 mol Au

= 7.65 x 10= 7.65 x 102222 atoms Au atoms Au Mass must always be converted Mass must always be converted

to moles before being converted to moles before being converted to atoms, and atoms must be to atoms, and atoms must be converted moles before converted moles before calculating their mass.calculating their mass.

11.3 Moles of Compounds11.3 Moles of Compounds

Chemical formula indicates types Chemical formula indicates types of atoms and number of each in of atoms and number of each in one unit of the compoundone unit of the compound

Ex: CClEx: CCl22FF22

Carbon = one atomCarbon = one atomChlorine = 2 atomsChlorine = 2 atomsFluorine = 2 atomsFluorine = 2 atoms

Ratio of carbon to chlorine to Ratio of carbon to chlorine to fluorine is 1 : 2 : 2fluorine is 1 : 2 : 2

Conversions with Conversions with Chemical FormulasChemical Formulas

How many moles of fluorine atoms How many moles of fluorine atoms are in 5.50 moles of freon are in 5.50 moles of freon (CCl(CCl22FF22)?)?

5.50 mol CCl5.50 mol CCl22FF2 2 x x 2 mol F atoms2 mol F atoms = 11.0 mol F atoms = 11.0 mol F atoms

1 mol CCl 1 mol CCl22FF22

Molar Mass of Molar Mass of CompoundsCompounds

Mass of a mole of a compound Mass of a mole of a compound equals the sum of the masses of equals the sum of the masses of every particle that makes up the every particle that makes up the compound.compound.

Suppose you want to determine the Suppose you want to determine the molar mass of potassium chromate molar mass of potassium chromate (K(K22CrOCrO44) )

# moles x molar mass = # grams# moles x molar mass = # grams 2.000 mol K x 2.000 mol K x 39.10 g K39.10 g K = 78.20 g K = 78.20 g K

1 mol K1 mol K

1.000 mol Cr x 1.000 mol Cr x 52.00 g Cr52.00 g Cr = 52.00 g Cr = 52.00 g Cr

1 mol Cr1 mol Cr

4.000 mol O x 4.000 mol O x 16.00 g O16.00 g O = 64.00 g O = 64.00 g O

1 mol O1 mol O

Molar mass = 78.20 g KMolar mass = 78.20 g K

52.00 g Cr52.00 g Cr

+ + 64.00 g O64.00 g O

194.20 g K194.20 g K22CrOCrO44

Converting Moles of a Converting Moles of a Compound to MassCompound to Mass

Step 1: Calculate molar mass of Step 1: Calculate molar mass of the compound.the compound.

Step 2: Convert moles to grams Step 2: Convert moles to grams using the molar mass as a using the molar mass as a conversion factor.conversion factor.

Converting Moles to MassConverting Moles to Mass Convert 2.50 mol CHClConvert 2.50 mol CHCl3 3 to mass in grams.to mass in grams.

Step one: Calculate the number of grams Step one: Calculate the number of grams in one mole of CHClin one mole of CHCl3 = 3 = 119.35 grams119.35 grams

Step up problem as beforeStep up problem as before What’s given What you wantWhat’s given What you want

What you want to get rid ofWhat you want to get rid of 2.5 mol CHCl2.5 mol CHCl3 3 119.35 grams of CHCl119.35 grams of CHCl33

1 mol of CHCl1 mol of CHCl33

= = 298.38298.38 grams of CHClgrams of CHCl33

Converting Mass of a Converting Mass of a Compound to MolesCompound to Moles

Use inverse of mole to mass conversion Use inverse of mole to mass conversion factorfactor

Converting Mass of a Converting Mass of a Compound to Number of Compound to Number of ParticlesParticles Step 1: Convert given mass to Step 1: Convert given mass to

moles by using the molar mass moles by using the molar mass as a conversion factor.as a conversion factor.

Step 2: Convert moles to Step 2: Convert moles to number of representative number of representative particles by multiplying by particles by multiplying by Avogadro’s number.Avogadro’s number.

11.4 Empirical and 11.4 Empirical and Molecular FormulasMolecular Formulas

Percent Composition-Percent Composition- percent by mass of percent by mass of each element in a compoundeach element in a compound

% composition = % composition = mass of elementmass of element x 100 x 100

mass of compoundmass of compound

Percent Composition Percent Composition from the Chemical from the Chemical FormulaFormula Percent composition is always Percent composition is always

the same, regardless of the size the same, regardless of the size of the sampleof the sample

To determine percent To determine percent composition, assume a sample composition, assume a sample size of one molesize of one mole

What is the percent What is the percent composition of water?composition of water?Percent Hydrogen:Percent Hydrogen:

2.02 g H2.02 g H x 100 = 11.2% H x 100 = 11.2% H

18.02 g H18.02 g H22OO

Percent Oxygen:Percent Oxygen:16.00 g O16.00 g O x 100 = 88.80% O x 100 = 88.80% O

18.02 g H18.02 g H22OO

STOP! YOUR TURN!STOP! YOUR TURN!

Page 331, #45Page 331, #45

Empirical FormulaEmpirical Formula

Empirical Formula-Empirical Formula- formula with formula with the smallest whole number mole the smallest whole number mole ratio of the elementsratio of the elements

Which of these do you think is Which of these do you think is the empirical formula?the empirical formula?

HO or HHO or H22OO2 ?2 ?

Empirical formula may be Empirical formula may be different from molecular formuladifferent from molecular formulaEx: hydrogen peroxideEx: hydrogen peroxide

Empirical formula: HOEmpirical formula: HOMolecular formula: HMolecular formula: H22OO22

Finding the Empirical Finding the Empirical FormulaFormula

If percent composition is given, If percent composition is given, assume a 100 g sample, so assume a 100 g sample, so change % to gramschange % to grams

Ex: percent composition is Ex: percent composition is 40.05% S and 59.95% O40.05% S and 59.95% O100.0 g of the sample is 40.05 100.0 g of the sample is 40.05

g S and 59.95 g Og S and 59.95 g O

Convert mass of each element to number Convert mass of each element to number of molesof moles

40.05 g S x 40.05 g S x 1 mol S1 mol S = 1.249 mol S = 1.249 mol S

32.07 g S32.07 g S 59.95 g O x 59.95 g O x 1 mol O1 mol O = 3.747 mol O = 3.747 mol O

16.00 g O16.00 g O

Ratio of S atoms to O atoms is Ratio of S atoms to O atoms is

1.249 : 3.7471.249 : 3.747 Must convert to whole numbersMust convert to whole numbers Since 1.249 is smallest, divide Since 1.249 is smallest, divide

both numbers by that valueboth numbers by that value

Continued…Continued…

1.249 mol S1.249 mol S = 1 mol S = 1 mol S

1.2491.249 3.747 mol O3.747 mol O = 3 mol O = 3 mol O

1.2491.249 Ratio of S atoms to O atoms is 1 : 3Ratio of S atoms to O atoms is 1 : 3 Empirical Formula = SOEmpirical Formula = SO33

STOP! YOUR TURN!STOP! YOUR TURN!

# 46 and 47 page 333# 46 and 47 page 333

Molecular FormulaMolecular Formula

Molecular Formula-Molecular Formula- specifies the specifies the actual number of atoms of each actual number of atoms of each element in one molecule or element in one molecule or formula unit of the substanceformula unit of the substance

Molecular formula = (empirical Molecular formula = (empirical formula) nformula) nn is the factor by which the n is the factor by which the

subscripts in the empirical subscripts in the empirical formula must be multiplied to formula must be multiplied to obtain molecular formulaobtain molecular formula

Determining Molecular Determining Molecular FormulaFormula

Empirical formula: CEmpirical formula: C22HH33OO2 2

Molar Mass CMolar Mass C22HH33OO2 2 = 59.04 g C= 59.04 g C22HH33OO2 2

(calculated value)(calculated value) Molar Mass succinic acid = 118.1 gMolar Mass succinic acid = 118.1 g

(given value)(given value)

n = n = molar mass succinic acid molar mass succinic acid

molar mass Cmolar mass C22HH33OO2 (empirical formula)2 (empirical formula)

n = n = 118.1 g118.1 g = 2.00 = 2.00

59.04 g59.04 g (C(C22HH33OO22) 2 = C) 2 = C44HH66OO44

STOP! YOUR TURN!STOP! YOUR TURN!

# 51 and 52# 51 and 52

Empirical Formula = HOEmpirical Formula = HO Given the molar mass is 34.014g/mol. Given the molar mass is 34.014g/mol.

What is the MOLECULAR FORMULA?What is the MOLECULAR FORMULA?

Class DiscussionClass Discussion

Why do one mol of sulfur not the same Why do one mol of sulfur not the same as one mol of hydrogen?as one mol of hydrogen?

CROSS OFF 11.5CROSS OFF 11.5

11.5 The Formula for a 11.5 The Formula for a HydrateHydrate

Hydrate-Hydrate- a compound with a a compound with a specific number of water specific number of water molecules bound to its atomsmolecules bound to its atoms

Analyzing a HydrateAnalyzing a Hydrate

In order to analyze a hydrate, In order to analyze a hydrate, water must be removed (usually water must be removed (usually from heating)from heating)

Substance remaining after Substance remaining after heating is “anhydrous” (meaning heating is “anhydrous” (meaning without water)without water)