1 the mole 6.02 x 10 23 chemistry cp– chapter 8 2 stoichiometrystoichiometry - the study of the...

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The MoleThe Mole

6.02 X 6.02 X 10102323

Chemistry cp– Chapter 8

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STOICHIOMETRYSTOICHIOMETRYSTOICHIOMETRYSTOICHIOMETRY

- the study of the - the study of the quantitative quantitative aspects of aspects of chemical chemical reactions.reactions.

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The MoleThe Mole

• A counting unit• Similar to a dozen, except instead

of 12, it’s 602 billion trillion 602,000,000,000,000,000,000,000

• 6.02 X 1023 (in scientific notation)• This number is named in honor of

Amedeo Amedeo Avogadro Avogadro (1776 – 1856)(1776 – 1856), who studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present

44

Just How Big is a Mole?Just How Big is a Mole?

• Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles.

• If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.

• If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

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Everybody Has Avogadro’s Everybody Has Avogadro’s Number!Number!

But Where Did it Come From?But Where Did it Come From?• It was NOT just picked!

It was MEASURED.• One of the better

methods of measuring this number was the Millikan Oil Drop Experiment

• Since then we have found even better ways of measuring using x-ray technology

66

Suppose we invented a new collection unit called a rapp. One rapp contains 8 objects.

1. How many paper clips in 1 rapp?

a) 1 b) 4 c) 8

2. How many oranges in 2.0 rapp?

a) 4 b) 8 c) 16

3. How many rapps contain 40 gummy bears?

a) 5 b) 10 c) 20

Learning CheckLearning Check

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1. How many pencils are in 1 dozen pencils?

a) 1 b) 12 c) 6.02 x 1023

2. How many pencils are in 1 mole pencils?

a) 1 b) 12 c) 6.02 x 1023

3. How many carbon atoms are in

1 molecule of C2H6 ?

a) 1 b) 2 c) 6.02 x 1023

4. How many carbon atoms are in 1 mole of C2H6 ?

a) 1 b) 2 c) 1.204 x 1024


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The MoleThe Mole• 1 dozen cookies = 12 cookies• 1 mole of cookies = 6.02 X 1023 cookies

• 1 dozen cars = 12 cars• 1 mole of cars = 6.02 X 1023 cars

• 1 dozen Al atoms = 12 Al atoms• 1 mole of Al atoms = 6.02 X 1023 atoms

Note that the NUMBER is always the same, but the MASS is very different!

Mole is abbreviated mol (gee, that’s a lot quicker to write, huh?)

99

= 6.02 x 1023 C atoms

= 6.02 x 1023 H2O molecules

= 6.02 x 1023 NaCl formula units(technically, ionics are compounds and are called

formula units, but some worksheets use “molecules”)

6.02 x 1023 Na+ ions and

6.02 x 1023 Cl– ions

A Mole of ParticlesA Mole of Particles Contains 6.02 x 1023 particles

1 mole C

1 mole H2O

1 mole NaCl

1010

6.02 x 1023 particles

1 mole

or

1 mole

6.02 x 1023 particles

Note that a particle could be an atom OR a molecule!

Avogadro’s Number as Avogadro’s Number as Conversion FactorConversion Factor

1111

1. Number of atoms in 0.500 mole of Ala) 500 Al atoms

b) 6.02 x 1023 Al atomsc) 3.01 x 1023 Al atoms

2.Number of moles of S in 1.8 x 1024 S atomsa) 1.0 mole S atomsb) 3.0 mole S atomsc) 1.1 x 1048 mole S atoms


1212

1. Number of atoms in 0.500 mole of Al

0.500 mol Al x 6.02 x 1023 Al atoms = 1 mole Al atoms

2.Number of moles of S in 1.8 x 1024 S atoms

1.8 x 1024 S atoms x 1 mole S atoms =

6.02 x 1023 S atoms


1313

1.How many Al atoms are in 15.8 mole of Al?

15.8 mole Al x 6.02 x 1023 Al atoms =

1 mole Al

2.How many moles are in 3.69 x 1016 S atoms?

3.69 x 1016 S atoms x 1 mole S =

6.02 x 1023 S atoms


1414

• The Mass of 1 mole (in grams)

• Equal to the numerical value of the average

atomic mass (get from periodic table)

1 mole of C atoms = 12.0 g

1 mole of Mg atoms = 24.3 g

1 mole of Cu atoms = 63.5 g

Where are these numbers from?

PERIODIC TABLE

Molar MassMolar Mass

1515

Other Names Related to Molar MassOther Names Related to Molar Mass

• Molecular Mass/Molecular Weight:

Single molecule, mass is measured in amu’s

instead of grams.

But, the molecular mass/weight is the

same numerical value as 1 mole of molecules.

Only the units are different

• Formula Mass/Formula Weight:

Same goes for compounds. But again, the numerical value

is the same. Only the units are different.

1616

Other Names Related to Molar MassOther Names Related to Molar Mass

• THE POINT: You may hear all of these terms which

mean the SAME NUMBER… just different units

• Molar Mass = Gram Formula Weight in our textbook

• With Avogadro’s #, you may also hear the terms:

molecules, atoms, formula units, ions, particles, “things”

IT DEPENDS ON WHAT YOU’RE TALKING ABOUT:

example: 1 dozen eggs versus 1 dozen roses

1 mole of H2O molecules vs. 1 mole of NaCl formula units

1717

Find the molar mass

(usually we round to the tenths place)

Learning Check!Learning Check!

A.1 mole of Br atomsB.1 mole of Sn atoms

= 79.9 g/mole

= 118.7 g/mole

1818

Mass in grams of 1 mole equal numerically to the sum of the atomic masses

1 mole of CaCl2 = 111.1 g/mol

(1 mole Ca x 40.1 g/mol )

+ (2 moles Cl x 35.5 g/mol) = 111.1 g/mol CaCl2

Molar Mass of Molecules and Molar Mass of Molecules and CompoundsCompounds

1919

Mass in grams of 1 mole equal numerically to the sum of the atomic masses

1 mole of N2O4

Molar Mass of Molecules and Molar Mass of Molecules and CompoundsCompounds

= 92.0 g/mol

2020

A. Molar Mass of K2O = ? grams/mole

B. Molar Mass of antacid Al(OH)3 =

? grams/mole

K2O = 94.2 g/mol Al(OH)3 = 78.0 g/mol


2121

Prozac, C17H18F3NO, is a widely used

antidepressant that inhibits the uptake

of serotonin by the brain. Find its molar

mass.

309.0 grams


2222

molar mass

Grams Moles

Calculations with Molar MassCalculations with Molar Mass

Do you multiply or divide by molar mass?It depends on which way you’re going.

Use conversion factors.

2323

Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?

3.00 moles Al ? g Al

Converting Moles and GramsConverting Moles and Grams

2424

1. Molar mass of 1 mole Al = 27.0 g Al

2. Conversion factors for Al

27.0 g Al or 1 mol Al

1 mol Al 27.0g Al

3. Setup 3.00 moles Al x 27.0 g Al =

1 mole Al

Answer = 81.0 g Al

2525

Iron (III) oxide is often called rust, it forms when iron metal reacts with moisture. How many moles of Fe2O3 are in 3.00 grams of Fe2O3?

3.00 grams of Fe2O3? moles Fe2O3

Converting Moles and GramsConverting Moles and Grams

2626

1. Molar mass of Fe2O3 YOU MUST CALCULATE IT!

2. Conversion factors for Fe2O3

? g Fe2O3 or 1 mol Fe2O3

1 mol Fe2O3 ? g Fe2O3

3. Setup 3.00 grams Fe2O3 x 1 moleFe2O3

? grams Fe2O3

Answer = 0.0188 mol Fe2O3

2727

1. Molar mass of Fe2O3 159.6 grams

2. Conversion factors for Fe2O3

159.6 g Fe2O3 or 1 mol Fe2O3

1 mol Fe2O3 159.6 g Fe2O3

3. Setup 3.00 grams Fe2O3 x 1 moleFe2O3

159.6 g Fe2O3

Answer = 0.0 188 mole Fe2O3

2828

The artificial sweetener aspartame

(Nutra-Sweet) formula C14H18N2O5 is

used to sweeten diet foods, coffee and

soft drinks. How many moles of

aspartame are present in 225 g of

aspartame?


2929

225 g C14H18N2O5 = ? mol C14H18N2O5

225g x _?__mol__ = mol

? g

Setting it up:Setting it up:

Do you know a relationship between moles and grams

for C14H18N2O5 ?

3030

225 g C14H18N2O5 = ? mol C14H18N2O5

The relationship is: MOLAR MASS!

1 mol = the sum of the atomic masses from the periodic table in grams!

225g x _1__mol__ = ? mol

? g


3131

225 g C14H18N2O5 = ? mol C14H18N2O5

225g x _1__mol__ = ? mol

294.3 g

How do you enter this in your calculator?


Enter first number first, multiply numerators,

divide by denominators.225 x 1 / 294.3 =

3232

Atoms/Molecules and GramsAtoms/Molecules and Grams

• Since 6.02 X 1023 particles = 1 mole AND

1 mole = molar mass (grams)

• You can convert atoms/molecules to moles and then moles to grams! (Two step process)

• You can’t go directly from atoms to grams!!!! You MUST go thru MOLES.

3333

molar mass Avogadro’s number Grams Moles particles

Everything must go through Moles!!!

CalculationsCalculations

3434

Atoms/Molecules and GramsAtoms/Molecules and Grams

How many atoms of Cu are present in 35.4 g of Cu?

35.4 g Cu 1 mol Cu 6.02 X 1023 atoms Cu 63.5 g Cu 1 mol Cu

= 3.4 X 1023 atoms Cu

3535


How many atoms of O are present in 78.1 g of oxygen (O2)?

78.1 g O2 1 mol O2 6.02 X 1023 molecules O2 2 atoms O 32.0 g O2 1 mol O2 1 molecule O2

3636


How many atoms of K are present in 78.4 g of K?

3737


What is the mass (in grams) of 1.20 X 1024 molecules of glucose (C6H12O6)?

3838

Molar VolumeMolar Volume

New fact:

For gases at STP: 0oC and 1 atm.

(a standard temperature and pressure)

1 mole = 22.4 L (our textbook uses dm3)

This creates two NEW conversion factors!

22.4 L OR 1 mole1 mole 22.4 L

3939


How many liters are in 5 moles of nitrogen dioxide gas at STP?

Start with given number and unit.Chose a conversion factor. 22.4 L OR 1 mole

1 mole 22.4 LCancel the units.Do the math.

5 mol NO2 x22.4 L NO2 =1 mol NO2

4040


How many moles are in 0.67 liters of carbon monoxide gas at STP?

Start with given number and unit.Chose a conversion factor. 22.4 L OR 1 mole

1 mole 22.4 LCancel the units.Do the math.

0.67 L CO x1 mol CO = 22.4 L

4141

Molar Volume & Molar MassMolar Volume & Molar Mass

How many grams are in 0.67 liters of carbon monoxide gas at STP?

Now, you need to stack up two conversion factors together. First is molar volume, then is molar mass, (which you have to calculate!)0.67 L CO x

1 mol CO x ? grams CO = 22.4 L 1 mol CO

= 0.84 g carbon monoxide

4242

Molarity, MMolarity, MNew fact:

For liquid solutions(typically “aqueous”, the substance dissolved in water)

1 L = # mol The # is given as “M” or molarity

For examples: A 5.0 M solution means : 5.0 moles = 1 L

1 L OR 5.0 mol 5.0 mol 1 L

A 0.37 M solution means : 5.0 moles = 1 L

1 L OR 0.37 mol

0.37 mol 1 L

4343

Molarity, MMolarity, MFor liquid solutions


This CHANGES based on the problem given. How many moles are in 7.0 L of a 4.0 M solution of NaCl?

7.0 L NaCl solution 4.0 mol NaCl solution

1 L NaCl solution

x

4444

Molarity, MMolarity, MFor liquid solutions


This CHANGES based on the problem given. How many moles are in 7.0 L of a 1.5 M solution of NaCl?

7.0 L NaCl solution 1.5 mol NaCl solution

1 L NaCl solution

x

4545

HomeworkHomework

4646

What is the percent carbon in C5H8NO4 (the

glutamic acid used to make MSG

monosodium glutamate), a compound used

to flavor foods and tenderize meats?

a) 8.22 %C

b) 24.3 %C

c) 41.1 %C

Percent CompositionPercent Composition

4747

Chemical Formulas of Chemical Formulas of CompoundsCompounds

(HONORS only)(HONORS only)

• Formulas give the relative numbers of atoms or Formulas give the relative numbers of atoms or moles of each element in a formula unit - always moles of each element in a formula unit - always a whole number ratio (the law of definite a whole number ratio (the law of definite proportions).proportions).

NONO22 2 atoms of O for every 1 atom of N 2 atoms of O for every 1 atom of N

1 mole of NO1 mole of NO22 : 2 moles of O atoms to : 2 moles of O atoms to

every 1 mole of N atomsevery 1 mole of N atoms

• If we know or can determine the relative number If we know or can determine the relative number of moles of each element in a compound, we can of moles of each element in a compound, we can determine a formula for the compound.determine a formula for the compound.

4848Types of FormulasTypes of Formulas(HONORS only)(HONORS only)

• Empirical FormulaEmpirical Formula

The formula of a compound that The formula of a compound that expresses the expresses the smallest whole number smallest whole number ratioratio of the atoms present. of the atoms present.

Ionic formula are always empirical formulaIonic formula are always empirical formula

• Molecular FormulaMolecular Formula

The formula that states the The formula that states the actualactual number of each kind of atom found in number of each kind of atom found in one one moleculemolecule of the compound. of the compound.

4949To obtain an To obtain an Empirical Empirical Formula Formula (HONORS only)(HONORS only)

1.1. Determine the mass in grams of each Determine the mass in grams of each element present, if necessary.element present, if necessary.

2.2. Calculate the number of Calculate the number of molesmoles of of each each element.element.

3.3. Divide each by the smallest number of moles Divide each by the smallest number of moles to obtain the to obtain the simplest whole number ratio.simplest whole number ratio.

4.4. If whole numbers are not obtainedIf whole numbers are not obtained** in step in step 3), multiply through by the smallest number 3), multiply through by the smallest number that will give all whole numbersthat will give all whole numbers

** Be careful! Do not round off numbers prematurelyBe careful! Do not round off numbers prematurely

5050A sample of a brown gas, a major air pollutant, is A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine a found to contain 2.34 g N and 5.34g O. Determine a formula for this substance.formula for this substance.

require require molemole ratios so convert grams to moles ratios so convert grams to moles

moles of N = moles of N = 2.34g of N 2.34g of N = 0.167 moles of N= 0.167 moles of N

14.0 g/mole14.0 g/mole

moles of O = moles of O = 5.34 g5.34 g = 0.334 moles of O = 0.334 moles of O

16.0 g/mole16.0 g/mole

Formula:Formula:

0.334 0.167ON 0.167 0.334 2

0.167 0.167

N O NO

(HONORS only)(HONORS only)

5151Calculation of the Molecular FormulaCalculation of the Molecular Formula(HONORS only)(HONORS only)

A compound has an empirical formula A compound has an empirical formula of NOof NO22. The colourless liquid, used in . The colourless liquid, used in

rocket engines has a molar mass of rocket engines has a molar mass of 92.0 g/mole. What is the 92.0 g/mole. What is the molecular molecular formula formula of this substance?of this substance?

5252

Empirical Formula from % Empirical Formula from % CompositionComposition (HONORS only)(HONORS only)

A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; 10.60 % H What is the empirical formula of the substance?

Consider a sample size of 100 gramsThis will contain 28.60 grams of B and 10.60

grams HDetermine the number of moles of eachDetermine the simplest whole number ratio

1 the mole 6.02 x 10 23 chemistry cp– chapter 8 2 stoichiometrystoichiometry - the study of the...

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