the mole what is the mole? 6.02 x 10 23 or what is a dozen? 1 dozen = 12

THE MOLETHE MOLE

What is the What is the MoleMole??

6.02 x 1023

OR

What is a dozen?What is a dozen?

1 dozen = 12

Why don’t we just say 12?Why don’t we just say 12?

…and it doesn’t matter what the objects are… a dozen means 12 whether it is a dozen eggs, a dozen roses, or a dozen ugly hats

It is often easier to group objects when counting them

2 dozen = 24 3 dozen = 36

A mole is a counting unit. It tells us how many objects there are.

A pair and a dozen are also counting units.

Pairmeans 2 objects

Dozen means 12 objects

Mole means6.02x1023 objects

So what is a mole?So what is a mole?

So what is a mole?So what is a mole?

It is just a term used to represent a numberIt is just a term used to represent a number

2 = pair2 = pair 12 = 1 dozen12 = 1 dozen 6.02 x 106.02 x 1023 23 = 1 mole= 1 mole

……and we call 6.02 x 10and we call 6.02 x 1023 23 Avagadro’s numberAvagadro’s number

Avogadro’s number = 6.02 x 10Avogadro’s number = 6.02 x 1023 23

= 602 000 000 000 000 000 000 000= 602 000 000 000 000 000 000 000

Avogadro -Avogadro -

He didn’t actually He didn’t actually identify the numberidentify the number

– – but it was named but it was named after him to honor his after him to honor his many contributions to many contributions to chemistrychemistry

What counting unit would you use for What counting unit would you use for these objects?these objects?

So why is it such a big number?So why is it such a big number?

PAIR



DOZEN



Since atoms and molecules are very small, the quantity used to measure them needs to be a very large number

MOLE


Since a mole is such a large number, it is Since a mole is such a large number, it is useful only for counting very small objects useful only for counting very small objects like atoms and molecules. A mole of like atoms and molecules. A mole of donuts is too many to eat. donuts is too many to eat.

Like a pair (2) or a dozen (12), the quantity Like a pair (2) or a dozen (12), the quantity of a mole (6.02 x 10of a mole (6.02 x 102323) never changes, but ) never changes, but unlike a pair or a dozen, its value is very, unlike a pair or a dozen, its value is very, very largevery large

6.02 x 106.02 x 102323 particles particles

1 mole1 mole

oror

1 mole1 mole

6.02 x 106.02 x 102323 particles particles

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

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

1.1. Number of atoms in 0.500 mole of AlNumber of atoms in 0.500 mole of Al

PracticePractice

a) 500 Al atomsa) 500 Al atomsb) 6.02 x 10b) 6.02 x 102323 Al atoms Al atomsc) 3.01 x 10c) 3.01 x 102323 Al atoms Al atoms


a) 1.0 mole S atomsa) 1.0 mole S atomsb) 3.0 mole S atomsb) 3.0 mole S atomsc) 1.1 x 10c) 1.1 x 104848 mole S atoms mole S atoms


2. Number of moles of S in 1.8 x 102. Number of moles of S in 1.8 x 102424 S atoms S atoms2. Number of moles of S in 1.8 x 102. Number of moles of S in 1.8 x 102424 S atoms S atoms

0.500 mole Al | 6.02*1023 atoms = |1 mole

0.500 mole Al | 6.02*1023 atoms = |1 mole



1.8 *1024 atoms S | 1 mole = | 6.02*1023 atoms

1.8 *1024 atoms S | 1 mole = | 6.02*1023 atoms



REPRESENTATIVE PARTICLES & MOLESREPRESENTATIVE PARTICLES & MOLES

ATOMIC ATOMIC NITROGENNITROGEN ATOMATOM NN 6.02x106.02x102323

NITROGEN NITROGEN GASGAS MOLECMOLEC.. NN22 6.02x106.02x102323

WATERWATER MOLEC.MOLEC. HH2200 6.02x106.02x102323

CALCIUM IONCALCIUM ION IONION CaCa2+2+ 6.02x106.02x102323

CALCIUM CALCIUM FLUORIDEFLUORIDE

FORMULA FORMULA UNITUNIT CaFCaF22 6.02x106.02x102323

What if I asked you how many atoms What if I asked you how many atoms are in a mole of a compound?are in a mole of a compound?– you must know how many atoms are in ayou must know how many atoms are in a

representative particlerepresentative particle or clusteror cluster of the of the compound.compound.

To do this you must know the To do this you must know the chem chem formulaformula– For example, each molecule of COFor example, each molecule of CO22 is is

composed ofcomposed of 1 C + 2 O’s = 3 atoms1 C + 2 O’s = 3 atoms1 mole of carbon dioxide molecules 1 mole of carbon dioxide molecules contains avogadro’s number of carbon contains avogadro’s number of carbon dioxide molecules.dioxide molecules.– Thus a mole of COThus a mole of CO22 contains contains three three

timestimes avogadro’s number of atomsavogadro’s number of atoms

What if I asked you how many atoms What if I asked you how many atoms are in a mole of a compound?are in a mole of a compound?– you must know how many atoms are in ayou must know how many atoms are in a

representative particlerepresentative particle or clusteror cluster of the of the compound.compound.

To do this you must know the To do this you must know the chem chem formulaformula– For example, each molecule of COFor example, each molecule of CO22 is is

composed ofcomposed of 1 C + 2 O’s = 3 atoms1 C + 2 O’s = 3 atoms1 mole of carbon dioxide molecules 1 mole of carbon dioxide molecules contains avogadro’s number of carbon contains avogadro’s number of carbon dioxide molecules.dioxide molecules.– Thus a mole of COThus a mole of CO22 contains contains three three

timestimes avogadro’s number of atomsavogadro’s number of atoms

To find the # of atoms in a mol of a To find the # of atoms in a mol of a compound, compound, – You 1You 1stst determine the # of atoms in a determine the # of atoms in a

representative particle of that compoundrepresentative particle of that compound– And thenAnd then multiplymultiply that # of atoms by that # of atoms by

avogadro’s #avogadro’s #

To find the # of atoms in a mol of a To find the # of atoms in a mol of a compound, compound, – You 1You 1stst determine the # of atoms in a determine the # of atoms in a

representative particle of that compoundrepresentative particle of that compound– And thenAnd then multiplymultiply that # of atoms by that # of atoms by

avogadro’s #avogadro’s #

How many atoms of carbon are in 2.12 mols of propane molecules (C3H8)?

How many atoms of carbon are in 2.12 mols of propane molecules (C3H8)?

Useful Info:1 mol C3H8 = 6.02x1023 molecules C3H8

1molecule C3H8 = 3 atoms of C

Useful Info:1 mol C3H8 = 6.02x1023 molecules C3H8

1molecule C3H8 = 3 atoms of C

11stst we need to see how many molecules we need to see how many molecules of propane we have if we have 2.12 of propane we have if we have 2.12

moles.moles.

11stst we need to see how many molecules we need to see how many molecules of propane we have if we have 2.12 of propane we have if we have 2.12

moles.moles.

6.02x1023molec C3H8

6.02x1023molec C3H8

1 mole C3H81 mole C3H8 2.12 moles C3H8

2.12 moles C3H8X molec C3H8X molec C3H8

==

X = 1.276x1024 molecules of C3H8

X = 1.276x1024 molecules of C3H8

(1molecC3H8)(X)=(1.276x1024molec•molsC3H8)

(1molecC3H8)(X)=(1.276x1024molec•molsC3H8)(1 molec C3H8)(1 molec C3H8) (1 molec C3H8)(1 molec C3H8)

22ndnd we need to see how many atoms of C we need to see how many atoms of C if we have 1.276x10if we have 1.276x102424 molecs of C molecs of C33HH88..

22ndnd we need to see how many atoms of C we need to see how many atoms of C if we have 1.276x10if we have 1.276x102424 molecs of C molecs of C33HH88..

3 atoms of C3 atoms of C

1 molecule C3H8

1 molecule C3H8

1.276x1024 molec C3H8

1.276x1024 molec C3H8X atoms CX atoms C

==

X = 3.83x1024 atoms of Carbon

X = 3.83x1024 atoms of Carbon

(1molec C3H8)(X)=(3.83x1024molec •

atoms C)(1molec C3H8)(X)=(3.83x1024molec •

atoms C)(1 molec C3H8)(1 molec C3H8) (1 molec C3H8)(1 molec C3H8)

So the mole can be used to measure any kind of So the mole can be used to measure any kind of particle – atoms, ions, molecules, formula unitsparticle – atoms, ions, molecules, formula units

It is possible to have a mole of iron atoms, a It is possible to have a mole of iron atoms, a mole of water molecules and a mole of sodium mole of water molecules and a mole of sodium chloride – all contain 6.02 x 10chloride – all contain 6.02 x 1023 23 particlesparticles

But do 1 mol of iron, 1 mol of water and 1 mol of But do 1 mol of iron, 1 mol of water and 1 mol of sodium chloride all have the same mass?sodium chloride all have the same mass?

NO!!NO!!

Do a dozen donuts, a Do a dozen donuts, a dozen books and a dozen books and a dozen bricks weigh dozen bricks weigh the same?the same?

NO, so neither do a NO, so neither do a mole of different mole of different atoms, ions or atoms, ions or molecules molecules

Each sample contains 1 molEach sample contains 1 mol(6.02 x 10(6.02 x 102323 atoms) atoms)

12.0g carbon 32.0g sulfur 65.38g zinc

Which element do you think has the heaviest atoms?

So now that we know what a mole So now that we know what a mole of atoms looks like…where did the of atoms looks like…where did the

number come from?number come from?

CARBON!!CARBON!!Scientists took 12g of pure carbon-12Scientists took 12g of pure carbon-12

(composed of 6 protons + 6 neutrons; mass number = 12)(composed of 6 protons + 6 neutrons; mass number = 12)

and counted how many carbon atoms and counted how many carbon atoms

were in the samplewere in the sample

Guess how many there were?

6.02 x 1023 atoms

Why use 12 grams? They wanted the mass of one mole to be the same as the mass number

6.02 x106.02 x102323 atoms of Carbon atoms of Carbon

This pile of carbon-12 weighs 12.0 grams This pile of carbon-12 weighs 12.0 grams and contains 6.02 x 10and contains 6.02 x 102323 carbon atoms carbon atoms

This is one mole of carbonThis is one mole of carbon

This pile of sulfur contains This pile of sulfur contains 6.02x106.02x102323 atoms of sulfur. atoms of sulfur.

This is one mole of sulfur.This is one mole of sulfur.

Review: A mole is a simple way of saying we Review: A mole is a simple way of saying we

have 6.02x10have 6.02x102323 objects. objects.

Atomic molar massAtomic molar mass of an element of an element = is the average mass (g) of one = is the average mass (g) of one mole of atoms of that elementmole of atoms of that element

Back to carbon…. Back to carbon….

Here is one mole of carbon which weighs 12.0 g Here is one mole of carbon which weighs 12.0 g

The atomic molar mass of carbon on the periodic The atomic molar mass of carbon on the periodic table is….table is….

Which means there are 12.01 g for every mol of carbon

12.01 g/molatomic molar mass of an element =

mass (g) of one mole of atoms of that element

Here is 65.38 grams of the element zinc. Here is 65.38 grams of the element zinc. How many moles of zinc do we have?How many moles of zinc do we have?

1 mole

.

atomic molar mass of an element = mass (g) of one mole of atoms of that element

This pile of sulfur contains 6.02x10This pile of sulfur contains 6.02x102323 atoms of sulfur (or 1 mole of sulfur)atoms of sulfur (or 1 mole of sulfur)

What is the mass, in grams, of this sample of sulfur? What is the mass, in grams, of this sample of sulfur?

atomic molar mass of an element = mass (g) of one mole of atoms of that element

32.06 g

0.50 moles x (63.55 g/mole) = 31.8g0.50 moles x (63.55 g/mole) = 31.8g

Here is 0.50 moles of copper. How many Here is 0.50 moles of copper. How many grams of copper do we have? grams of copper do we have?

31.8g

0.50 moles | 63.55 g0.50 moles | 63.55 g= 31.8g= 31.8g | 1 mole) | 1 mole)

Molar massMolar mass = the mass of one = the mass of one mole of a substancemole of a substance

So now we’re not talking about individual So now we’re not talking about individual elements but molecules and compoundselements but molecules and compounds

I.e. What is the molar mass of water?I.e. What is the molar mass of water?

The formula for water is:The formula for water is:

HH22O , O , so one molecule contains 2 so one molecule contains 2

hydrogen atoms and 1 oxygen atomhydrogen atoms and 1 oxygen atom

Atomic molar mass of H = 1.01g/mol x 2 = 2.02 g/molAtomic molar mass of H = 1.01g/mol x 2 = 2.02 g/mol

Atomic molar mass of O = 16.00g/mol x 1 = Atomic molar mass of O = 16.00g/mol x 1 = 16.00g/mol16.00g/mol

Molar mass of water HMolar mass of water H22O is O is 18.02g/mol18.02g/mol

Molar massMolar mass = the mass of one = the mass of one mole of a substancemole of a substance

Other Names Related to Molar MassOther Names Related to Molar Mass

Molecular Mass/Molecular Weight:Molecular Mass/Molecular Weight: If you have a single If you have a single

molecule, mass is measured in amu’s instead of grams. But, molecule, mass is measured in amu’s instead of grams. But,

the molecular mass/weight is the the molecular mass/weight is the same numerical valuesame numerical value as 1 as 1

mole of molecules. Only the units are different. (This is the mole of molecules. Only the units are different. (This is the

beauty of Avogadro’s Number!)beauty of Avogadro’s Number!)

Formula Mass/Formula Weight:Formula Mass/Formula Weight: Same goes for Same goes for

compounds. But again, compounds. But again, the numerical value is the samethe numerical value is the same. .

Only the units are different.Only the units are different.

THE POINT: You may hear THE POINT: You may hear allall of these terms of these terms

which mean the which mean the SAME NUMBERSAME NUMBER… just different units… just different units

Molar massMolar mass

Now you try it…Now you try it…

What is the molar mass of methane CHWhat is the molar mass of methane CH4(g) 4(g) ??

C = 12.01 g/mol x 1 = 12.01 g/mol

H = 1.01g/mol x 4 = 4.04 g/mol

Molar mass of methane = 16.05 g/mol

Now you try it…Now you try it…

What is the molar mass of methanol CHWhat is the molar mass of methanol CH33OH?OH?

C = 12.01 g/mol x 1 = 12.01 g/mol

H = 1.01g/mol x 4 = 4.04 g/mol

O = 16.00g/mol x 1 = 16.00 g/mol

Molar mass of methanol = 32.05 g/mol

Molar massMolar mass

Find the molar mass of SnBrFind the molar mass of SnBr

PracticePractice

A.1 mole of Br atomsB.1 mole of Sn atomsC.1 mole of SnBr formula units

= 79.90 g/mole

= 118.70 g/mole

= 198.60 g/mole

Converting between mass, molar Converting between mass, molar mass and molesmass and moles

m = quantity of matter (mass) in gramsm = quantity of matter (mass) in grams

n = quantity of matter in molesn = quantity of matter in moles

M = molar massM = molar mass

m = n x Mm = n x MSo if you wanted to know the mass of 2 mol of carbonSo if you wanted to know the mass of 2 mol of carbon

m = (2 mol) x (12.01g/mol) orm = (2 mol) x (12.01g/mol) or2 mol C | 12.01 g C2 mol C | 12.01 g C | 1 mole C| 1 mole C

= 24.02 g C= 24.02 g C

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

1 mole of CaCl1 mole of CaCl22 = 111.1 g/mol = 111.1 g/mol

1 mole Ca1 mole Ca x 40.1 g/mol x 40.1 g/mol

+ + 2 moles Cl2 moles Cl x 35.5 g/mol = 111.1 g/mol CaCl x 35.5 g/mol = 111.1 g/mol CaCl22

1 mole of N1 mole of N22OO44 = 92.0 g/mol= 92.0 g/mol

Molar Mass of Molecules and Molar Mass of Molecules and CompoundsCompounds

A.A. Molar MassMolar Mass of K of K22O = ? Grams/moleO = ? Grams/mole

B. B. Molar MassMolar Mass of antacid Al(OH) of antacid Al(OH)33 = ? = ? Grams/moleGrams/mole

Al= 1*26.98 =26.98Al= 1*26.98 =26.98

O =3 *16. = 48.0O =3 *16. = 48.0

H= 3*1.008 =3.024 78.004g/molH= 3*1.008 =3.024 78.004g/mol

PracticePractice

Prozac, CProzac, C1717HH1818FF33NO, is a widely used NO, is a widely used

antidepressant that inhibits the uptake antidepressant that inhibits the uptake

of serotonin by the brain. Find its molar of serotonin by the brain. Find its molar

mass.mass.

PracticePractice

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

3.00 moles Al ? g Al 3.00 moles Al ? g Al

Converting Moles and GramsConverting Moles and Grams

1. Molar mass of Al1. Molar mass of Al 1 mole Al = 27.0 g Al1 mole Al = 27.0 g Al

2. Conversion factors for Al2. Conversion factors for Al

27.0g Al27.0g Al or or 1 mol Al 1 mol Al

1 mol Al 27.0 g Al1 mol Al 27.0 g Al

3. Setup3. Setup 3.00 moles Al | 27.0 g Al 3.00 moles Al | 27.0 g Al

1 mole Al1 mole Al

Answer Answer = 3.00* 27 g Al = = 3.00* 27 g Al = 81.0 g 81.0 g AlAl

The artificial sweetener aspartame The artificial sweetener aspartame

(Nutra-Sweet) formula C(Nutra-Sweet) formula C1414HH1818NN22OO55 is is

used to sweeten diet foods, coffee and used to sweeten diet foods, coffee and

soft drinks. How many moles of soft drinks. How many moles of

aspartame are present in 225 g of aspartame are present in 225 g of

aspartame?aspartame?

PracticePractice

Atoms/Molecules and GramsAtoms/Molecules and Grams

Since 6.02 X 10Since 6.02 X 102323 particles = 1 mole particles = 1 mole ANDAND

1 mole = molar mass (grams)1 mole = molar mass (grams)You can convert atoms/molecules to You can convert atoms/molecules to moles and then moles to grams! moles and then moles to grams!

(Two step process)(Two step process)You can’t go directly from atoms to You can’t go directly from atoms to grams!!!! You MUST go thru MOLES.grams!!!! You MUST go thru MOLES.That’s like asking 2 dozen cookies weigh That’s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first! You have to convert to dozen first!

molar mass Avogadro’s numbermolar mass Avogadro’s number Grams Grams MolesMoles particles particles

Everything must go through Everything must go through Moles!!!Moles!!!

CalculationsCalculations

Atoms/Molecules and GramsAtoms/Molecules and GramsHow many atoms of Cu are present How many atoms of Cu are present

in 35.4 g of Cu?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

PracticePractice

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

PracticePractice

What is the mass (in grams) of 1.20 X 10What is the mass (in grams) of 1.20 X 102424 molecules of glucose (Cmolecules of glucose (C66HH1212OO66)?)?

PracticePractice

How many How many atomsatoms of O are present in 78.1 g of O are present in 78.1 g of oxygen?of oxygen?

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

22.4 L CO22.4 L CO

1 mole CO1 mole CO .500 mol CO.500 mol CO

X L COX L CO==

*Remember*1 mol CO = 22.4 L CO

*Remember*1 mol CO = 22.4 L CO

(1mol CO)(X L CO)= (.500 mol CO)(22.4 L CO(1mol CO)(X L CO)= (.500 mol CO)(22.4 L CO

(1mol CO)(1mol CO)

(1mol CO)(1mol CO)

X = 12.2 L of COX = 12.2 L of CO

If you have a 35.67g piece of If you have a 35.67g piece of Chromium metal on your carChromium metal on your car, how , how many atoms of Chromium are in this many atoms of Chromium are in this piece of metal?piece of metal?

If you have a 35.67g piece of If you have a 35.67g piece of Chromium metal on your carChromium metal on your car, how , how many atoms of Chromium are in this many atoms of Chromium are in this piece of metal?piece of metal?

•You are given mass and asked for number of particles

•Set it up as a factor label problem

•You are given mass and asked for number of particles

•Set it up as a factor label problem

PracticePracticePracticePractice

We are We are given a given a massmass




We are We are asked for asked for

atomsatoms

We are We are asked for asked for

atomsatoms •It’s going to take us 2 conversions, we just need to follow the arrows

• 11stst we must convert our given mass of we must convert our given mass of Chromium to moles of ChromiumChromium to moles of Chromium–So we need to use the periodic table to

calculate the mass of 1 mole of Chromium

• 11stst we must convert our given mass of we must convert our given mass of Chromium to moles of ChromiumChromium to moles of Chromium–So we need to use the periodic table to

calculate the mass of 1 mole of Chromium

51.996g Cr51.996g Cr

1 mole Cr1 mole Cr X mol CrX mol Cr

35.67g Cr35.67g Cr==

(51.996gCr)(X mol Cr) =(51.996gCr)(X mol Cr) =(35.67gCr)(1 mol

Cr)(35.67gCr)(1 mol

Cr)X = .6860 mol CrX = .6860 mol Cr

• 22ndnd we must convert our newly found we must convert our newly found moles of Cr to atoms of Crmoles of Cr to atoms of Cr– So we need to remember that 1 mole of So we need to remember that 1 mole of

anything there are 6.02x10anything there are 6.02x102323 particles particles

• 22ndnd we must convert our newly found we must convert our newly found moles of Cr to atoms of Crmoles of Cr to atoms of Cr– So we need to remember that 1 mole of So we need to remember that 1 mole of

anything there are 6.02x10anything there are 6.02x102323 particles particles

6.02x1023 atoms Cr

6.02x1023 atoms Cr1 mole Cr1 mole Cr

X atoms Cr

X atoms Cr

.6860 mol Cr

.6860 mol Cr

==

(1 mol Cr)(X atoms Cr) =(1 mol Cr)(X atoms Cr) =(6.02x1023 atoms Cr)

(.6860 mol Cr)(6.02x1023 atoms Cr)

(.6860 mol Cr)

X = 4.13x1023 atoms Cr

X = 4.13x1023 atoms Cr

Factor label one step methodFactor label one step method

Given: Given: 35.67g Cr35.67g Cr

Want: atoms CrWant: atoms Cr

Conversions: Conversions:

1 1 mole Crmole Cr = 6.02*10 = 6.02*1023 atoms atoms

1 1 mole Crmole Cr = = 51.996g Cr

Set up

35.67g Cr35.67g Cr | 1 1 mole Crmole Cr |6.02*106.02*1023 atoms atoms | 51.996g Cr | 1 1 mole Crmole Cr

= = 35.68 *1* 6.02*1035.68 *1* 6.02*1023 atoms atoms= = 2.148*102.148*102525 atoms = atoms = 4.131*10 4.131*10 23 23 atoms

51.996 51.996 51.996 51.996

Percent Composition Percent Composition Atomic weights can be found by using the Atomic weights can be found by using the

Periodic Table of the Elements. Periodic Table of the Elements.

Find the atomic weight of each element. Find the atomic weight of each element.

Multiply the number of atoms by the atomic Multiply the number of atoms by the atomic weight, and add all of these weights per weight, and add all of these weights per compound together.compound together.

Divide each atom (or ion's) individual atomic Divide each atom (or ion's) individual atomic mass by the total chemical mass *100mass by the total chemical mass *100

Percent Composition Percent Composition

FeO =FeO =

Fe = 55.845g/mol Fe = 55.845g/mol

O = 15.999 g/mol O = 15.999 g/mol

FeO= (55.845 +15.999)= 71.844FeO= (55.845 +15.999)= 71.844


FeO = 71.844 FeO = 71.844

Fe = 55.845g/mol /71.844 Fe = 55.845g/mol /71.844

0 = 15.999 g/mol / 71.844 0 = 15.999 g/mol / 71.844

= 0.777= 0.777

= 0.223= 0.223


Fe = 0.777*100= 77.700%Fe = 0.777*100= 77.700%

0 = 0.223 *100 = 22.300%0 = 0.223 *100 = 22.300%

Percent CompositionPercent Composition

LiLi33P - Lithium PhosphideP - Lithium Phosphide

Li = Li =

P =P = 1* 30.97 = 1* 30.97 =

20.823 20.823 3* 6.941 = 3* 6.941 =

30.97 30.97

51.793 51.793

0.402 0.402 /51.793 = /51.793 =

/51.793 = /51.793 = 0.598 0.598

What is the percent carbon in CWhat is the percent carbon in C55HH88NONO44 (the (the

glutamic acid used to make MSG glutamic acid used to make MSG

monosodium glutamate), a compound used monosodium glutamate), a compound used

to flavor foods and tenderize meats?to flavor foods and tenderize meats?

a) 8.22 %Ca) 8.22 %C

b) 24.3 %Cb) 24.3 %C

c) 41.1 %Cc) 41.1 %C

Percent CompositionPercent Composition

C=5*12.01 = 60.050H= 8*1.01 = 8.080N = 1*14.01 = 14.01O= 4* 16. =64.0CC55HH88NONO44 =145.140 =145.140

C=5*12.01 = 60.050H= 8*1.01 = 8.080N = 1*14.01 = 14.01O= 4* 16. =64.0CC55HH88NONO44 =145.140 =145.140

C= 60.050 / 145.140 = 0.411 0.411*100 = 41.1%C= 60.050 / 145.140 = 0.411 0.411*100 = 41.1%

Chemical Formulas of Chemical Formulas of CompoundsCompounds

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.

Types of FormulasTypes of Formulas

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.

Simplest and molecular formulaeSimplest and molecular formulaeConsider NaCl (ionic) vs. HConsider NaCl (ionic) vs. H22OO22 (covalent) (covalent)

Cl Na

Na Cl

Cl

Cl

Na

Na

• Chemical formulas are either “simplest” (a.k.a. “empirical”) or “molecular”. Ionic compounds are always expressed as simplest formulas.

• Covalent compounds can either be molecular formulas (I.e. H2O2) or simplest (e.g. HO)

HOO

H HOO H H

OO H

Simplest and molecular formulaeSimplest and molecular formulaeConsider NaCl (ionic) vs. HConsider NaCl (ionic) vs. H22OO22 (covalent) (covalent)

Cl Na

Na Cl

Cl

Cl

Na

Na

Q - Write simplest formulas for propene (C3H6),

C2H2, glucose (C6H12O6), octane (C8H14)

Q - Identify these as simplest formula, molecularformula, or both H2O, C4H10, CH, NaCl

HOO

H HOO H H

OO H

AnswersAnswersQ - Write simplest formulas for propene (CQ - Write simplest formulas for propene (C33HH66), ),

CC22HH22, glucose (C, glucose (C66HH1212OO66), octane (C), octane (C88HH1414))

Q - Identify these as simplest formula, molecularQ - Identify these as simplest formula, molecularformula, or both Hformula, or both H22O, CO, C44HH1010, CH, NaCl, CH, NaCl

A - CH2

A - H2O is both simplest and molecular

C4H10 is molecular (C2H5 would be simplest)

CH is simplest (not molecular since CH can’t form a molecule - recall Lewis diagrams)

NaCl is simplest (it’s ionic, thus it doesn’t form molecules; it has no molecular formula)

CH CH2O C4H7

To obtain an To obtain an Empirical Empirical Formula Formula

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

A 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

14.01 g/mole14.01 g/mole

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

16.00 g/mole16.00 g/mole

Formula:Formula:

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

moles of N 0.167 moles of N 0.167

moles of O 0.334 moles of O 0.334

/0.167 /0.167 =1=1

/0.167 /0.167 =2=2

N1O2N1O2

NO2NO2

Empirical Formula from % Empirical Formula from % CompositionComposition

A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; 10.60 % H10.60 % HWhat is the empirical formula of the substance?What is the empirical formula of the substance?

Na = 60.80 gNa = 60.80 g

B = 28.60 gB = 28.60 g

H = 10.60 gH = 10.60 g

/ 22.99 =/ 22.99 =2.6452.645

/ 10.811 =/ 10.811 = 2.6452.645

/ 1.008 =/ 1.008 = 10.51610.516

/ 2.645 / 2.645 = 1= 1

/ 2.645 / 2.645 = 1= 1

/ 2.645 / 2.645 = 3.976 =4= 3.976 =4

NaBH4NaBH4

Calculation of the Molecular FormulaCalculation of the Molecular Formula

Molecular formula is actual formula of Molecular formula is actual formula of the compound. the compound.

To determine the molecular formula To determine the molecular formula from the empirical formula you must from the empirical formula you must have the mass of the molecular have the mass of the molecular formula. formula. (Always Given to you)(Always Given to you)

Divide the mass of molecular formula Divide the mass of molecular formula by the mass of the empirical formula.by the mass of the empirical formula.

This will give you a whole number that This will give you a whole number that you must multiply the subscripts in the you must multiply the subscripts in the empirical formula by.empirical formula by.

Calculation of the Molecular Calculation of the Molecular FormulaFormula

CHCH2O is the empirical formula for a compound with O is the empirical formula for a compound with

a molecular mass of 180.18 g.a molecular mass of 180.18 g.

CHCH2O = 12 + 2.02 + 16 = 30.02g/molO = 12 + 2.02 + 16 = 30.02g/mol

Divide 180.18 by 30.03 Divide 180.18 by 30.03

180.18/30.03 = 6180.18/30.03 = 6

6 (CH6 (CH2O) = CO) = C66HH1212OO66

Calculation of the Molecular FormulaCalculation of the Molecular Formula

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?

N2O4N2O4

A compound contains 0.80 mol C, 4.0 moles A compound contains 0.80 mol C, 4.0 moles H and 1.60 mol O, and 0.80 mol of N, H and 1.60 mol O, and 0.80 mol of N, and has a molecular mass of 252.3 and has a molecular mass of 252.3 g/mol. What is the molecular formula for g/mol. What is the molecular formula for the compound? the compound?

CO2 H5N = Empirical CO2 H5N = Empirical

CO2 H5N = 63.050g/molCO2 H5N = 63.050g/mol

252.3 / 63.050 = 4252.3 / 63.050 = 44(CO2 H5N) = C4O8H20N4 4(CO2 H5N) = C4O8H20N4

the mole what is the mole? 6.02 x 10 23 or what is a dozen? 1 dozen = 12

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