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Stoichiometry: ConversionsStoichiometry: ConversionsAt the conclusion of our time At the conclusion of our time together, you should be able to:together, you should be able to:

1. Convert a mole of a chemical to particles or grams of that chemical

2. Convert grams of a chemical to moles or particles

3. Convert particles of a chemical to moles or grams

Review of Molar MassReview of Molar Mass

The Mass of 1 mole (in grams)

Equal to the numerical value of the average

atomic mass (use your periodic table, round

to 2 places)

1 mole of C atoms =

12.01 g

1 mole of Mg atoms =

24.31 g

1 mole of Cu atoms =

63.55 g

Other Names Related to Molar MassOther Names Related to Molar Mass

Molecular Mass: If you have a single molecule, mass is

measured in amu’s instead of grams. The molecular mass

is the same numerical value as 1 mole of molecules, only

the units are different - grams and not amu’s.

(This is the beauty of Avogadro’s Number!)

Formula Mass: Same goes for ionic compounds. But

again, the numerical value is the same, only the units are

different.

Molar Mass of Molecules and Molar Mass of Molecules and CompoundsCompounds

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

1 mole of CaCl2 =

1 mole Ca x 40.08 g/mol

+ 2 moles Cl x 35.45 g/mol =

110.98 g/mol CaCl2

1 mole of N2O4 =

92.02 g/mol N2O4

Learning Check!Learning Check!

A. Molar Mass of K2O = ? g/mol

94.20 g/mol

B. Molar Mass of antacid Al(OH)3 = ? g/mol

78.01 g/mol

Calculations with Molar MassCalculations with Molar Mass

molar mass

Grams Moles

Molar Mass as a Conversion FactorMolar Mass as a Conversion Factor

Molar Mass of the Compound 1 mole

or

1 mole

Molar Mass of the Compound

Note that the molar mass could be that of an atom

OR a molecule!

Calculations with Molar MassCalculations with Molar Mass

molar mass

Grams Moles

To convert Grams to Moles: x by

1 mole

Molar Mass of the Compound

Calculations with Molar MassCalculations with Molar Mass

molar mass

Grams Moles

To convert Moles to Grams: x by

Molar Mass of the Compound 1 mole

Example of Converting Moles to Example of Converting Moles to GramsGrams

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

1. Molar mass of Al 1 mole Al = 26.98 g Al

2. Conversion factors for Al 26.98 g Al or 1 mol Al

1 mol Al 26.98 g Al

3. Setup 3.00 moles Al x 26.98 g Al 1 mole Al

Answer = 80.94 g Al

Learning Check!Learning Check!

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?

= 0.764 mol

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

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!

Example of Avogadro’s Number as a Example of Avogadro’s Number as a Conversion FactorConversion Factor

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

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

2.Number of moles of S in 1.8 x 1024 S atoms a) 1.0 mole S atoms b) 3.0 mole S atoms c) 1.1 x 1048 mole S atoms

Atoms/Molecules to GramsAtoms/Molecules to 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.

CalculationsCalculations

molar mass Avogadro’s number Grams Moles particles

Everything must go through Moles!!!

Atoms/Molecules to GramsAtoms/Molecules to Grams

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

= 3.35 X 1023 atoms Cu

35.4 g Cu x 1 mol Cu

63.55 g Cu

x 6.02x1023 atoms Cu

1 mol Cu

Grams to Atoms/MoleculesGrams to Atoms/Molecules

How many grams of Cu are present in 5.4 x 1023 atoms of Cu?

= 57 g Cu

5.4 x 1023 atoms Cu x 1 mol Cu

6.02 x 1023 atoms Cux 63.55 g Cu

1 mol Cu

Stoichiometry: ConversionsStoichiometry: ConversionsLet’s see if you can:Let’s see if you can:

1. Convert a mole of a chemical to particles or grams of that chemical

2. Convert grams of a chemical to moles or particles

3. Convert particles of a chemical to moles or grams

Learning Check!Learning Check!

How many atoms of O are present in 78.1 g 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

2.94 x 1024 atoms of O

Learning CheckLearning Check

Prozac, C17H18F3NO, is a widely used

antidepressant that inhibits the uptake of

serotonin by the brain. Find its molar

mass.

309.36 g/mol

Learning Check!Learning Check!

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

= 1.21 x 1024 atoms of K

Learning Check!Learning Check!

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

= 327 g of glucose