Regents ChemistryRegents Chemistry

What’s a Mole???What’s a Mole???

One mole of donuts contains 6.022 x 1023 donuts One mole of H2O contains 6.022 x 1023 molecules One mole of nails contains 6.022 x 1023 nails One mole of Fe contains 6.022 x 1023 atoms One mole of dogs contains 6.022 x 1023 dogs One mole of electrons contains 6.022 x 1023 electrons

One mole of ANY specified entity contains 6.022 x 1023 of that entity. For example:

(Covalently bonded)

These are Formula units!

How can we measure a mole?How can we measure a mole? A mole = 6.022 x 1023 particles Could be a mole of an ionic compound

– contains 6.022 x 1023 formula units (made of ions) Could be a mole of a molecular compound

– contains 6.022 x 1023 molecules (made of elements) A mole of an element = the average atomic mass listed

on the periodic table A mole of a compound = total mass of the moles in the

compound

Finding the Mass of a Mole of a Compound

Example #1

Example #2

SummarySummary

Formula mass - mass of the smallest unit of an ionic compound; sum of atomic masses in amus

Gram Formula Mass - same as formula mass except in grams

Molecular Mass – same as FM except for used for molecular substances

Mole – 6.022 x 1023 particles of anything! Just know it is also the GFM of any substance

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Mass, Mole and Particle conversions

The Conversion FlowchartThe Conversion Flowchart

Mole

Number ofParticles

Mass of compound

divide bymolar mass

multiply bymolar mass

divide by6.02 x 1023

multiply by6.02 x 1023

Liters of Gas

multiply by22.4 liters

divide by22.4 liters

Practice mole to massPractice mole to massHow many grams are in 2 moles of CuCl2?

How many grams are in 3.5 moles of H2O

2 moles CuCl2 x 134g per mole = 268 g

3.5 moles H2O x 18g per mole = 63 g

Mass to MoleMass to MoleHow many moles of NO are in 67.0g of

NO?

How many moles of KCl are in 125.0g of KCl?

67.0 g NO / 30.0 g per mole = 2.2 moles NO

125.0 g KCl / 74.5 g per mole = 1.68 moles KCl

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Finding Percent Composition

What is Percent Composition?What is Percent Composition?Formulas represent the composition of a

substanceIf we use the subscripts and atomic masses of

the elements, we can find the percent by mass of each element in a substance

Essentially, Percent Composition finds how much of each element is in a substance

How do we do this????How do we do this????1. We can add up the total molar mass of all

elements involved in the substance

2. We next simply divide the total of the element in question by the total molar mass and multiply by 100%

Example #1Example #1Find the percent composition (in grams) of

oxygen in potassium chlorate

1. Find the molar mass KClO3

K - 1 mole x 39.1 grams = 39.1 g Cl - 1 mole x 35.5 grams = 35.5 g O - 3 moles x 16.0 grams = 48.0 g

Molar mass = 122.6 g

2. Divide and multiply by 100%

%O = 48.0 g

122.6 gx 100%

%O = 39.2%

Moles and molecules/formula unitsMoles and molecules/formula units

Moles - measured in gramsmolecules / formula units - measured in amu

(atomic mass units) So… grams make up moles of a substanceand amu (atomic mass units) make up

individual molecules/formula unitsUse the same numbers from the PT!

It’s the same process to find the % of It’s the same process to find the % of amu in a 1 molecule or formula unit!amu in a 1 molecule or formula unit!

Find the percent composition (in amu) of oxygen in potassium chlorate

1. Find the mass in amu KClO3

K - 1 atom x 39.1 amu = 39.1 amu Cl - 1 atom x 35.5 amu = 35.5 amu O - 3 atoms x 16.0 amu = 48.0 amu

Formula mass = 122.6 amu

2. Divide and multiply by 100%

%O = 48.0 amu

122.6 amux 100%

%O = 39.2%

Example #2Example #2Find the percent composition (in amu) of

water in sodium carbonate crystals

Na2CO3 • 10H2O

1. Formula Mass = 286.0 amu

2. Total formula mass of H2O = 180.0 amu

3. Divide

%H2O = 180.0 amu x 100% --------------- 286.0 amu

%H2O = 62.9%

worksheet

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Mole Relations in Balanced Equations

RECAPRECAP

The Law of Conservation of Mass tells us:– Moles (and atoms) in equations must be

balanced– Since moles (and atoms) have mass, mass

is also balanced (we did this by finding missing mass)

– So we have relationship between reactants and products

– Thus if we change the moles of reactants (or number of atoms) we change the moles /# of atoms of products..HOW?

Mole RelationsMole Relations

Balanced Chemical Equation:

2C2H6 + 7O2 4CO2 + 6H2O

Moles C2H6 Moles O2 Moles H2OMoles CO2

2 7 4 6

4 14 8 12

1 3.5 2 3

Sample ProblemSample Problem

How many moles of water will be produced from the complete combustion of 3.0 mol of ethane?

2C2H6 + 7O2 4CO2 + 6H2O

moles ethane:moles water = 2:6

3.0 mole C2H6 = x

2.0 mole C2H6 6 mole H2O

x = 9.0 mole H2O

Finding the Mass ProducedFinding the Mass Produced

Sample Problem Cont..How many grams of water are

produced9.0 mole H2O produced

#g H2O = 9.0 mole H2O 18.0g H2O = 162 g H2O

1 mole H2O( )

Sample Problem #2Sample Problem #2

How many moles of iron (III) oxide are produced from the combination of 6 moles of Fe ? How many grams? 4Fe + 3O2 2Fe2O3

6 mole Fe = x mole Fe2O3

4 mole Fe 2 mole Fe2O3

x = 3 mole Fe2O3 equals 480g Fe2O3