formula mass & % comp

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Formula Mass&

Molecular Mass

Formula Mass

Formula mass is the total of all the atomic masses

in a chemical formula.

Formula Mass& Molecular Mass

Every molecular mass

is a formula mass...

Formula Mass& Molecular Mass

but not every formula

mass is a molecular

mass.

Formula Mass& Molecular Mass

Can you explain why?

Formula Mass& Molecular Mass

Are molecules the

only things that have

chemical formulas?

What is the

formula mass

of C2H5OH?

What was the

definition of a

formula mass?

The total of all the atomic masses

in a chemical formula.

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X 2 X 6 X 1

C2H5OH

The total of all the atomic masses

in a chemical formula.

A t o m i c M a s s U n i t s

amu or u

The units offormula mass are:

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C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Formula Mass Calculation

How to do formula masscalculations.

C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Formula Mass Calculation

Write thechemicalsymbolslike this.

C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Formula Mass Calculation

Write theatomicmass ofeach.

C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Formula Mass Calculation

Multiplyby thesubscriptof each.

C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Formula Mass Calculation

Equals

C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Formula Mass Calculation

Circle your answer.Show the units.

C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Formula Mass Calculation

SO4

+2

S = 32 X 1 = 32

O = 16 X 4 = 64

96 u

Formula Mass Calculation

SO4

+2

S = 32 X 1 = 32

O = 16 X 4 = 64

96 u

Formula Mass Calculation

Practice

Calculating

Formula

Mass

What is the

formula mass of

iron (II) sulfate?

FeSO4

FeSO4

Fe

S

O

FeSO4

Fe = 56

S = 32

O = 16

FeSO4

Fe = 56 X 1

S = 32 X 1

O = 16 X 4

FeSO4

Fe = 56 X 1 = 56

S = 32 X 1 = 32

O = 16 X 4 = 64

FeSO4

Fe = 56 X 1 = 56

S = 32 X 1 = 32

O = 16 X 4 = 64

152 u

Formula

Mass

Homework

Assignment

Hydrated Crystals

Crystals that have water

molecules chemically

bonded to

the ions in

the crystal.

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This occurs when a

highly ionic substance

crystallizes from a

water solution.

Although these crystals

are solids, the water

molecules can be

forced out of the crystal

lattice by heating.

CuSO4 5H2O

The formula for "hydrated"

copper (II) sulfate above

indicates there are 5 water

molecules for every 1

copper (II) sulfate.

CuSO4 5H2O

What is the formula mass of

copper (II) sulfate pentahydrate

HINT: treat water as aseparate element in the formula.

CuSO4 5H2O

Cu = 1 X 64 = 64

S = 1 X 32 = 32

O = 4 X 16 = 64

H2O = 5 X 18 = 90250 amu

How much water (in grams) is in 5 gramsof copper (II) sulfate pentahydrate?

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CuSO4 5H2O looks

something like this:

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Anhydrous CuSO4 looks

something like this:

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Percentage Composition

Each element makes up

a % of the substance.

Add one step

to a formula

mass calculation.

Percentage Composition

What is the percentage

composition of C2H5OH?

Percentage Composition

C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Percentage Composition

C2H5OH

C = 12 X 2 = 24

H = 1 X 6 = 6

O = 16 X 1 = 16

46 u

Percentage Composition

Now divide EACH

atomic mass by

the formula mass.

C2H5OH

C = 12 X 2 = 24 / 46 = 52 % C

H = 1 X 6 = 6 / 46 = 13 % H

O = 16 X 1 = 16 / 46 = 35 % O

46 u

Percentage Composition

Practice

Calculating

Percentage

Composition

What is the complete

percentage composition

of sulfuric acid?

H = 1 X 2 = 2

S = 32 X 1 = 32

O = 16 X 4 = 64

H2SO4

98Work as a

formula mass

problem

H = 1 X 2 = 2

S = 32 X 1 = 32

O = 16 X 4 = 64

H2SO4

98

/98 /98

/98

Then divide the

total into each one

H = 1 X 2 = 2

S = 32 X 1 = 32

O = 16 X 4 = 64

H2SO4

98

/98 = 2% H/98 = 33% S

/98 = 65% O

This is the answer

to a % comp problem

Percentage

Composition

Homework

Assignment

Sugar In Bubble Gum