Calculating molar mass comp.ppt

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Chemical Reactions and Quantities

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Molar Mass

The molar mass

is the mass of one mole

of an element or compound.

is the atomic mass

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Molar Mass from Periodic Table

Molar mass is

the atomic mass

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Give the molar mass for each (to the tenths decimal place).

A. 1 mole K atoms = ________

B. 1 mol Sn atoms = ________

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Give the molar mass for each (to the tenths decimal place).

A. 1 mole K atoms = 39.1 g

B. 1 mole Sn atoms =118.7 g

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Molar Mass of a Compound

The molar mass of a compound is the sum of the molar masses of the elements in the formula.

Example: Calculate the molar mass of CaCl2.

Element Number of Moles

Atomic Mass Total Mass

Ca 1 40.1 g/mole 40.1 g

Cl 2 35.5 g/mole 71.0 g

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Molar Mass of K

3

PO

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Calculate the molar mass of K3PO4.

Element Number of Moles

Atomic Mass Total Mass

in K3PO4

K 3 39.1 g/mole 117.3 g

P 1 31.0 g/mole 31.0 g

O 4 16.0 g/mole 64.0 g

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Some One-mole Quantities

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What is the molar mass of each of the following?

A. K2O

B. Al(OH)3

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A. K2O 94.2 g/mole

2 mole K (39.1 g/mole) + 1 mole O (16.0 g/mole) 78.2 g + 16.0 g = 94.2 g

B. Al(OH)3 78.0 g/mole

1 mole Al (27.0 g/mole) + 3 mol O (16.0 g/mole) + 3 mol H (1.01 g/mole)

27.0 g + 48.0 g + 3.03 g = 78.0 g

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Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?

1) 40.1 g/mole 2) 262 g/mole 3) 309 g/mole

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Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?

3) 309 g/mole

17 C (12.0) + 18 H (1.01) + 3 F (19.0) + 1 N (14.0) + 1 O (16.0) =

204 + 18.2 + 57.0 + 14.0 + 16.0 = 309 g/mole

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Molar mass conversion factors

are written from molar mass.

relate grams and moles of an element or compound.

Example: Write molar mass factors for methane, CH4,

used in gas stoves and gas heaters. Molar mass:

1 mol CH4 = 16.0 g

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Acetic acid C2H4O2 gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid.

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Calculating Percent Composition

The formula is found on table T of the

reference table.

Mass of the part

Mass of the Whole X100

NaCl

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Claculating Percent Composition

To determine the % composition of

sodium in NaCl

Mass of sodium in formula 22.99

Mass of entire formula 58.44 X100

39.34 %

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Determining Percent

Composition

What is the percent composition of

Chlorine in NaCl?

Total mass of Cl in formula 35.45

Total mass of formula 58.44

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Determining % Composition

What is the % composition of oxygen in

CuSO4?

Cu = 1 X 63.55 = 63.55

S = 1 X 32.07 = 32.07

O = 4 X 15.99 = 63.96

Total mass 159.58

Mass of Oxygen 63.96

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Acetic acid C2H4O2 gives the sour taste to vinegar. Write two molar mass factors for acetic acid.

Calculate molar mass:

24.0 + 4.04 + 32.0 = 60.0 g/mole

1 mole of acetic acid = 60.0 g acetic acid Molar mass factors

1 mole acetic acid and 60.0 g acetic acid

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Molar mass factors are used to convert between the grams of a substance and the number of moles.

Calculations Using Molar Mass

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Aluminum is often used to build lightweight bicycle frames. How many grams of Al are in 3.00 mole Al?

Molar mass equality: 1 mole Al = 27.0 g Al

Setup with molar mass as a factor:

3.00 mole Al x 27.0 g Al = 81.0 g Al 1 mole Al

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Learning Check

Allyl sulfide C6H10S is a

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Calculate the molar mass of C6H10S.

(6 x 12.0) + (10 x 1.01) + (1 x 32.1) = 114.2 g/mole

Set up the calculation using a mole factor.

225 g C6H10S x 1 mole C6H10S

114.2 g C6H10S

molar mass factor (inverted)

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Grams, Moles, and Particles

A molar mass factor and Avogadro’s number convert

grams to particles.

molar mass Avogadro’s number

g mole particles

particles to grams.

Avogadro’s molar mass number

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Learning Check

How many H2O molecules are in 24.0 g H2O?

1) 4.52 x 1023

2) 1.44 x 1025

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Solution

How many H2O molecules are in 24.0 g H2O?

3) 8.02 x 1023

24.0 g H2O x 1 mole H2O x 6.02 x 1023 H

2O molecules

18.0 g H2O 1 mole H2O

= 8.03 x 1023 H

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Learning Check

If the odor of C6H10S can be detected from 2 x 10-13 g

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Solution

If the odor of C6H10S can be detected from 2 x 10-13 g

in one liter of air, how many molecules of C6H10S are present?

2 x 10-13 g x 1 mole x 6.02 x 1023 molecules

114.2 g 1 mole = 1 x 109 molecules C

Figure

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References

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