Percent Composition Percent Composition & &

Types of MassTypes of Mass

Types of Mass

• Formula Mass – sumsum of atomic masses in a formula

• Ex: HH22O= 18.02 amu NaCl= 58.45 amuO= 18.02 amu NaCl= 58.45 amu

• Molar Mass – sum of atomic masses in a formula in g/moleg/mole. Molar mass can be used in calculations as a conversion factor.

• Ex HH22O= 18.02 g/mole NaCl= 58.45 g/moleO= 18.02 g/mole NaCl= 58.45 g/mole

Examples• How many moles are in 77.1 g Cl2?

2(35.45) = 70.90 g 2(35.45) = 70.90 g

77.1 g 1 mole77.1 g 1 mole = 1.09 mol = 1.09 mol

11 70.90 g 70.90 g

• How many moles are in 4.15 x 10–3 g C6H12O6?

6(12.01) + 6(16.00) + 12(1.01) = 180.18 g 6(12.01) + 6(16.00) + 12(1.01) = 180.18 g

4.15 x 104.15 x 10–3–3 g 1 mole g 1 mole = 2.30 x 10 = 2.30 x 10-5-5 mol mol

11 180.18 g 180.18 g

How many molecules are in each of the above?

1.09 mole 6.02 x 101.09 mole 6.02 x 1023 23 moleculesmolecules = 6.56 x 10 = 6.56 x 102323 molecules Clmolecules Cl22

11 1 mole1 mole

2.30 x 102.30 x 10-5-5 mole 6.02 x 10 mole 6.02 x 1023 23 moleculesmolecules = =

11 1 mol 1 mol

1.38 x 101.38 x 101919

moleculesmolecules

CC66HH1212OO66

• Percent Composition – the percent by mass of each element in a compound.

grams of element Xgrams of element X grams of grams of compoundcompound

x 100x 100

% Mass of an Element% Mass of an Element

==

Percent Composition

Percent Composition of Percent Composition of WaterWater

H = H = 2.022.02 x 100 = 11% x 100 = 11% 18.02 18.02

O = O = 16.0016.00 x 100 = 89% x 100 = 89% 18.02 18.02

Percent Composition of Water

11%

89%

H O

Example

• What is the percent of carbon in carbon monoxide?

Mass of CO = 12.01 + 16.00 = 28.01Mass of CO = 12.01 + 16.00 = 28.01

12.0112.01 x 100 = 42.88 % C x 100 = 42.88 % C

28.0128.01

• What would the percent of oxygen be?

16.0016.00 x 100 = 57.12 % O x 100 = 57.12 % O

28.0128.01

OR 100 - 42.88 = 57.12 % OOR 100 - 42.88 = 57.12 % O

An Example Just For You!

Your Turn!

• What is the percent of carbon in ethanol (C2H5OH)?

Mass of CMass of C22HH55OH = (2)12.01 + (6)1.01 + 16.00 = 46.08OH = (2)12.01 + (6)1.01 + 16.00 = 46.08

24.0224.02 x 100 = 52.13 % C x 100 = 52.13 % C

46.0846.08

• What would the percent of oxygen be?

16.0016.00 x 100 = 34.72 % O x 100 = 34.72 % O

46.0846.08

• What would the percent of hydrogen be?

6.066.06 x 100 = 13.15 % H x 100 = 13.15 % H

46.0846.08

• 9.03 g of Mg combines completely with 3.48 g N to form a compound. What is the percent composition of this compound?Mass of Mg – 9.03 gMass of Mg – 9.03 gMass of N – 3.48 gMass of N – 3.48 gMass of Compound - (9.03 + 3.48) Mass of Compound - (9.03 + 3.48)

=12.51=12.51• 9.039.03 x 100 = 72.18 % Mg x 100 = 72.18 % Mg

12.5112.51• 100 – 72.18 = 27.82 % N100 – 72.18 = 27.82 % N

Give it a Whirl!

• Determine the percentage composition of Al2(SO4)3? gmm Algmm Al22(SO(SO44))33 = (2)26.98 + (3)32.07 + = (2)26.98 + (3)32.07 +

12(16.00) = 342.17g12(16.00) = 342.17g• 53.9653.96 x 100 = 15.77 % Al x 100 = 15.77 % Al 342.17342.17• 96.2196.21 x 100 = 28.12 % S x 100 = 28.12 % S 342.17342.17• 192.00192.00 x 100 = 56.11 % O x 100 = 56.11 % O 342.17342.17• 15.77 + 28.12 + 56.11 = 100 % Al15.77 + 28.12 + 56.11 = 100 % Al22(SO(SO44))33

A Little Tougher One!

Why is Thanksgiving turkey sometimes called “Tom Turkey”?

The legend says Ben Franklin wanted the wild turkey to be the US official bird.

Thomas Jefferson opposed the idea so to mock Jefferson, Franklin coined the term “Tom Turkey”.