Percent Compositionpreap

Percent Composition & Types of Mass

Types of Mass • Formula Mass – sum of atomic masses in a formula • Ex: H2O= 18.02 amu NaCl= 58.45 amu • Molar Mass – sum of atomic masses in a formula in g/mole. g/mole Molar mass can be used in calculations as a conversion factor. • Ex H2O= 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 77.1 g 1 •

1 mole

= 1.09 mol

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 4.15 x 10–3 g

1 mole

1

= 2.30 x 10-5 mol

180.18 g

How many molecules are in each of the above? 1.09 mole 6.02 x 1023 molecules = 6.56 x 1023 molecules Cl2 1

1 mole

2.30 x 10-5 mole 1

1.38 x 1019

6.02 x 1023 molecules = molecules 1 mol

C6H12O6

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

% Mass of an Element = grams of element X grams of compound

x 100

Example Percent Composition of Water

Percent Composition of Water

H = 2.02 x 100 = 11% 18.02

11%

O = 16.00 x 100 = 89% 18.02

89% H

O

An Example Just For You! • What is the percent of carbon in carbon monoxide? Mass of CO = 12.01 + 16.00 = 28.01 12.01 x 100 = 42.88 % C 28.01 • What would the percent of oxygen be? 16.00 x 100 = 57.12 % O 28.01 OR 100 - 42.88 = 57.12 % O

Your Turn! •

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

Mass of C2H5OH = (2)12.01 + (6)1.01 + 16.00 = 46.08 24.02 x 100 = 52.13 % C 46.08 •

What would the percent of oxygen be?

16.00 x 100 = 34.72 % O 46.08 •

What would the percent of hydrogen be?

6.06 x 100 = 13.15 % H 46.08

Give it a Whirl! • 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 g  Mass of N – 3.48 g

 Mass of Compound - (9.03 + 3.48) =12.51 • 9.03 x 100 = 72.18 % Mg 12.51 • 100 – 72.18 = 27.82 % N

A Little Tougher One! • Determine the percentage composition of Al2(SO4)3?  gmm Al2(SO4)3 = (2)26.98 + (3)32.07 + 12(16.00) = 342.17g • 53.96 x 100 = 15.77 % Al 342.17 • 96.21 x 100 = 28.12 % S 342.17 • 192.00 x 100 = 56.11 % O 342.17 • 15.77 + 28.12 + 56.11 = 100 % Al2(SO4)3

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”.