Chapter 8 Percentage Composition

Water is made of hydrogen and oxygen. How many grams of each are in the sample of water below?

Percent Composition Mass of element Formula Mass of compound X 100 X 100 % = Percent composition is the percent by mass of an element within a compound. Divide the mass of each element by the formula mass of the compound

Percent Composition of H 2 O 2 X H = 2 X 1.0 g = 2.0 g 1 X O = 1 X 16.0 g = 16.0 g gram formula mass = 2.0 g g = 18.0 g % H = 2.0g X 100 = 11.2% 18.0g % O = 16.0g X 100 = 88.8% 18.0g

Percent Composition of H 2 O 2 X H = 2 X 1.0 g = 2.0 g 1 X O = 1 X 16.0 g = 16.0 g gram formula mass = 2.0 g g = 18.0 g % H = 2.0g X 100 = 11.2% 18.0g % O = 16.0g X 100 = 88.8% 18.0g What does this mean?

Pure water’s mass is 11.2% hydrogen and 88.8% oxygen. (0.112)(128.98g) = 14.45g H (.888)(128.98g) = g O or g – 14.45g = g O 11.2% H 88.8% O

Percentage Composition Remember that you have to calculate the formula mass!

Determine the Percent Composition of C 6 H 12 O 6

6 X C = 6 X 12.0 g = 72.0g 12 X H = 12 X 1.0g = 12.0g 6 X O = 6 X 16.0g = 96.0g gfm = grams/mole

Determine the Percent Composition of C 6 H 12 O 6 6 X C = 6 X 12.0 g = 72.0g 12 X H = 12 X 1.0g = 12.0g 6 X O = 6 X 16.0g = 96.0g gfm = grams/mole % C = % H = % O = (72.0g/180.0g) X 100 = 40.0% (12.0g/180.0g) X 100 = 6.67% (96.0g/180.0g) X 100 = 53.3%

How many grams of carbon are in 156g C 6 H 12 O 6 6 (156g)(0.400) = 62.4g carbon 12 6 Molar % C = % H = % O = (72.0g/180.0g) X 100 = 40.0% (12.0g/180.0g) X 100 = 6.67% (96.0g/180.0g) X 100 = 53.3%

What is this? a

Iron Pyrite “Fool’s Gold” (FeS 2 ) a

How many grams of sulfur are in this 28.8g sample of iron pyrite FeS 2 ? a

a 15.4g S

How many grams of sulfur are in this 28.8g sample of iron pyrite FeS 2 ? a 15.4g S Fe + 2(S) ( 32.1) = g/mol %S = 64.2/120.0 x 100= 53.5%S 28.8g x = 15.4g S

Homework  Molarity Worksheet (Due Tomorrow).  Percentage Composition Worksheet (Due in 2 Days).