Percentage CompositionPercentage Composition

PercentPercent

PartPart

WholeWholeX 100%X 100%

Mass of elementMass of elementMass of compoundMass of compound

X 100%X 100%

Percent by mass =Percent by mass =

Percent CompositionPercent Composition

use chemical formula & assume 1 moleuse chemical formula & assume 1 mole

divide mass each element by formula divide mass each element by formula mass (FM) of compoundmass (FM) of compound

Percent Composition of HPercent Composition of H22OO2 H’s = 2 x 1.0 g = 2.0 g2 H’s = 2 x 1.0 g = 2.0 g1 O = 1 x 16.0 g = 16.0 g1 O = 1 x 16.0 g = 16.0 g

Molar mass = 2.0 g + 16.0 g = 18.0Molar mass = 2.0 g + 16.0 g = 18.0g/molg/mol

% H = % H = 2.0g2.0g x 100% = 11.11% x 100% = 11.11% 18.0g18.0g

% O = % O = 16.0g16.0g x 100% = 88.89% x 100% = 88.89% 18.0g18.0g

Percent Composition of CPercent Composition of C66HH1212OO66

6 C’s = 6 x 12g = 72g6 C’s = 6 x 12g = 72g

12 H’s = 12 x 1g = 12g12 H’s = 12 x 1g = 12g

6 O’s = 6 x 16g = 96g6 O’s = 6 x 16g = 96g

Molar mass = 180.0 grams/moleMolar mass = 180.0 grams/mole

% C =% C =

% H = % H =

% O =% O =

(72g/180g) X 100% = 40.00%(72g/180g) X 100% = 40.00%

(12g/180g) X 100% = 6.67%(12g/180g) X 100% = 6.67%

(96g/180g) X 100% = (96g/180g) X 100% = 53.33%53.33%

100%

Percentage CompositionPercentage Composition

Remember to Remember to calculate FMcalculate FM!!•Nowhere in word problem will it Nowhere in word problem will it

tell you that!tell you that!

•Sum of individual element %’s Sum of individual element %’s mustmust add up to add up to exactlyexactly 100% 100%

HydratesHydrates group salts that have water group salts that have water

molecules stuffed in their empty molecules stuffed in their empty spacesspaces

Formulas are distinctiveFormulas are distinctive Ex: CuSOEx: CuSO445H5H22OO

means means ““is associated withis associated with”” or or ““includedincluded”” Does NOT refer to multiplication Does NOT refer to multiplication

Not true chemical bond:Not true chemical bond:

What can say about CuSOWhat can say about CuSO445H5H22O?O?

ItIt’’s hydrated salt – s hydrated salt – hydrate = waterhydrate = water• 1 mole CuSO1 mole CuSO44 contains 5 moles water contains 5 moles water• 1 molecule of CuSO1 molecule of CuSO44 contains 5 molecules of contains 5 molecules of

waterwater

When heated, water is driven off & When heated, water is driven off & anhydrous salt is left: CuSOanhydrous salt is left: CuSO4 4 – – anhydrous = anhydrous = without waterwithout water

If had 2 moles of CuSOIf had 2 moles of CuSO445H5H22O, how much O, how much water would you lose on heating?water would you lose on heating?

CuSOCuSO445H5H22OO

Count up the atoms!Count up the atoms!

1 Cu1 S4 O + 5x1 O = 9 O5x2 H =10 H

total = 21 atoms

5CuSO5CuSO445H5H22OO

Count up the atoms!Count up the atoms!

5 = Cu5 = S5x4 O + 5x5x1 O = 45 O5x5x2 H = 50 H

total = 105 atoms

FIND THE PERCENT WATER FIND THE PERCENT WATER CuSOCuSO445H5H22OO

1 Cu = 1 x 64 = 641 S = 1 x 32 = 329 O = 9 x 16 = 14410 H = 10 x 1 = 10

total = 240

Just water5 O = 5 x 16 = 8010 H = 10 x 1 = 10

total = 90

90/240 x 100 = 37.5% water