Topic: Percentage Composition Do Now:

Percent Composition use chemical formula & assume 1 mole use chemical formula & assume 1 mole Calculate formula mass then divide mass each element by formula mass (FM) of compound Calculate formula mass then divide mass each element by formula mass (FM) of compound

Percent Composition of H 2 O 2 H’s = 2 x 1.0 g = 2.0 g 1 O = 1 x 16.0 g = 16.0 g Molar mass = 2.0 g g = 18.0g/mol % H = 2.0g x 100% = 11.11% 18.0g 18.0g % O = 16.0g x 100% = 88.89% 18.0g 18.0g

Percent Composition of C 6 H 12 O 6 6 C’s = 6 x 12g = 72g 12 H’s = 12 x 1g = 12g 6 O’s = 6 x 16g = 96g Molar mass = grams/mole % C = % H = % O = (72g/180g) X 100% = 40.00% (12g/180g) X 100% = 6.67% (96g/180g) X 100% = 53.33% 100%

Percentage Composition Remember to calculate FM! Remember to calculate FM! Nowhere in word problem will it tell you that!Nowhere in word problem will it tell you that! Sum of individual element %’s must add up to exactly 100%Sum of individual element %’s must add up to exactly 100%

Hydrates = contain water group salts that have water molecules stuffed in their empty spaces group salts that have water molecules stuffed in their empty spaces Formulas are distinctive Formulas are distinctive Ex: CuSO 4  5H 2 O Ex: CuSO 4  5H 2 O  means “is associated with” or “included” Does NOT refer to multiplication Does NOT refer to multiplication Not true chemical bond: When heated, water is driven off = anhydrate When heated, water is driven off = anhydrate

What can say about CuSO 4  5H 2 O? 1 mole CuSO 4 contains 5 moles water 1 mole CuSO 4 contains 5 moles water 1 molecule of CuSO 4 contains 5 molecules of water 1 molecule of CuSO 4 contains 5 molecules of water When heated, water is driven off & anhydrous salt is left: CuSO 4 When heated, water is driven off & anhydrous salt is left: CuSO 4 – anhydrous = without water mole ratio in formula can be used to predict how much water found in any size sample mole ratio in formula can be used to predict how much water found in any size sample If had 2 moles of CuSO 4 5H 2 O, how much water would you lose on heating? If had 2 moles of CuSO 4 5H 2 O, how much water would you lose on heating? 10 moles

CuSO 4  5H 2 O REVIEW: Counting atoms! REVIEW: Counting atoms! 1 Cu 1 S 4 O + 5x1 O = 9 O 5x2 H =10 H total = 21 atoms

5CuSO 4  5H 2 O Count up the atoms! Count up the atoms! 5 = Cu 5 = S 5x4 O + 5x5x1 O = 45 O 5x5x2 H = 50 H total = 105 atoms

FIND THE PERCENT WATER CuSO 4  5H 2 O FIND THE PERCENT WATER CuSO 4  5H 2 O 1 Cu = 1 x 64 = 64 1 S = 1 x 32 = 32 9 O = 9 x 16 = H = 10 x 1 = 10 total = 240g Just water 5 O = 5 x 16 = H = 10 x 1 = 10 total = 90g 90/240 x 100 = 37.5% water