Percent Composition From a Chemical Formula

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Percent CompositionFrom a Chemical Formula

• Chemistry 11
• Ms. McGrath

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Percentage CompositionFrom a Chemical Formula

• Percentage composition
• Refers to the relative mass of each
• element in a compound.

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Percentage CompositionFrom a Chemical Formula

• We previously learned how to determine
• percentage composition using mass. This
• is helpful when we do not have the
• chemical formula.
• Often we use the chemical formula to
• determine the percentage composition.
• This is useful when extracting a certain
• element from a compound.

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Percentage CompositionFrom a Chemical Formula

• We use the molar mass and the
• chemical formula of the compound to
• calculate its percentage composition.
• Example
• We want to determine the percentage
• composition of HgS. We can assume that
• we have one mole of HgS to find the mass
• percents of mercury and sulfur.

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Percentage CompositionFrom a Chemical Formula

• Mass percent of HgS Mass of Hg in 1 mol HgS x
  100
  
  Mass of 1 mol of HgS
• 200.59 g x
  100
• 232.66 g
• 86.22
• Mercury (II) sulfide is 86.22 mercury by mass.
  Since
• there are only two elements in HgS, we can
  subtract the mass
• percent of mercury from 100 to find the mass
  percent of sulfur.
• Mass percent of S in HgS 100 - 86.22
• 
  13.78

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Percentage CompositionFrom a Chemical Formula

• You try!
• What is the percentage composition of
• hydrogen peroxide, H2O2?

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Percentage CompositionFrom a Chemical Formula

• You try!
• What is the percentage composition of hydrogen
• peroxide, H2O2?
• H Mass of H in 1 mol H2O2 x 100
  
  
  Mass of 1 mol of H2O2
• 2.02 g x 100
• 34.02 g
• 5.94
• Now, lets calculate oxygen

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Percentage CompositionFrom a Chemical Formula

• Now, lets calculate oxygen
• O Mass of O in 1 mol H2O2 x 100
  
  
  Mass of 1 mol of H2O2
• 32.00 g x 100
• 34.02 g
• 94.06

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Percentage CompositionFrom a Chemical Formula

• See sample problem page 84, 85
• Try page 85 5 - 8

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