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Percent Composition

Published on Feb 24, 2016

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PRESENTATION OUTLINE

Percent Composition

Hydrates
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Percent Composition of Hydrates

  • Hydrates - crystal structures that incorporate water into their structures.
  • When you measure a certain quantity of the compound, you need to know how much the water molecules contribute to the mass.
Photo by Vincent_AF

Reading a Hydrate Formula

  • When a compound is crystallized from a water solution, there is water present.
  • That water is reflected in the chemical formula.
  • i.e. - CuSO4*5H2O
Photo by Paul's Lab

Reading a Hydrate Formula

  • CuSO4*5H2O
  • You will notice that 1 mole of CuSO4 contains 5 mols of H2O.
  • The water molecules attribute to the total mass of the formula
Photo by Paul's Lab

Calculating Percent Water in a Hydrate

  • Since the water contribute to the total mass
  • You have to treat the water molecule as if it were another element in the formula.

Calculating Percent Water in a Hydrate

  • Find the formula mass of H20
  • multiply it by the number of moles in the formula
  • divide by the total mass of the compound CuSO4*5H2O

Practice

  • Na2CO3*10H2O
  • NiI2*6H20
  • AlBr3*6H2O
  • Honors - (NH4)2 Fe(CN)6 * 3H2O
Photo by Mik Hartwell