Hydrates

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Hydrates
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Hydrates

• substances that include water into their formula
• water is not actually part of the chemical
  substance and this is reflected in the way the
  formula is written

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Example CuSO4 . 5 H2O

• For every one CuSO4, there are five water
  molecules
• The dot IS NOT a multiplication sign. Remember,
  this is chemistry, not math.

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F.Y.I.

• No, the substance is not wet, it appears dry.
• There are some hydrates that have a wet
  appearance, but most appear perfectly dry to the
  eye and to the touch.

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copper(II) sulfate pentahydrate

• penta meaning five and hydrate meaning water
• CuSO4 . 5 H2O

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Practice Problems
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Problem 1

• Suppose you heard "trihydrate." What would you
  write?

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Answer

• . 3 H2O

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Problem 2

• Suppose you heard "octahydrate." What would you
  write?

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Answer

• . 8 H2O

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Problem 3

• Name this substance MgSO4 . 9 H2O

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Answer

• Magnesium sulfate nonahydrate

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Problem 4

• Write the formula for barium chloride dihydrate

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Answer

• BaCl2 . 2 H2O

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Finding Molar Mass

• Keep waters mass separate in calculation
• CuSO4 . 5 H2O
• Cu 63.5 g
• S 32.1 g
• O 16.0 x 4 64.0 g
• H2O 18.0 g x 5 90.0g
• Add them all together to get the molar mass
• Total 249.6 g (MOLAR MASS)

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Percent Composition of H2O

• Calculating the accepted value
• How much water did we have?
• 90.0 grams H2O
• What was the total molar mass?
• 249.6 grams
• 90.0 g x 100 36.1 H2O
• 249.6 g

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Experimental Composition

• You begin an experiment with 15.0 grams of
  hydrate.
• You place the hydrate in an evaporating dish and
  place the Bunsen burner below.
• You weigh your resulting product, 13.2 grams of
  anhydrous salt (a compound with all the water
  removed).
• Determine the experimental percent composition of
  water within the compound

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• 15.0 grams 13.2 grams 1.8 grams of water that
  was evaporated (removed)
• 1.8 g x 100 12.0 H2O
• 15.0 g

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The End