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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
For every one CuSO4, there are five water molecules
The dot IS NOT a multiplication sign. Remember, this is chemistry, not math.
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.
penta meaning five and hydrate meaning water
CuSO4 . 5 H2O
Suppose you heard "trihydrate." What would you write?
. 3 H2O
Suppose you heard "octahydrate." What would you write?
. 8 H2O
Name this substance: MgSO4 . 9 H2O
Magnesium sulfate nonahydrate
Write the formula for: barium chloride dihydrate
BaCl2 . 2 H2O
Keep water’s 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)
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
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
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