Hydrates (11.5)
• Hydrate- compound with a specific amount
of water molecules bound to it
• Hydrates are often used as drying agents
or desiccators because they can absorb
moisture
• Silica gel- used in electronic equipment
packaging, cat litter
• Chemicals that do not contain water in
their structures are called anhydrous
(without water)
• Hydrates are easy to spot because their
formulas show the water molecules
Anhydrous cobalt (ii) chloride
CoCl2
Cobalt (II) chloride hexahydrate
CoCl2 x 6H2O
To determine hydrate formula
1. Determine moles of water and of
anhydrous compound
2. Find x =
moles of water
moles of anhydrous compound
3. Plug in x
Formula for compound X H2O
• A mass of 2.50 g blue hydrated copper sulfate
(CuSO4 x XH2O) is place in a crucible and heated.
After heating, 1.59 g of copper sulfate remains. What
is the formula for the hydrate?
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2.50 = CuSO4 + H2O
CuSO4= 1.59 g
2.50 = 1.59 + H2O
H2O = 0.91 g
CuSO4 = 63.5 + 32.1 + 4 x 16 = 159.6 g/mol
CuSO4 = 1.59 / 159.6 = 0.010 mol
H2O = 2 x 1 + 16 = 18 g/mol
H2O = 0.91 / 18 = 0.050 mol
X = 0.050 / 0.010 = 5
CuSO4 x 5H2O
What is the mole ratio of the hydrate
CuSO4 x ___H2O, if the anhydrous mass of
CuSO4 is 25.42g and mass of water is 14.3 g?
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CuSO4 = 63.5 + 32.1 + 4 x 16 = 159.6 g/mol
CuSO4 = 25.42 / 159.6 = 0.159 mol
H2O = 2 x 1 + 16 = 18 g/mol
H2O = 14.3 / 18 = 0.79 mol
X = 0.79 / 0.159 = 4.96 ~ 5
CuSO4 x 5H2O
1:5
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What is the mole ratio of hydrate
Na2CO3 x ____ H2O, if the original mass of the
hydrated Na2CO3 was 43.69 g and the mass of the
anhydrous Na2CO3 is 16.19g?
Hydrate = anhydrous + H2O
43.69 = 16.19 + H2O
H2O = 27.50 g
Na2CO3 = 16.19 g
Na2CO3 = 2 x 24.3 + 12 + 3 x 16 = 108.6 g/mol
Na2CO3 = 16.19 / 108.6 = 0.15 mol
H2O = 2 x 1 + 16 = 18 g/mol
H2O = 27.50 / 18 = 1.5 mol
X = 1.5 / 0.15 = 10
Na2CO3 x 10 H2O