Hydrated Ionic Compounds. and how they fit into the molecular formula thing. Many ionic compounds crystallize from aqueous solution with one or more water molecules incorporated into their crystal structure. These are called hydrated ionic compounds, or “hydrates” to their close friends.
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Hydrated Ionic Compounds
and how they fit into the
molecular formula thing
Many ionic compounds crystallize from aqueous solution with one or more water molecules incorporated into their crystal structure.
These are called hydrated ionic compounds, or “hydrates” to their close friends.
Hydrates have a specific number of water molecules associated with each formula unit (fu) of the compound.
eg. copper II sulfate·x hydrate—blue
The water molecules are weakly bonded, and can be removed by
CuSO4·xH2O(s) + heat CuSO4(s) + xH2O(g)
3.Usually the number of waters of hydration is a whole number.
Let’s say you want to determine the number of waters of hydration in hydrated barium hydroxide, Ba(OH)2·xH2O.
How would do this? What measurements would you take?
6.00 g of barium hydroxide hydrate is heated over a bunsen burner flame to drive off the waters of hydration.
After heating, 3.26 g of anhydrous Ba(OH)2 remains. Determine the number of waters of hydration in hydrated barium hydroxide.
Calculate the formula of Ba(OH)2·xH2O.
set up a ratio:
mm Ba(OH)2:mass Ba(OH)2 obtained
mm Ba(OH)2·xH2Omass hydrateheated
171.4 g:3.26 g
cross-multiply to solve for y:
y = 315.5 g which is
the molar mass of the hydrate.
mass of water in hydrate =
315.5 g – 171.4 g = 144.1 g which is
mass of H2O/mol hydrate. Convert to mol H2O
144.1 g/18.02 g/mol = 8 mol H2O. And so...
Ba(OH)2·8H2O is the formula of hydrate.
p 277 13 – 18
p 278 52, 54, 57 – 60
We’ll do a version of Inv 6-C on p 286
Section Review and Chapter Review Questions are all good. Knock yourself out . . .