Question

What hydrated salt has a water weight of water weight of 14.83%?

Answer 1

Hi it is not possible to get your answer directly, because a hydrate is a solid compound with water bound to its crystal structure. Different compounds have different hydrated salts and even one compound shows different hydrated salts such as CaSO₄ [gypsum (CaSO₄. 2H₂O), hemihydrate or plaster of paris (CaSO₄. 1/2H₂O) and anhydrite (CaSO₄).] The formula to calculate

percent water (H₂O) = (mass H₂O / mass hydrate) x 100%

I request you to go through a video less than 2 minutes on how to calculate percent water on youtube

https://www.youtube.com/watch?time_continue=101&v=dQ8BXI8ibuE

at least if we know the anhydrous salt, then we can reverse calculate the how much it is hydrated.

let's take calcium sulfate as an example

Plaster of paris:

mw of H2O = 18.015 g/mol
mw of CaSO4 = 136.14 g/mol (anhydrous)
mw of CaSO4*(1/2)H2O = 145.15 g/mol (hemihydrate)
mw of CaSO4*2H2O = 172.172 g/mol (dihydrate)
% H2O in CaSO4*(1/2)H2O = [(mass water)/(mass CaSO4*(1/2)H2O)]*100%
In CaSO4*(1/2)H2O there is only 1/2 mole of water for each mole of CaSO4*(1/2)H2O
% H2O = [(18.015 g/mol)(1/2 mol)/(145.15 g)]*100% = 6.21% H2O
Gypsum:
% H2O in CaSO4*2H2O is worked the same way.
% H2O in CaSO4*2H2O = [(mass water)/(mass CaSO4*2H2O)]*100%
mass water in CaSO4*2H2O = (18.015 g/mol)(2 mol) = 36.030 g H2O
mass 1 mole CaSO4*2H2O = 172.172 g
% H2O = [(36.030 g)/(172.172 g)]*100% = 20.9% H2O in CaSO4*2H2O

Hope this helped you!

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