SnailsAttack
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Registered: 7-2-2022
Location: The bottom of Lake Ontario
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Quantifying hygroscopicity
Hygroscopicity seems to exist as a spectrum ranging from "deliquescence that's as much of a pain in the ass to work with as it is to spell" to
"doesn't even form hydrates".
I'm planning to conduct some tests to see which chemicals will absorb water in a moist container (without actual contact with the water) and quantify
the time it takes for hygroscopic chemicals to dry out under standard conditions (my bedroom).
Has anyone done something like this before? Is there a way to predict a chemical's degree of hygroscopicity? Also, do hygroscopics always form
hydrates?
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chornedsnorkack
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Plenty of scientists have done it, and published the redults, which are scattered around literature.
One way to quantify it is humidity (absolute or relative) where the chemical is in equilibrium with its hydrate - its vapour pressure.
Hygroscopics do not always form hydrates. A "hydrate" is a solid of fixed composition and thus vapour pressure of a given temperature. Whereas
"deliquescence" leads to solution of variable concentration. Some hygroscopics have high solubility and thus low vapour pressure in saturated
solution, but the solid in saturated solution is not a hydrate.
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