# Re: CaSO4.2H2O Solubility

KL wrote:
Does anybody know on the web where I can find some data on the solubility of
Gypsum as a function of temperature and/or pH? I have tried searching
google but come up empty handed.

Regards,
K

CaSO4.2H2O is a salt of strong acid & a strong base.These salts don't
undergo hydrolysis & hence cause no change in the pH of water.
If "s" be solubility in moles /l
CaSO4-------->Ca+2 + SO4-2
s s

Here Ksp=s^2

s can be written as "ca" where "a" is the degree of dissociation
(constant), and "c" is the concentration.also c is inversly propotional
to the volume of the system.If we take 1 mol of CaSO4, then

c=1/V.----------------------------------------(1)

Now as the temperature (T) increases, the volume of the system keeps on
decreasing(as the water starts evaporating when T>=100 C)
or V=1/T-------------------------------------(2)

From (1) & (2) we can say that,

c=1/T-----------------------------------------(3)

since s = ca, s is directly propotional to c or inversly propotional
toT.

Hence s o< 1/T (o< means propotional to)

It may not be perfect but that's what I think should be the solution.

.

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