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Name: Zak
Status: educator
Grade: 9-12
Location: TX
Country: N/A
Date: 2/1/2006


Question:
Will you please name some ionic compounds whose solubility decreases when temperature increases other than cerium (III) sulfate and lithium sulfate?


Replies:
Ce2(SeO4)3, another cerium salt, shows decreasing solubility in water as the temperature increases. So do calcium sulfate (CaSO4) and calcium hydroxide (Ca(OH)2).

source: General Chemistry by Ebbing and Gammon, (8th ed., Houghton Mifflin, New York, 2005).

Dr. Topper


Sodium sulfate and cesium sulfate both decrease in solubility with increasing temperature. In general, the effect of temperature on solubility is best determined experimentally since there is even no exact correlation between the sign of enthalpy of solution with solubility-temperature dependence.

Roberto Gregorius


Ni(IO3)2.4H2O,
Copper iodate

Nd((CH3)2PO4)3
MnSO4.7H2O (not sure about this one)
Lanthanum sulfate

Lu2(SO4)3.8H2O (essentially all the rare-earth sulfates)

HCl (because it evaporates not crystallizes; gas has high entropy)

CO2 likewise; less ionicity.

Ce(III) selenate (toxic, unusual, possibly not helpful)

Calcium: sulfate, selenate, citrate (decimal-slip misprint?),

glycero-phosphate, hypophosphite, isobutyrate, acetate Zinc Benzoate chromium (III) sulfate?

Barium acetate-hydrate, succinate

There are not to many hot-spots, for casual crystal-growing uses. Some good ones probably merely do not have enough published data to look it up. Rare eaths and, not so much, transition metals help. It looks like complex anions help. So check out some iodates, permanganates, dichromates, phosphates and organic anions.

Jim Swenson



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