Most solubility references (e.g. this one) say that there are "few" insoluble salts of alkali metals.
Are there any exceptions?
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Sign up to join this communityMost solubility references (e.g. this one) say that there are "few" insoluble salts of alkali metals.
Are there any exceptions?
Lithium carbonate has poor water solubility. Cesium triphenylcyanoborate is insoluble in water.
They would advertise $\ce{NaBPh4}$ as a reagent to determine $\ce{K+}$ gravimetrically. Old-timers may remember the feared Kalignost. $\ce{XBPh4-}$, for X=$\ce{Rb+, Cs+, NH4+,Tl+}$ is similarly insoluble.
Thanksfully, now there is methods like AAS, and we plague the kids with that in Instrumental Analysis/Analytical Chemistry classes instead.
Perhaps the simplest case involving limited (<0.1 molar) solubility is lithium fluoride, whose solubility is only about one part in 750 by mass at 25°C (about 0.05 molar).
There are some cations whose Group I/ammonium salts are not soluble in water. For example, (thanks Nicolau) the diuranate of ammonium is insoluble in water.
Additionally, (as I just found) the hydrides (H-) of alkali metals are not soluble, it seems, in any room-temperature liquid solvent. They hydrolyze violently (http://goo.gl/Dl8Bd4), and the hydride ion has never been observed in solution.