[mahesh]

Hi!
Just thought about this.. how do I calculate the amount of 25%NH3 solution required to precipitate out all the ammonium sulfate in 100 ml water by common ion effect? The Ksp for ammonium sulfate is 791.5. The amount of ammonium sulfate in water is 29gm.
Sorry, this could be stupid, but I really dont remember how to do it.

[Borek]

No such thing as "precipitate out all by common ion effect" - there is always something left, you have to put a limit (99.9% for example).

In this case you will not calculate anything with even remote accuracy, as solution is so concentrated activities are way too high to be calculated.

Not to mention other problems with the question...

[AWK]

Hi!
Just thought about this.. how do I calculate the amount of 25%NH3 solution required to precipitate out all the ammonium sulfate in 100 ml water by common ion effect? The Ksp for ammonium sulfate is 791.5. The amount of ammonium sulfate in water is 29gm.
Sorry, this could be stupid, but I really dont remember how to do it.

This is rather wrongly stated problem. A concentrated ammonia in fact increase solubility of different ammonium salts in water.
Common ion effect in this case needs ammonium ion from ammonia which have a very small concentration (in this case of order 0.0001 M from ammonia).
Hence ammonium ion from ammonia practically do not change solubility od ~2 M (NH4)2SO4 through the common ion effect.