[tdtd]

This is just a general question and is not really related to a particular problem.  When a precipitation reaction occurs (assuming that the exact molar proportions of reactants are present), can the yield be less than 100%? 

It seemed to me like there could be SOME loss of product because some ions just wouldn't precipitate, maybe because of the water hydration shell or something.  Is this true?  If so, how much are we talking about?  1%?  .01%?

Thank you.

[nj_bartel]

Yes it's possible.  The major reason for this is that "insoluble" compounds are in actuallity only mostly insoluble - they still release some ions.  The amount of ions released depends on the compound.

[tdtd]

So is it in general safe to say that the less "insoluble" a precipitated compound, the lower the yield is likely to be for that precipitation reaction?

[Borek]

So is it in general safe to say that the less "insoluble" a precipitated compound, the lower the yield is likely to be for that precipitation reaction?

Yes, although below some level of solubility you will not see any effects. Imagine you are trying to precipitate 1 gram of substance from 1L of solution. CaSO₄ is considered insoluble, but the saturated solution is 0.005M - almost 0.7g per liter. AgCl is considered insoluble as well - saturated solution is about 10^-5M, so you loose about 1.4 mg per liter. AgI is even less soluble - something like 10^-9M - so you loose around 2*10^-7g. From practical standpoint both AgI and AgCl are completely insoluble when it comes to collecting precipitate, which can't be said about CaSO₄.

Note - I am too lazy to check exact numbers, so I can be slightly off, especially with AgI.