So in the Finkelstein reaction, the iodide ion is supposed to replace another halogen(say chlorine) through SN2 mechanism. But here, Acetone is used, which is a polar aprotic solvent. And in acetone, iodide ion is the weakest nucleophile. So how can it replace the chlorine?
Aren't we better off if we use water or ethanol(which are polar protic solvents) since (I-) acts as the strongest nucleophile?