Fajans–Paneth–Hahn Law


The Fajans–Paneth–Hahn Law, in chemistry, is a rule governing how a small amount of one substance is carried down to a precipitate of another substance present in much larger amount by coprecipitation or adsorption.
The rule states that:
The amount carried down is strongly affected by presence of complexing species regardless if it occurs by formation of mixed crystals or adsorption.
The law is named after chemists Kazimierz Fajans, Friedrich Paneth and Otto Hahn.
The Fajans-Paneth-Hahn law is essential for understanding the behaviour of minute amounts of substances in solutions. Note that the tracer is precipitated from the solution even when present at concentration far below its solubility limit. The law is also applied for separation of tracer substances by co-precipitation.