Fajans-Paneth-Hahn Law
Encyclopedia
The Fajans-Paneth-Hahn Law (also Fajans precipitation rule, Fajans-Peneth precipitation and adsorption rule, Hahn law of precipitation and adsorption), in chemistry
, is a rule governing how a small amount of one substance (tracer) is carried down to a precipitate of another substance present in much larger amount (carrier) by co-precipitation 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 (e.g., carrier-free radioisotopes) 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.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, is a rule governing how a small amount of one substance (tracer) is carried down to a precipitate of another substance present in much larger amount (carrier) by co-precipitation or adsorption
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
.
The rule states that:
- the lower the solubilitySolubilitySolubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
of the tracer cation with the anion of the carrier, the greater the amount of the tracer carried down by the carrier through co-precipitates or adsorption; - when the tracer substance forms a mixed crystal, then the separation by co-precipitation only weakly depends on the conditions;
- the tracer will adsorb on the surface of the carrier precipitate if the precipitate acquired a surface chargeSurface chargeSurface charge is the electric charge present at an interface. There are many different processes which can lead to a surface being charged, including adsorption of ions, protonation/deprotonation, and the application of an external electric field...
opposite to that of the carrier ions in the solution; and then the separation strongly depends on the condition of precipitation.
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
Kazimierz Fajans
-External links:*...
, Friedrich Paneth
Friedrich Paneth
Friedrich Adolf Paneth was an Austrian-born British chemist. Fleeing the Nazis, he escaped to Britain and became a British citizen in 1939 but returned as director of the Max Planck Institute for Chemistry in 1953....
and Otto Hahn
Otto Hahn
Otto Hahn FRS was a German chemist and Nobel laureate, a pioneer in the fields of radioactivity and radiochemistry. He is regarded as "the father of nuclear chemistry". Hahn was a courageous opposer of Jewish persecution by the Nazis and after World War II he became a passionate campaigner...
.
The Fajans-Paneth-Hahn law is essential for understanding the behaviour of minute amounts of substances (e.g., carrier-free radioisotopes) 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.