Argentometry

The argentometry is a method for the quantitative determination of certain types of ions. Depending on the technique can distinguish between different processes.

Argentometry due to the low solubility of some silver compounds in water. This relates to the compounds of silver chloride, silver bromide, silver iodide, silver cyanide and silver thiocyanate to quantitatively precipitate from aqueous solutions. As the only halide can not determine with fluoride argentometry because silver (I ) fluoride is readily soluble in water. Since the determination by titration, one can call the argentometry as precipitation titration.

General Procedure

As standard solutions for the titration are used for the chloride, bromide, iodide, cyanide or Thiocyanatebestimmung silver nitrate solutions with precisely known concentration. In contrast, if the silver content of a solution can be determined, ammonium thiocyanate is used as the titer.

The general reaction for the precipitation of a halide is:

Specific methods

Distinction can be made between different methods depending on the reaction conditions and indicators used, each named after their discoverers.

Mohr titration can be applied to chloride and bromide. It uses potassium chromate as an indicator at the equivalence point falls silver chromate as a red-brown precipitate.

The titration according to Volhard can be applied for all kinds of ions. Used as an indicator of iron ( III ) ions, which form a red complex with thiocyanate. Direct can be determined only silver, the rest are determined by back-titration.

The titration according to Fajans is again a direct determination of halide ions with silver nitrate as the titer. Since after the equivalence point, the precipitate is positively charged by another silver, this then can eosin or fluorescein used as an indicator - adsorb a change in color - depending on titrierendem ion.

The titration according to Liebig can only be applied for cyanide. This makes the silver initially a soluble complex, at the equivalence point then falls off the silver cyanide and displays it like that.

Potentiometry

The argentometry can also potentiometrically perform. The potential difference between a silver plate and a silver salt-containing solution is measured. The reference electrode is a calomel electrode, but they must not plunge directly into the solution due to the diffusion of disruptive potassium chloride. Therefore, the calomel electrode is immersed in a solution of ammonium nitrate, which is connected by a bridge to the measurement solution.