Fajans titration

The titration Fajans is a method for quantitative determination of chloride -, bromide and iodide ions . It is counted to argentometry . It is named after the Polish-American chemist Kasimir Fajans .

The crux of the Fajans method is the use of adsorption indicators; H. of dyes that make the end point of the titration easier to identify.

Titration

This is a direct titration of a solution containing chloride, bromide or iodide with a standard silver nitrate solution. Organic dyes such as eosin or fluorescein serve as indicators . This titration method should be used in acetic acid solution.

${\displaystyle \mathrm {Br^{-}(aq)+Ag^{+}(aq)+NO_{3}^{-}(aq)\longrightarrow AgBr\downarrow +NO_{3}^{-}(aq)} }$

Titration of bromide with silver nitrate, silver bromide precipitates as a colloid

At the equivalence point , the precipitated is silver - colloid positively charged and thus can adsorb Eosinanionen by changing the color.

The indication can also take place potentiometrically with a silver electrode as the indicator electrode . This allows the determination of bromide in addition to chloride and iodide.

A determination of silver is also possible with the help of the basic dye Rhodamine 6G.

Related procedures

Other methods of determination for halide ions are the Volhard titration and the Mohr titration .

Historical

Kasimir Fajans , who had been a professor at the University of Munich since 1917, had published a work on ion adsorption on silver bromide in 1922 in connection with the photographic process. His first studies on the new titration method with the use of adsorption indicators he published in 1923 and 1924. From 1936 Fajans worked at the University of Michigan at Ann Arbor ; There he published in 1938 a summary on titration with adsorption indicators as a book chapter. In addition to Fajans, Izaak Kolthoff also developed the method further and published a review on it.

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Jander, Blasius: Introduction to the inorganic-chemical practical course , 14th edition, 1995

Individual evidence

1. ↑ Gerhart Jander, Karl Friedrich year, Jürgen Simon: Measure analysis: theory and practice of titrations with chemical and physical indications . 17th edition. De Gruyter, 2009, ISBN 978-3-11-019447-0 , pp. 142 .
2. ↑ Freddy Litten: Kasimir Fajans - short biography. March 8, 2004, accessed January 1, 2015 . 
3. ↑ Kasimir Fajans: Influence of the photochemical sensitivity of bromide silver by ion adsorption . In: Journal of Electrochemistry and Applied Physical Chemistry . tape 28 , no. 23-24 , December 1922, pp. 499-505 , doi : 10.1002 / bbpc.19220282305 .
4. ↑ Kasimir Fajans, O. Hassel: A new method for titration of silver and halogen ions with organic dye indicators . In: Journal of Electrochemistry and Applied Physical Chemistry . tape 29 , no. 19-20 , 1923, pp. 495-500 , doi : 10.1002 / bbpc.19230291909 .
5. ↑ Kasimir Fajans, H. Wolff: About the titration of silver and halogen ions with organic dye indicators . In: Journal of Inorganic and General Chemistry . tape 137 , no. 1 , 1924, p. 221-245 , doi : 10.1002 / zaac.19241370118 .
6. ↑ Kasimir Fajans: Newer Methods Of Volumetric Chemical Analysis . Ed .: Wilhelm Böttger. D. Van Nostrand Company, Inc., New York 1938, Part VII. Adsorption Indicators for Precipitation Titrations, p. 203–250 ( online at archive.org [accessed January 1, 2015]).
7. ^ Izaak Maurits Kolthoff: Adsorption Indicators . In: Chemical Reviews . tape 16 , no. 1 , February 1935, p. 87-98 , doi : 10.1021 / cr60053a008 .