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[td]==Methods==[/td] [td]===Volhard===[/td]
[td]===Volhard===[/td] [td]An example of [[back titration]], the Volhard method, named after [[Jacob Volhard]], involves the addition of excess silver nitrate to the analyte; the silver chloride is filtered, and the remaining silver nitrate is titrated against [[ammonium thiocyanate]],<ref name = yoder/> with [[ferric ammonium sulfate]] as an indicator which forms blood-red [[Thiocyanate#Test for iron.28III.29|[Fe(OH<sub>2</sub>)<sub>5</sub>(SCN)]<sup>2+</sup>]] at the end point:[/td]
[td]An example of [[back titration]], the Volhard method, named after [[Jacob Volhard]], involves the addition of excess silver nitrate to the analyte; the silver chloride is filtered, and the remaining silver nitrate is titrated against [[ammonium thiocyanate]],<ref name = yoder/><ref>{{Cite web |last=Rosanoff |first=M. A. |last2=Hill |first2=Arthur E. |date=2002-05-01 |title=A NECESSARY MODIFICATION OF VOLHARD'S METHOD FOR THE DETERMINATION OF CHLORIDES.1 |url=https://pubs.acs.org/doi/pdf/10.1021/ja01957a003 |access-date=2025-09-03 |website=ACS Publications |language=EN |doi=10.1021/ja01957a003}}</ref><ref>{{Cite journal |last=Schales |first=Otto |last2=Schales |first2=Selma S. |date=1941-09 |title=A SIMPLE AND ACCURATE METHOD FOR THE DETERMINATION OF CHLORIDE IN BIOLOGICAL FLUIDS |url=https://doi.org/10.1016/s0021-9258(18)72872-x |journal=Journal of Biological Chemistry |volume=140 |issue=3 |pages=879β884 |doi=10.1016/s0021-9258(18)72872-x |issn=0021-9258}}</ref> with [[ferric ammonium sulfate]] as an indicator which forms blood-red [[Thiocyanate#Test for iron.28III.29|[Fe(OH<sub>2</sub>)<sub>5</sub>(SCN)]<sup>2+</sup>]] at the end point:[/td] [td][/td]
[td][/td] [td]: Ag<sup>+</sup> (aq) + SCN<sup>β</sup> (aq) β AgSCN (s) (''K''<sub>sp</sub> = 1.16 Γ 10<sup>−12</sup>)[/td]
[td]: Ag<sup>+</sup> (aq) + SCN<sup>β</sup> (aq) β AgSCN (s) (''K''<sub>sp</sub> = 1.16 Γ 10<sup>−12</sup>)[/td] [td][/td]
[td][/td] [td]===Fajans===[/td]
[td]===Fajans===[/td] [td]In the Fajans method, named after [[Kazimierz Fajans]], typically [[dichlorofluorescein]] is used as an indicator; the end-point is marked by the green suspension turning pink. Prior to the end-point of the titration, chloride ions remain in excess. They adsorb on the AgCl surface, imparting a negative charge to the particles. Past the equivalence point, excess silver(I) ions adsorb on the AgCl surface, imparting a positive charge. Anionic dyes such as dichlorofluorescein are attracted to the particles, and undergo a colour change upon adsorption, representing the end-point. [[Eosin]] (tetrabromofluorescein) is suitable for titrating against [[bromide]], [[iodide]], and [[thiocyanate]] anions, giving a sharper end-point than dichlorofluorescein. It is not suitable for titrating against [[chloride]] anions because it binds to AgCl more strongly than [[chloride]] does.<ref>{{cite book |author=Harris, Daniel Charles |title=Quantitative chemical analysis |publisher=W.H. Freeman |location=San Francisco |year=2003 |pages=142β143 |isbn=0-7167-4464-3 | edition = 6th }}</ref>[/td]
[td]In the Fajans method, named after [[Kazimierz Fajans]], typically [[dichlorofluorescein]] or another absorption dye<ref>{{Cite journal |last=Deucher |first=Nayane Cristina |last2=Silva de Souza |first2=Roberto Jr. |last3=Borges |first3=Endler Marcel |date=2025-01-14 |title=Teaching Precipitation Titration Methods: a Statistical Comparison of Mohr, Fajans, and Volhard Techniques |url=https://doi.org/10.1021/acs.jchemed.4c01037 |journal=Journal of Chemical Education |volume=102 |issue=1 |pages=364β371 |doi=10.1021/acs.jchemed.4c01037 |issn=0021-9584}}</ref> is used as an indicator; the end-point is marked by the green suspension turning pink. Prior to the end-point of the titration, chloride ions remain in excess. They adsorb on the AgCl surface, imparting a negative charge to the particles. Past the equivalence point, excess silver(I) ions adsorb on the AgCl surface, imparting a positive charge. Anionic dyes such as dichlorofluorescein are attracted to the particles, and undergo a colour change upon adsorption, representing the end-point. [[Eosin]] (tetrabromofluorescein) is suitable for titrating against [[bromide]], [[iodide]], and [[thiocyanate]] anions, giving a sharper end-point than dichlorofluorescein. It is not suitable for titrating against [[chloride]] anions because it binds to AgCl more strongly than [[chloride]] does.<ref>{{cite book |author=Harris, Daniel Charles |title=Quantitative chemical analysis |publisher=W.H. Freeman |location=San Francisco |year=2003 |pages=142β143 |isbn=0-7167-4464-3 | edition = 6th }}</ref>[/td] [td][/td]
[td][/td] [td]==See also==[/td]
[td]==See also==[/td]
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[td]==Methods==[/td]Revision as of 01:31, 3 September 2025
[/td][td]==Methods==[/td] [td]===Volhard===[/td]
[td]===Volhard===[/td] [td]An example of [[back titration]], the Volhard method, named after [[Jacob Volhard]], involves the addition of excess silver nitrate to the analyte; the silver chloride is filtered, and the remaining silver nitrate is titrated against [[ammonium thiocyanate]],<ref name = yoder/> with [[ferric ammonium sulfate]] as an indicator which forms blood-red [[Thiocyanate#Test for iron.28III.29|[Fe(OH<sub>2</sub>)<sub>5</sub>(SCN)]<sup>2+</sup>]] at the end point:[/td]
[td]An example of [[back titration]], the Volhard method, named after [[Jacob Volhard]], involves the addition of excess silver nitrate to the analyte; the silver chloride is filtered, and the remaining silver nitrate is titrated against [[ammonium thiocyanate]],<ref name = yoder/><ref>{{Cite web |last=Rosanoff |first=M. A. |last2=Hill |first2=Arthur E. |date=2002-05-01 |title=A NECESSARY MODIFICATION OF VOLHARD'S METHOD FOR THE DETERMINATION OF CHLORIDES.1 |url=https://pubs.acs.org/doi/pdf/10.1021/ja01957a003 |access-date=2025-09-03 |website=ACS Publications |language=EN |doi=10.1021/ja01957a003}}</ref><ref>{{Cite journal |last=Schales |first=Otto |last2=Schales |first2=Selma S. |date=1941-09 |title=A SIMPLE AND ACCURATE METHOD FOR THE DETERMINATION OF CHLORIDE IN BIOLOGICAL FLUIDS |url=https://doi.org/10.1016/s0021-9258(18)72872-x |journal=Journal of Biological Chemistry |volume=140 |issue=3 |pages=879β884 |doi=10.1016/s0021-9258(18)72872-x |issn=0021-9258}}</ref> with [[ferric ammonium sulfate]] as an indicator which forms blood-red [[Thiocyanate#Test for iron.28III.29|[Fe(OH<sub>2</sub>)<sub>5</sub>(SCN)]<sup>2+</sup>]] at the end point:[/td] [td][/td]
[td][/td] [td]: Ag<sup>+</sup> (aq) + SCN<sup>β</sup> (aq) β AgSCN (s) (''K''<sub>sp</sub> = 1.16 Γ 10<sup>−12</sup>)[/td]
[td]: Ag<sup>+</sup> (aq) + SCN<sup>β</sup> (aq) β AgSCN (s) (''K''<sub>sp</sub> = 1.16 Γ 10<sup>−12</sup>)[/td] [td][/td]
[td][/td] [td]===Fajans===[/td]
[td]===Fajans===[/td] [td]In the Fajans method, named after [[Kazimierz Fajans]], typically [[dichlorofluorescein]] is used as an indicator; the end-point is marked by the green suspension turning pink. Prior to the end-point of the titration, chloride ions remain in excess. They adsorb on the AgCl surface, imparting a negative charge to the particles. Past the equivalence point, excess silver(I) ions adsorb on the AgCl surface, imparting a positive charge. Anionic dyes such as dichlorofluorescein are attracted to the particles, and undergo a colour change upon adsorption, representing the end-point. [[Eosin]] (tetrabromofluorescein) is suitable for titrating against [[bromide]], [[iodide]], and [[thiocyanate]] anions, giving a sharper end-point than dichlorofluorescein. It is not suitable for titrating against [[chloride]] anions because it binds to AgCl more strongly than [[chloride]] does.<ref>{{cite book |author=Harris, Daniel Charles |title=Quantitative chemical analysis |publisher=W.H. Freeman |location=San Francisco |year=2003 |pages=142β143 |isbn=0-7167-4464-3 | edition = 6th }}</ref>[/td]
[td]In the Fajans method, named after [[Kazimierz Fajans]], typically [[dichlorofluorescein]] or another absorption dye<ref>{{Cite journal |last=Deucher |first=Nayane Cristina |last2=Silva de Souza |first2=Roberto Jr. |last3=Borges |first3=Endler Marcel |date=2025-01-14 |title=Teaching Precipitation Titration Methods: a Statistical Comparison of Mohr, Fajans, and Volhard Techniques |url=https://doi.org/10.1021/acs.jchemed.4c01037 |journal=Journal of Chemical Education |volume=102 |issue=1 |pages=364β371 |doi=10.1021/acs.jchemed.4c01037 |issn=0021-9584}}</ref> is used as an indicator; the end-point is marked by the green suspension turning pink. Prior to the end-point of the titration, chloride ions remain in excess. They adsorb on the AgCl surface, imparting a negative charge to the particles. Past the equivalence point, excess silver(I) ions adsorb on the AgCl surface, imparting a positive charge. Anionic dyes such as dichlorofluorescein are attracted to the particles, and undergo a colour change upon adsorption, representing the end-point. [[Eosin]] (tetrabromofluorescein) is suitable for titrating against [[bromide]], [[iodide]], and [[thiocyanate]] anions, giving a sharper end-point than dichlorofluorescein. It is not suitable for titrating against [[chloride]] anions because it binds to AgCl more strongly than [[chloride]] does.<ref>{{cite book |author=Harris, Daniel Charles |title=Quantitative chemical analysis |publisher=W.H. Freeman |location=San Francisco |year=2003 |pages=142β143 |isbn=0-7167-4464-3 | edition = 6th }}</ref>[/td] [td][/td]
[td][/td] [td]==See also==[/td]
[td]==See also==[/td]
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