Question

At what stage interfering radicles interfere

Answer 1

What are the interfering radicals? How do they interfere in systematic separation of cationic radicals? Why is it necessary to remove them before IIIrd gr analysis? Why don't they interfere in Ist or IInd group analysis? Interfering radicals are oxalate, tartrate, fluoride, borate and phosphate and they are anionic radicals. They form complex with IIIrd gr group reagent ammonium chloride and ammonium hydroxide. This leads to incomplete precipitation of IIIrd group cations and causes immature precipitation of IVth and Vth group cations in alkaline medium. Let’s try to understand it.

Oxalate, tartrate, fluoride, borate, silicate and phosphate of the metals are soluble in acidic medium. 


If you remember, for 1stand 2nd analysis medium remain acidic (dilute HCl) that’s why they do not interfere then. But for 3rd group analysis the medium becomes alkaline by group reagents ammonium chloride and ammonium sulphide. Here interfering radicals come into action and disturb the solubility product of cations which causes their premature or incomplete precipitation