Question

2. A solution that may contain Sn.Bi. Cu? and Cdions is treated with thioacetamide in an acidic medium. The black precipitate that forms is partly soluble in a strongly alkaline solution. The precipitate that remains is soluble in 6M HNO, and gives a blue solution when treated with excess NH Based on this information, which ions are present, which are absent, and which are still in doubt? Present Absent Snut Cu 2+ Bi 34 3. Explain how controlling the solution pH allows separation of Group II cations from those of Group III.

Answer 1

Ou- A solution that may contana su bil, Cut and Cd2+ ious is thated with the oacetamide an acidic medium the black ppt that fosus dis paulty soluble in a strongly alkaline solution . The ppt that remains selulele in 6M HNO₃ and ques a deep blue sol" when dieated with cucess NH₃. Sased on this information venich dois are present, nehich are alesent and weluch are still in doulet. The aclution may contain (det i 31, Su, cu 24 saules entita a t ata to Since to the question states that precipate formed is black in colour so the solution doesuust contain Cd as its se prepi pateite his of Yellow en colour. Now there is elos I doubt in Cu2+, sute 4 Bist. aa ou te Aloo shut wiforms yellow precipitate , vela but the ques say the precipitate y black so Sutt is also not them. 9 yellow ppt is formed which doesuot dissolue in (NH4)2long excess then it is Syut Now we are left with cult t 8i 31, The black ppt is partly soluble in stronglly alkaline solution : the rolulele pact ! contains Bi 31 or Cu 27. Now this in HNO2 followed by encess NHg tay.) forms blue solution. This confirms Сu 21 due to jounation of cu (NH3) 4 4

However in ou not performed er in question perdormed, so its the test presence ide for for Bizt is is in doulet Bi 31, the the test solution after being ay HNO3 treated fonus white gelatinous påt. then si st is present this on treatment ith soduum Staunite Chanes to black. so to Wolow absent dla Doubt lesent lotigong 6 at Bi 31 question watasaib Libbo a and whether leat was t o leuw done for this ) Cu 27 syut has not mentioned Cuplain how I sepuration is controlling the solution pH allows Group II Catious from those Аромош! Group I (lyzt, si 3+, (d?, Hg2+, As? * &b3 + , sutt) are very unsoluble sulfides in nature having ksp 10 so they can be precipitated easily even if 827 Lonc. is low, Air acidic solution provides low Conc. of s²-ious and only these sulphides are pucipitated .. Group in (Alst, G3t, fest, I2+, Ni24 Co2+, le 2 ay slighty soluble (Ksp more than 10 ) 4 need mores AO by increasing pH as lease is added, these I can be precipitated. fa

HS is weak acid so in presence of th strong and it dissociates less due to an Сош Мои Дом и еt , Has 24 va s2 - nevitostne ht u t w eile since cone of products (ht) increases of dissociation 9 ns is less as according to he Chateliars principle , equilibrium is towards left, 4 s² is less in come to only precipitate out group I ions hehen base is added dissociation of H₂S increases as the tt is neutralised and 'equilibrium shifts to right. 0 1