A student was given a sample of colourless solution containing three cations and was asked to identify the cations. Student carried out a series of reactions as given below.
(i) Precipitates ‘A’, ‘B’ and ‘C’ are respectively :
Text Solution
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(i) Sample 
Precipitate ‘A’ insoluble chloride (AgCl) + Filtrate (Ba 2+ and Zn 2+ )
ppt. ‘C’ insoluble hydroxide (Zn(OH) 2 ) 
Filtrate (Zn 2+ ) + ppt. ‘B’ insoluble sulphate (BaSO 4 )
Ag + + Cl – 
AgCl ↓ (white) ; 3AgCl + Na 3 AsO 3 
Ag 3 AsO 3 ↓ (yellow) + 3NaCl
Ba 2+ + SO 4 2 
BaSO 4 ↓ (white) ; Ba 2+ salts give apple green colour to the Bunsen flame.
Zn 2+ + 2NH 3 + 2H 2 O 
Zn(OH) 2 ↓ (white) + 2NH 4
Zn(OH) 2 ↓ + 4NH 4 
[Zn(NH 3 ) 4 ] 2+ + 2OH – (ii) AgCl + 2NH 3 
[Ag(NH 3 ) 2 ]Cl soluble complex
2M HCl is group reagent of 1
st group but in concentrated HCl, AgCl dissolves forming [AgCl 2 ] – complex
AgCl + 2CN – 
[Ag(CN) 2 ] – (soluble complex) + Cl –
AgCl + 2S 2 O 3 2– 
[Ag(S 2 O 3 ) 2 ] 3– (soluble complex) + Cl –
(iii) CoO . ZnO = Rinmann's green reagent used as green pigment.
BaSO 4 ↓ + H 2 SO 4 (conc.) 
Ba 2+ + HSO 4 –
2AgCl ↓ (white) 
2Ag ↓ (black) + Cl 2
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