Explanation
The chronyl chloride test entrails heating a sample suspected of containing chloride with potassium dichromate and concentrated H2SO4. If chloride is present, chromyl chloride is formed and red fumes of CrO2Cl2 are evident. This chromyl chloride upon treating with NaOH followed by lead accetate gives lead chromate (PbCrO4) which is a yellow colored PPt. K2Cr2O7 + 4NaCl + 6H2SO4 →2Cr2O2Cl2↑ + 2KHSO2+4NaHSO4+3H2O
CrO2Cl2 + 4NaOH →2NaCl + Na2Cr2O4+2H2O (red fumes)
Na2CrO4+(CH3COO)2Pb →2CH3COONa+PbCrO4 (lead chromate)
When a freshly prepared acidified solution of ferrous sulphate is added to a solution of nitrate ions, in the presence of conc. H2SO4, a deep brown ring is formed. This deep brown ring is due to the formation of the complex sphere [(FeCH2O)5NO]SO4. i.e. Ferrous nitrosulphate.
Black precipitate will form in many metal ions due to the presence of sulphide ion (S2- ) ion.
Zn2+ will give zinc sulphide, upon treating with ammonical H2S. i.e. Zn2+ +H2S →Zns + 2H+ where as Al3+ and Fe3+ from respective hydroxide and Mg2+ from respective bicarbonate upon treating with ammonical H2S.
Fe3+ in Fe(OH)3 does not easily form a comparable ions. Hence Fe(OH)3 is insoluble in excess sodium hydroxide solution.
In the Complex, [Fe (H2O)5NO]SO4,
NO:11 electrons = σ1(2e-) σ2*(2e-) π1(4e-) σ3(2e-) π2*(1e-) σ4*(0e-)
NO is radial. For oxidation state purposes it is removed from a complex in a closed shell configuration as [NO]+. Because the [Fe(H2O)5NO]2+ complex ion has an overall two +ve charge, the central atom Fe is Fe(1). Thus the univalent character of atom in the complex is justified by the presence of a coordinated NO+ group.
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