Category : JEE Main & Advanced
Group I : When dil. HCl is added to original solution, insoluble chlorides of lead, silver mercurous mercury are precipitated.
\[Pb{{(N{{H}_{3}})}_{2}}+2HCl\xrightarrow[\,]{}PbC{{l}_{2}}+2HN{{O}_{3}}\];
\[AgN{{O}_{3}}+HCl\xrightarrow{\,}AgCl+HN{{O}_{3}}\]
\[Hg{{(N{{O}_{3}})}_{2}}+2HCl\xrightarrow{\,}HgC{{l}_{2}}+2HN{{O}_{3}}\]
\[\mathbf{P}{{\mathbf{b}}^{\mathbf{2+}}}\](lead)
(i) \[PbC{{l}_{2}}\]is soluble in hot water and on cooling white crystals are again formed.
(ii) The solution of \[PbC{{l}_{2}}\] gives a yellow precipitate with potassium chromate solution which is insoluble in acetic acid but soluble in sodium hydroxide.
\[PbC{{l}_{2}}+{{K}_{2}}Cr{{O}_{4}}\xrightarrow{\,}\underset{\text{yellow ppt}\text{.}}{\mathop{PbCr{{O}_{4}}}}\,+2KCl\];
\[PbCr{{O}_{4}}+4NaOH\xrightarrow{\,}N{{a}_{2}}Pb{{O}_{2}}+N{{a}_{2}}Cr{{O}_{4}}+2{{H}_{2}}O\]
(iii) The solution of \[PbC{{l}_{2}}\]forms a yellow precipitate with potassium iodide solution.
\[PbC{{l}_{2}}+2KI\xrightarrow{\,}\underset{\text{Yellow}\,\,\text{ppt}.}{\mathop{Pb{{I}_{2}}}}\,+2KCl\]
(iv) White precipitate of lead sulphate is formed with dilute \[{{H}_{2}}S{{O}_{4}}.\] The precipitate is soluble in ammonium acetate,
\[PbC{{l}_{2}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{\,}PbS{{O}_{4}}+\,2HCl\];
\[PbS{{O}_{4}}+2C{{H}_{3}}COON{{H}_{4}}\xrightarrow{\,}Pb{{(C{{H}_{3}}COO)}_{2}}+{{(N{{H}_{4}})}_{2}}S{{O}_{4}}\]
\[A{{g}^{+}}\](silver)
(i) \[AgCl\] dissolves in ammonium hydroxide, \[AgCl+2N{{H}_{4}}OH\xrightarrow{\,}\underset{\text{chloride}}{\mathop{\underset{\text{Diammine silver (I)}}{\mathop{Ag{{(N{{H}_{3}})}_{2}}Cl+2{{H}_{2}}O}}\,}}\,\]
(ii) On adding dilute \[HN{{O}_{3}}\] to the above solution, white precipitate is again obtained
\[\begin{align} & Ag{{(N{{H}_{3}})}_{2}}Cl+2HN{{O}_{3}}\xrightarrow{\,}AgCl+2N{{H}_{4}}N{{O}_{3}} \\ & ,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{White ppt}\text{.} \\ \end{align}\]
(iii) On adding KI to the complex solution, yellow precipitate is obtained.
\[Ag{{(N{{H}_{3}})}_{2}}Cl+KI\xrightarrow{\,}AgI+KCl+2N{{H}_{3}}\]
\[\mathbf{Hg}_{\mathbf{2}}^{\mathbf{2+}}\](mercurous)
(i) \[H{{g}_{2}}C{{l}_{2}}\] turns black with \[N{{H}_{4}}OH\], \[H{{g}_{2}}C{{l}_{2}}+2N{{H}_{4}}OH\xrightarrow{{}}\underbrace{Hg+Hg(N{{H}_{2}})Cl}_{\text{Black}}+N{{H}_{4}}Cl+2{{H}_{2}}O\]
(ii) The black residue dissolves in aqua-regia forming mercuric chloride.
\[3HCl+HN{{O}_{3}}\xrightarrow{\,}NOCl+2{{H}_{2}}O+2Cl\]
\[2Hg(N{{H}_{2}})Cl+6Cl\xrightarrow{\,}2HgC{{l}_{2}}+4HCl+{{N}_{2}}\]
\[Hg+2Cl\xrightarrow{\,}HgC{{l}_{2}}\]
(iii) The solution of \[HgC{{l}_{2}}\] forms white or slate-coloured precipitate with stannous chloride.
\[2HgC{{l}_{2}}+SnC{{l}_{2}}\xrightarrow{\,}\underset{\text{white ppt}\text{.}}{\mathop{H{{g}_{2}}C{{l}_{2}}}}\,+SnC{{l}_{4}}\]
\[H{{g}_{2}}C{{l}_{2}}+SnC{{l}_{2}}\xrightarrow{\,}\underset{\text{Grey ppt}\text{.}}{\mathop{2Hg}}\,+SnC{{l}_{4}}\]
(iv) The solution of \[HgC{{l}_{2}}\] with copper turning forms a grey deposit.
\[HgC{{l}_{2}}+Cu\xrightarrow{\,}\underset{\text{Grey}\,\text{ppt}\text{.}}{\mathop{Hg}}\,+CuC{{l}_{2}}\]
Group II : When hydrogen sulphide is passed in acidified solution, the radicals of second group are precipitated as sulphides. The precipitate is treated with yellow ammonium sulphide. The sulphides of IIB are first oxidised to higher sulphides which then dissolve to form thio-compounds.
\[A{{g}_{2}}{{S}_{3}}+2{{(N{{H}_{4}})}_{2}}{{S}_{2}}\xrightarrow{\,}2{{(N{{H}_{4}})}_{2}}S+A{{s}_{2}}{{S}_{5}}\]
\[S{{b}_{2}}{{S}_{3}}+2{{(N{{H}_{4}})}_{2}}{{S}_{2}}\xrightarrow{\,}2{{(N{{H}_{4}})}_{2}}S+S{{b}_{2}}{{S}_{5}}\]
\[SnS+{{(N{{H}_{4}})}_{2}}{{S}_{2}}\xrightarrow{\,}{{(N{{H}_{4}})}_{2}}S+Sn{{S}_{2}}\]
\[A{{s}_{2}}{{S}_{5}}+3(N{{H}_{4}})S\xrightarrow{{}}\underset{\text{thioarsenate}}{\mathop{\underset{\text{Ammonium}}{\mathop{2{{(N{{H}_{4}})}_{3}}As{{S}_{4}}}}\,}}\,\]
\[S{{b}_{2}}{{S}_{5}}+3{{(N{{H}_{4}})}_{2}}S\xrightarrow{{}}\underset{\text{thioantimonate}}{\mathop{\underset{\text{Ammonium}}{\mathop{2{{(N{{H}_{4}})}_{2}}Sb{{S}_{4}}}}\,}}\,\]
\[Sn{{S}_{2}}+{{(N{{H}_{4}})}_{2}}S\xrightarrow{{}}\underset{\text{thiostannate}}{\mathop{\underset{\text{Ammonium}}{\mathop{{{(N{{H}_{4}})}_{2}}Sn{{S}_{3}}}}\,}}\,\]
All the three are soluble.
In case, the precipitate does not dissolve in yellow ammonium sulphide, it may be either \[HgS\] or \[PbS\] or \[B{{i}_{2}}{{S}_{3}}\] or \[CuS\]or \[CdS.\] The precipitate is heated with dilute \[HN{{O}_{3}}.\] Except \[HgS\], all other sulphides of \[IIA\] are soluble.
\[3PbS+8HN{{O}_{3}}\to 3Pb{{(N{{O}_{3}})}_{2}}+2NO+3S+4{{H}_{2}}O\]
\[B{{i}_{2}}{{S}_{3}}+8HN{{O}_{3}}\to 2Bi{{(N{{O}_{3}})}_{3}}+2NO+3S+4{{H}_{2}}O\]
\[3CuS+8HN{{O}_{3}}\to 3Cu{{(N{{O}_{3}})}_{2}}+2NO+3S+4{{H}_{2}}O\]
\[3CdS+8HN{{O}_{3}}\to 3Cd{{(N{{O}_{3}})}_{2}}+2NO+3S+4{{H}_{2}}O\]
\[\mathbf{H}{{\mathbf{g}}^{\mathbf{+}}}\](mercuric)
\[HgS\] is dissolved in aqua-regia,
\[3HgS+2HN{{O}_{3}}+6HCl\to 3HgC{{l}_{2}}+3S+2NO+4{{H}_{2}}O\]
The solution is divided into two parts:
Part I : Stannous chloride solution reduces \[HgC{{l}_{2}}\] first into white \[H{{g}_{2}}C{{l}_{2}}\] and then to grey metallic mercury.
Part II : Copper displaces \[Hg\] from \[HgC{{l}_{2}}\] which gets coated on copper turnings as a shining deposit.
\[\mathbf{P}{{\mathbf{b}}^{\mathbf{2+}}}\](lead)
In case the sulphide dissolves in dilute \[HN{{O}_{3}},\] a small part of the solution is taken. Dilute \[{{H}_{2}}S{{O}_{4}}\] is added. If lead is present, a white precipitate of lead sulphate appears, \[Pb{{(N{{O}_{3}})}_{2}}+{{H}_{2}}S{{O}_{4}}\to \underset{\text{(White ppt}\text{.)}\,\,\,\,\,}{\mathop{PbS{{O}_{4}}+}}\,2HN{{O}_{3}}\]
In absence of lead, the remaining solution is made alkaline by the addition of excess of \[N{{H}_{4}}OH.\] Bismuth forms a white precipitat of \[Bi{{(OH)}_{3}},\] copper forms a deep blue coloured solution while cadmium forms a colourless soluble complex,
\[\begin{align}& Bi{{(N{{O}_{3}})}_{3}}+3N{{H}_{4}}OH\xrightarrow{}Bi{{(OH)}_{3}}+3N{{H}_{4}}N{{O}_{3}} \\ & \text{ White ppt}\text{.} \\ \end{align}\]
\[\begin{align} & Cu{{(N{{O}_{3}})}_{2}}+4N{{H}_{4}}OH\xrightarrow{\,}[Cu{{(N{{H}_{3}})}_{4}}]\,{{(N{{O}_{3}})}_{2}}+4{{H}_{2}}O; \\ & \text{ Tetrammine cupric nitrate} \\ & \text{ (deep blue solution)} \\ \end{align}\]
\[\begin{align} & Cd{{(N{{O}_{3}})}_{2}}+4N{{H}_{4}}OH\xrightarrow{\,}[Cd\,{{(N{{H}_{3}})}_{4}}]\,{{(N{{O}_{3}})}_{2}}+4{{H}_{2}}O \\ & \text{ Tetrammine cadmium nitrate} \\ & \text{ (colourless solution)} \\ \end{align}\]
\[\mathbf{B}{{\mathbf{i}}^{\mathbf{3+}}}\](bismuth) : The precipitate dissolves in dilute HCl, \[Bi\,{{(OH)}_{3}}+3HCl\xrightarrow{\,}BiC{{l}_{3}}+3{{H}_{2}}O\]
Part I : Addition of excess of water to \[BiC{{l}_{3}}\] solution gives a white precipitate due to hydrolysis.
\[\begin{align} & BiC{{l}_{3}}+{{H}_{2}}O\xrightarrow{\,}BiOCl+2HCl \\ & \text{ Bismuth Oxychloride (White ppt}\text{.)} \\ \end{align}\]
Part II : The solution of \[BiC{{l}_{3}}\] is treated with sodium stannite when a black precipitate of metallic bismuth is formed,
\[2BiC{{l}_{3}}+\underset{\text{Sod}\text{. stannite}}{\mathop{3N{{a}_{2}}Sn{{O}_{2}}}}\,+6NaOH\xrightarrow{\,}\]\[\underset{\text{Sod}\text{. stannate}}{\mathop{3N{{a}_{2}}Sn{{O}_{3}}}}\,+2Bi+6NaCl+3{{H}_{2}}O\]
\[\mathbf{C}{{\mathbf{u}}^{\mathbf{2+}}}\](copper) : Blue coloured solution is acidified with acetic acid. When potassium ferrocyanide is added a chocolate coloured precipitate is formed,
\[Cu{{(N{{H}_{3}})}_{4}}{{(N{{O}_{3}})}_{2}}+4C{{H}_{3}}COOH\xrightarrow{\,}\]\[Cu{{(N{{O}_{3}})}_{2}}+4C{{H}_{4}}COON{{H}_{4}}\]
\[\begin{align} & 2Cu{{(N{{O}_{3}})}_{2}}+{{K}_{4}}[Fe{{(CN)}_{6}}]\xrightarrow{\,}C{{u}_{2}}[Fe{{(CN)}_{6}}+4KN{{O}_{3}} \\ & \text{ Chocolate ppt}\text{.}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{ } \\ \end{align}\]
\[\mathbf{C}{{\mathbf{d}}^{\mathbf{2+}}}\] (cadmium) : \[{{H}_{2}}S\] is passed through colourless solution. The appearance of yellow precipitate confirms the presence of cadmium,
\[Cd\,{{(N{{H}_{3}})}_{4}}{{(N{{O}_{3}})}_{2}}+{{H}_{2}}S\xrightarrow{\,}\underset{\text{Yellow ppt}\text{.}}{\mathop{CdS+2N{{H}_{4}}N{{O}_{3}}}}\,+N{{H}_{3}}\]
Group IIB : In case the precipitate dissolves in yellow ammonium sulphide, the tests of the radicals arsenic, antimony and tin are performed. The sulphide is treated with concentrated hydrochloric acid. Antimony and tin sulphide dissolve while arsenic sulphide remains insoluble.
\[\mathbf{A}{{\mathbf{s}}^{\mathbf{3+}}}\] (arsenic) : The insoluble sulphide is treated with concentrated nitric acid which is then heated with ammonium molybdate. Yellow precipitate of ammonium arsenomolybdate is formed.
\[A{{s}_{2}}{{S}_{5}}+10HN{{O}_{3}}\xrightarrow{\,}\underset{\text{Arsenic acid}\ \ \ \ \ \ \ \ \ \ \text{ }}{\mathop{2{{H}_{3}}As{{O}_{4}}+10N{{O}_{2}}+2{{H}_{2}}O+5S}}\,\]
\[{{H}_{3}}As{{O}_{4}}+12{{(N{{H}_{4}})}_{2}}Mo{{O}_{4}}+21HN{{O}_{3}}\xrightarrow{\,}\]\[\underset{\text{Yellow ppt}\text{.}}{\mathop{{{(N{{H}_{4}})}_{3}}As{{O}_{4}}}}\,.\,\,12Mo{{O}_{3}}+21N{{H}_{4}}N{{O}_{3}}+12{{H}_{2}}O\]
\[\mathbf{S}{{\mathbf{n}}^{\mathbf{2+}}}\] or \[\mathbf{S}{{\mathbf{n}}^{\mathbf{4+}}}\] (tin) : Solution of sulphide in concentrated HCl is reduced with iron fillings or granulated zinc.
\[Sn{{S}_{2}}+4HCl\xrightarrow{\,}\underset{\text{White ppt}\text{.}}{\mathop{SnC{{l}_{4}}2{{H}_{2}}S}}\,\]
\[SnC{{l}_{4}}+Fe\xrightarrow{}\underset{\text{Grey}}{\mathop{SnC{{l}_{2}}}}\,+FeC{{l}_{4}}\]
\[HgC{{l}_{2}}\] solution is added to above solution which gives first a white precipitate that turns to grey.
\[\begin{align} & 2HgC{{l}_{2}}+SnC{{l}_{2}}\xrightarrow{\,}HgC{{l}_{2}}+SnC{{l}_{4}} \\ & \text{ White ppt}\text{.} \\ \end{align}\]
\[\begin{align} H{{g}_{2}}C{{l}_{2}}+SnC{{l}_{ 2}}\xrightarrow{\,}2Hg+SnC{{l}_{4}} \\ \text{ Grey} \\ \end{align}\]
\[\mathbf{S}{{\mathbf{b}}^{\mathbf{2+}}}\](antimony) : Filtrate of sulphide in concentrated HCl is divided into two parts.
Part I : On dilution with excess of water, a white precipitate of antimony oxychloride is obtained.
\[SbC{{l}_{3}}+{{H}_{2}}O\xrightarrow{\,}\underset{\text{White ppt}\text{. }\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{SbOCl+2HCl}}\,\]
Part II : \[{{H}_{2}}S\] is circulated. Orange precipitate is formed, \[2SbC{{l}_{3}}+3{{H}_{2}}S\xrightarrow{\,}\underset{\text{Orange ppt}\text{.}}{\mathop{S{{b}_{2}}{{S}_{3}}}}\,+6HCl\]
Group III : Hydroxides are precipitated on addition of excess of ammonium hydroxide in presence of ammonium chloride.
\[AlC{{l}_{3}}+3N{{H}_{4}}OH\xrightarrow{\,}\underset{\text{ Gelatinous ppt}\text{.}}{\mathop{Al{{(OH)}_{3}}}}\,+3N{{H}_{4}}Cl\]
\[CrC{{l}_{3}}+3N{{H}_{4}}OH\xrightarrow{}\underset{\text{Green ppt}\text{.}}{\mathop{Cr{{(OH)}_{3}}}}\,+3N{{H}_{4}}Cl\]
\[FeC{{l}_{3}}+3N{{H}_{4}}OH\xrightarrow{}\underset{\text{Brownish red ppt}\text{.}}{\mathop{Fe{{(OH)}_{3}}}}\,+3N{{H}_{4}}Cl\]
\[\mathbf{F}{{\mathbf{e}}^{\mathbf{3+}}}\] (iron) : The brownish red precipitate dissolves in dilute HCl. The solution is divided into two parts.
Part I :\[{{K}_{4}}\,[Fe{{(CN)}_{6}}]\] solution is added which forms deep blue solution or precipitate.
\[Fe{{(OH)}_{3}}+3HCl\xrightarrow{\,}FeC{{l}_{3}}+3{{H}_{2}}O\]
\[4FeC{{l}_{3}}+3{{K}_{4}}[Fe{{(CN)}_{6}}]\xrightarrow{\,}\underset{\text{Prussian blue}}{\mathop{F{{e}_{4}}{{[Fe{{(CN)}_{6}}]}_{3}}}}\,+12KCl\]
Part II : Addition of potassium thiocyanate solution gives a blood red colouration.
\[FeC{{l}_{3}}+3KCNS\xrightarrow{\,}\underset{\text{Blood red colour}}{\mathop{Fe{{(CNS)}_{3}}}}\,+3KCl\]
\[\mathbf{C}{{\mathbf{r}}^{\mathbf{3+}}}\](chromium) : The green precipitate is fused with fusion mixture \[(N{{a}_{2}}C{{O}_{3}}+KN{{O}_{3}}).\]The fused product is extracted with water or the precipitate is heated with \[NaOH\] and bromine water.
\[2Cr{{(OH)}_{3}}+3KNO+2N{{a}_{2}}C{{O}_{3}}\xrightarrow{}\]\[2N{{a}_{2}}Cr{{O}_{4}}+3KN{{O}_{2}}+2C{{O}_{2}}+3{{H}_{2}}O\]
or \[2NaOH+B{{r}_{2}}\xrightarrow{\,}NaBr{{O}_{4}}+NaBr+{{H}_{2}}O\]
\[NaBrO\xrightarrow{\,}NaBr+[O]\]
\[2Cr{{(OH)}_{3}}+4NaOH+3[O]\]\[\xrightarrow{\,}2NaCr{{O}_{4}}+5{{H}_{2}}O\]
The solution thus obtained contains sodium chromate. The solution is acidified with acetic acid and treated with lead acetate solution. A yellow precipitate appears.
\[N{{a}_{2}}Cr{{O}_{4}}+Pb{{(C{{H}_{3}}COO)}_{2}}\xrightarrow{\,}\underset{\text{Yellow ppt}\text{.}}{\mathop{PbCr{{O}_{4}}}}\,+2C{{H}_{3}}COONa\]
\[\mathbf{A}{{\mathbf{l}}^{\mathbf{3+}}}\](aluminium) : The gelatinous precipitate dissolves in \[NaOH\], \[Al{{(OH)}_{3}}+NaOH\xrightarrow{\,}\underset{\text{Soluble}}{\mathop{NaAl{{O}_{2}}}}\,+2{{H}_{2}}O\]
The solution is boiled with ammonium chloride when \[Al{{(OH)}_{3}}\] is again formed.
\[NaAl{{O}_{2}}+N{{H}_{4}}Cl+{{H}_{2}}O\xrightarrow{\,}Al{{(OH)}_{3}}+NaCl+N{{H}_{3}}\]
Group IV : On passing \[{{H}_{2}}S\] through the filtrate of the third group, sulphides of fourth group are precipitated. NiS and CoS are black and insoluble in concentrated HCl while MnS (buff coloured), ZnS (colourless) are soluble in conc. HCl.
\[\mathbf{Z}{{\mathbf{n}}^{\mathbf{2+}}}\] (zinc) : The sulphide dissolves in HCl. \[ZnS+2HCl\xrightarrow{\,}ZnC{{l}_{2}}+{{H}_{2}}S\]
When the solution is treated with \[NaOH,\] first a white precipitate appears which dissolves in excess of \[NaOH\]
\[ZnC{{l}_{2}}+2NaOH\xrightarrow{}\underset{\text{White ppt}\text{.}}{\mathop{Zn{{(OH)}_{2}}}}\,+2NaCl\]
\[Zn{{(OH)}_{2}}+2NaOH\xrightarrow{\,}\underset{\text{(Soluble)}}{\mathop{N{{a}_{2}}Zn{{O}_{2}}}}\,+2{{H}_{2}}O\]
On passing \[{{H}_{2}}S\], white precipitate of zinc sulphide is formed \[N{{a}_{2}}Zn{{O}_{2}}+{{H}_{2}}S\xrightarrow{\,}\underset{\text{White ppt}\text{.}}{\mathop{ZnS}}\,+2NaOH\]
\[\mathbf{M}{{\mathbf{n}}^{\mathbf{2+}}}\](manganese) : Manganese sulphide dissolves in HCl \[MnS+2HCl\xrightarrow{\,}MnC{{l}_{2}}+{{H}_{2}}S\]
On heating the solution with \[NaOH\] and \[B{{r}_{2}}\]-water, manganese dissolve gets precipitated.
\[MnC{{l}_{2}}+2NaOH\xrightarrow{}Mn{{(OH)}_{2}}+2NaCl\]
\[Mn{{(OH)}_{2}}+O\xrightarrow{}Mn{{O}_{2}}{{H}_{2}}O\]
The precipitate is treated with excess of nitric acid and \[Pb{{O}_{2}}\] or \[P{{b}_{3}}{{O}_{4}}\] (red lead). The contents are heated. The formation of permanganic acid imparts pink colour to the supernatant liquid.
\[2Mn{{O}_{2}}+4HN{{O}_{3}}\xrightarrow{\,}2Mn{{(N{{O}_{3}})}_{2}}\]\[+2{{H}_{2}}O+{{O}_{2}}\]
\[2Mn{{(N{{O}_{3}})}_{2}}+5P{{b}_{3}}{{O}_{4}}+26HN{{O}_{3}}\xrightarrow{\,}\]\[\underset{\text{Permanganic acid (pink)}}{\mathop{2HMn{{O}_{4}}+15\,Pb {{(N{{O}_{3}})}_{2}}+12\,{{H}_{2}}O}}\,\]
The above test fails in presence of HCl.
\[\mathbf{N}{{\mathbf{i}}^{\mathbf{2+}}}\] (nickel) and \[\mathbf{C}{{\mathbf{o}}^{\mathbf{2+}}}\] (cobalt)
The black precipitate is dissolved in aqua- regia.
\[3NiS+6HCl+2HN{{O}_{3}}\xrightarrow{}2NiC{{l}_{2}}+2NO+3S+2{{H}_{2}}O\]
\[3CoS+6HCl+2HN{{O}_{3}}\xrightarrow{}3CoC{{l}_{2}}+2NO+3S+4{{H}_{2}}O\]
The solution is evaporated to dryness and residue extracted with dilute HCl. It is divided into three parts.
Part I : Add \[N{{H}_{4}}OH\] (excess) and dimethyl glyoxime. A rosy red precipitate appears, if nickel is present,
Part II : Add \[C{{H}_{3}}COOH\] in excess and \[KN{{O}_{2}}.\] The appearance of yellow precipite confirms the presence of cobalt.
\[KN{{O}_{2}}+C{{H}_{3}}COOH\xrightarrow{\,}C{{H}_{3}}COOK+HN{{O}_{2}}\]
\[CoC{{l}_{2}}+2KN{{O}_{2}}\xrightarrow{\,}Co{{(N{{O}_{2}})}_{2}}+2KCl\]
\[Co{{(N{{O}_{2}})}_{2}}+2HN{{O}_{2}}\xrightarrow{\,}Co{{(N{{O}_{2}})}_{3}}+NO+{{H}_{2}}O\]
\[Co{{(N{{O}_{2}})}_{3}}+3KN{{O}_{2}}\xrightarrow{\,}{{K}_{3}}[Co{{(N{{O}_{2}})}_{6}}]\]
Part III : Solution containing either nickel or cobalt is treated with \[NaHC{{O}_{3}}\] and bromine water. Appearance of apple green colour is observed, the solution is heated when black precipited is formed, which shows the presence of nickel,
\[CoC{{l}_{2}}+2NaHC{{O}_{3}}\xrightarrow{}Co{{(HC{{O}_{3}})}_{2}}+2NaCl\]
\[Co{{(HC{{O}_{3}})}_{2}}+4NaHC{{O}_{3}}\xrightarrow{\,}N{{a}_{4}}Co{{(C{{O}_{3}})}_{3}}+3{{H}_{2}}O+3C{{O}_{2}}\]
\[B{{r}_{2}}+{{H}_{2}}O\xrightarrow{\,}2HBr+O\]
\[2N{{a}_{4}}Co{{(C{{O}_{3}})}_{3}}+{{H}_{2}}O+O\xrightarrow{\,}\underset{\begin{smallmatrix} \text{sod}\text{. cobalti carbonate} \\ \text{(Green colouration)} \end{smallmatrix}}{\mathop{2N{{a}_{3}}Co{{(C{{O}_{3}})}_{3}}}}\,+2NaOH\]
\[NiC{{l}_{2}}+2NaHC{{O}_{3}}\xrightarrow{}NiC{{O}_{3}}+2NaCl+{{H}_{2}}O+C{{O}_{2}}\]
\[2NiC{{O}_{3}}+[O]\xrightarrow{{}}\underset{\text{(Black)}}{\mathop{N{{i}_{2}}{{O}_{3}}}}\,+2C{{O}_{2}}\text{ }\]
Group V : Ammonium carbonate precipitates V group radicals in the form of carbonates are soluble in acetic acid.
\[BaC{{O}_{3}}+2C{{H}_{3}}COOH\xrightarrow{\,}{{(C{{H}_{3}}COO)}_{2}}Ba+C{{O}_{2}}+{{H}_{2}}O\]
\[SrC{{O}_{3}}+2C{{H}_{3}}COOH\xrightarrow{\,}{{(C{{H}_{3}}COO)}_{2}}Sr+C{{O}_{2}}+{{H}_{2}}O\]
\[CaC{{O}_{3}}+2C{{H}_{3}}COOH\xrightarrow{\,}{{(C{{H}_{3}}COO)}_{2}}Ca+C{{O}_{2}}+{{H}_{2}}O\]
\[\mathbf{B}{{\mathbf{a}}^{\mathbf{2+}}}\] (barium) : Barium chromate is insoluble and precipitated by the addition of potassium chromate solution, \[Ba{{(C{{H}_{3}}COO)}_{2}}+{{K}_{2}}Cr{{O}_{4}}\xrightarrow{}BaCr{{O}_{4}}+2C{{H}_{3}}COOK\]
\[\mathbf{S}{{\mathbf{r}}^{\mathbf{2+}}}\] (Strontium) : Strontium sulphate is insoluble and precipitated by the addition of ammonium sulphate solution, \[Sr{{(C{{H}_{3}}COO)}_{2}}+{{(N{{H}_{4}})}_{2}}S{{O}_{4}}\xrightarrow{\,}\underset{\text{White ppt}\text{.}}{\mathop{SrS{{O}_{4}}}}\,+2C{{H}_{3}}COON{{H}_{4}}\]
\[\mathbf{C}{{\mathbf{a}}^{\mathbf{2+}}}\] (calcium) : Calcium oxalate is insoluble and precipitated by the addition of ammonium oxalate.
\[Ca{{(C{{H}_{3}}COO)}_{2}}+{{(N{{H}_{4}})}_{2}}{{C}_{2}}{{O}_{4}}\xrightarrow{\,}\underset{\text{White ppt}\text{.}}{\mathop{Ca{{C}_{2}}{{O}_{4}}}}\,+2C{{H}_{3}}COON{{H}_{4}}\]
Group VI : In the filtrate of V group, some quantity of ammonium oxalate is added as to remove \[Ba,Ca\] and \[Sr\] completely from the solution. The clear solution is concentrated and made alkaline with \[N{{H}_{4}}OH.\] Disodium hydrogen phosphate is now added, a white precipitate is formed.
\[MgC{{l}_{2}}+N{{a}_{2}}HP{{O}_{4}}+N{{H}_{4}}OH\xrightarrow{\,}\]\[\underset{\text{(White ppt}\text{.)}}{\mathop{\underset{\text{Megnesium ammonium phosphate}}{\mathop{Mg(N{{H}_{4}})P{{O}_{4}}+2NaCl+{{H}_{2}}O}}\,}}\,\]
Zero group \[\mathbf{NH}_{\mathbf{4}}^{\mathbf{+}}\] (ammonium) : The substance (salt or mixture) when heated with \[NaOH\]solution evolves ammonia.
\[N{{H}_{4}}Cl+NaOH\xrightarrow{\,}NaCl+N{{H}_{3}}+{{H}_{2}}O\]
When a rod dipped in HCl is brought on the mouth of the test tube, white fumes of ammonium chloride are formed, \[N{{H}_{3}}+HCl\xrightarrow{\,}\underset{\text{White fumes}}{\mathop{N{{H}_{4}}Cl}}\,\]
To the aqueous solution of ammonium salt when Nessler’s reagents is added, brown coloured precipitate is formed.
\[2{{K}_{2}}Hg{{I}_{4}}+N{{H}_{4}}Cl+4KOH\xrightarrow{{}}\]
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