Systematic Procedure For Qualitative Analysis Of Inorganic Salts
Category : JEE Main & Advanced
It involves the following steps : (1) Preliminary tests (2) Wet tests for acid radicals and (3) Wet tests for basic radicals.
(1) Preliminary tests
(i) Physical examination : It involves the study of colour, smell, density etc.
| Colour | Salt |
| Black |
Oxides : \[Mn{{O}_{2}},FeO,CuO,C{{o}_{3}}{{O}_{4}}\], \[N{{i}_{2}}{{O}_{3}}\] Sulphides : \[A{{g}_{2}}S,CuS,C{{u}_{2}}S,FeS,CoS,NiS\], \[PbS,HgS\],\[B{{i}_{2}}{{S}_{3}}\] (blackish brown) |
|
Blue
|
Hydrated \[CuS{{O}_{4}}\], anhydrous \[CoS{{O}_{4}}\]
|
|
Orange
|
\[K{{O}_{2}}\], some dichromate \[({{K}_{2}}C{{r}_{2}}{{O}_{7}}),S{{b}_{2}}{{S}_{3}}\], ferricyanides
|
|
Green
|
Nickel salts, hydrated ferrous salts, potassium permanganate \[(KMn{{O}_{4}})\], some copper (II) salts
|
|
Brownish yellow
|
\[SnS\]
|
|
Dark brown
|
\[Pb{{O}_{2}},A{{g}_{2}}O,CdO,F{{e}_{2}}{{O}_{3}},CuCr{{O}_{4}},FeC{{l}_{3}}\] (but yellow in aq. solution)
|
|
Pale brown
|
\[MnC{{O}_{3}}\]
|
|
Light pink
|
Hydrated manganese salts
|
|
Reddish pink
|
Hydrated cobalt (II) salts
|
|
Red
|
\[Hg{{I}_{2}},P{{b}_{3}}{{O}_{4}}\]
|
|
Yellow
|
\[CdS,Pb{{I}_{2}},AgBr,\,AgI\], chromates
|
(ii) Dry heating : Substance is heated in a dry test tube.
| Observation | Result |
| (a) A gas or vapour is evolved. | Compounds with water of crystallisation |
| Vapour, evolved, test with litmus paper. | Ammonium salts, acid salts, and hydroxides. (usually accompanied by change of colour) |
| The vapour is alkaline. | Ammonium salts. |
| The vapour is acidic. | Readily decomposable salts of strong acids. |
| Oxygen is evolved | Nitrates,chlorates and certain oxides. |
| Dinitrogen oxide | Ammonium nitrate or nitrate mixed with an ammonium salt. |
| Dark-brown or reddish fumes (oxides of nitrogen), acidic in reaction. | Nitrates and nitrites of heavy metals. |
| \[C{{O}_{2}}\]is evolved, lime water becomes turbid. | Carbonates or hydrogen carbonates. |
| \[N{{H}_{3}}\]is evolved which turns red litmus blue. | Ammonium salts. |
| \[S{{O}_{2}}\]is evolved, which turns acidified \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\] green, decolourises fuschin colour. | Sulphates and thiosulphates. |
| \[{{H}_{2}}S\] is evolved, turns lead acetate paper black, or cadmium acetate yellow. | Hydrates, sulphides or sulphides in the presence of water. |
| \[C{{l}_{2}}\]is evolved, yellowish green gas, bleaches litmus paper, turns KI ? starch blue, poisonous. | Unstable chlorides e.g., copper chlorides in the presence of oxidising agents. |
| \[B{{r}_{2}}\]is evolved (reddish brown, turns fluorescent paper red). | Bromides in the presence of oxidising agents. |
| \[{{I}_{2}}\] is evolved, violet vapours condensing to black crystals | Free iodine and certain iodides |
| (b) A sublimate is formed | Ammonium and mercury salts. |
| White sublimate | \[A{{s}_{2}}{{O}_{3}},\,S{{b}_{2}}{{O}_{3}}\] |
| Grey sublimate | \[Hg\] |
| Steel grey, garlic odour | \[\text{As}\] |
| Yellow sublimate | \[S,\,A{{s}_{2}}{{S}_{3}}\,Hg{{I}_{2}}(\operatorname{Re}d)\] |
Action of heat on different compounds : Many inorganic salts decomposes on heating, liberating characteristic gases. A few such reactions are tabulated as follows,
| \[\underset{(\operatorname{Re}d)}{\mathop{2HgO}}\,\xrightarrow{\Delta }\underset{(Silvery\,deposit)}{\mathop{2Hg}}\,+{{O}_{2}}\] | \[\underset{(\operatorname{Re}d)}{\mathop{2P{{b}_{3}}{{O}_{4}}}}\,\xrightarrow{\Delta }\underset{(Yellow)}{\mathop{6PbO}}\,+{{O}_{2}}\] | \[\underset{(Brown)}{\mathop{2Pb{{O}_{2}}}}\,\xrightarrow{\Delta }\underset{{}}{\mathop{2PbO}}\,+{{O}_{2}}\] | |
| \[\underset{(Green)}{\mathop{CuC{{O}_{3}}}}\,\xrightarrow{\Delta }CuO+C{{O}_{2}}\] | \[\underset{(White)}{\mathop{Zn{{O}_{3}}}}\,\xrightarrow{\Delta }\underset{\underset{White\,(cold)}{\mathop{Yellow\,(hot)}}\,}{\mathop{ZnO}}\,+C{{O}_{2}}\] | \[\underset{(Blue)}{\mathop{CuS{{O}_{4}}.5{{H}_{2}}O}}\,\xrightarrow{\Delta }\underset{(White)}{\mathop{CuS{{O}_{4}}}}\,+5{{H}_{2}}O\] | |
| \[CuS{{O}_{4}}\xrightarrow{\Delta }CuO+S{{O}_{3}}\] | \[2FeS{{O}_{4}}\xrightarrow{\Delta }F{{e}_{2}}{{O}_{3}}+S{{O}_{2}}+S{{O}_{3}}\] | \[2A{{g}_{2}}O\to 4Ag+{{O}_{2}}\] | |
| \[\underset{(White)}{\mathop{2Zn{{(N{{O}_{3}})}_{2}}}}\,\xrightarrow{\Delta }2ZnO+\underset{(Brown)}{\mathop{4N{{O}_{2}}}}\,+{{O}_{2}}\] | \[2AgN{{O}_{3}}\xrightarrow{450{}^\circ C}2Ag+2N{{O}_{2}}+{{O}_{2}}\] | \[2Cu{{(N{{O}_{3}})}_{2}}\to 2CuO+4N{{O}_{2}}+{{O}_{2}}\] | |
| \[2A{{g}_{2}}C{{O}_{3}}\to 4Ag+2C{{O}_{2}}+{{O}_{2}}\] | \[2Pb{{(N{{O}_{3}})}_{2}}\to 2PbO+4N{{O}_{2}}+{{O}_{2}}\] | \[\underset{\text{(Orange)}}{\mathop{{{(N{{H}_{4}})}_{2}}C{{r}_{2}}{{O}_{7}}}}\,\to {{N}_{2}}+\underset{\text{(Green)}}{\mathop{C{{r}_{2}}{{O}_{3}}}}\,+4{{H}_{2}}O\] | |
| \[2NaHC{{O}_{3}}\to N{{a}_{2}}C{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O\] | \[N{{H}_{4}}HC{{O}_{3}}\to N{{H}_{3}}+C{{O}_{2}}+{{H}_{2}}O\] | \[CaC{{O}_{3}}\to CaO+C{{O}_{2}}\] | |
| \[2NaN{{O}_{3}}\to 2NaN{{O}_{2}}+{{O}_{2}}\] | \[MgC{{O}_{3}}\to MgO+C{{O}_{2}}\] | \[2N{{H}_{3}}\xrightarrow{\text{Red hot}}{{N}_{2}}+3{{H}_{2}}\] | |
| \[2Mg{{(N{{O}_{3}})}_{2}}\to 2MgO+4N{{O}_{2}}+{{O}_{2}}\] | \[2Ca{{(N{{O}_{3}})}_{2}}\to 2CaO+4N{{O}_{2}}+{{O}_{2}}\] | \[A{{l}_{2}}{{(S{{O}_{4}})}_{3}}\xrightarrow{\text{Red hot}}A{{l}_{2}}{{O}_{3}}+3S{{O}_{3}}\] | |
| \[2CaS{{O}_{4}}.2{{H}_{2}}O\to \underset{\text{(Plaster of Paris)}}{\mathop{2CaS{{O}_{4}}.{{H}_{2}}O}}\,+2{{H}_{2}}O\] | \[2AlC{{l}_{3}}.6{{H}_{2}}O\to A{{l}_{2}}{{O}_{3}}+6HCl+9{{H}_{2}}O\] | \[2BeS{{O}_{4}}\xrightarrow{\Delta }2BeO+2S{{O}_{2}}+{{O}_{2}}\] | |
| \[2AgN{{O}_{3}}\xrightarrow{{{350}^{o}}C}2AgN{{O}_{2}}+{{O}_{2}}\] | \[2MgS{{O}_{4}}\xrightarrow{\Delta }2MgO+2S{{O}_{2}}+{{O}_{2}}\] | \[2ZnS{{O}_{4}}\xrightarrow{\Delta }2ZnO+2S{{O}_{2}}+{{O}_{2}}\] | |
| \[{{(COO)}_{2}}Sn\xrightarrow{\Delta }SnO+C{{O}_{2}}+CO\] | \[Ca{{C}_{2}}{{O}_{4}}\to CaC{{O}_{3}}+CO\] | \[N{{H}_{4}}N{{O}_{2}}\to {{N}_{2}}+2{{H}_{2}}O\] | |
| \[N{{H}_{4}}N{{O}_{3}}\to {{N}_{2}}O+2{{H}_{2}}O\] | \[2KCl{{O}_{3}}\to 2KCl+3{{O}_{2}}\] | \[2FeC{{l}_{3}}\to 2FeC{{l}_{2}}+C{{l}_{2}}\] | |
| \[L{{i}_{2}}C{{O}_{3}}\to L{{i}_{2}}O+C{{O}_{2}}\] | \[{{(COO)}_{2}}Fe\to FeO+CO+C{{O}_{2}}\] | \[2KMn{{O}_{4}}\to {{K}_{2}}Mn{{O}_{4}}+Mn{{O}_{2}}+{{O}_{2}}\] | |
| \[MgC{{l}_{2}}.\,6{{H}_{2}}O\to HgC{{l}_{2}}+Hg\] | \[N{{H}_{4}}Cl\to N{{H}_{3}}+HCl\] | \[2LiN{{O}_{3}}\to L{{i}_{2}}O+2N{{O}_{2}}+\frac{1}{2}{{O}_{2}}\] | |
| \[Hg{{(N{{O}_{3}})}_{2}}\to Hg+2N{{O}_{2}}+{{O}_{2}}\] | \[2CuC{{l}_{2}}\xrightarrow{\Delta }C{{u}_{2}}C{{l}_{2}}+C{{l}_{2}}\] | \[2Co{{(N{{O}_{3}})}_{2}}\xrightarrow{\Delta }2CoO+4N{{O}_{2}}+{{O}_{2}}\] | |
| \[4{{K}_{2}}C{{r}_{2}}{{O}_{7}}\to 4{{K}_{2}}Cr{{O}_{4}}\]+\[2C{{r}_{2}}{{O}_{3}}+3{{O}_{2}}\] | \[2Mg(N{{H}_{4}})P{{O}_{4}}\xrightarrow{\Delta }M{{g}_{2}}{{P}_{2}}{{O}_{7}}+{{H}_{2}}O+2N{{H}_{3}}\] | ||
| \[2Zn(N{{H}_{4}})P{{O}_{4}}\xrightarrow{\Delta }Z{{n}_{2}}{{P}_{2}}{{O}_{7}}+{{H}_{2}}O+2N{{H}_{3}}\] | \[{{K}_{4}}Fe{{(CN)}_{6}}\xrightarrow{\Delta }4KCN+Fe+2C+{{N}_{2}}\] | ||
| \[ZnC{{l}_{2}}.\,2{{H}_{2}}O\xrightarrow{\Delta }Zn(OH)Cl+HCl+{{H}_{2}}O\] | \[2(ZnC{{l}_{2}}.{{H}_{2}}O)\xrightarrow{\Delta }Z{{n}_{2}}OC{{l}_{2}}+2HCl+{{H}_{2}}O\] | ||
| \[2[FeC{{l}_{3}}.6{{H}_{2}}O]\xrightarrow{\Delta }F{{e}_{2}}{{O}_{3}}+9{{H}_{2}}O+6HCl\] | \[2ZnS{{O}_{4}}\xrightarrow{{{800}^{o}}C}2ZnO+2S{{O}_{2}}+{{O}_{2}}\] | ||
| \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}.10{{H}_{2}}O\xrightarrow{\Delta }N{{a}_{2}}{{B}_{4}}{{O}_{7}}\xrightarrow{\Delta }\underset{\text{(Glassy bead)}}{\mathop{2NaB{{O}_{2}}+{{B}_{2}}{{O}_{3}}}}\,\] | |||
| \[{{H}_{3}}B{{O}_{3}}\xrightarrow{{{100}^{o}}C}HB{{O}_{2}}\xrightarrow{{{160}^{o}}C}{{H}_{2}}{{B}_{4}}{{O}_{7}}\]\[\xrightarrow{\text{Red hot}}{{B}_{2}}{{O}_{3}}\] | |||
| \[ZnS{{O}_{4}}.7{{H}_{2}}O\underset{-{{H}_{2}}O}{\mathop{\xrightarrow{{{70}^{o}}C}}}\,ZnS{{O}_{4}}.6{{H}_{2}}O\underset{-5{{H}_{2}}O}{\mathop{\xrightarrow{{{100}^{o}}C}}}\,ZnS{{O}_{4}}.{{H}_{2}}O\xrightarrow{\text{45}{{\text{0}}^{\text{o}}}C}ZnS{{O}_{4}}\] | |||
(iii) Flame test
Characteristic flame colour : Certain metals and their salts impart specific colours to Bunsen burner flame.
(a) Pb imparts pale greenish colour to the flame.
(b) Cu and Cu salts impart blue or green colour to the flame.
(c) Borates also impart green colour to the flame.
(d) Ba and its salts impart apple green colour to the flame.
(e) Sr imparts crimson red colour to the flame.
(f) Ca imparts brick red colour to the flame.
(g) Na imparts yellow colour to the flame.
(h) K imparts pink-violet (Lilac) colour to the flame.
(i) Li imparts crimson-red, Rb imparts violet and Cs imparts violet colours to the flame.
(j) Livid- blue flame is given by As, Sb and Bi.
(iv) Borax bead test : The transparent glassy bead \[(NaB{{O}_{2}}+{{B}_{2}}{{O}_{3}})\] when heated with inorganic salt and the colour produced gives some idea of cation present in it.
| Colour of bead in oxidising flame | Colour of bead in reducing flame | Basic radical present |
| Greenish when hot, blue in cold. | Red and opaque | Cu |
| Dark green in hot and cold | Same | Cr |
| Deep ? blue | Deep blue | Co |
| Yellow when hot | Green | Fe |
| Violet in hot and cold | Colourless | Mn |
| Brown in cold | Grey or black or opaque | Ni. |
Microcosmic salt bead test : Microcosmic salt, \[Na(N{{H}_{4}})HP{{O}_{4}}.4{{H}_{2}}O\] is also used to identify certain cations just like borax. When microcosmic salt is heated in a loop of platinum wire, a colourless transparent bead of sodium metaphosphate is formed.
\[Na\,(N{{H}_{4}})HP{{O}_{4}}.4{{H}_{2}}O\to Na(N{{H}_{4}})HP{{O}_{4}}+4{{H}_{2}}O\]
\[Na(N{{H}_{4}})HP{{O}_{4}}\to NaP{{O}_{3}}+N{{H}_{3}}+{{H}_{2}}O\]
Now \[NaP{{O}_{3}}\] reacts with metallic oxides to give coloured orthophosphates.
\[NaP{{O}_{3}}+CuO\to NaCuP{{O}_{4}}\] (Blue);
\[NaP{{O}_{3}}+CoO\to NaCoP{{O}_{4}}\] (Blue);
\[NaP{{O}_{3}}+C{{r}_{2}}{{O}_{3}}\to NaP{{O}_{3}}.C{{r}_{2}}{{O}_{3}}\] (Green)
(v) Charcoal cavity test
| (a) Compound fused in cavity directly | |
| Nature and colour of bead | Cation |
| Yellow, brittle bead | \[B{{i}^{3+}}\] |
| Yellow, soft bead which marks on paper | \[P{{b}^{2+}}\] |
| White, brittle | \[S{{b}^{3+}}\] |
| White yellow when hot | \[ZnO\] |
| White garlic odour | \[A{{s}_{2}}{{O}_{3}}\] |
| Brown | \[CdO\] |
| Grey metallic particles attracted by magnet | \[Fe,\,Ni,\,CO\] |
| Maleable beads | Ag and Sn (White), Cu (Red flakes) |
(b) Compound mixed with \[N{{a}_{2}}C{{O}_{3}}\] Crystalline
(b) Compound mixed with \[N{{a}_{2}}C{{O}_{3}}\] Crystalline
\[\begin{matrix} \text{Sustance } \\ \text{Decrepitates} \\ \end{matrix}\,\,\,\,\,\text{Salts,}\,\text{NaCl, KCl}\];
\[\begin{matrix} \text{Substance} \\ \text{deflagrates} \\ \end{matrix}\,\,\,\,\,\underset{NO_{3}^{-},\,NO_{2}^{-\,}\text{chlorates}}{\mathop{\ \ \ \text{Oxidising agents like }}}\,\]
Substance infusible, perform test (a)
(vi) Cobalt Nitrate test
| Colour | Composition | Result |
| Blue residue | \[CoO\,.\,A{{l}_{2}}{{O}_{3}}\] | \[Al\] |
| Green residue | \[CoO\,.\,ZnO\] | \[ZnO\] |
| Pink dirty residue | \[CoO\,.\,MgO\] | MgO |
| Blue residue | \[NaCoP{{O}_{4}}\] | \[PO_{4}^{3-}\] in absence of Al. |
(2) Wet tests for acid radicals : Salt or mixture is treated with dil. \[{{H}_{2}}S{{O}_{4}}\] and also with conc. \[{{H}_{2}}S{{O}_{4}}\] separately and by observing the types of gases evolved. Confirmatory tests of anions are performed.
Observations with Dilute \[{{H}_{2}}S{{O}_{4}}\]
| Observations | Acid Radical | Confirmatory test |
|
Brisk effervescence with evolution of colourless and odourless gas.
|
\[CO_{3}^{2-}\] (carbonate) |
Gas turns lime water milky but milkyness disappears on passing gas inexcess, \[N{{a}_{2}}C{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{\,}N{{a}_{2}}S{{O}_{4}}+{{H}_{2}}O+C{{O}_{2}}\] \[\underset{\text{lime water}}{\mathop{Ca{{(OH)}_{2}}}}\,+C{{O}_{2}}\xrightarrow{\,}\underset{\text{milky}}{\mathop{CaC{{O}_{3}}}}\,+{{H}_{2}}O\] \[CaC{{O}_{3}}+{{H}_{2}}O+C{{O}_{2}}\xrightarrow{\,}\underset{\text{soluble}}{\mathop{Ca{{(HC{{O}_{3}})}_{2}}}}\,\] |
| Brown fumes |
\[NO_{2}^{-}\] (Nitrite) |
Add KI and starch solution blue colour \[2NaN{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{\,}N{{a}_{2}}S{{O}_{4}}+2HN{{O}_{2}}\]; \[HN{{O}_{2}}\xrightarrow{\,}NO\](colourless); \[2NO+{{O}_{2}}(\text{air) }\xrightarrow[\,]{}2N{{O}_{2}}\](brown) \[2KI+{{H}_{2}}S{{O}_{4}}+2NH{{O}_{2}}\xrightarrow{\,}{{K}_{2}}S{{O}_{4}}+2{{H}_{2}}O+2NO+{{I}_{2}}\] \[{{I}_{2}}+\]starch\[\xrightarrow{}\]blue colour |
|
Smell of rotten eggs \[({{H}_{2}}S\]smell) on heating |
\[{{S}^{2-}}\] (sulphide) |
Gas turn lead acetate paper black Sodium carbonate extract \[{{(SE)}^{*}}\]+ sodium nitroprusside - purple colour, \[N{{a}_{2}}S+{{H}_{2}}S{{O}_{4}}\xrightarrow{}{{H}_{2}}S+N{{a}_{2}}S{{O}_{4}}\] \[{{H}_{2}}S+{{(C{{H}_{3}}COO)}_{2}}Pb\xrightarrow{\,}\underset{\,\text{(black)}}{\mathop{PbS}}\,+2C{{H}_{3}}COOH\] \[\begin{align} & N{{a}_{2}}S+N{{a}_{2}}[Fe{{(CN)}_{5}}NO]\xrightarrow{\,}N{{a}_{4}}[Fe{{(CN)}_{5}}\,\,NOS] \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{sodium nitroprusside}\,\,\,\,\,\,\,\,\text{(purple)} \\ \end{align}\] |
| Colourless gas with pungent smell of burning sulphur |
\[SO_{3}^{2-}\] (sulphite) |
Gas turns acidified \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\] solution green [different from \[CO_{3}^{2-}]\] since gas also turns lime water milky \[N{{a}_{2}}S{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{\Delta }N{{a}_{2}}S{{O}_{4}}+{{H}_{2}}O+S{{O}_{2}}\] \[C{{r}_{2}}O_{7}^{2-}+3S{{O}_{2}}+2{{H}^{+}}\xrightarrow{{}}\underset{(\text{green})}{\mathop{2C{{r}^{3+}}+3SO_{4}^{2}}}\,+{{H}_{2}}O\] \[Ca{{(OH)}_{2}}+S{{O}_{2}}\xrightarrow{{}}\underset{\text{(milky)}}{\mathop{CaS{{O}_{3}}}}\,\] |
| Solution gives smell of vinegar |
\[C{{H}_{3}}CO{{O}^{-}}\] (acetate) |
Aq. Solution + neutral \[FeC{{l}_{3}}\to \]blood red colour \[3C{{H}_{3}}COONa+\underset{\text{neutral}}{\mathop{FeC{{l}_{3}}}}\,\xrightarrow{\,}\underset{\,\text{(red)}}{\mathop{Fe{{(C{{H}_{3}}COO)}_{3}}}}\,+3NaCl\] |
| White or yellowish white turbidity on warming |
\[{{S}_{2}}O_{3}^{2-}\] (thiosulphate) |
Aq. Solution + \[AgN{{O}_{3}}\to \] white ppt. changing to black (viii) on warming , \[N{{a}_{2}}{{S}_{2}}{{O}_{3}}+2AgN{{O}_{3}}\xrightarrow{}\underset{\,\text{white ppt}\text{.}}{\mathop{A{{g}_{2}}{{S}_{2}}{{O}_{3}}}}\,+2NaN{{O}_{3}}\] \[A{{g}_{2}}{{S}_{2}}{{O}_{3}}+{{H}_{2}}O\xrightarrow{\,}\underset{\text{black ppt}\text{.}}{\mathop{A{{g}_{2}}S+{{H}_{2}}S{{O}_{4}}}}\,\]. |
Observation with concentrated \[{{H}_{2}}S{{O}_{4}}\]
| Observation | Acid Radical | Confiramatory Test |
|
Colourless pungent gas giving white fumes with aq. \[N{{H}_{4}}OH\] |
\[C{{l}^{-}}\] (chloride) |
Add \[Mn{{O}_{2}}\] in the same test tube and heat-pale green \[C{{l}_{2}}\] gas (i) S.E.+\[HN{{O}_{3}}+AgN{{O}_{3}}\] solution-white ppt. soluble in aq. \[N{{H}_{3}}\] (ii) Chromyl chloride test (iii) |
| Reddish brown fumes |
\[B{{r}^{-}}\] (bromide) |
Add \[M{{n}_{2}}O\] and heat ?yellowish brown \[B{{r}_{2}}\] gas (iv) S.E.+\[HN{{O}_{3}}+AgN{{O}_{3}}\] solution ?pale yellow ppt. partially soluble aq. \[N{{H}_{3}}\] (v) Layer test (vi) |
| Violet pungent vapours turning starch paper blue. |
\[{{I}^{-}}\] (iodide) |
S.E.+\[HN{{O}_{3}}+AgN{{O}_{3}}\]\[\to \] yellow ppt. insoluble in aq. \[N{{H}_{3}}\] (vii) Layer test (vi) |
| Brown pungent fumes intensified by the addition of Cu- turnigs. |
\[NO_{3}^{-}\] (nitrate) |
Ring test (viii) |
| Colourless gases turning lime water milky and burning with blue flame. |
\[{{C}_{2}}O_{4}^{2-}\] (oxalate) |
Acidified \[KMn{{O}_{4}}\]solution is decolorised (ix) \[S.E.+C{{H}_{3}}COOH+CaC{{l}_{2}}\] white ppt. decolorising acidified \[KMn{{O}_{4}}\] solution (x). |
Reactions
Chloride :
(i) \[KCl+\text{conc}\text{.}{{H}_{2}}S{{O}_{4}}\xrightarrow{\,}KHS{{O}_{4}}+HCl\,\]
\[HCl+N{{H}_{3}}\xrightarrow{\,}\underset{(\text{white fumes)}}{\mathop{N{{H}_{4}}Cl}}\,\]
\[4HCl+Mn{{O}_{2}}\xrightarrow{\Delta }MnC{{l}_{2}}+C{{l}_{2}}+2{{H}_{2}}O\]
(ii) \[KCl+AgN{{O}_{3}}\xrightarrow{\,}\underset{\text{white ppt}\text{.}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }{\mathop{AgCl\downarrow \,+KN{{O}_{3}}}}\,\]
\[AgCl+aq.\,2N{{H}_{3}}\xrightarrow{\,}\underset{\text{soluble}}{\mathop{[Ag{{(N{{H}_{3}})}_{2}}]\,Cl}}\,\]
(iii) Chromyl- chloride test :
Chloride + \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}(\text{solid})+\text{conc}\text{. }{{\text{H}}_{\text{2}}}S{{O}_{4}}\xrightarrow{\text{heat}}\]reddish brown vapours of chromyl-chloride \[(Cr{{O}_{2}}C{{l}_{2}}).\] Pass these vapours into \[NaOH,\] when yellow \[N{{a}_{2}}Cr{{O}_{4}}\] solution is formed. On adding \[C{{H}_{3}}COOH\] and \[{{(C{{H}_{3}}COO)}_{2}}\] Pb, yellow ppt. of lead chromate \[(PbCr{{O}_{4}})\] is formed.
\[KCl+\text{conc}\text{.}{{H}_{2}}S{{O}_{4}}\xrightarrow{\Delta }KHS{{O}_{4}}+HCl\];
\[{{K}_{2}}C{{r}_{2}}{{O}_{7}}+\underset{\text{conc}\text{.}}{\mathop{2{{H}_{2}}S{{O}_{4}}}}\,\xrightarrow{\Delta }2KHS{{O}_{4}}+2Cr{{O}_{3}}+{{H}_{2}}O\]
\[Cr{{O}_{3}}+2HCl\xrightarrow{\,}Cr{{O}_{2}}C{{l}_{2}}+2{{H}_{2}}O\]
\[Cr{{O}_{2}}C{{l}_{2}}+4NaOH\xrightarrow{\,}N{{a}_{2}}Cr{{O}_{4}}+2NaCl+2{{H}_{2}}O\]
\[N{{a}_{2}}Cr{{O}_{4}}+{{(C{{H}_{3}}COO)}_{2}}Pb\xrightarrow{\,}\underset{\text{yellow ppt}\text{.}}{\mathop{PbCr{{O}_{4}}\downarrow }}\,+2C{{H}_{3}}COONa\]
Bromide : (iv) \[KBr+\text{conc}\text{.}\,{{H}_{2}}S{{O}_{4}}\xrightarrow{\Delta }KHS{{O}_{4}}+H\];
\[4HBr+Mn{{O}_{2}}\xrightarrow{\Delta }B{{r}_{2}}+2{{H}_{2}}O+MnB{{r}_{2}}\]
(v) \[NaBr+AgN{{O}_{3}}\xrightarrow{\,}\underset{\text{pale yellow ppt}\text{.}\ \ \ \ \ \ \ \ \ \ \ \ \ \ }{\mathop{AgBr\downarrow +\,NaN{{O}_{3}}}}\,\]
\[AgBr+\text{aq}\text{.}\,2N{{H}_{3}}\xrightarrow{\,}\underset{\text{ partially soluble}}{\mathop{[Ag{{(N{{H}_{3}})}_{2}}]Br}}\,\]
(vi) Layer Test : \[S.E.+C{{l}_{2}}\] water +\[CHC{{l}_{3}}\]\[\xrightarrow{\text{shake}}\] yellowish orange colour in\[CHC{{l}_{3}}\] layer \[(C{{S}_{2}}\]or \[CC{{l}_{4}}\] can be taken instead of \[CHC{{l}_{3}}\]);
\[2NaBr+C{{l}_{2}}\xrightarrow{\,}2NaCl+\underset{\begin{smallmatrix} \text{orange yellow} \\ \text{(soluble in CHC}{{\text{l}}_{\text{3}}}) \end{smallmatrix}}{\mathop{B{{r}_{2}}}}\,\]
In case of \[{{I}^{-}}\], violet colour of \[{{I}_{2}}\] in \[CHC{{l}_{3}}\]layer, \[2NaI+C{{l}_{2}}\xrightarrow{}2NaCl+{{I}_{2}}\,\](violet)
Iodide : (vii) \[KI+\text{conc}\text{.}\,{{H}_{2}}S{{O}_{4}}\xrightarrow{\Delta }KHS{{O}_{4}}+HI\];
\[2HI\,\,+\,\,{{H}_{2}}S{{O}_{4}}\xrightarrow{\,}{{I}_{2}}\]+\[2{{H}_{2}}O+S{{O}_{2}}\]
Nitrate : \[NaN{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{\,}NaHS{{O}_{4}}+HN{{O}_{3}}\]
\[4HN{{O}_{3}}\xrightarrow{\,}\underset{\text{brown fumes}\,}{\mathop{4N{{O}_{2}}+\,{{O}_{2}}2{{H}_{2}}O}}\,\] ;
\[Cu+4HN{{O}_{3}}\xrightarrow{}Cu\,{{(N{{O}_{3}})}_{2}}+\,2N{{O}_{2}}+2{{H}_{2}}O\]
(viii) Ring test : To water extract (all \[NO_{3}^{-}\] are water soluble) add freshly prepared \[FeS{{O}_{4}}\] solution and then conc. \[{{H}_{2}}S{{O}_{4}}\] carefully by the side of the test- tube. A dark brown ring of \[{{[Fe\,{{({{H}_{2}}O)}_{5}}NO]}^{2+}}SO_{4}^{2-}\] at the interface between the two liquids is formed.
\[2NaN{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{\,}2NaHS{{O}_{4}}+2HN{{O}_{3}}\];
\[2HN{{O}_{3}}+6Fe\,S{{O}_{4}}+\,3{{H}_{2}}S{{O}_{4}}\xrightarrow{\,}\] \[3F{{e}_{2}}{{(S{{O}_{4}})}_{3}}\,+\,2NO+4{{H}_{2}}O\]
\[[Fe\,{{({{H}_{2}}O)}_{6}}]\,S{{O}_{4}}+NO\xrightarrow{\,}{{[Fe{{({{H}_{2}}O)}_{5}}NO]}^{2+}}\,SO_{4}^{2-}+{{H}_{2}}O\]
Oxalate : \[N{{a}_{2}}{{C}_{2}}{{O}_{4}}+{{H}_{2}}S{{O}_{4}}\xrightarrow{}N{{a}_{2}}S{{O}_{4}}+{{H}_{2}}O+CO+C{{O}_{2}}\]
CO burns with blue flame and \[C{{O}_{2}}\] turns lime water milky.
(ix) \[5{{C}_{2}}O_{4}^{2-}+\underset{(\text{violet)}}{\mathop{2MnO_{4}^{-}}}\,+16{{H}^{+}}\xrightarrow{\,}\underset{\text{colourless}}{\mathop{10\,C{{O}_{2}}+2M{{n}^{2+}}}}\,+8{{H}_{2}}O\]
(x) \[CaC{{l}_{2}}+Na{{C}_{2}}{{O}_{4}}\xrightarrow{}\underset{\text{white ppt}\text{.}}{\mathop{Ca{{C}_{2}}{{O}_{4}}\downarrow }}\,+\,2NaCl\] \[Ca{{C}_{2}}{{O}_{2}}\] decolourises acidified \[KMn{{O}_{4}}.\]
Specific test in solution
(i) Sulphate : S.E. add dil. (to decompose \[CO_{3}^{2-}\]until reaction ceases). Add \[BaC{{l}_{2}}\]solution. White ppt. insoluble in conc. \[HN{{O}_{3}}\], \[BaC{{l}_{2}}+NaS{{O}_{4}}\xrightarrow{\,}\underset{\text{white ppt}\text{.}}{\mathop{BaS{{O}_{4}}\downarrow }}\,+2NaCl\]
(ii) Borate : lgnite the mixture containing borate, conc. \[{{H}_{2}}S{{O}_{4}}\]. And ethanol in a china-dish with a burning splinter ?green edged flame of ethyl borate.
\[\underset{\text{(conc}\text{.)}}{\mathop{2N{{a}_{3}}B{{O}_{3}}+3{{H}_{2}}S{{O}_{4}}}}\,\to 2{{H}_{3}}B{{O}_{3}}+3N{{a}_{2}}S{{O}_{4}}\];
\[{{H}_{3}}B{{O}_{3}}+\underset{ethanol}{\mathop{3{{C}_{2}}{{H}_{5}}OH}}\,\xrightarrow{\Delta }\underset{\begin{smallmatrix} \text{burns with green flame} \\ \text{(volatile)} \end{smallmatrix}}{\mathop{{{({{C}_{2}}{{H}_{5}}O)}_{3}}B}}\,+3{{H}_{2}}O\]
In presence of \[C{{u}^{2+}}\], perform this test in a test tube since \[C{{u}^{2+}}\] salts are not volatile.
(iii) \[S.E.+HN{{O}_{3}}+\] ammonium molybdate solution. Heat, yellow crystalline ppt. confirms
\[N{{a}_{3}}P{{O}_{4}}+12{{(N{{H}_{4}})}_{2}}Mo{{O}_{4}}+24HN{{O}_{3}}\xrightarrow{\Delta }\] \[\underset{\text{yellow ppt}\text{.}}{\mathop{{{(N{{H}_{4}})}_{3}}P{{O}_{4}}}}\,.\,\,12Mo{{O}_{3}}+21N{{H}_{4}}N{{O}_{3}}+3NaN{{O}_{3}}+12{{H}_{2}}O\]
Arsenic also gives this test. Hence presence of phosphate should also be checked after group II.
(iv) Fluoride : Sand +salt \[({{F}^{-}})\] +conc. \[{{H}_{2}}S{{O}_{4}};\] heat and bring a water wetted rod in contact with vapours at the mouth of the test tube. A white deposit on the rod shows the presence to \[{{F}^{-}}\]
\[NaF+{{H}_{2}}S{{O}_{4}}\xrightarrow{\Delta }NaHS{{O}_{4}}+HF\]
\[Si{{O}_{2}}+4HF\xrightarrow{\Delta }Si{{F}_{4}}+2{{H}_{2}}O\]
\[3Si{{F}_{4}}4{{H}_{2}}O\xrightarrow{\,}2{{H}_{2}}Si{{F}_{6}}+\underset{\text{white}}{\mathop{{{H}_{4}}Si{{O}_{4}}}}\,\]
(3) Wet tests for basic radicals : Analysis of Basic Radicals
| Group | Basic radicals | Group reagent | Ppt. as | Explanation |
| I | \[A{{g}^{+}},Hg_{2}^{2+}\text{(I),}P{{b}^{2+}}\] | dil HCl | Chloride \[(AgCl,H{{g}_{2}}C{{l}_{2}},PbC{{l}_{2}})\] | \[{{K}_{SP}}\] values of chlorides are low, hence precipitated. Others have higher \[{{K}_{SP}}\] values hence not precipitated. |
| II |
\[C{{u}^{2+}},C{{d}^{2+}},P{{b}^{2+}}\], \[H{{g}^{2+}}\](II), \[B{{i}^{3+}},\,A{{s}^{3+}}\], \[S{{b}^{3+}},S{{n}^{2+}}\] |
\[{{H}_{2}}S\] gas in presence of dil. HCl | Sulphides (\[CuS,A{{s}_{2}}{{S}_{3}}\] etc.) | \[{{K}_{SP}}\] values of sulphides are low hence precipitated by low \[[{{S}^{2-}}]\] ion. \[HCl\] (with common \[{{H}^{+}}\] ion) decreases ionization of \[{{H}_{2}}S\] which gives low \[[{{S}^{2-}}]\]. Hence II group is precipitated. Others with higher \[{{K}_{SP}}\] values not precipitated. |
| III |
\[A{{l}^{3+}},C{{r}^{3+}},F{{e}^{3+}}\] |
\[N{{H}_{4}}OH\] in presence of \[N{{H}_{4}}Cl\] | Hydroxide, \[Al{{(OH)}_{3}}\] etc. | \[{{K}_{SP}}\] values of \[Al{{(OH)}_{3}}\] etc. are low. \[N{{H}_{4}}Cl\] (with common \[NH_{4}^{+}\] ion) decreases ionization of \[N{{H}_{4}}OH\] giving low \[[O{{H}^{-}}]\]. Hence group III is precipitated. |
| IV |
\[Z{{n}^{2+}},N{{i}^{2+}},M{{n}^{2+}},C{{o}^{2+}}\] |
\[{{H}_{2}}S\] in ammonical medium | Sulphides (\[ZnS\] etc.) | \[{{K}_{SP}}\] values of sulphides of group IV are high hence precipitation takes place in higher \[[{{S}^{2-}}]\]. Basic medium increases ionization of \[{{H}_{2}}S\] increasing \[[{{S}^{2-}}]\] hence precipitation of group IV. |
| V |
\[C{{a}^{2+}},B{{a}^{2+}},S{{r}^{2+}}\] |
\[{{(N{{H}_{4}})}_{2}}C{{O}_{3}}+N{{H}_{4}}Cl\] | Carbonates (\[CaC{{O}_{3}}\] etc.) | \[{{K}_{SP}}\] values of carbonate are less than that of group VI \[(M{{g}^{2+}})\] hence precipitation before \[M{{g}^{2+}}\]. |
| VI |
\[M{{g}^{2+}},(N{{a}^{+}},{{K}^{+}}\] also included) |
\[N{{H}_{4}}OH+N{{a}_{2}}HP{{O}_{4}}\] (only for \[M{{g}^{2+}}\]) | White ppt. \[(MgHP{{O}_{4}})\] | – |
| 0 (Zero) |
\[NH_{4}^{+}\] |
– | – | Tested independently from original solution. |
You need to login to perform this action.
You will be redirected in
3 sec
