Question

ideNTIFY THE CATIONIC AND ANIONIC RADICAL IN GIVEN UNKNOWN SALT A BY PERFORMING DRY AND WET TEST FOR CATIONIC RADICAL AND ANIONIC RADICAL IN ENGLISH PRATICAL

Answer 1

DRY TEST :- the most commonly employed the dry test on solid sample are:-

1.BORAX BEAD TEST :- Borax (Na2B2O7.10H2O) is first heated on platinum wire where it is dehydrated completely forming glass like beads consisting of NaBO2 and B2O3 . The bead is then mixed with salt to be tested and heated further where colored metal metaborates are formed.e.g.,
CuO + B2O3 ---> Cu(BO2)2 (green in hot and blue in cold)
results of Borax bead test with some common metal is summarized in the following ( in oxidizing flame ) :
metal ---------------- hot---------------cold
Cu---------------green ---------------blue
Fe-------- -yellowish-brown ------- yellow
Cr --------- yellow ---------------- Green
Mn -------- Violet ----------------- Amethyst
Co --------- blue --------------- blue
Ni ---------- violet -------------- reddish-brown

2.MICROCOSMIC SALT BEAD TEST :- the microcosmic salt ( Na(NH4)HPO4.4H2O) is heated on platinum wire where transparent colorless beads consisting sodium metaphosphate is formed.

(Na(NH4)HPO4.4H2O) -----> NaPO3 + H2O + NH3↑
salt is then mixed with bead and heated further where colored metal phosphate is formed e.g.,
NaPO3 + CoO ----> NaCoPO4

color of some of metal phosphate is summarized below in oxidizing flame :-
metal ---- Hot -------cold
Cu ----- Green --- blue
Fe ---- yellowish brown ---- yellow
Cr ----Green ---- green
Mn -----violet ----- violet
Co ----- Blue -----Blue
Ni------Brown ---- brown


WET TEST
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WET TEST FOR CATION
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Group 1 ions :- test of Ag+
when reagent - dil HCl
observation - white ppt of AgCl
remark - dissolve in conc.HCl forming [AgCl2]-

when reagent - NH3 (aq)
observation - Brown ppt - Ag2O
remark - dissolve in excess of NH3 forming [Ag(NH3)2]+

test of Pb2+
reagent - dil HCl
observation - PbCl2 - white ppt
remark - insoluble in cold but soluble in hot
soluble in excess of chloride due to formation of [PbCl4]²-

reagent - NH3 (aq)
observation - pb(OH)2-white ppt
remark - insoluble in excess reagent


Group II ions - test of Mercury (Hg2²+)
reagent - NH3
observation - HgO.Hg(NH2)NO3↓white

test of copper (Cu²+)
reagent - NH3 + H2SO4
Observation - Cu(OH)2.CuSO4↓blue
remark - ppt dissolve in excess of reagent giving deep blue solution of [Cu(NH3)4]²+

test of Bi³+
reagent - NH3 (aq)
observation- Bi(OH2)NO3↓white
remark - insoluble in excess ammonia , difference from Cu(II)


Group III ions :- test of Fe³+
reagent - NH3
observation - Fe(OH)3 ↓ brown
remark - insoluble in excess reagent

test of Al³+
reagent - NH3
observation - Al(OH)3↓ white
remark - insoluble in excess reagent

test of Cr³+
reagent - NH3
observation - Cr(OH)3 ↓green
remark - slightly soluble in excess reagent forming [Cr(NH3)6]³+

test of Mn²+
reagent - NaOH (aq)
observation - Mn(OH)2↓ white
remark - insoluble in excess reagent

test of Zn²+
reagent - NH3 (aq)
observation - Zn(OH)2↓ white
remark - dissolve in excess reagent and forming [Zn(NH3)4]²+

Group IV ions : Ba(II) and Ca(II)
reagent - NH3 (aq)
observation - no ppt of Ba(OH)2 and Ca(OH)2
remark - no ppt. Ca(OH)2 is highly soluble.

Group V ions : Mg²+
reagent - NH3(aq)
observation - Mg(OH)2↓ partial ppt ions
remark - insoluble in excess reagent but readily soluble in solution of ammonium salt.

WET TEST OF ANIONS :-
wet test of anions shown in figure .
Pic -A - detection of S²-
pic-B - detection of SO4²-
pic -C - detection of NO3-
pic -D - detection of Cl-
pic - E - detection of Br-
pic - F - detection of I-