Question

identify the cation icon and a ionic radical in unknown salt by performing dry and wet test for cationic and anionic

Answer 1

Test of cation (basic radicals)

★ Group reagent is mentioned next to group cations.
★ Test mentioned next to cation isthe preliminary; ones under it ,are confirmatory tests for it.

★ When sulphate is detected,Ba2+,Ca2+, Pb2+, and Sr2+ are not present as sulphates of these radicals are insoluble.

★ When phosphate is detected, cations of group III and later are absent.


Group 0 – NH4+(ammonium): No group reagent.
Sodium hydroxide test: Salt + NaOH = pungent smelling gas;gives white fumes when a glass rod dipped in conc HCl is brought near mouth of test tube.
Nessler's reagent test: (salt + acid + water) original solution +NaOH + Nessler's reagent =
Brown / yellow ppt.

Group I – Pb2+ (lead):original solution ( salt + acid + water) + dil HCl = white ppt; add water, boil, and divide into three parts.
part 1:- Leave original solution undisturbed = white crystals formed on cooling.
Part 2:- Potassium iodide test: original solution + KI = yellow ppt.
part 3:- Potassium chromate test: original solution + K2CrO4 = yellow ppt.

Group II –group reagent is H2S in dilute acidic
medium.Cu2+ (copper):Original solution + dil HCl + H2S = black ppt
1.Throw off extra sol, retain ppt, and dissolve in a few drops of conc HNO3 = bluish green sol,ppt dissolves; divide into two
parts.
1.Part 1 + excess NH4OH = blue coloured solution.
2. Potassium ferrocyanide test: Part2 + acetic acid + K4[Fe(CN)6] = reddish brown /
chocolate coloured ppt (this test is difficult to get).

Group III – Fe2+, Fe3+ (iron), Al3+
(aluminium): original solution + solid NH4Cl + excess NH4OH
1. Fe2+ / Fe3+: ferrous salts are green in colour, ferric salts are brown in colour. If ferrous salt has been given, convert to ferric: original solution + conc HNO3 + heat = brown ppt;then do reaction with groupreagent now,
Brown ppt + HCl; then divide into two parts,
1. Potassium ferrocyanide test: Part 1 + K4[Fe(CN)6] = blue ppt /colour

2. Potassium thiocyanate test: Part 2 + KCNS = bloodred colour.

2. Al3+: Gelatinous white ppt Blue lake test: Retain ppt + dil HCl = clear solution.
1. Sol + blue litmus and NH4OH (drop-by-drop) = blue colour layer ('lake')floats over colourless solution.

continues with Group III – Co2+(cobalt), Ni2+(nickel),Mn2+ (manganese), Zn2+ (zinc):original solution + solid NH4Cl + excess NH4OH +pass H2S gas.

1. Co2+ / Ni2+: Black ppt; dissolve ppt in aqua regia and evaporate sol to dryness to get residue.

1. Co2+: Blue residue; turns pink / purple when dissolved in water; divide into two parts,

1. Part 1 + dil acetic acid + KNO2 + warm = yellow ppt
2. Part 2 + ether (1 mL) + solid NH4CNS = blue colour in ether

2. Ni2+: Yellow residue; turns green when dissolved in water; divide into two parts
1.dimethyl glyoxime (DMG) test: Part 1 +
excess NH4OH + DMG = bright red ppt

2. Part 2 + NaOH + bromine water + boil = black ppt.
2. Mn2+: Buff / skin color ppt; divide into two parts
1. Part 1 + dil HCl + boil off H2S + NaOH = white ppt; which turns black / brown on adding bromine water.

2. Lead dioxide test: Part 2 +PbO2 + conc HNO3 + boil = after cooling; pink coloration.

3. Zn2+: Greyish white ppt; divide into two parts,
1. Part 1 + excess NaOH =white ppt dissolves
2. Potassium ferrocyanide test: Part 2 + K4[Fe(CN)6] = white / bluish white ppt.

Group IV – Ba2+ (barium), Sr2+(strontium), Ca2+ (calcium): original solution + (NH4)2CO3 + NH4Cl + NH4OH = white ppt; add dil acetic acid, divide sol into three parts and test for following in order :

1. Ba2+: Part 1+ excess K2CrO4(aq) = yellow ppt

2. Sr2+: Part 2 + (NH4)2SO4(aq) =white ppt.
3. Ca2+: Part 3+(NH4)2C2O4(aq) + NH4OH (only if nothing appears at first) = white ppt.
4. Flame test: Take salt and make a paste by mixing with conc HCl. Take paste on tip of glass rod / platinum wire, and put in Bunsen
burner flame.
1. Ba2+: Green flame
2. Sr2+: Crimson red flame
3. Ca2+: Brick red flame

Group V – Mg2+ (magnesium) :- No group reagent .When reagent - NH3 : Mg(OH)2↓ (partial ppt ion)
when reagent - NaOH:Mg(OH)2↓ (white ppt)
When reagent -(phNHNH)2=0 : violet - red ppt with Mg(OH)2
When reagent - Titan yellow test : deep red ppt with Mg(OH)

remark :- insoluble in excess reagent but readily soluble in solution of ammonium salt.

Answer 2

Explanation:

Original solution (O.S.) treated with few drops of potassium ferrocyanide solution chocolate brown ppt. indicates the presence of _______ cation/radical. *