DAY-14

Lecture -6 ecture-6 Radicals Tests In Inorganic Chemistry two types of test are observed : cationic and anionic. Anionic Test : In case of anionic test we use the following reagents. — H2SO4/HCl dil. — H2SO4 conc. H2SO4/HCl (dilute) On adding dil. H2SO4 or dil. HCl the observation is (1) A brown colour gas is coming out. Gas ⇒ NO2, Radical ⇒ NO2– (2) A gas is coming out with vinegar smell. Gas ⇒ CH3COOH, Radical ⇒ CH3COO– Note : (3) A gas comes out which turns lead acetate paper black. Gas ⇒ H2S, Radical ⇒ S– – Smell of rotten eggs. (4) A gas comes out which is having suffocating smell and turns K2Cr2O7 (orange) into green. Gas ⇒ SO2, Radical ⇒ SO3– – (5) If a gas comes out with brisk effervescence. Gas ⇒ CO2, Radical ⇒ CO3– – 1.71

Example : Find out all the given in the reaction.

Ans. A = Na2S, C = H2S. Note : Thiosulphate S2O3– – Hypo (Sodium Thio Sulphate) Na2S2O3 If a compound remove the color of violet iodine then it is Na2S2O3. +2

+2.5

Na2 S 2 O 3  I2    NaI+Na2 S 4O 6 (Iodomatic Test) Violet

Disappear

Na2S2O3 on reaction with AgBr gives white ppt. this white ppt. become black on standing and gives a compound Na3[Ag(S2O3)2] which is used as fixer in photography.

Sodium Argento thio sulphate (used as fixer in photography) Note : If salt is heated with dil. HCl it gives white turbidity and turbidity give clear solution with HNO3. Na2 S 2 O 3  HCl    S (white turbidity) dil.

S + HNO 3 dil  No + H 2 SO 4 (clear solution) 1.72

Test By Conc. H2SO4 If conc. H2SO4 is added. (1) Brown colour gas with brown ring Test. Gas = NO2,

Radical = NO3–

(2) A dark brown colour gas comes out without brown ring test. Gas = Br2,

Radical = Br–

(3) A violet coloured gas comes out Gas = I2,

Radical = I–

(4) If HCl comes out ⎯→ Cl– Note : In case of F– and Cl–. Gases F2 and Cl2 are not coming because F2 and Cl2 are good oxidiser due to this F– and Cl– are not oxidised by H2SO4. But in case of Br– and I– oxidation is easily possible.

Special Tests :

1.75

(5) If a gaseous mixture comes out which burns with blue flame.

•

Gas

=

Radical

=

CO + CO2

C2O4– – + Fe+2 ⎯→ [Fe(C2O4)2]2– Yellow Complex

•

+ H2SO4 ⎯→ CO + CO2 + H2O

Chromyle Chloride Test It is given by only chloride ion of a metal. It is not given by chlorides of Hg, Sn, Ag, Pb, and Sb.

Q 1.

Sol. 1.76

X = NH4Cl.

Some Important Tests (Anionic) (i) I2 gives violet layer, with chloroform. (ii) F– test NaF +H 2 SO 4    NaHSO 4  HF (Conc.)

HF + SiO 2    SiF4  H 2 O SiF4  H 2 O    H 2 [SiF6 ]  H 4 SiO 4  Waxy, deposite

(iii) Borate (BO3– –)

(iv) Sulphate (SO4– –)

(v) Phosphate (PO4– –)

1.77

Note : For Cromyl chloride test : (i) The test tube must be dry otherwise chromyl chloride may hydrolyse. CrO2Cl2 + 2H2O ⎯→ H2CrO4 + 2HCl (ii) Bromides and iodides do not give chromyl chloride test and in this test they evolve Br2 and I2. (iii) If NaOH solution is incompletely acidified, then white ppt. of lead hydroxide may be obtained. (iv) In the organic layer test of Br–, chlorine water must not be used in excess, otherwise layer attains pale yellow colour due to formation of bromine monochloride or it may be colourless due to formation hypobromous acid. Br2 + Cl2 ⎯→ 2BrCl (Bromine monochloride) Br2 + 2H2O + Cl2 ⎯→ 2HBrO + 2HCl Colourless

(v) In the organic layer test of I–, excess of chlorine water must be avoided otherwise the layer becomes colourless due to formation of iodic acid. I2 + 5Cl2 + 6H2O ⎯→ 2HIO3 + 10HCl (vi) Ring test is not reliable in presence of NO2–, Br– and I–. (vii) Smell of NH3 also indicates the presence of NO3–, (if nitrate salt is boiled with Zn/NaOH or Al/NaOH. Zn + 2NaOH ⎯→ Na2ZnO2 + 2(H) Al + NaOH + H2O ⎯→ NaAlO2 + 3[H] NaNO2 + 8[H] ⎯→ NaOH + 2H2O + NH3↑ (viii) HF is corrosive and causes blisters on skin, so its contact to skin must be also it should not be inhaled. (ix) If on heating mixture with conc. H2SO4, a red oily substance is condensed on colder parts of test tube, then Cl– and CrO4– (or Cr2O72–) both may be present in the mixture. 1.78

(x) During testing with conc. H2SO4, the solution must not be heated to boiling, otherwise H2SO4 will get decomposed and evolution of SO 2 will make identification of other gases difficult. (xi) In the organic layer test of Br– and I–, HNO3, CaOCl2, KMnO4, NaOCl or chloramine may also be used in place of chlorine water.

1. 2.

Which will not give cromyl chloride test (d) CaCl2 (a) AgCl (b) NaCl (c) NH4Cl A gas is coming out by conc. H2SO4 reacting with salt 'X'. Which burns with blue flame and this salt can be converted by the heating of 'Y'. X Y Gas (a)

HCOONa

(b)

3. 4. 5.

HCOONa

CO + CO2 CO + CO2

(c) Na2CO3 HCOONa CO + CO2 (d) HCOONa Na2CO3 CO + CO2 Which will not evolve gas with conc. H2SO4 (a) NaCl (b) NaF (c) NaBr (d) a and b H2SO4 + K2Cr2O7 gives brown color gas with 'X' then this 'X' may be (a) NaCl (b) NaBr (c) Both (d) None If 'A' on reaction with BaCl2 gives 'B' and this 'B' is insoluble in water then 'A' is containing (a) NaNO3 (b) Na2SO4 (c) NH4NO3 (d) NH4NO2

1.

(d)

2.

(d)

3.

(a)

4.

(b)

5.

(b) 1.79

Lecture -2 ecture-2 d-Block Compound (1) When HgS reacts with Nascent Hydrogen it give Hg. (2) When sulphide reacts with Nitroprosside then it gives another complex.

(3) Ring test is not possible in presence of bromide, iodide and nitride. Substance sublime of Heating and colour of sublimate Colour Greenish-Black Yellow Yellow-Blue/violet Gray White

Substance HgS S, HgI2, As2S3 I2 As Sb2O3, HgCl2, Hg2Cl2, As2O3, AlCl3, Amm. Halides.

Example : CrO3 is an acidic oxide. Explain. Solution : CrO3 dissolves readily in water to give chromic acid which acts as strong acid and oxidising agent. CrO3 + H2O ⎯⎯→ H2CrO4 (chromic acid) 9.17