chemistry

CLASS A (II):

GASES OR ACID VAPOURS EVOLVED WITH CONC. SULPHURIC ACID 

Chloride (Cl-) :

Conc. Sulphuric acid : chloride ion decomposes with the evolution of HCl.
Cl- + H2SO4 → HCl + HSO4

Siver nitrate Solution : White , curdy ppt. of AgCl insoluble in water and in dil. nitric acid , but soluble in dilute ammonia solution .

Cl- + Ag+ → AgCl ↓
AgCl ↓ + 2NH3 → [Ag(NH3)2]Cl
Ag(NH3)2Cl + 2H+ → AgCl + 2NH4+

Bromide (Br-) :

Conc. Sulphuric acid : gives reddish brwon vapours of bromine accompany the hydrogen bromide.
2KBr + H2SO4 → K2SO4 + 2HBr
2HBr + H2SO4 → 2H2O + SO2 ↑ + Br2↑(reddish brown)

Silver nitrite Solution : Curdy pale yellow ppt. of Silver bromide is obtained . This ppt. is sprangily soluble in dil. but readliy soluble in conc. ammonia solution and insoluble in dil. HNO3
Br- + Ag+ → AgBr

Iodide (I-) :

Conc. Sulphuric Acid : Gives violet vapours of iodine .
2I- + H2SO4 → I2(violet vapours) + SO42- + 2H2O + SO2 ↑

Silver nitrite Solution : Yellow curdy ppt. of silver iodide AgI , very slightly soluble in conc. ammonia solution and insoluble in dil. nitric acid .
I- + Ag+ → AgI

Nitrate (NO3-) :

Conc. Sulphuric Acid : gives reddish brown vapours of nitrogen dioxide .
4NO3- + 2H4SO4 → 4NO2↑ + 2SO4- + 2H2O + O2↑

Brown Ring Test : When freshly saturated solution of iron(II) sulphate is added to nitrate solution and pour conc. H2SO4 slowly down the side of the test tube , a brown ring is obtained .
2NO- + 4H2SO4 + 6Fe2+ → 6Fe3+ + 2NO + 4SO4- + 4H2O
Fe2+ + NO ↑ → [Fe(NO)]
On shaking and warmong the mix , the brown colour disappears , nitric oxide is evolved and a yellow solution of iron (III) ions remain.