Dry Test Analysis for action of concentrated H2SO4

 

Treat 1 gm of mixture with 2 cm³ of concentrated H₂SO₄ in a test tube. If no reaction occurs in the cold, warm it gently.

If the mixture reacted with dilute H₂SO₄ , the addition of concentrated acid ay result in a vigorous reaction and rapid evolution of gas, which may be accompanied by a very fine spray of acid. In such a case it is best to add dil.(2N) H₂SO₄ to another portion of the mixture until action ceases, and then add 1 cm³ of concentrated H₂SO₄.

Sr. No.	Observations	Interferences
1	Colourless gas evolved with pungent odour and white fumes in the air; white fumes NH4Cl in contact with glass rod wet with NH4OH solution. Cl2 evolved on addition of MnO2 (reddens, then bleaches litmus paper).	Cl’ HCl from chloride.
2	Gas evolved with pungent odour, reddish colour and fumes in moist air. On addition of MnO2 increased amount of red fumes with odour of Br2.	Br’ HBr and Br2 from bromide.
3	Violet vapours evolved, accompanied by pungent acid fumes and often SO2 and even H2S.	I’ HI and I2 from iodide.
4	Pungent acid fumes evolved, often coloured brown by NO2: colour deepens upon addition of copper turnings (if nitrite absent).	NO3’ HNO3 and NO2 from nitrate.
5	Colourless gas evolved; renders lime water turbid. And may also burn with a blue flame; no blackening.	CO and CO2 from oxalate. (C2O4’’)
6	CO and CO2 are evolved and charring with burning smell of Sulphur (SO2) is given.	Tartrate (C4H3O6’’’).
7	Odour of vinegar.	CH3COOH from acetate. (CH3COO’)