Dry Heating Test Assignment Help | Dry Heating Test Homework Help

Dry Heating Test

In this test, a little of the substance is heated in a dry test-tube. As a result, the substance undergoes decomposition, or oxidation with evolution of gases along with some characteristic changes which throw light on the cation or anion present as described below.

(a)    Evolution of gases

(i)    Non-alkali metal carbonates and all bicarbonates decompose on heating with the evolution of CO2 gas.

BaCO3     →     BaO + CO2
2NaHCO3     →     Na2CO3 + CO2 + H2O

(ii)    Hydrated sulphides such as Na2.S.2H2O give H2S

Na2S . 2H2O    →    2NaOH + H2S

(iii)    Hydrated chlorides such as CuCI2.H2O produce HCI gas

CuCI2 . H2O   →    CuO + 2HCI

(iv)    Bromides and iodides get oxidized to produce bromine or iodine gases as

2CdBr2 + O2    →     2CdO + 2Br2
2CdI2 + O2      →      2CdO + 2I2

(v)    Heavy metal nitrates such as Pb(NO3)2 produce NO2

2Pb(NO3)2    →    2PbO + 4NO2 + O2

(vi)    Ammonium salts decomposes liberating NH3 gas

(NH4)2SO4   →    NH4HSO4 + NH3

(b) Condensation of water vapours. Hydrated salts such as CuSO4. 5H2O or  7H2O on heating lose water of crystallization and form anhydrous salt. The water vapours thus produced get deposited on cooler portion of the test-tube.

CuSO4 . 5H2O   →   CuSO4 + 5H2O

For more help in Dry Heating Test click the button below to submit your homework assignment