Charcoal Cavity Test Assignment Help | Charcoal Cavity Test Homework Help

Charcoal Cavity Test

Some salts on heating with fusion mixture (Na2CO3 + K2CO3) in the charcoal vanity decompose to form their corresponding oxides which appear as colored incrustation or residue as :

ZnSO4 + Na2CO3     →     ZnCO3 + Na2SO4
                ZnCO3       →     ZnO + CO2

In the above reaction, zinc oxide is yellow when hot and white when cold.
In some cases. the metallic oxide thus formed gets reduced by carbon to metallic bead or scale as

Pb(NO3)2 + Na2CO3    →   PbCO3 + 2NaNO3
                       PbCO3     →      PbO + CO2

PbO + C    →     Pb          +  CO
                           Metallic bead