[aeacfm]

some times we measure sulfide by  oxidation (conversion to sulfate and then determine sulfate)  but during the expirement there are some observations which i cant explain !!

the steps like that :
- sample containing sulfide + Na2CO3 +Na2O2 .
- heating 30 min  in a crusible after that the contents coverted to dark red solid in the crusible when it is left to cool.
- dissolve the solid material in the crusible with water , here come what i cant explain, during the dissolution  a strong effervescence occure and the crusible's temperature increases ( it seemsit is exothermic reaction ) and the solid dissolved in amazing way

the completeness of steps is addition of  Whatman accelerator and boiing  + neutralization with HCl and filter and measure sulfide as sulfate .
for your knowledge the sample contain (FeS , Fe2O3 , FeCO3 , CaCO3 , NaCl )

thanks in advance