In the charcoal cavity cobalt nitrate test, heating an unknown white powder yields a distinct blue m — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Thenard's blue is formed by the reaction of Aluminium oxide with Cobalt oxide ($Al_2O_3 + CoO \rightarrow CoO \cdot Al_2O_3$). In this double oxide (Cobalt aluminate), the Cobalt atom derived from $CoO$ retains a +2 oxidation state.