Answer to Question #149944 in Chemistry for Salim Abdallah Ahmed

Question

Explain briefly the reasons for the following observations supporting your discussion, wherever possible by means of balanced chemical or ionic equations or structures
i) When mineral pyrolusite, MnO2, is mixed with sodium carbonate and the mixture melted in presence of air, the melt is coloured green. When the cooled melt is dissolved in water, the solution formed made just acidic, a brown precipitate forms. The solution that results is purple coloured

Answer 1

When mineral pyrolusite, MnO₂, is mixed with sodium carbonate and the mixture melted in presence of air, a deep green solid of sodium manganate and carbon dioxide gas are formed:

2MnO₂ + 2Na₂CO₃ + O₂ $\rightarrow$ 2Na₂MnO₄ + 2CO₂$\uparrow$ .

When the melt of sodium manganate is dissolved in water, sodium permanganate, pyrolusite and sodium hydroxide are produced:

3Na₂MnO₄ + 2H₂O $\rightarrow$ 2NaMnO₄ + MnO₂$\downarrow$ + 4NaOH.

The solution of sodium permanganate NaMnO₄ is purple colored.