To solve this intriguing chemistry problem, we need to identify the compounds A, B, and C based on the reactions described. The blackish-brown solid A is likely to be a form of manganese oxide, specifically manganese dioxide (MnO2). When fused with an alkali metal hydroxide in the presence of air, it forms a dark green compound, which is potassium manganate (K2MnO4). Upon electrolytic oxidation in an alkaline medium, this compound transforms into a dark purple compound, potassium permanganate (KMnO4). Let’s break down the reactions involved step by step.
Identifying the Compounds
Compound A: Manganese Dioxide (MnO2)
Manganese dioxide is a blackish-brown solid commonly found in nature. It is often used in various chemical reactions due to its oxidizing properties.
Compound B: Potassium Manganate (K2MnO4)
When manganese dioxide reacts with an alkali metal hydroxide (like potassium hydroxide, KOH) in the presence of air, it undergoes a fusion reaction to produce potassium manganate, which is characterized by its dark green color.
Compound C: Potassium Permanganate (KMnO4)
Electrolytic oxidation of potassium manganate in an alkaline medium leads to the formation of potassium permanganate, a well-known dark purple compound used in various applications, including as a disinfectant and in analytical chemistry.
Reactions Involved
Reaction 1: Formation of Potassium Manganate
The first reaction involves the fusion of manganese dioxide with potassium hydroxide in the presence of air:
- 4 MnO2 + 4 KOH + O2 → 4 K2MnO4 + 2 H2O
This reaction shows how manganese dioxide reacts with potassium hydroxide and oxygen to produce potassium manganate.
Reaction 2: Electrolytic Oxidation to Potassium Permanganate
The second reaction is the electrolytic oxidation of potassium manganate:
- 3 K2MnO4 + 2 H2O → 2 KMnO4 + 2 KOH + 2 e-
In this process, potassium manganate is oxidized to form potassium permanganate, along with the release of electrons and the formation of potassium hydroxide.
Summary of the Compounds and Reactions
To summarize, the blackish-brown solid A is manganese dioxide (MnO2), the dark green compound B is potassium manganate (K2MnO4), and the dark purple compound C is potassium permanganate (KMnO4). The reactions illustrate the transformation of manganese compounds through oxidation and reduction processes, showcasing the fascinating chemistry of manganese.
