Problem 83 - A Complete Resource Book in Chemistry for JEE Main

Question

When \(\mathrm{MnO}_{2}\) is fused with KOH, a coloured compound is formed. The product and its colour is (a) \(\mathrm{K}_{2} \mathrm{MnO}_{4}\), purple green (b) \(\mathrm{KMnO}_{4}\), purple (c) \(\mathrm{Mn}_{2} \mathrm{O}_{3}\), brown (d) \(\mathrm{Mn}_{3} \mathrm{O}_{4}\), black

Step-by-Step Solution

Answer

The product formed is \( \mathrm{K}_{2} \mathrm{MnO}_{4} \), which is green.

Step 1: Identify Reactants

In this reaction, the reactant given is \( \mathrm{MnO}_{2} \) (Manganese(IV) oxide) is fused with \( \mathrm{KOH} \) (potassium hydroxide).

Step 2: Analyze The Reaction

When \( \mathrm{MnO}_{2} \) is fused with \( \mathrm{KOH} \), it will result in a high-temperature oxidation process. Manganese is in a +4 oxidation state in \( \mathrm{MnO}_{2} \) and will undergo further oxidation.

Step 3: Determine Oxidation Product

The fusion of \( \mathrm{MnO}_{2} \) with \( \mathrm{KOH} \) typically forms \( \mathrm{K}_{2} \mathrm{MnO}_{4} \), where manganese is in the +6 oxidation state. The formula for the product is \( \mathrm{K}_{2} \mathrm{MnO}_{4} \).

Step 4: Assign Colour to the Product

The compound \( \mathrm{K}_{2} \mathrm{MnO}_{4} \) is known to have a green colour. This is a characteristic property of the tetravalent manganese compound.

Step 5: Match With Options Provided

Now, compare the product and its properties with the ones given in the options. Option (a) \( \mathrm{K}_{2} \mathrm{MnO}_{4} \), green, matches the product and its colour.

Key Concepts

Manganese Compounds

Manganese is a versatile transition metal that forms numerous compounds, each possessing unique properties. Among these, manganese oxides are especially significant in both industrial applications and chemical reactions. Manganese compounds can have various oxidation states, ranging from +2 to +7, which directly influence their colour and chemical behavior.

• Manganese Dioxide \(\mathrm{MnO}_2 \): This is one of the most stable forms and is commonly used as a catalyst and in dry cell batteries.
• Potassium Manganate \(\mathrm{K}_2\mathrm{MnO}_4 \): Formed by fusing \(\mathrm{MnO}_2 \) with \(\mathrm{KOH} \), this compound is green and exemplifies the +6 oxidation state of manganese.

Manganese allows for creativity in chemistry due to its ability to change oxidation states and participate in diverse reactions. These changes often produce visually striking colors, which can be beneficial in identifying compounds during experiments.

Oxidation States

Oxidation state, often used interchangeably with oxidation number, refers to the degree of oxidation of an atom within a compound. Manganese is renowned for exhibiting a wide range of oxidation states from +2 to +7. This property is fundamental to its ability to form an extensive array of compounds and participate in redox reactions. - In the instance of \(\mathrm{MnO}_2 \), manganese exists in the +4 oxidation state. When subjected to high temperature with potassium hydroxide (\(\mathrm{KOH}\)), it undergoes oxidation to form \(\mathrm{K}_2\mathrm{MnO}_4 \), where manganese is in the +6 oxidation state.

• Importance in Chemical Reactions: The oxidation state indicates how many electrons an atom gains, loses, or shares when bonding, influencing the compound's reactivity and color.
• Determining Properties: Understanding oxidation states helps predict the compound structure and potential reactions, aiding in applications like battery design and catalysis.

Every change in oxidation state provides new insight into the chemical behavior of manganese, making it a fascinating element to study in redox chemistry.

Chemical Reactions

Chemical reactions involve the transformation of substances through breaking and forming of bonds, leading to products with different properties and compositions. In the case of manganese compounds, these reactions are particularly intriguing due to the transition of oxidation states and the resultant color variations.- The fusion of \(\mathrm{MnO}_2 \) with \(\mathrm{KOH} \) is a classical example of employing heat to drive a chemical reaction that facilities the oxidation of manganese.

• Fusion Reaction: This specific reaction requires heat to achieve the transition of manganese from a +4 to a +6 oxidation state.
• Product Formation: The fusion yields \(\mathrm{K}_2\mathrm{MnO}_4 \), recognized by its distinctive green color, confirming the formation of a new compound and oxidation state.

This example underscores the principles of redox reactions — essential mechanisms in chemistry where oxidation and reduction occur simultaneously. Observing such reactions can provide deep insight into the electron transfer processes and compound stability under various conditions.