Problem 26 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

When a small amount of \(\mathrm{KMnO}_{4}\) is added to concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\), a green oily compound is obtained which is highly explosive in nature. Compound may be : (a) \(\mathrm{MnSO}_{4}\) (b) \(\mathrm{Mn}_{2} \mathrm{O}_{7}\) (c) \(\mathrm{MnO}_{2}\) (d) \(\mathrm{Mn}_{2} \mathrm{O}_{3}\)

Step-by-Step Solution

Answer

The compound is (b) \(\mathrm{Mn}_{2}\mathrm{O}_{7}\).

Step 1: Understanding the reaction context

When potassium permanganate (\(\mathrm{KMnO}_{4}\)) is added to concentrated sulfuric acid (\(\mathrm{H}_{2}\mathrm{SO}_{4}\)), the conditions are very strong, often leading to the formation of higher oxidation state compounds or unusual species.

Step 2: Observing chemical properties

The reaction that takes place under these strong acidic conditions can produce an oxidizing agent in the form of a compound with a higher oxidation state of manganese, especially due to the presence of the concentrated sulfuric acid.

Step 3: Identifying possible products

Among the given options, \(\mathrm{Mn}_{2}\mathrm{O}_{7}\) is known for being a green oily liquid that is highly explosive, which matches the description in the problem statement. Other options such as \(\mathrm{MnSO}_{4}\), \(\mathrm{MnO}_{2}\), and \(\mathrm{Mn}_{2}\mathrm{O}_{3}\) do not fit the description of being green and oily or explosive.

Step 4: Confirming the correct compound

The description of a green oily compound that is explosive aligns well with the chemical characteristics of \(\mathrm{Mn}_{2}\mathrm{O}_{7}\). This compound is formed by the dehydration of permanganic acid when potassium permanganate reacts with concentrated sulfuric acid.

Key Concepts

Potassium Permanganate

Potassium permanganate, often represented as \( \mathrm{KMnO}_{4} \), is a common chemical compound known for its intense purple color. It is a powerful oxidizing agent, which means it can easily accept electrons from other substances, leading to various chemical reactions. This characteristic is harnessed in numerous applications, from water treatment to laboratory experiments.

• **Oxidizing Agent**: It has a high oxidation potential, making it useful in redox reactions.
• **Color Indicator**: Its distinct purple color often helps in indicating the presence of oxygen due to oxidation processes.
• **Industrial Use**: Used in disinfectants and as a treatment to remove iron and hydrogen sulfide from well water.

When mixed with strong acids like sulfuric acid, potassium permanganate can produce compounds in unusual oxidation states. Such mixtures can lead to interesting transformations and serve as compelling demonstrations of chemical phenomena.
In the exercise context, the addition of \( \mathrm{KMnO}_{4} \) into concentrated \( \mathrm{H}_{2}\mathrm{SO}_{4} \) results in the formation of a green oily compound, indicative of its ability to participate in violent and energetic reactions.

Sulfuric Acid

Sulfuric acid, \( \mathrm{H}_{2}\mathrm{SO}_{4} \), is one of the most widely used chemicals in the industrial world. It's a strong acid that is highly reactive and plays a crucial role in the synthesis of various chemicals. Being a concentrated form of an acid, it provides an environment conducive to many unique and vigorous chemical reactions.

• **Powerful Dehydrating Agent**: It can remove water molecules from other substances, which is why concentrated sulfuric acid often results in the formation of oxides from certain compounds.
• **Supports Oxidations**: In reactions with potassium permanganate, the acid not only acts as a medium but also supports the oxidation of manganese to higher states.
• **Versatile Use**: Besides industrial manufacturing, it is crucial in producing fertilizers, refining petroleum, and processing metals.

In the context of the exercise, sulfuric acid's strong dehydrating ability leads to the formation of a highly unusual manganese compound, \( \mathrm{Mn}_{2}\mathrm{O}_{7} \), which is explosive.
Understanding sulfuric acid's powerful characteristics allows us to predict and explain the outcomes of such compelling chemical transformations.

Manganese Compounds

Manganese is a transition metal that forms a variety of chemical compounds with different oxidation states. This gives rise to numerous manganese-based chemicals, each exhibiting unique properties. Among them, permanganates and manganese oxides are particularly notable.

• **Variable Oxidation States**: Manganese compounds vary from \( +2 \) to \( +7 \) states, with each state having different chemical behaviors and appearances.
• **Common Compounds**: Examples include manganese dioxide (\( \mathrm{MnO}_{2} \)), manganese sulfate (\( \mathrm{MnSO}_{4} \)), and permanganates (e.g., \( \mathrm{KMnO}_{4} \)).
• **Reactivity and Stability**: Compounds like \( \mathrm{Mn}_{2}\mathrm{O}_{7} \) are highly reactive and less stable, while others like \( \mathrm{MnO}_{2} \) serve as robust catalysts.

In this exercise, the produced \( \mathrm{Mn}_{2}\mathrm{O}_{7} \) is a prime example of manganese's versatility, being a green, oily, and explosive compound.
This compound is formed by the oxidation of manganese from its original state in potassium permanganate when mixed with a powerful acid like sulfuric acid.
A good understanding of manganese chemistry helps in identifying and predicting such complex chemical behavior, highlighting manganese's role in intriguing and vital chemical reactions.