Problem 216 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements regarding sulphur is incorrect? (a) At \(600^{\circ} \mathrm{C}\) the gas mainly consists of \(\mathrm{S}_{2}\) molecules. (b) The vapour at \(200^{\circ} \mathrm{C}\) consists mostly of \(\mathrm{S}_{8}\) rings. (c) \(\mathrm{S}^{2}\) molecule is paramagnetic. (d) The oxidation state of sulphur is never less than +4 in its compounds.

Step-by-Step Solution

Answer

The incorrect statement is (d).

Step 1: Analyze Statement (a)

Statement (a) claims that at \(600^{\circ} C\), the gas mainly consists of \(\mathrm{S}_{2}\) molecules. At this high temperature, \(\mathrm{S}_{8}\) rings break down into smaller \(\mathrm{S}_{2}\) molecules due to thermal decomposition. This statement is correct.

Step 2: Analyze Statement (b)

Statement (b) states that at \(200^{\circ} C\), the vapor consists mostly of \(\mathrm{S}_{8}\) rings. Until approximately \(444.6^{\circ} C\), sulphur vapor largely contains \(\mathrm{S}_{8}\) rings, making this statement correct.

Step 3: Analyze Statement (c)

Statement (c) mentions that \(\mathrm{S}_{2}\) molecule is paramagnetic. \(\mathrm{S}_{2}\) is known to have unpaired electrons, making it paramagnetic. Therefore, this statement is correct.

Step 4: Analyze Statement (d)

Statement (d) suggests that the oxidation state of sulphur is never less than +4 in its compounds. This statement is incorrect because sulphur can have negative oxidation states, such as \(-2\) in hydrogen sulfide \(\left( \mathrm{H}_{2}\mathrm{S} \right)\).

Key Concepts

Paramagnetic Properties

Paramagnetic properties refer to the tendency of a material to be attracted by a magnetic field due to the presence of unpaired electrons. In the context of sulfur chemistry, the \(S_{2}\) molecule is a notable example. This molecule behaves as paramagnetic because it contains two unpaired electrons in its antibonding molecular orbitals. Unlike diamagnetic substances, which have all their electrons paired and do not have this attraction to magnetic fields, paramagnetic substances like \( S_{2}\) are drawn toward external magnetic forces.
This property can be analyzed using molecular orbital theory, which predicts the electronic configuration of \( S_{2}\) to include unpaired electrons. This simple fact explains why \( S_{2}\) responds to a magnetic field, a behavior well-supported by experimental observations. Understanding this feature is crucial for interpreting the magnetic characteristics of sulfur and other similar molecular systems.

Oxidation States

Oxidation states represent the degree of oxidation (loss of electrons) of an atom in a chemical compound. Sulfur can exhibit a wide range of oxidation states, making it quite versatile in chemical reactions. A common misconception, as highlighted in statement (d) of the exercise, is that sulfur's oxidation state is never less than +4. However, sulfur can also have negative oxidation states.
For example, in hydrogen sulfide (\( H_{2}S \)), sulfur is in the \( -2 \) oxidation state, indicating it has gained electrons. Conversely, sulfur's highest oxidation state observed is +6, as seen in sulfuric acid \( H_{2}SO_{4} \).

• This flexibility allows sulfur to participate in diverse chemical environments.
• It also contributes to its ability to form various structures and compounds.

Understanding these various states assists in grasping the complex chemistry of sulfur and its role in both inorganic and organic systems.

Sulphur Molecules

Sulfur is unique due to its capability to form a variety of molecular structures, the most prominent being \( S_{8}\) rings. At room temperature, sulfur predominantly exists in the form of octatomic rings, \(S_{8}\). These molecules consist of a crown shape ring structure that is relatively stable.
As the temperature rises, particularly beyond \( 444.6^{\circ}C\), these rings can break into smaller units, such as \( S_{2}\), due to thermal agitation. Such transformations speak to the adaptability of sulfur in response to environmental changes.

• The ability to form various allotropes is crucial for its role in industrial applications.
• Sulfur's diverse molecular forms are foundational in reactions involving sulfur compounds, both in nature and in synthetic chemistry.

Understanding the dynamics of these molecules helps predict and explain the behavior of sulfur under different conditions.

Thermal Decomposition of Sulphur

Thermal decomposition refers to the breaking down of a chemical compound into simpler substances when heat is applied. Sulfur undergoes profound transformations with changes in temperature, offering excellent examples of this phenomenon.
At temperatures around \( 600^{\circ}C\), sulfur's typical \( S_{8}\) rings start breaking into \( S_{2}\), driven by increased kinetic energy of the molecules. This decomposition into smaller diatomic molecules reflects the flexibility in sulfur's bonding capabilities.

• This behavior of sulfur is essential for understanding its role in high-temperature chemical processes.
• It also helps in comprehending how these transformations impact sulfur's physical and chemical properties.

By studying these thermal processes, chemists can predict sulfur's behavior in various industrial and environmental contexts, which is vital for creating temperature-resistant materials and understanding atmospheric chemistry.