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

Option (d) is incorrect.

Step 1: Analyze Option (a)

The statement claims that at \(600^{\circ} \mathrm{C}\), sulphur gas mainly consists of \(\mathrm{S}_2\) molecules. Sulphur molecules can indeed break down into smaller units as temperature increases. \(\mathrm{S}_2\) molecules become significant in the gas phase at high temperatures, supporting this statement.

Step 2: Analyze Option (b)

This option indicates that at \(200^{\circ} \mathrm{C}\), the vapour consists mostly of \(\mathrm{S}_8\) rings. At lower temperatures, sulphur is known to exist predominantly as \(\mathrm{S}_8\) rings in the vapour, which confirms that this statement is correct.

Step 3: Examine Option (c)

It is stated that the \(\mathrm{S}_2\) molecule is paramagnetic. Paramagnetism in molecules is usually due to unpaired electrons. \(\mathrm{S}_2\) is similar to \(\mathrm{O}_2\) in having unpaired electrons, hence it is also paramagnetic. This statement is accurate.

Step 4: Evaluate Option (d)

The option claims that the oxidation state of sulphur is never less than \(+4\). However, sulphur often exhibits oxidation states lower than \(+4\), such as \(+2\) in \(\mathrm{H}_2\mathrm{S}\), or \(0\) in elemental sulphur. Therefore, this statement is incorrect.

Key Concepts

Sulfur Molecular Forms

Sulfur is a fascinating element with the ability to exist in several molecular forms, also known as allotropes. This flexibility occurs because sulfur can form strong bonds with itself, creating a variety of stable catenated structures. At room temperature, the most common form of sulfur is the orthorhombic form, consisting of eight sulfur atoms arranged in a ring, known as \(\mathrm{S}_8\). When heated, sulfur undergoes a fascinating transformation.

As the temperature increases, sulfur's ring structures can open up and recombine to form different configurations. For instance:

• At around \(119^{\circ} \mathrm{C}\), sulfur transitions from the solid \(\mathrm{S}_8\) form into liquid sulfur.
• Further heating to around \(200^{\circ} \mathrm{C}\) results in sulfur vapor that mainly comprises \(\mathrm{S}_8\) rings, but with increased temperature, the molecule begins to break down to smaller units.
• At temperatures nearing \(600^{\circ} \mathrm{C}\), the majority of the vapor phase is composed of \(\mathrm{S}_2\) molecules, which resemble double-bonded oxygen (\(\mathrm{O}_2\)).

Understanding the behavior of sulfur at different temperatures can give insights into its versatility and the myriad of chemical reactions it can participate in.

Oxidation States of Sulfur

Sulfur is versatile in terms of oxidation states, ranging from \(-2\) to \(+6\). This wide range of possible oxidation states is a testament to its ability to both accept and donate electrons, participating in a variety of reactions. Here’s how sulfur behaves in different compounds:

• Elemental sulfur, commonly found in nature, has an oxidation state of \(0\).
• In \(\mathrm{H}_2\mathrm{S}\), where sulfur is bound to hydrogen, it has the lowest oxidation state of \(-2\), indicating it has gained electrons.
• Compounds like \(\mathrm{SO}_2\) feature sulfur in a \(+4\) oxidation state. In \(\mathrm{SO}_4^{2-}\) (sulfate ions), sulfur is at the highest common oxidation state of \(+6\).

Sulfur’s ability to have multiple oxidation states is integral to its role in biological systems, industrial processes, and environmental chemistry. It's crucial to note that, contrary to some beliefs, sulfur can and often adopts oxidation states below \(+4\) in various compounds.

Paramagnetism in Sulfur Compounds

Paramagnetism in molecules is an interesting phenomenon resulting from unpaired electrons within the molecule. For sulfur, the paramagnetic behavior is most prominently observed in the \(\mathrm{S}_2\) molecule.

Much like oxygen (\(\mathrm{O}_2\)), \(\mathrm{S}_2\) can exhibit paramagnetism due to the presence of two unpaired electrons in its antibonding molecular orbitals. These unpaired electrons produce magnetic moments that align with an external magnetic field, thus showing paramagnetic properties.

Generally speaking, paramagnetism in sulfur compounds is rare, as most of its common forms, like \(\mathrm{S}_8\), do not feature unpaired electrons. However, understanding the electronic configuration of \(\mathrm{S}_2\) sheds light on the distinctive magnetic properties sulfur can exhibit under specific conditions, adding to its chemical complexity and fascinating behavior in varied environments.