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

Statement (d) is incorrect.

Step 1: Analyze Each Statement

We need to evaluate each statement based on known chemical properties of sulfur. Starting with statement (a): At higher temperatures, like \(600^{\circ} \mathrm{C}\), sulfur vapor mainly consists of \(\mathrm{S}_2\) molecules, which has some similarity to oxygen molecules (\(\mathrm{O}_2\)) because it is simpler and smaller. Thus, statement (a) is correct.

Step 2: Examine Statement b

Statement (b) claims that at \(200^{\circ} \mathrm{C}\), sulfur vapor largely consists of \(\mathrm{S}_8\) rings. Generally, at lower temperatures, sulfur rings like \(\mathrm{S}_8\) are stable and prevalent, meaning statement (b) is also correct.

Step 3: Assess Statement c

Statement (c) states that \(\mathrm{S}^2\) molecules are paramagnetic. Paramagnetism arises from unpaired electrons. Since the \(\mathrm{S}_2\) molecule has similar electronic properties to \(\mathrm{O}_2\), which is paramagnetic, statement (c) is true.

Step 4: Evaluate Statement d

Statement (d) asserts that sulfur's oxidation state is never less than \(+4\) in its compounds. However, in compounds like hydrogen sulfide \(\mathrm{H}_2\mathrm{S}\) and in sulfide ions \(\mathrm{S}^{2-}\), sulfur exhibits an oxidation state of \(-2\). Therefore, statement (d) is incorrect.

Key Concepts

Sulfur Compounds

Sulfur is a versatile element known for forming a wide range of compounds. These include sulfides, sulfates, and sulfoxides, among many others. Each type of compound features different structural and chemical properties which can make them useful in diverse applications such as fertilizers, medicinal drugs, and even in gunpowder.
A common example is hydrogen sulfide (H_2S), which is a notable sulfur compound with a distinct smell of rotten eggs.

• Sulfur Dioxide (SO_2): an important compound often used as a preservative and disinfectant.
• Sulfuric Acid (H_2SO_4): widely used in industry and manufacturing, particularly in fertilizers.
• Sulfonamides: essential in the pharmaceutical industry for the creation of antibiotics.

These compounds vary widely in their properties and uses but share the central role of sulfur as a key element.

Oxidation States

The oxidation state is a concept in chemistry that denotes the degree of oxidation of an atom. Sulfur can exhibit a range of oxidation states, from -2 to +6. This variability allows sulfur to participate in various chemical reactions.
Common oxidation states of sulfur include:

• -2: Found in compounds like hydrogen sulfide (H_2S) or in sulfide ions (S^{2-}).
• 0: Elemental sulfur (S), such as sulfur flowers.
• +4: Present in sulfur dioxide (SO_2), a key compound in atmospheric processes.
• +6: Seen in sulfuric acid (H_2SO_4), one of the most significant industrial chemicals.

Understanding oxidation states is crucial for predicting the reactivity and properties of sulfur compounds.

Paramagnetism

Paramagnetism is a form of magnetism that occurs in materials with unpaired electrons. Unlike diamagnetic substances, which are weakly repelled by magnetic fields, paramagnetic materials are attracted to them.
The molecule S_2, similar to oxygen (O_2), exhibits paramagnetism due to the presence of unpaired electrons. These electrons respond to external magnetic fields, aligning in a way that enhances the material's magnetic properties.
Analyzing paramagnetism in molecules provides insights into their electronic structures and bonding characteristics, making it a significant concept in advanced chemical studies.

S8 Rings

Sulfur commonly exists in nature in the form of S_8 rings. These are cyclic molecules composed of eight sulfur atoms. They are the most stable and abundant form of elemental sulfur.

Structure and Stability

The S_8 ring structure resembles a crown, with each sulfur atom forming two single bonds to its neighbors, creating a puckered ring. This configuration provides the right balance of stability and reactivity:

• Provides a vibrant yellow color to sulfur.
• The crown shape ensures minimal strain within the ring.

Behavior Under Temperature

As temperature increases, S_8 rings can break into smaller sulfur molecules like S_2, influencing their chemical behavior and physical properties.

Thermal Properties of Sulfur

Sulfur is known for its distinct thermal properties, often changing structures based on temperature. At room temperature, it forms S_8 rings, but upon heating, these rings break down into shorter chains.

• At about 120^{6}C, sulfur enters a plastic state, becoming more flexible yet maintaining its shape.
• Further heating to about 159^{6}C, sulfur melts into a viscous, dark liquid containing many chain-like structures.
• As temperature continues to rise, reaching around 600^{6}C, the S_2 gaseous form becomes dominant.

Due to these properties, sulfur is used in various applications that require temperature regulation, such as vulcanization in the rubber industry.