Problem 8 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Oxidation state of sulphur in anions \(\mathrm{SO}_{3}^{2-}, \mathrm{S}_{2} \mathrm{O}_{4}^{2-}\) and \(\mathrm{S}_{2} \mathrm{O}_{6}^{2-}\) increases in the orders : [Main Online April 22, 2013] (a) \(\mathrm{S}_{2} \mathrm{O}_{6}^{2-}<\mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{SO}_{3}^{2-}\) (b) \(\mathrm{SO}_{6}^{2-}<\mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{S}_{2} \mathrm{O}_{6}^{2-}\) (c) \(\mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{SO}_{3}^{2-}<\mathrm{S}_{2} \mathrm{O}_{6}^{2-}\) (d) \(\mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{S}_{2} \mathrm{O}_{6}^{2-}<\mathrm{SO}_{3}^{2-}\)

Step-by-Step Solution

Answer

(c) \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{SO}_{3}^{2-}<\mathrm{S}_{2} \mathrm{O}_{6}^{2-} \)

Step 1: Determine oxidation state of sulfur in \( \mathrm{SO}_{3}^{2-}\)

The sulfate ion \(\mathrm{SO}_{3}^{2-}\) consists of sulfur and oxygen. The oxidation state of oxygen is typically \(-2\). Let the oxidation state of sulfur be \(x\).Given the ion's charge of \(-2\): \[ x + 3(-2) = -2 \]Simplifying gives: \[ x - 6 = -2 \]\[ x = +4 \]Therefore, the oxidation state of sulfur in \(\mathrm{SO}_{3}^{2-}\) is +4.

Step 2: Determine oxidation state of sulfur in \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} \)

The ion \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} \) has two sulfur atoms and four oxygen atoms. Let the oxidation state of each sulfur atom be \( x \). Each oxygen atom has an oxidation state of \(-2\).Given the ion's charge of \(-2\): \[ 2x + 4(-2) = -2 \]Simplifying gives: \[ 2x - 8 = -2 \]\[ 2x = +6 \]\[ x = +3 \]Therefore, the oxidation state of each sulfur in \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} \) is +3.

Step 3: Determine the oxidation state of sulfur in \( \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \)

The ion \( \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \) contains two sulfur atoms and six oxygen atoms. Let \( x \) be the oxidation state of each sulfur atom. Oxygen has an oxidation state of \(-2\).Considering the ion's charge as \(-2\): \[ 2x + 6(-2) = -2 \]Simplifying gives: \[ 2x - 12 = -2 \]\[ 2x = +10 \]\[ x = +5 \]Therefore, the oxidation state of each sulfur in \( \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \) is +5.

Step 4: Compare oxidation states of sulfur in each ion

The oxidation states of sulfur are as follows:- \( \mathrm{SO}_{3}^{2-} \): +4- \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} \): +3- \( \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \): +5The increasing order of oxidation states is: \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} < \mathrm{SO}_{3}^{2-} < \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \).

Key Concepts

Sulfur Chemistry

Sulfur is a non-metal and an essential element that plays various roles in chemistry. It is primarily known for its versatility in forming different compounds, including the well-known oxoanions. These include sulfate (\( \mathrm{SO}_{3}^{2-} \)), thiosulfate (\( \mathrm{S}_{2}\mathrm{O}_{4}^{2-} \)), and dithionate (\( \mathrm{S}_{2}\mathrm{O}_{6}^{2-} \)). Understanding sulfur chemistry involves looking at its oxidation states, which vary in different compounds, indicating how many electrons the sulfur atom shares, gains, or loses in a bonded form. The oxidation state can vary significantly, especially in sulfur compounds, influencing the chemical behavior of the ions.

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded together that act as a single charged particle. For example, the sulfate ion (\( \mathrm{SO}_{3}^{2-} \)) consists of one sulfur and three oxygen atoms bonded in a specific arrangement, resulting in an overall charge of \(-2\). Similarly, the thiosulfate (\( \mathrm{S}_{2}\mathrm{O}_{4}^{2-} \)) and dithionate (\( \mathrm{S}_{2}\mathrm{O}_{6}^{2-} \)) ions show how multiple sulfur and oxygen atoms create complex polyatomic ions with different properties and oxidation states. Understanding the structure and composition of these ions is crucial for predicting their reactivity and interactions in reactions.

Chemical Bonding

In understanding chemical bonding, particularly in polyatomic ions like \( \mathrm{S}_{2}\mathrm{O}_{4}^{2-} \) and \( \mathrm{S}_{2}\mathrm{O}_{6}^{2-} \), covalent bonds play a vital role. Each sulfur atom can form bonds with multiple oxygen atoms, sharing electrons to achieve a more stable electronic configuration. This sharing of electrons can vary, leading to differing oxidation states across different compounds. The variation demonstrates the nature of chemical bonding in sulfur-containing ions, highlighting how sulfur can exhibit different levels of electron sharing in various chemical environments. It's the arrangement and type of bonds that helps determine the overall structure and stability of these ions.

Redox Reactions

Redox (reduction-oxidation) reactions involve the transfer of electrons between chemical species. In these reactions, the oxidation state of atoms change as electrons are gained or lost. For sulfur compounds, determining the changes in its oxidation state helps understand redox behavior. With ions like \( \mathrm{SO}_{3}^{2-} \), \( \mathrm{S}_{2}\mathrm{O}_{4}^{2-} \), and \( \mathrm{S}_{2}\mathrm{O}_{6}^{2-} \), redox chemistry reveals how these ions participate in chemical reactions by either donating electrons (undergoing oxidation) or accepting electrons (undergoing reduction). By knowing the changing oxidation states, chemists can predict the potential chemical reactions and the stability of the compounds involved.