Problem 140 - A Complete Resource Book in Chemistry for JEE Main

Question

The oxidation states of sulphur in the anions \(\mathrm{SO}_{3}^{2-}\), \(\mathrm{S}_{2} \mathrm{O}_{4}^{2-}\) and \(\mathrm{S}_{2} \mathrm{O}_{6}^{2-}\) follow the order (a) \(\mathrm{S}_{2} \mathrm{O}_{6}^{2-}<\mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{SO}_{3}^{2-}\) (b) \(\mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{S}_{2} \mathrm{O}_{6}^{2-}<\mathrm{SO}_{3}^{2}\) (c) \(\mathrm{SO}_{3}^{2-}<\mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{S}_{2} \mathrm{O}_{6}^{3}\) (d) \(\mathrm{S}_{2} \mathrm{O}_{4}^{2-}<\mathrm{SO}_{3}^{2-}<\mathrm{S}_{2} \mathrm{O}_{6}^{2}\)

Step-by-Step Solution

Answer

Option (d) is correct: \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} < \mathrm{SO}_{3}^{2-} < \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \).

Step 1: Determine the Oxidation State of Sulfur in \( \mathrm{SO}_{3}^{2-} \)

First apply the sum of oxidation states rule. Let the oxidation state of sulfur be \( x \). Oxygen typically has an oxidation state of \(-2\). For \( \mathrm{SO}_{3}^{2-} \): \[ x + 3(-2) = -2 \] Solve for \( x \): \[ x - 6 = -2 \] \[ x = +4 \] So, the oxidation state of sulfur in \( \mathrm{SO}_{3}^{2-} \) is +4.

Step 2: Determine the Oxidation State of Sulfur in \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} \)

Consider the compound \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} \). Let the oxidation state of each sulfur be \( y \). Calculate using the total charge:\[ 2y + 4(-2) = -2 \] \[ 2y - 8 = -2 \] \[ 2y = +6 \] \[ y = +3 \] So, 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 \( \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \)

Now consider \( \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \). Let the oxidation state of each sulfur be \( z \). The total charge gives:\[ 2z + 6(-2) = -2 \] \[ 2z - 12 = -2 \] \[ 2z = +10 \] \[ z = +5 \] So, the oxidation state of each sulfur in \( \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \) is +5.

Step 4: Rank the Oxidation States

The oxidation states are now known:- \( \mathrm{SO}_{3}^{2-} \): +4- \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} \): +3- \( \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \): +5Rank the oxidation states from lowest to highest: \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} < \mathrm{SO}_{3}^{2-} < \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \).

Step 5: Select the Correct Answer

Match the order obtained: \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} < \mathrm{SO}_{3}^{2-} < \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \) Option \( (d) \) \( \mathrm{S}_{2} \mathrm{O}_{4}^{2-} < \mathrm{SO}_{3}^{2-} < \mathrm{S}_{2} \mathrm{O}_{6}^{2-} \) is the correct choice.

Key Concepts

Sulfur Compounds

Sulfur compounds are fascinating because they exhibit a variety of chemical behaviors due to their diverse oxidation states. In nature and in chemistry, sulfur can form multiple types of compounds, from simple diatomic molecules like sulfur dioxide (SO extsubscript{2}) to large complex structures like proteins in biological systems. Sulfur is found in different states in compounds, typically ranging from ext{-2} to +6.
This versatility is driven by sulfur's ability to form bonds with other sulfur atoms and various elements, including oxygen, resulting in a wide array of compounds. Sulfur compounds can be gaseous, liquid, or solid and are important in both environmental chemistry and industrial processes.
Some notable sulfur-containing compounds include:

• Sulfides (like H extsubscript{2}S) where sulfur has an oxidation state of ext{-2}.
• Sulfates (like Na extsubscript{2}SO extsubscript{4}) where sulfur is at the +6 oxidation state.

Understanding these states helps in predicting how sulfur compounds react, especially in redox reactions.

Anion Chemistry

Anions are negatively charged ions formed when atoms gain electrons. In chemistry, the behavior of anions is crucial for understanding various chemical reactions. When sulfur combines with oxygen to form anions such as SO extsubscript{3} extsuperscript{2-} , S extsubscript{2}O extsubscript{4} extsuperscript{2-}, and S extsubscript{2}O extsubscript{6} extsuperscript{2-}, it involves the interaction of their oxidation states and charges.
Anion chemistry often involves the concept of charge balance and stoichiometry. When calculating oxidation states for elements within anions, such calculations ensure that the net charge is consistent with the total of all oxidation states.
Key points about anions include:

• Anions are frequently formed by non-metals, like sulfur and oxygen, due to their tendency to gain electrons.
• They play a pivotal role in the chemistry of salts, where they are paired with cations to form neutral compounds.

Mastering the understanding of anion chemistry aids significantly in predicting the behavior and reactivity of complex ions, especially in aqueous solutions.

Redox Reactions

Redox reactions are chemical processes involving the transfer of electrons between two substances. These reactions include oxidation, where a substance loses electrons, and reduction, where a substance gains electrons.
In the context of sulfur compounds, redox reactions can drastically change the oxidation state of sulfur, influencing the properties and reactivity of the compound.
For example, consider sulfur's transition from SO extsubscript{3} extsuperscript{2-} to S extsubscript{2}O extsubscript{6} extsuperscript{2-}:

• Involves an oxidation of sulfur from +4 to +5.
• Indicates loss of electrons (oxidation step).
• Accompanied by a gain of electrons elsewhere in the reaction (reduction step).

Redox reactions are fundamental in energy conversion processes, such as in batteries and metabolic pathways. Understanding these reactions allows chemists to create and manipulate chemical processes for desired outcomes, from industrial manufacturing to biochemistry applications. Studying redox reactions enhances comprehension of broader chemical principles and is critical for anyone looking to advance in chemistry fields.