Problem 1 - A Complete Resource Book in Chemistry for JEE Main

Question

Among which of the following pairs of ions, the lower oxidation state in aqueous solution is more stable than the other? (a) \(\mathrm{Ti}^{+}, \mathrm{Ti}^{3+}\) (b) \(\mathrm{V}^{2+}, \mathrm{VO}^{2+}\) (c) \(\mathrm{Cr}^{2+}, \mathrm{Cr}^{3+}\) (d) \(\mathrm{Cu}^{+}, \mathrm{Cu}^{2+}\)

Step-by-Step Solution

Answer

Pair (b) V^{2+}, VO^{2+} is correct.

Step 1: Understanding the Problem

We are given pairs of ions and asked to determine for which pair the ion with the lower oxidation state is more stable in aqueous solution than the ion with the higher oxidation state.

Step 2: Analyzing Pair (a)

For Ti ions, Ti^{3+} is more common and stable compared to Ti^{+} which is rare and unstable. Hence, in pair (a), Ti^{3+} is more stable than Ti^{+}.

Step 3: Analyzing Pair (b)

For vanadium ions, V^{2+} is more stable than VO^{2+} in aqueous solution due to the oxidation potential and common existence of V^{2+} compared to VO^{2+}.

Step 4: Analyzing Pair (c)

For chromium ions, Cr^{3+} is more stable in aqueous solution than Cr^{2+}, as Cr^{3+} is non-reducing and is found more frequently.

Step 5: Analyzing Pair (d)

For copper ions, Cu^{2+} is more stable in aqueous solutions than Cu^{+} because Cu^{+} which tends to disproportionate into Cu and Cu^{2+}.

Step 6: Identify the Correct Pair

From the analysis, in pair (b), the lower oxidation state V^{2+} is more stable than VO^{2+}, the higher oxidation state.

Key Concepts

Stability of Ions

In the world of chemistry, understanding the stability of ions is crucial. Ions with different oxidation states can exhibit varied stability under certain conditions, such as in an aqueous solution.
The stability of an ion depends on several factors including its electronic configuration, environment, and the type of solvent it's in. For example:

• **Electronic Configuration**: Full or half-full electron shells often lend more stability to ions. This is why Ti³⁺, which has a partially filled d-shell, is more stable than Ti⁺.
• **Environmental Conditions**: Some ions are more stable in aqueous solutions due to solvation effects, where water molecules surround and stabilize the ion.
• **Disproportionation**: For some ions like Cu⁺, they tend to disproportionate, which means they split into two products of different oxidation states, such as Cu and Cu²⁺.

Overall, recognizing the most stable oxidation state for ions helps predict their behavior, such as their preference to participate in redox reactions, which we'll explore further.

Transition Metals

Transition metals are fascinating elements found in the central block of the periodic table. They are characterized by having partially filled d-orbitals, allowing them to form various oxidation states.
This ability to switch oxidation states makes them versatile in forming compounds. Let's explore a few traits:

• **Variable Oxidation States**: Transition metals like vanadium and chromium can have multiple stable oxidation states such as V²⁺ and Cr³⁺. These states can easily interconvert based on the environment or chemical reactions.
• **Colorful Compounds**: Due to d-d electronic transitions, compounds like those formed with Cr²⁺ and V²⁺ often display vivid colors.
• **Catalytic Properties**: They are frequently used as catalysts in various chemical processes because of their ability to change oxidation states easily.

These properties make transition metals especially important in industrial applications and biological systems.

Redox Chemistry

Redox chemistry revolves around reduction and oxidation reactions where electrons are transferred between species. This process is essential for driving various biochemical and industrial reactions.
Understanding key aspects of redox reactions helps in predicting how reactions proceed:

• **Oxidation States**: By examining the changes in oxidation states of elements like copper ( Cu^{+} to Cu^{2+}) during chemical reactions, one can determine which elements are oxidized and which are reduced.
• **Electrode Potentials**: Practically, using standard electrode potential values can help identify the likelihood of a redox reaction occurring, as well as the preferred direction of electron flow.
• **Balancing Redox Equations**: A solid understanding of oxidation and reduction allows chemists to balance chemical equations involving electron transfer efficiently.

Being adept at redox chemistry helps chemists create processes for energy storage, metal extraction, and even biochemical pathways like cellular respiration.