Vanadium Stability in Aqueous Solutions

The question asks to identify the most stable vanadium species when dissolved in water (aqueous medium) from the given options.

Vanadium is a transition metal that can exist in several oxidation states, commonly +2, +3, +4, and +5, in aqueous solutions. The stability of these oxidation states depends on various factors, including pH and the presence of oxidizing or reducing agents.

Common Vanadium Species and Oxidation States in Water

Here are some common hydrated or oxo-species of vanadium and their oxidation states:

• Vanadium(II): Vλtex output: ²⁺ (e.g., λtex output: \( \text{[V(H}_2\text{O)}_6\text{]}^{2+} \)) - Violet, a strong reducing agent.
• Vanadium(III): Vλtex output: ³⁺ (e.g., λtex output: \( \text{[V(H}_2\text{O)}_6\text{]}^{3+} \)) - Green, also a reducing agent, though weaker than Vλtex output: ²⁺.
• Vanadium(IV): VOλtex output: ²⁺ (e.g., λtex output: \( \text{[VO(H}_2\text{O)}_5\text{]}^{2+} \)) - Blue vanadyl ion, relatively stable to redox reactions in air-saturated water.
• Vanadium(V): VOλtex output: \( _2^+ \) (e.g., λtex output: \( \text{[VO}_2\text{(H}_2\text{O)}_4\text{]}^{+} \)) or various vanadates (e.g., λtex output: \( \text{VO}_3^- \)) - Yellow to orange, an oxidizing agent. The species depends heavily on pH.

Analyzing the Given Options

Let's determine the oxidation state of vanadium in each given species:

1. λtex output: \( \text{[V(H}_2\text{O)}_5\text{(OH)]}^{2+} \)
   • In this complex, Hλtex output: \( _2 \)O is neutral (charge 0) and OHλtex output: \( ^- \) has a charge of -1.
   • Let the oxidation state of V be x.
   • x + 5(0) + (-1) = +2
   • x - 1 = +2
   • x = +3
   • This species contains Vanadium(III).
2. λtex output: \( \text{[VO(H}_2\text{O)}_5\text{]}^{2+} \)
   • This complex contains the vanadyl ion, VOλtex output: \( ^{2+} \). In VOλtex output: \( ^{2+} \), the oxygen is typically considered Oλtex output: \( ^{2-} \).
   • Let the oxidation state of V be x.
   • x + (-2) = +2 (the charge of the VO group)
   • x = +4
   • This species contains Vanadium(IV) as the hydrated vanadyl ion.
3. λtex output: \( \text{[VO(H}_2\text{O)}_5\text{]}^{+} \)
   • This complex contains the VOλtex output: \( ^+ \) group. Assuming oxygen is Oλtex output: \( ^{2-} \).
   • Let the oxidation state of V be x.
   • x + (-2) = +1 (the charge of the VO group)
   • x = +3
   • This species contains Vanadium(III), possibly as a less common oxo-species or hydrate.
4. λtex output: \( \text{[V(H}_2\text{O)}_4\text{(OH)}_2\text{]}^{2+} \)
   • In this complex, Hλtex output: \( _2 \)O is neutral (charge 0) and OHλtex output: \( ^- \) has a charge of -1. There are two OHλtex output: \( ^- \) ions.
   • Let the oxidation state of V be x.
   • x + 4(0) + 2(-1) = +2
   • x - 2 = +2
   • x = +4
   • This species contains Vanadium(IV) as a dihydroxo complex.

Comparing Stability

In aerobic aqueous solutions, Vanadium(II) and Vanadium(III) species are relatively easily oxidized to higher oxidation states. Vanadium(V) species (like VOλtex output: \( _2^+ \)) are oxidizing agents.

Vanadium(IV), primarily existing as the vanadyl ion VOλtex output: \( ^{2+} \), is known to be the most stable oxidation state of vanadium under ambient conditions in a wide pH range in aqueous solution, especially compared to Vλtex output: \( ^{2+} \), Vλtex output: \( ^{3+} \) and Vλtex output: \( ^{5+} \) which are more reactive (reducing or oxidizing).

Among the options provided:

• Options 1 and 3 are Vanadium(III) species, which are less stable against oxidation than V(IV).
• Options 2 and 4 are Vanadium(IV) species. Option 2 is the well-known hydrated vanadyl ion λtex output: \( \text{[VO(H}_2\text{O)}_5\text{]}^{2+} \), which is the predominant and most stable form of V(IV) in aqueous solution. Option 4 is a hydroxo complex of V(IV), likely formed under specific pH conditions and less generally stable than the vanadyl ion itself.

Therefore, the vanadyl ion species, λtex output: \( \text{[VO(H}_2\text{O)}_5\text{]}^{2+} \), is the most stable vanadium species among the given options in aqueous medium.

Conclusion

Based on the stability of vanadium oxidation states and the common species formed in water, the Vanadium(IV) species, specifically the hydrated vanadyl ion, is the most stable. Option 2 represents this species.