Vanadium (V): Properties, Reactions & Applications (JEE/NEET/CBSE)

Introduction

Vanadium (V) is a versatile transition metal renowned for its variable oxidation states and catalytic properties. Its primary importance stems from its use in strengthening steel alloys and its role as a crucial catalyst in various industrial processes, notably sulfuric acid production. Vanadium’s compounds exhibit a striking range of colours, making it a fascinating element for studying redox chemistry.

CBSE/JEE Quick Revision Notes

• Symbol: V
• Atomic Number: 23
• Atomic Mass: 50.94 g/mol
• Electronic Configuration: [Ar] 3d³ 4s²
• Group: 5
• Period: 4
• Block: d-block (Transition Metal)
• Common Oxidation States: +2, +3, +4, +5 (Most stable in aqueous solution: +5)
• Nature: Silvery-grey, malleable, ductile transition metal. Forms coloured compounds due to d-d transitions and charge transfer. Exhibits paramagnetic properties.

Electron Configuration & Bonding Behavior

Vanadium’s electronic configuration, [Ar] 3d³ 4s², is crucial for understanding its chemical behaviour. Being a transition metal, it exhibits variable oxidation states, primarily by involving both its 4s and 3d electrons in bonding.

• Oxidation States: Vanadium can exhibit oxidation states from +2 to +5.
  • +2 (V²⁺ - Vanadium(II) ion): Violet colour, strong reducing agent. Formed by losing both 4s and one 3d electron.
  • +3 (V³⁺ - Vanadium(III) ion): Green colour, reducing agent. Formed by losing both 4s and two 3d electrons.
  • +4 (VO²⁺ - Vanadyl ion): Blue colour. Often found as the vanadyl ion, where oxygen is strongly double-bonded to vanadium.
  • +5 (VO₂⁺ - Pervanadyl ion / VO₄³⁻ - Orthovanadate ion): Yellow/Orange colour. Most stable oxidation state, especially in acidic aqueous solutions (VO₂⁺) and basic solutions (VO₄³⁻ or polyvanadates). In +5 state, bonding often has significant covalent character, as seen in V₂O₅.

Crucial Chemical Reactions

Vanadium’s reactions often involve redox processes, demonstrating the interconversion of its various oxidation states.

1. Formation of Vanadium(V) oxide: When heated in air, vanadium metal forms its most stable oxide. 2V(s) + 5O₂(g) → 2V₂O₅(s)

2. Reduction of Vanadium(V) compounds: Vanadium(V) compounds can be sequentially reduced to lower oxidation states using appropriate reducing agents (e.g., Zn, SO₂, Sn²⁺). This is often observed in acidic aqueous solutions.

   • V(+5) to V(+4): 2VO₂⁺(aq, yellow) + SO₂(g) + 2H₂O(l) → 2VO²⁺(aq, blue) + SO₄²⁻(aq) + 4H⁺(aq) (Pervanadyl ion to Vanadyl ion)

   • V(+4) to V(+3): 2VO²⁺(aq, blue) + Zn(s) + 4H⁺(aq) → 2V³⁺(aq, green) + Zn²⁺(aq) + 2H₂O(l) (Vanadyl ion to Vanadium(III) ion)

   • V(+3) to V(+2): 2V³⁺(aq, green) + Zn(s) → 2V²⁺(aq, violet) + Zn²⁺(aq) (Vanadium(III) ion to Vanadium(II) ion)

3. Reaction with strong acids (oxidizing): Vanadium metal reacts with hot concentrated oxidizing acids. 2V(s) + 6H₂SO₄(conc) → V₂ (SO₄)₃ (aq) + 3SO₂(g) + 6H₂O(l) (Forms V³⁺ initially, further oxidation to VO²⁺ or VO₂⁺ is possible depending on conditions)

Industrial and Biological Importance

Industrial Importance

• Metallurgy (Alloys): Vanadium is primarily used as an alloying agent.
  • Ferrovanadium: An iron-vanadium alloy (typically 35-85% V) is added to steel.
  • Vanadium Steel: Increases tensile strength, toughness, elasticity, and resistance to fatigue and corrosion. Used in high-strength tools, engine parts (crankshafts, axles), springs, and surgical instruments.
  • Titanium Alloys: Vanadium is also alloyed with titanium (e.g., Ti-6Al-4V) for aerospace applications due to high strength-to-weight ratio.
• Catalysis: Vanadium(V) oxide (V₂O₅) is a critical industrial catalyst.
  • Contact Process: Essential catalyst for the production of sulfuric acid (H₂SO₄) from sulfur dioxide (SO₂). 2SO₂(g) + O₂(g) --(V₂O₅, 400-450°C)--> 2SO₃(g)
  • Maleic Anhydride Production: Catalyzes the oxidation of n-butane or benzene to maleic anhydride.
  • Oxidation of Ethanol: Used in the catalytic oxidation of ethanol to ethanal.

Biological Importance

• Trace Element: Vanadium is an essential trace element for some organisms, although its role in humans is not fully understood.
• Enzyme Cofactor:
  • In certain bacteria and fungi, vanadium is part of vanadium nitrogenases, enzymes involved in nitrogen fixation.
  • In some algae, vanadium haloperoxidases utilize vanadium to catalyze the oxidation of halides.
• Bioaccumulation: Some marine organisms, particularly sea squirts (tunicates), can accumulate vanadium in their blood cells at concentrations millions of times higher than seawater, though its precise biological function here is debated (possibly oxygen transport or defense).
• Pharmacology (Research): Vanadium compounds are being investigated for potential insulin-mimetic effects and anti-cancer properties, but these are still largely in research stages and not established therapeutic uses.