Transition metals act as effective catalysts because of their ability to change their oxidation states. In the Contact process, V ₂ O ₅ catalyses the oxidation of SO ₂ to SO ₃ . During this catalytic cycle, the V ₂ O ₅ is initially reduced to an intermediate compound before being re-oxidised by atmospheric oxygen. What is the oxidation state of vanadium in this intermediate compound?

Step-by-step solution

The catalytic action of V ₂ O ₅ in the Contact process involves a change in the oxidation state of vanadium. The reaction proceeds via the following mechanism: SO ₂ + V ₂ O ₅ SO ₃ + V ₂ O ₄ V ₂ O ₄ + 1 2 O ₂ V ₂ O ₅ In the intermediate compound V ₂ O ₄ , the oxidation state of vanadium is +4. It is then re-oxidised by oxygen back to the +5 state in V ₂ O ₅ . Answer: +4