Question

6. Give reasons for the following:
i. Transition elements act as catalysts
ii. It is difficult to obtain oxidation state greater than two for Copper.
iii. Cr2O72- is a strong oxidising agent in acidic medium whereas WO3 and MoO3 are no​

Answer 1

Answer:

• Transition metals have partially filled d- orbitals so they can easily withdraw the electrons from the reagents or give electrons to them depending on the nature of the reaction. They also have a tendency to show large no. of oxidation states and the ability to form complexes which makes them a good catalyst.
• Copper are sufficiently stable after removal of 2 electrons from their valence shell hence it would require a greater amount of energy to remove a third electron from their already stabilised shell. Therefore, it is difficult to obtain oxidation state greater than Cu.

Explanation:

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Answer 2

Answer:

(i)Due to large surface area and ability to show variable oxidation states

(ii)Due to high value of third ionisation enthalpy  

(iii) Mo(VI) and W(VI) are more stable than Cr(VI).