Question 8.3:
Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why?
Answer:
Mn (Z = 25) = 3d5 4s2
Mn has the maximum number of unpaired electrons present in the d-subshell (5 electrons). Hence, Mn exhibits the largest number of oxidation states, ranging from +2 to +7.
Question 8.4:
The Eθ(M2+/M) value for copper is positive (+0.34V). What is possibly the reason for this? (Hint: consider its high ΔaHθ and low ΔhydHθ)
Answer:
The Eθ(M2+/M) value of a metal depends on the energy changes involved in the following:
1. Sublimation: The energy required for converting one mole of an atom from the solid state to the gaseous state.
2. Ionization: The energy required to take out electrons from one mole of atoms in the gaseous state.
3. Hydration: The energy released when one mole of ions are hydrated.
Now, copper has a high energy of atomization and low hydration energy. Hence, the Eθ(M2+/M) value for copper is positive.