Page No 217: - Chapter 8 - D & F - Block Elements - Intext Solutions - Ncert Solutions class 12 - Chemistry

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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 E^θ(M²⁺/M) value for copper is positive (+0.34V). What is possibly the reason for this? (Hint: consider its high Δ_aH^θ and low Δ_hydH^θ)

Answer:

The E^θ(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 E^θ(M²⁺/M) value for copper is positive.