Problem 113 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the correct statement (a) \(\mathrm{Ti}^{4+}, \mathrm{Mn}^{2+}\) are stable oxidation states (b) The most common oxidation state of 3 d-series is \(+2\) (c) The lowest oxidation state of \(\mathrm{Cr}\) and \(\mathrm{Cu}\) is \(+1\) while for others it is \(+2\). (d) All of these

Step-by-Step Solution

Answer

The correct statement is (b).

Step 1: Analyze Statement (a)

Consider the stability of the oxidation states of \(\mathrm{Ti}^{4+}\) and \(\mathrm{Mn}^{2+}\). Tetravalent titanium (\(\mathrm{Ti}^{4+}\)) is very stable due to its noble gas configuration. Manganese commonly exists in a stable \(2+\) state, leading to the conclusion that Statement (a) is correct.

Step 2: Analyze Statement (b)

Assess the oxidation states in the 3d transition series. Many of these elements, including Fe, Ni, and Zn, commonly occur in the \(+2\) oxidation state. This makes Statement (b) correct since \(+2\) is a common oxidation state across the 3d series.

Step 3: Analyze Statement (c)

Evaluate the lowest oxidation state of \(\mathrm{Cr}\), \(\mathrm{Cu}\), and others. Cr typically shows a lowest oxidation state of \(+2\), while Cu can show a \(+1\) state commonly. For most other elements in the series, the lowest state is indeed \(+2\), making Statement (c) incorrect.

Step 4: Conclusion: Verify Statement (d)

Determine if all previous statements are correct, which would validate Statement (d). Since Statement (c) was found to be incorrect, Statement (d) cannot be correct.

Key Concepts

3d Transition Series

The 3d transition series consists of elements found in the first row of the transition metals in the periodic table, specifically from scandium (Sc) to zinc (Zn). These elements are characterized by the gradual filling of the 3d orbitals. Among the most interesting properties of these elements is their ability to exhibit a wide range of oxidation states. This is mainly because the energy difference between the 3d and 4s orbitals is not significant, allowing for electrons to be easily gained or lost. For example:

• Iron (e) can have oxidation states of +2 and +3.
• Manganese (Mn) exhibits states from +2 to +7.
• Copper (Cu) most commonly exists in +1 and +2 oxidation states, even though it is a part of the same series.

Understanding these oxidation states is crucial for identifying redox reactions in both organic and inorganic chemistry.

Stability of Ions

The stability of ions in the 3d transition series is influenced by their electronic configuration. A stable electronic configuration is often reached when an ion has a noble gas configuration or half-filled or completely filled d orbitals. Ti⁴⁺ and Mn²⁺ are examples of stable products:

• Tetravalent Titanium (Ti⁴⁺): It achieves a stable configuration similar to argon, with a completely empty 3d level.
• Divalent Manganese (Mn²⁺): Here, Mn has a half-filled d orbital (3d⁵), which is especially stable due to exchange energy and symmetrical distribution.

The role of the 3d and 4s electrons in stabilizing different oxidation states highlights the transitional nature of these metals, adapting to different chemical environments. But, not all ions conform to a simplistic stable-in-every-situation model. External conditions like temperature and presence of ligands can also affect stability.

Titanium and Manganese Stability

Titanium and manganese exemplify the diverse oxidation state behavior in the transition series.

Titanium - Stability in Oxidation States

Titanium commonly occurs in the +4 oxidation state, where it resembles the noble gas configuration which is highly stable. This tetravalent state makes it less reactive in many circumstances. Beyond +4, additional oxidation states are not typically observed in common chemistry for titanium, due to their instability.

Manganese - Unique Oxidative Flexibility

Manganese shows extraordinary versatility with oxidation states ranging from -3 to +7. However, among the more stable and prevalent states is the +2 oxidation state. This state is preferred due to the half-filled d⁵ configuration, offering greater electronic stability. Other states like +7 (in permanganates) are also stable but usually require specific conditions. These elements underline how transition metals can adapt their oxidation numbers based on their surrounding environments, making them integral to various chemical processes ranging from industrial catalysis to biological systems.