Question

When Ethane-1,2-diamine is added progressively to an aqueous solution of Nickel (II) chloride, the sequence of colour change observed will be:

• A. Green \(\rightarrow\) Pale Blue \(\rightarrow\) Blue \(\rightarrow\) Violet
• B. Pale Blue \(\rightarrow\) Blue \(\rightarrow\) Green \(\rightarrow\) Violet
• C. Pale Blue \(\rightarrow\) Blue \(\rightarrow\) Violet \(\rightarrow\) Green
• D. Violet \(\rightarrow\) Blue \(\rightarrow\) Pale Blue \(\rightarrow\) Green

Hint:

The color changes in coordination compounds depend on the nature of ligands and the metal ion.

Answer 1

The Correct Option is C

- As ethane-1,2-diamine is added to the solution, the nickel (II) complex undergoes changes in coordination, resulting in a series of color transitions. Initially, the solution is pale blue and then turns blue, followed by violet, and finally green. 
Final Answer: Option (3).

Answer 2

Step 1: Understand the reaction and ligands involved.
Ethane-1,2-diamine (also known as ethylenediamine) is a bidentate ligand, which means it can form two bonds with a metal ion. When ethane-1,2-diamine is added to an aqueous solution of Nickel (II) chloride (NiCl₂), it forms complexes with the nickel ion. These complexes will have different colors based on the number of ligands coordinating with the metal ion and the overall structure of the complex.

Step 2: Analyze the sequence of colour changes.
Nickel (II) chloride in water gives a pale blue solution. As ethane-1,2-diamine is added progressively, it forms various coordination complexes with Ni²⁺ ions, and the color changes due to the formation of these complexes.
1. Initially, the solution is **pale blue** due to the presence of hydrated Ni²⁺ ions (Ni(H₂O)₆)²⁺. 2. As ethane-1,2-diamine is added, it begins forming a **blue** complex, typically a 1:1 complex such as [Ni(en)₂](Cl)₂. 3. With further addition of ethane-1,2-diamine, the solution turns **violet**, indicating the formation of a 1:2 complex such as [Ni(en)₃](Cl)₂. 4. Finally, the solution becomes **green** when an excess of ethane-1,2-diamine forms a **green** 1:3 complex like [Ni(en)₃]²⁺.

Step 3: Conclusion.
The sequence of color change observed as ethane-1,2-diamine is progressively added to the aqueous solution of Nickel (II) chloride is:
**Pale Blue → Blue → Violet → Green.**

Final Answer:
\[ \boxed{\text{Pale Blue} \rightarrow \text{Blue} \rightarrow \text{Violet} \rightarrow \text{Green}}. \]