Question

The metallic sodium dissolves in liquid ammonia to form a deep blue coloured solution. The deep blue colour is due to formation of: (a) Solvated electron, e \(\left(\mathrm{NH}_{3}\right) \mathrm{x}^{-}\) (b) Solvated atomic sodium, \(\mathrm{Na}\left(\mathrm{NH}_{3}\right) \mathrm{y}\) (c) \(\left[\mathrm{Na}^{+}+\mathrm{Na}^{-}\right]\) (d) \(\mathrm{NaNH}_{2}+\mathrm{H}_{2}\)

Short answer

The deep blue color is due to the formation of solvated electrons, (a) is the correct answer.

Step-by-step solution

Understanding the Chemical Reaction

When metallic sodium (Na) is dissolved in liquid ammonia (NH₃), it forms a deep blue colored solution. This solution's color arises from the formation of species as a result of this dissolution.

Identifying Reaction Components

The deep blue color in the solution suggests the presence of free electrons that are solvated by ammonia molecules, not involving the formation of compounds such as sodium amide or hydrogen gas.

Explaining the Solvated Electron

The free electrons from sodium are surrounded by solvent molecules (in this case, NH₃), which is termed as 'solvated electrons'. These solvated electrons are responsible for the deep blue color of the solution.

Determining the Correct Option

From the given options: (a) Solvated electron, e(\(\text{NH}_3\))x\(^{-}\) correctly describes the deep blue solution formed as it refers to the free electron surrounded by ammonia molecules. Other options describe different chemical species and reactions.

Key concepts

Metallic Sodium

Metallic sodium is a highly reactive element. It is a soft, silvery metal that can be easily cut with a knife. Sodium is known for its vigorous reactions, especially with water, where it produces hydrogen gas and heat. This metal is part of the alkali metals family and is placed in group 1 of the periodic table.
One of sodium's interesting properties is that it stores a lot of potential chemical energy. When introduced to different solvents, like liquid ammonia, this energy can be released through fascinating chemical reactions.
In these reactions, metallic sodium often donates electrons, which is a key aspect of its chemical behavior. Understanding these properties is crucial when studying reactions like the one with liquid ammonia.

Liquid Ammonia

Liquid ammonia (NH₃) serves as an unreactive solvent with unique properties. At room temperature, ammonia is a gas, but it becomes a liquid upon cooling to -33.34 °C. In its liquid state, ammonia can dissolve a wide range of substances, even metals.
This makes ammonia a versatile solvent for various chemical reactions. One special feature of liquid ammonia is its ability to dissolve alkali metals, such as sodium. During this process, the ammonia molecules provide a stabilizing environment.
Ammonia's polar nature allows for these metals to dissolve without reacting violently, creating a stable solution where interesting phenomena, such as the formation of solvated electrons, can occur.

Chemical Reaction

The chemical reaction between metallic sodium and liquid ammonia is a great example of a system forming fascinating compounds. When sodium dissolves in liquid ammonia, it does not form a typical compound but rather a complex structure involving solvated electrons.
Here's how it unfolds:

• Sodium donates its outer electron, which then becomes solvated, or surrounded by, ammonia molecules.
• This process results in the formation of free electrons, which are crucial to the properties of the resulting solution.

The importance of this reaction lies in its non-traditional nature. It's not about creating a stable compound but maintaining a stable solution that exhibits unique coloration, thanks to the free electrons.

Deep Blue Colour

The deep blue color seen when metallic sodium dissolves in liquid ammonia is a defining feature of this reaction. This color stems from the interaction of free electrons with the ammonia molecules in the solution.
The electrons from the sodium are not bound in the same way they are in metallic sodium but exist as solvated entities, freely interacting with the surrounding molecules. These free electrons absorb certain wavelengths of light.
As these wavelengths are absorbed, the remaining light gives the solution its characteristic deep blue color. This color change is an easy-to-see indication that the sodium-ammonia reaction has taken place.

Free Electron

Free electrons play a pivotal role in the reaction between sodium and ammonia. When sodium dissolves, it releases electrons that are no longer tied to any atomic nucleus.
These free electrons become surrounded by ammonia molecules, a process called 'solvation.' The solvated electrons are stable due to this solvation, and their presence in the solution is what leads to the deep blue hue.
Understanding free electrons and their interactions with solvents is fundamental to grasping this reaction. Free electrons in solvated states showcase how unique environments like liquid ammonia can drastically change the behavior and appearance of a substance.