Problem 130 - A Complete Resource Book in Chemistry for JEE Main

Question

Highly pure dilute solution of sodium in liquid ammonia 1\. shows blue colour 2\. exhibits electrical conductivity 3\. produces sodium amide 4\. produces hydrogen gas (a) 1,2 (b) \(1,2,3\) (c) \(2,3,4\) (d) all of these

Step-by-Step Solution

Answer

(d) all of these

Step 1: Understanding the Problem

The question asks us to identify which of the given physical and chemical properties are exhibited by a highly pure dilute solution of sodium in liquid ammonia. We need to consider each property and determine if it is true for both physical (colour, conductivity) and chemical (products formed) aspects.

Step 2: Checking Physical Properties

Firstly, a dilute solution of sodium in liquid ammonia shows a blue colour. This is due to the solvated electrons in the solution, which absorb light and exhibit a characteristic blue color. Additionally, these solvated electrons also cause the solution to conduct electricity, thereby exhibiting electrical conductivity.

Step 3: Analyzing Chemical Reactions

In a highly pure dilute solution, sodium reacts with ammonia to produce sodium amide ( ext{NaNH}_2) and hydrogen gas ( ext{H}_2). This reaction can be represented as: \ \[\text{2Na + 2NH}_3 \rightarrow \text{2NaNH}_2 + \text{H}_2} \] This confirms that in addition to physical properties, specific chemical reactions also take place in the solution.

Step 4: Assessment of Options

The solution exhibits all four characteristics listed in the options: blue colour, electrical conductivity, production of sodium amide, and hydrogen gas. Therefore, all properties mentioned in the question apply.

Key Concepts

Blue Colour of Sodium Solution

A highly pure dilute solution of sodium in liquid ammonia notably exhibits a stunning blue color. This intriguing phenomenon occurs due to the presence of solvated electrons. In simple terms, when sodium dissolves in liquid ammonia, it releases electrons which become trapped in the solvent's cavities. These electrons absorb visible light and impart a characteristic blue hue to the solution. Hence, the blue color is a direct indication of solvated electrons.

• Solvated electrons are responsible for the unique coloration.
• It is due to their ability to absorb and reflect light.

The remarkable visual change, from metallic sodium to a beautiful blue liquid, is one of the most noticeable traits when sodium dissolves in liquid ammonia.

Electrical Conductivity of Solutions

Electrical conductivity in a solution of sodium in liquid ammonia is another key characteristic to highlight. This property also arises due to the solvated electrons. These free electrons are capable of moving through the solution and carry charge, thus enabling the solution to conduct electricity effectively.

• Conductivity is due to the presence of mobile charge carriers, i.e., the solvated electrons.
• The solution behaves like an electrolyte because of its conductive nature.

The ability to conduct electricity is essential for various applications and fundamental studies involving sodium solutions in different solvents.

Chemical Reactions of Sodium

Sodium shows fascinating chemical behavior when dissolved in liquid ammonia. One of the significant reactions is its transformation into sodium amide. In this process, sodium reacts with ammonia to form sodium amide (NaNH₂) and hydrogen gas (H₂). The chemical equation for this reaction is:
\[\text{2Na + 2NH}_3 \rightarrow \text{2NaNH}_2 + \text{H}_2\]

• The reaction involves sodium splitting the ammonia molecule.
• Sodium amide and hydrogen gas are the primary products.

This chemical transformation highlights sodium's reactivity and its potential to form useful compounds when dissolved in ammonia.

Sodium Amide Formation

The formation of sodium amide is a crucial chemical process when sodium is dissolved in liquid ammonia. Sodium amide (NaNH₂) is a compound that forms as a result of the interaction between sodium and ammonia molecules.

• Sodium amide is a reactive species, often used in organic synthesis.
• The reaction liberates hydrogen gas, demonstrating the generation of new compounds.

Understanding the formation of sodium amide in this context is vital for appreciating the broader spectrum of sodium's chemical behavior.