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

The correct answer is (d) all of these.

Step 1: Understand the Context

A solution of sodium in liquid ammonia is being considered. Sodium metal placed into liquid ammonia forms a blue solution due to the presence of solvated electrons.

Step 2: Evaluate Each Option

1. The solution forms a blue color because the electrons become solvated by the ammonia molecules, creating solvated electrons, which are responsible for the distinctive blue color. This option is true. 2. The solution exhibits electrical conductivity because these solvated electrons can move freely, allowing the solution to conduct electricity. This option is true as well. 3. Over time, sodium in liquid ammonia reacts with the ammonia to form sodium amide and hydrogen gas. So, this option is also true. 4. The same reaction mentioned above will produce hydrogen gas. Thus, this option is true.

Step 3: Determine the Correct Answer

Since all four observations (blue color, electrical conductivity, sodium amide production, and hydrogen gas production) hold true for a dilute solution of sodium in liquid ammonia, all listed conditions are correct.

Key Concepts

Solvated Electrons

When sodium is dissolved in liquid ammonia, something fascinating occurs. The sodium atoms release electrons, which become solvated by the ammonia molecules. These are known as "solvated electrons," and they give the solution its characteristic deep blue color.
Solvated electrons are free electrons that are surrounded by a solvent cage of ammonia molecules. This is important because:

• They impart a striking blue hue to the solution.
• They are stable in the ammonia environment, allowing unique chemical reactions to occur.
• Despite being negatively charged, they do not reduce the solvent or themselves react aggressively.

Solvated electrons are pivotal in understanding why solutions of metals like sodium in liquid ammonia behave as they do.

Electrical Conductivity

The presence of solvated electrons contributes significantly to the electrical conductivity of a sodium-in-liquid ammonia solution. These electrons move freely through the liquid, acting as charge carriers.

• Think of them like tiny particles that zip around the solution, carrying electrical charge very efficiently.
• This free movement enables the solution to conduct electricity, much like how saltwater conducts electricity due to the movement of ions.

This conductivity is a direct result of the unbound nature of the solvated electrons, making these solutions a fascinating area of study in electrochemistry.

Sodium Amide Production

Over time, solutions of sodium in liquid ammonia do not remain static. They undergo chemical reactions leading to the formation of sodium amide (\(NaNH_2\)). The reaction can be summarized as:\[ 2 ext{Na} + 2 ext{NH}_3 ightarrow 2 ext{NaNH}_2 + ext{H}_2 \]
In this reaction, sodium reacts with ammonia, producing sodium amide and hydrogen gas. This process is peculiar to such alkali metal solutions.

• Sodium amide is a useful chemical in organic synthesis, serving as a strong base.
• The formation of sodium amide from this solution highlights the complex chemical transformations possible in metal-ammonia solutions.

Understanding the production of sodium amide provides insights into ammonia's role as a reaction medium.

Hydrogen Gas Production

Simultaneously with sodium amide formation, hydrogen gas is released as a byproduct of the same reaction. The reaction equation reiterates this:\[ 2 ext{Na} + 2 ext{NH}_3 ightarrow 2 ext{NaNH}_2 + ext{H}_2 \]
Production of hydrogen gas is significant because:

• It demonstrates how metals and ammonia can be a source of hydrogen, a valuable resource in many industrial processes.
• This gas production is a direct application of the chemical properties of solvated electrons and their involvement in reducing reactions.

This aspect of sodium in liquid ammonia solutions highlights their potential for studies in hydrogen enrichment processes and more.