Question

Give an account of what happens when Na dissolves in liquid \(\mathrm{NH}_{3}\)

Short answer

Sodium dissolves in liquid ammonia, forming sodium cations and solvated electrons that give the solution its blue color, conductivity, and reducing properties.

Step-by-step solution

Understanding the Dissolution Process

When sodium (1Na) dissolves in liquid ammonia (11NH_{13}), we need to first understand what "dissolution" means in this context. The dissolution is a physical process where a solute dissolves in a solvent to form a homogeneous mixture, known as a solution.

Sodium and Ammonia Interaction

As sodium is introduced into liquid ammonia, it begins to dissolve. The sodium atoms lose one electron each to form sodium cations (1Na^+1) and free electrons. These electrons, being free and loosely associated, give rise to the chemical reactivity of the solution.

Formation of Solvated Electrons

The free electrons released by the sodium atoms become solvated by the nonpolar solvent of ammonia. This means that ammonia molecules surround these electrons, creating a rich blue solution. These solvated electrons are responsible for the deep blue color of the solution, as they absorb light in the visible spectrum.

Properties of the Resulting Solution

The solution of sodium in liquid ammonia is conductive due to the presence of free electrons, making it a good conductor of electricity. The solution is also paramagnetic and has a strong reducing nature, which are properties closely linked to the presence of excess solvated electrons.

Key concepts

Dissolution Process

When sodium (\( \text{Na} \)) dissolves in liquid ammonia (\( \text{NH}_3 \)), the process begins with the breaking down of the solid sodium into individual atoms in the solvent. This dissolution process is not just mixing; it involves physical and chemical changes where sodium atoms are dispersed throughout the ammonia. As each sodium atom enters the solvent, it experiences interactions with ammonia molecules. These interactions eventually lead to ionization, where sodium atoms lose an electron and become positively charged ions (\( \text{Na}^+ \)). Thus, the dissolution process is the whole transformation of sodium from its metallic state to a state where it forms ions and free electrons in solution.

This process results in a homogeneous mixture. Liquid ammonia acts as the solvent that accommodates the rearrangement of sodium from a metallic form to its ionic and electronically separated form. The unique properties of sodium in liquid ammonia start with this essential dissolution process.

Formation of Solvated Electrons

Once sodium dissolves in ammonia, the sodium atoms release electrons that freely roam in the solvent. These are not merely free-floating electrons; they become 'solvated.' In a solvated state, ammonia molecules encircle the electrons. This means that the electron is no longer solely free but stabilized by its interactions with surrounding molecules of the solvent.

The solvated electrons endow the solution with its characteristic deep blue color. This blue color arises because the solvated electrons absorb certain wavelengths of visible light. The color is an indicator of the electron's presence and their interaction with light. This unique feature makes the solution of sodium in liquid ammonia visually distinctive and chemically intriguing.

Conductive Properties of Solution

The presence of solvated electrons and sodium ions (\( \text{Na}^+ \)) in the solution significantly affects its physical properties. Notably, the solution becomes highly conductive. This conductivity is due to the free movement of electrons, which facilitate the transfer of electric charge through the solution. Unlike typical solutions, the free electrons provide a continuous pathway for electricity, making it behave in some respects like a metal in liquid form.

Beyond conductivity, this solution is paramagnetic, meaning it's attracted to magnetic fields. It also has a strong reducing capability because of the availability of free electrons, which can donate electrons readily in chemical reactions. These properties make sodium in liquid ammonia a versatile reagent in many chemical processes, especially those requiring a strong reducing agent.