Question

The metal that dissolves in liquid ammonia, giving a dark blue coloured solution is: (a) Lead (b) Tin (c) Silver (d) Sodium

Short answer

The metal is sodium (d).

Step-by-step solution

Identify the Unique Behavior in Ammonia

Certain metals, when dissolved in liquid ammonia, form a dark blue colored solution. This distinct reaction is not something all metals exhibit.

Recall Metal-Ammonia Reaction

Among common metals, alkali metals have a known reaction with liquid ammonia. The reaction results in solvated electrons that can impart color to the solution.

Focus on Alkali Metals

Within the provided options, check for alkali metals. Sodium is an alkali metal, whereas lead, tin, and silver are not. Alkali metals are known for dissolving in liquid ammonia to produce dark blue solutions.

Confirm the Metal

Sodium is confirmed to dissolve in liquid ammonia to give a blue solution. Lead, tin, and silver do not exhibit this behavior.

Key concepts

Metal-Ammonia Reaction

When metals interact with liquid ammonia, a fascinating chemical process occurs, especially with certain types of metals. This reaction is quite famous for producing a characteristic dark blue solution. Not all metals showcase this behavior, making it a unique trait among those that do. The color arises from the formation of solvated electrons, which are free electrons that become trapped in the ammonia solution. These electrons absorb visible light, giving the solution its notable blue color. Solvated electrons also contribute to the solution's paramagnetic properties, adding an interesting layer to the study of these reactions. While some transition metals can engage in these reactions, it is chiefly the alkali metals that exhibit this pronounced effect.

Alkali Metals Solubility

The group 1 elements, known as alkali metals, display a striking ability to dissolve in liquid ammonia, creating a dark blue solution. This group includes lithium, sodium, potassium, rubidium, and cesium, all of which react with liquid ammonia in this distinctive fashion. Their electron configuration makes them quite reactive, allowing them to easily give up their single valence electron to form cations and solvated electrons. Additionally, the ammonia molecules act as solvents, surrounding and stabilizing the positive metal ions and free electrons. This solvation process is what leads to the dark blue color. It's important for students to note that not all metals can dissolve in ammonia, but the alkali metals can, due to their unique electronic properties and the nature of the solvent.

Sodium in Liquid Ammonia

Sodium, a classic example of an alkali metal, reacts famously with liquid ammonia to give a deep blue solution. During this reaction, sodium loses its outermost electron, which then becomes solvated by the surrounding ammonia molecules. This results in the characteristic dark blue coloration due to the solvated electrons absorbing specific wavelengths of light in the visible spectrum. Since sodium is a typical alkali metal, it behaves predictably by dissolving in liquid ammonia through this process. This dissolved sodium is quite different from typical ionic solutions as the solvated electrons confer unique properties such as electrical conductivity and a vibrant color. Understanding sodium's behavior in liquid ammonia solutions is essential for grasping the broader principles of alkali metal reactions in different solvents.