Question

On heating sodium metal in a current of dry ammonia, the compound formed is: (a) Sodium hydride (b) Sodium amide (c) Sodium azide (d) Sodium nitride

Short answer

The compound formed is sodium amide (b).

Step-by-step solution

Identify the Reaction Medium

The problem describes sodium metal being heated in a current of dry ammonia. This is an important clue because ammonia (NH_3) acts as both a solvent and a reactant.

Consider the Possible Reactions

Sodium metal can react with ammonia under high temperatures. Generally, the reaction of an alkali metal with dry ammonia leads to the formation of sodium amide (NaNH_2) along with the release of hydrogen gas. This is the expected and typical reaction when dry ammonia is used as the medium.

Balance the Chemical Equation

The balanced chemical equation for the reaction between sodium and ammonia is: \[ 2\,\text{Na} + 2\,\text{NH}_3 \rightarrow 2\,\text{NaNH}_2 + \text{H}_2 \]This equation shows that two moles of sodium react with two moles of ammonia to produce two moles of sodium amide and one mole of hydrogen gas.

Conclusion

Based on the reaction and the balanced equation, the compound formed when sodium is heated in a current of dry ammonia is sodium amide. This is consistent with the chemical behavior of sodium in these reaction conditions.

Key concepts

Chemical Reactions

Understanding chemical reactions is a fundamental aspect of chemistry. A chemical reaction occurs when substances interact to form new substances. In the context of our exercise, sodium metal reacts with dry ammonia in a way that transforms these reactants into sodium amide and hydrogen gas.
Chemical reactions are often characterized by five main signs:

• Color change
• Temperature change
• Gas production
• Precipitate formation
• Light emission (sometimes)

Each of these signs can help identify that a chemical reaction has occurred. For example, in the reaction of sodium with ammonia, the production of hydrogen gas is a clear indicator of a chemical change.

Alkali Metals

Alkali metals are a fascinating group in the periodic table, known for their high reactivity. They occupy Group 1 and include elements like lithium, sodium, and potassium. These metals are particularly reactive with water and other substances like ammonia.
Sodium, as an alkali metal, is highly reactive due to its single electron in the outermost shell. This electron can be easily lost to form a positive ion (Na⁺), which makes sodium highly reactive in chemical processes. When sodium reacts with dry ammonia, it demonstrates typical alkali metal behavior, actively interacting to form sodium amide.

Dry Ammonia

Ammonia is a compound composed of nitrogen and hydrogen with the formula NH₃. In its gaseous state, known as 'dry ammonia,' it is a colorless gas with a strong pungent odor. Dry ammonia refers specifically to the ammonia gas in its pure, anhydrous state, without any water content.
In chemical reactions, dry ammonia acts as both a solvent and a reactant. It plays a critical role by providing a nitrogen source and participating actively in the reaction with sodium. The presence of ammonia is essential for the formation of sodium amide, due to its ability to stabilize the formation of this compound while simultaneously producing hydrogen gas as a byproduct.

Sodium Metal

Sodium is a soft, silver-white metal that is highly reactive, especially when exposed to air or moisture. It is one of the many alkali metals located in the first column of the periodic table.
Under controlled conditions, heating sodium in dry ammonia leads to a specific reaction outcome. Sodium's reactivity is harnessed to form sodium amide, clearly demonstrating the powerful chemical interactions that alkali metals can have with non-metals such as nitrogen from ammonia. This property is exploited in various industrial processes where such reactive behavior is beneficial.

Inorganic Chemistry

Inorganic chemistry deals with compounds that are not categorized as organic. This includes metals, minerals, and organometallic compounds. Sodium's reaction with ammonia falls squarely within the realm of inorganic chemistry.
Key topics in inorganic chemistry include understanding the behavior of elements, reaction mechanisms, and the synthesis of inorganic compounds. The formation of sodium amide from sodium and ammonia exemplifies the principles of reaction mechanisms studied in inorganic chemistry.
This exercise is a good example of how inorganic reactions can lead to the formation of important industrial compounds, demonstrating the practical significance of inorganic chemistry in real-world applications.