Animated Solution for Chemistry - s and p-Block Elements: The nitrogen containing compound produced in the reaction of ${\text{HNO}}_3$ with ${\text{P}}_4{\text{O}}_{10}$

This question is a beautiful exploration of the chemistry of p-block elements, specifically focusing on the reactions and properties of nitrogen oxides and oxoacids. Let's embark on a step-by-step journey to unravel the mystery compound and evaluate each given statement.

The problem begins with a classic reaction: the interaction between nitric acid ($HN{O}_3$) and phosphorus pentoxide ($P_4{O}_{10}$). To understand this, we must recall the primary chemical personality of $P_4{O}_{10}$—it is an exceptionally powerful dehydrating agent.

When $P_4{O}_{10}$ encounters $HN{O}_3$, it aggressively strips water molecules from the nitric acid. This dehydration process converts the nitric acid into its corresponding anhydride. The chemical equation for this transformation is:

The nitrogen-containing compound produced is dinitrogen pentoxide ($N_2{O}_5$). Now that we have identified our target molecule, we can systematically evaluate the four options provided.

The Direct Reaction

Option (A) suggests that $N_2{O}_5$ can also be prepared by the direct reaction of white phosphorus ($P_4$) and nitric acid ($HN{O}_3$). Let's test this hypothesis.

Nitric acid is a strong oxidizing agent. When it reacts with elemental phosphorus, a vigorous redox reaction occurs. Phosphorus is oxidized to its highest oxidation state, forming phosphoric acid ($H_{3}P{O}_4$), while nitric acid is reduced to nitrogen dioxide ($N{O}_2$).

The nitrogen-containing product here is $N{O}_2$, not $N_2{O}_5$. Therefore, option (A) is incorrect.

Magnetic Properties

Option (B) claims that the compound is diamagnetic. To verify this, we need to look at the electronic structure of $N_2{O}_5$.

In the $N_2{O}_5$ molecule, all the valence electrons of the nitrogen and oxygen atoms are fully engaged in forming covalent bonds or exist as paired lone pairs. There are absolutely no unpaired electrons residing in any molecular orbital. Because all electrons are paired, $N_2{O}_5$ does not interact strongly with magnetic fields, making it diamagnetic. Thus, option (B) is correct.

Structural Insights

Option (C) states that the compound contains one N-N bond. Let's visualize the molecular architecture of $N_2{O}_5$.

The structure consists of two $N{O}_2$ groups bridged by a central oxygen atom. This creates an $N-O-N$ linkage. The nitrogen atoms are not directly bonded to each other; they are separated by the bridging oxygen.

Because there is no direct nitrogen-nitrogen bond in the molecule, option (C) is incorrect.

Reaction with Sodium

Finally, option (D) proposes that the compound reacts with sodium metal to produce a brown gas. Let's see what happens when $N_2{O}_5$ meets an active metal like sodium ($Na$).

Sodium is highly electropositive and acts as a strong reducing agent. When it reacts with $N_2{O}_5$, it reduces the nitrogen, leading to the formation of sodium nitrate ($NaN{O}_3$) and the evolution of nitrogen dioxide gas ($N{O}_2$).

Nitrogen dioxide ($N{O}_2$) is famously known for its characteristic reddish-brown color. Since the reaction indeed produces a brown gas, option (D) is correct.

By carefully analyzing the initial dehydration reaction and the subsequent chemical and physical properties of dinitrogen pentoxide, we have successfully determined that the correct statements are (B) and (D).