Problem 84 - A Complete Resource Book in Chemistry for JEE Main

Question

A metal \(\mathrm{X}\) on heating in nitrogen gas gives Y. Y on treatment with \(\mathrm{H}_{2} \mathrm{O}\) gives a colourless gas which when passed through \(\mathrm{CuSO}_{4}\) solution gives a blue colour. Y is (a) \(\mathrm{Mg}_{3} \mathrm{~N}_{2}\) (b) \(\mathrm{MgO}\) (c) \(\mathrm{NH}_{3}\) (d) \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

Y is \(\text{Mg}_3\text{N}_2\) (option a).

Step 1: Identify Initial Reaction

A metal X reacts with nitrogen to form compound Y. We need to consider how metals typically form compounds with nitrogen. Generally, metals like magnesium form metal nitrides such as \(\text{Mg}_3\text{N}_2\).

Step 2: Identify Products from Water Reaction

Compound Y, when treated with water, produces a colorless gas. Metal nitrides like \(\text{Mg}_3\text{N}_2\) react with water to produce ammonia \(\text{NH}_3\), which is a colorless gas.

Step 3: Analyze Reaction with Copper(II) Sulfate

The colorless gas produced passes through \(\text{CuSO}_4\) solution, giving a blue color. \(\text{NH}_3\) reacts with \(\text{CuSO}_4\) to form a deep blue complex, confirming the presence of ammonia.

Step 4: Verify Components and Pattern

The pattern of reactions suggests that metal X is forming a nitride with nitrogen (most likely \(\text{Mg}_3\text{N}_2\)), which upon hydrolysis, releases \(\text{NH}_3\). This pattern corresponds to the behavior of magnesium nitride.

Key Concepts

Metal Nitride Formation

Metal nitride formation is a fascinating chemical reaction where metals react with nitrogen gas to form compounds known as metal nitrides. This process typically occurs at high temperatures, where the metal provides electrons to nitrogen, facilitating the strong bond formation.

• Metal nitrides are generally stable, hard compounds.
• They often exhibit high melting points due to the strong metal-nitrogen bonds.

For example, magnesium reacts with nitrogen to form magnesium nitride (\(\text{Mg}_3\text{N}_2\)). The reaction can be represented as:\[3\text{Mg} + \text{N}_2 \rightarrow \text{Mg}_3\text{N}_2\]In this reaction, magnesium atoms provide electrons to the nitrogen molecule, creating a stable compound that can further react chemically with other substances.

Ammonia Production

Ammonia production during chemical reactions often involves the conversion of compounds containing nitrogen. When metal nitrides, like magnesium nitride (\(\text{Mg}_3\text{N}_2\)), come into contact with water, a reaction occurs resulting in the decomposition of the nitride.

• This decomposition produces ammonia, a colorless gas, and a metal hydroxide.

The reaction between magnesium nitride and water is as follows:\[\text{Mg}_3\text{N}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Mg(OH)}_2 + 2\text{NH}_3\]Ammonia (\(\text{NH}_3\)) is often associated with a distinct, pungent odor and is soluble in water. It serves various industrial purposes, including fertilizers and chemical synthesis. In laboratory settings, the production of ammonia through nitride hydrolysis is also a common way to demonstrate chemical concepts related to metal reactions.

Reaction with Copper Sulfate

The reaction between ammonia and copper(II) sulfate (\(\text{CuSO}_4\)) is an interesting chemical event, primarily due to the formation of a complex ion. When ammonia gas is bubbled through a solution of copper sulfate, a noticeable blue color forms, indicating the creation of a deep blue complex known as the tetraamminecopper(II) ion.

• The chemical equation for this complex formation is:\[\text{Cu}^{2+} + 4\text{NH}_3 \rightarrow [\text{Cu}(\text{NH}_3)_4]^{2+}\]
• This complexation reaction highlights ammonia's role as a ligand, where it donates lone pair electrons from nitrogen to form a coordination complex.

Such reactions are valuable in analytical chemistry for detecting the presence of certain ions and understanding ligand behavior during complex formation. The dazzling blue color is characteristic of \([\text{Cu}(\text{NH}_3)_4]^{2+}\) and is a visual confirmation of the reaction's occurrence.