Problem 101 - A Complete Resource Book in Chemistry for JEE Main

Question

A metal (A) heating in nitrogen gas gives (B). (B) on treatment with \(\mathrm{H}_{2} \mathrm{O}\) gives a colourless gas which on passing through \(\mathrm{CuSO}_{4}\) solution turns it deep blue. Here (B) is (a) \(\mathrm{NH}_{z}\) (b) \(\mathrm{MgO}\) (c) \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) (d) \(\mathrm{Mg}_{3} \mathrm{~N}_{2}\)

Step-by-Step Solution

Answer

(B) is \mathrm{Mg}_3 \mathrm{N}_2 oexpand.

Step 1: Understanding the Reaction for (A)

Metal (A) is heated in nitrogen gas to give compound (B). This suggests that metal (A) reacts with nitrogen (N_2 oexpand) to form a nitride. Hence, (B) could be a nitride of metal (A).

Step 2: Examine the Reaction of (B) with Water

(B) reacts with H_2O oexpand to produce a colorless gas. Metal nitrides typically react with water to release ammonia (NH_3 oexpand), which is colorless.

Step 3: Identifying the Result of the Colorless Gas

Ammonia gas turns copper sulfate (CuSO_4 oexpand) solution deep blue due to the formation of a complex ion, [Cu(NH_3)_4]^{2+} oexpand.

Step 4: Identifying Compound (B)

Given the properties from previous steps, (B) must be magnesium nitride (Mg_3N_2 oexpand), as it fits the description of forming ammonia gas when reacting with water, turning copper sulfate solution blue.

Key Concepts

Chemical Reactions

Chemical reactions are fundamental processes where substances, known as reactants, transform into new substances, called products. In the context of metal nitrides, we investigate how metals interact with nitrogen gas to form compounds that possess significant reactive properties.
For example, in our exercise, a metal identified as Magnesium (Mg) is heated in nitrogen gas (0N_2) to produce magnesium nitride (0Mg_3N_2). This type of reaction is an example of a synthesis reaction, where two or more reactants combine to form a single, more complex product. Such reactions are often driven by the need for metals to fulfill their octet requirements by forming stable nitrides.
Understanding the conditions and catalysts that facilitate these reactions can be crucial in predicting product formation and purity.

Complex Ion Formation

Complex ions are formed when simple ions bind with other molecules or ions, leading to a composite particle with unique properties. The role of complex ions in chemistry is extensively observed in various applications, including the transformation of substances in solutions.
In our example, the presence of ammonia (0NH_3), a colorless gas, leads to the formation of a complex ion when it interacts with copper sulfate (0CuSO_4) solution. The process involves the coordination of ammonia molecules with copper (II) ions, resulting in a strikingly deep blue solution of 0[Cu(NH_3)_4]^{2+}, known as tetraamminecopper(II).
Important characteristics of complex ions include:

• Specific color changes that can be indicators of certain reactions
• Unique shapes and structures that dictate their chemical behavior

Understanding complex ion formation helps in analyzing chemical behaviors and has practical implications in qualitative analysis and other industrial applications.

Ammonia Production

Ammonia (0NH_3) is a vital compound in both industrial processes and biological systems. It is commonly produced through the Haber process at an industrial scale, but in laboratory settings, other methods may be explored. In this exercise, ammonia is generated by the reaction of metal nitrides with water.
When water (0H_2O) reacts with magnesium nitride (0Mg_3N_2), the products include magnesium hydroxide (0Mg(OH)_2) and ammonia gas (0NH_3). This is a decomposition reaction where the nitride breaks down in the presence of water, liberating ammonia.
Key aspects of ammonia production include:

• Its gaseous, colorless, and pungent nature
• Ability to form complex ions with transition metals
• Critical role in the nitrogen cycle and fertilizers

The understanding of these chemical interactions not only illustrates foundational ammonia production but also its impact on biological and industrial processes.