Problem 5 - Chemistry in 30 days

Question

A metal \(\mathrm{X}\) on heating in nitrogen gas gives Y. \(\mathrm{Y}\) on treatment with \(\mathrm{H}_{2} \mathrm{O}\) gives a colourless gas which on passing through \(\mathrm{CuSO}_{4}\) solution tums it deep blue. \(\mathrm{Y}\) is (a) \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) (b) \(\mathrm{Mg}_{3} \mathrm{~N}_{2}\) (c) \(\mathrm{NH}_{1}\) (d) \(\mathrm{MgO}\)

Step-by-Step Solution

Answer

Y is \( \mathrm{Mg}_3 \mathrm{~N}_2 \), corresponding to option (b).

Step 1: Identify the Metal Reaction Product Y

The metal X reacts with nitrogen to form Y. In chemical terms, this reaction typically forms a metal nitride. So the metal nitride, in this context, is likely to be magnesium nitride, \( \mathrm{Mg}_3 \mathrm{~N}_2 \).

Step 2: Write the Reaction with Water

When \( \mathrm{Mg}_3 \mathrm{~N}_2 \) reacts with water, it will produce ammonia (\( \mathrm{NH}_3 \)) and magnesium hydroxide, according to the reaction: \[ \mathrm{Mg}_3 \mathrm{~N}_2 + 6\mathrm{H}_2 \mathrm{O} \rightarrow 3\mathrm{Mg(OH)}_2 + 2\mathrm{NH}_3 \].

Step 3: Identify and Describe Gas Produced

The colorless gas produced in the reaction from Step 2 is \( \mathrm{NH}_3 \). This is confirmed by the solution of copper sulfate (\( \mathrm{CuSO}_4 \)) turning deep blue upon adding ammonia, which forms a complex. This is known as the tetraamminecopper(II) sulfate complex, which is deep blue.

Step 4: Confirm the Identity of Y

From Steps 1-3, we have established that \( \mathrm{Y} \) is \( \mathrm{Mg}_3 \mathrm{~N}_2 \) because upon reacting with water, it produces ammonia, which then reacts with \( \mathrm{CuSO}_4 \) to turn it deep blue, consistent with the given problem description.

Key Concepts

Magnesium Nitride

Magnesium nitride, represented chemically as \( \mathrm{Mg}_3 \mathrm{N}_2 \), is formed when magnesium metal reacts with nitrogen gas. This is a type of metal nitride reaction, known for producing ionic compounds between metals and nitrogen. During the reaction, magnesium, which is a strong reducing agent, donates electrons to nitrogen molecules, forming a stable nitride. Magnesium nitride is a yellowish-white powder and is known for its reactivity with water, making it a crucial component in this chemical process.

Ammonia Production

Ammonia (\( \mathrm{NH}_3 \)) is produced when magnesium nitride reacts with water. The chemical equation representing this reaction is: \[ \mathrm{Mg}_3 \mathrm{~N}_2 + 6\mathrm{H}_2 \mathrm{O} \rightarrow 3\mathrm{Mg(OH)}_2 + 2\mathrm{NH}_3 \] Ammonia is a colorless gas with a distinct, pungent smell. This reaction is significant industrially, as ammonia is a vital chemical used in fertilizers, cleaning agents, and synthesis of various nitrogen-containing compounds. In this exercise, the mention of ammonia hints at the identification of the produced gas from the metal nitride reaction.

Chemical Reactions with Water

Chemical reactions between metal nitrides and water are not uncommon and often yield interesting results. For magnesium nitride, the reaction with water produces both ammonia gas and magnesium hydroxide.

• The magnesium nitride decomposes in the presence of water.
• Ammonia is released as a gaseous product.
• Magnesium hydroxide forms as an insoluble solid or precipitate in the solution.

These types of reactions are essential for understanding how metal compounds interact with water and change states, offering insight into their potential applications and behaviors in different environments.

Copper Sulfate Complexes

Copper sulfate solutions are quite informative when it comes to chemical reaction demonstrations. When ammonia gas is introduced to a copper sulfate (\( \mathrm{CuSO}_4 \)) solution, it creates a noticeable deep blue color. This change is due to the formation of a complex ion, tetraamminecopper(II) sulfate:\[ \mathrm{CuSO}_4 + 4\mathrm{NH}_3 + \mathrm{H}_2O \rightarrow \left[\mathrm{Cu(NH}_3\right]_4\right]^{2+} + \mathrm{SO}_4^{2-} \]

• This complex formation indicates the presence of ammonia.
• It visually confirms the chemical reaction and production of ammonia from magnesium nitride.

Such reactions are commonly used to identify ammonia and demonstrate copper's complexation chemistry.