Question

A metal \(X\) 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) \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) (b) \(\mathrm{Mg}_{3} \mathrm{~N}_{2}\) (c) \(\mathrm{NH}_{3}\) (d) \(\mathrm{MgO}\)

Short answer

(b) \( \text{Mg}_3\text{N}_2 \)

Step-by-step solution

Understand the Chemical Reaction

When a metal \( X \) is heated in nitrogen gas, it forms a compound \( Y \). This reaction typically forms a nitride of the metal, \( X_3N_2 \), when nitrogen gas reacts with an active metal like magnesium (\( \text{Mg} \)). So, \( Y \) is likely a nitride compound.

Reaction of Y with Water

The compound \( Y \) reacts with water to produce a colorless gas. When magnesium nitride (\( \text{Mg}_3\text{N}_2 \)) reacts with water, it forms magnesium hydroxide (\( \text{Mg(OH)}_2 \)) and ammonia gas (\( \text{NH}_3 \)), which is colorless: \[ \text{Mg}_3\text{N}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Mg(OH)}_2 + 2\text{NH}_3 \] This suggests that \( Y \) is \( \text{Mg}_3\text{N}_2 \).

Test with Copper Sulfate Solution

The colorless gas \( \text{NH}_3 \) formed passes through \( \text{CuSO}_4 \) solution and turns it blue. The reaction is due to the formation of a complex \( \text{Cu(NH}_3)_4\text{SO}_4 \), which is blue. This confirms the presence of \( \text{NH}_3 \) from \( Y \).

Conclusion

Based on the reactions, the product \( Y \) formed when metal \( X \) is heated in nitrogen and then reacts with water to produce \( \text{NH}_3 \), supports \( Y \) being \( \text{Mg}_3\text{N}_2 \).

Key concepts

Chemical Reactions

Chemical reactions occur when substances interact to form new compounds. These processes involve breaking and forming bonds, resulting in changes in energy levels and properties of the reactants and products. Inorganic chemistry, which deals with non-organic substances, often involves reactions between metals and nonmetals, like nitrogen.

• In our scenario, a metal labeled \( X \) is heated in nitrogen gas, leading to the formation of a new compound \( Y \).
• This process involves a combination reaction where nitrogen molecules break and atoms bond with the metal atoms.
• The resulting product \( Y \) is typically a nitride, a compound where nitrogen bonds with a metal.

Understanding these reactions is crucial as they form the basis of more complex chemical processes.

Metal Nitrides

Metal nitrides are compounds formed by combining metals with nitrogen. They are typically created through a direct reaction between the metal and nitrogen gas at high temperatures.

• These compounds have unique properties such as high melting points and strength, making them useful in various industrial applications.
• In our example, magnesium nitride \( \text{Mg}_3\text{N}_2 \) is formed by heating magnesium metal in nitrogen.
• Metal nitrides, like \( \text{Mg}_3\text{N}_2 \), often react readily with water to form secondary compounds, demonstrating their reactivity and usefulness.

These characteristics underscore the significance of nitrides in both practical applications and educational chemical reactions.

Ammonia Formation

The formation of ammonia, a key process in our exercise, highlights the versatility of chemical reactions. When magnesium nitride \( \text{Mg}_3\text{N}_2 \) reacts with water, ammonia \( \text{NH}_3 \) is released as a colorless gas.

• The balanced chemical equation for this reaction is: \[ \text{Mg}_3\text{N}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Mg(OH)}_2 + 2\text{NH}_3 \]
• Ammonia is known for its pungent smell and is a common nitrogen source in fertilizers.
• In the lab, observing the release and properties of ammonia helps confirm the involvement of metal nitrides in chemical reactions.

Ammonia’s formation through simple reactions is a great demonstration of chemical transformation.

Copper Sulfate Reaction

The reaction between ammonia and copper sulfate \( \text{CuSO}_4 \) solution provides a visual confirmation of chemical processes at work. Ammonia, when passed through \( \text{CuSO}_4 \), forms a deep blue complex, \( \text{Cu(NH}_3)_4\text{SO}_4 \).

• This complex is known as tetraamminecopper sulfate, highlighting the role of ammonia in ligand formation and complex chemistry.
• The vivid blue color indicates the strong interaction between copper ions and ammonia molecules.
• This experiment visually confirms the presence of ammonia, reinforcing the results of the preceding reactions.

Such vivid color changes are not only fascinating but also valuable for analyzing and confirming chemical identities and interactions in the lab.