Problem 98 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following equations is not correct? (1) \(2 \mathrm{Na}+2 \mathrm{NH}_{3} \longrightarrow{\Delta}{\longrightarrow} 2 \mathrm{NaNH}_{2}+\mathrm{H}_{2}\) (2) \(4 \mathrm{NH}_{3}+2 \mathrm{NaOCl} \longrightarrow 2 \mathrm{NH}_{4} \mathrm{Cl}^{2}+2 \mathrm{NaNH}_{2}\) (3) \(\mathrm{NH}_{3}+3 \mathrm{Cl}_{2} \stackrel{\text { Excess }}{\text { Excess }}+\mathrm{O}_{2}^{4}\) (4) \(\mathrm{NH}_{3}+3 \mathrm{Cl}_{2}^{2} \stackrel{\text { Excess }}{\longrightarrow} \mathrm{NCl}_{3}+3 \mathrm{HCl}\) (a) 2 and 3 only (b) 1 and 4 only (c) 3 only (d) 2 only

Step-by-Step Solution

Answer

Option (a) 2 and 3 only are incorrect.

Step 1: Analyze Equation (1)

The equation given is \(2 \mathrm{Na} + 2 \mathrm{NH}_{3} \longrightarrow \Delta \longrightarrow 2 \mathrm{NaNH}_{2} + \mathrm{H}_{2}\). This equation describes the reaction between sodium (Na) and ammonia (NH₃) to form sodium amide (NaNH₂) and hydrogen gas (H₂). This equation is balanced as both sides have: 2 Na, 2 N, 6 H on the reactant side and 2 Na, 2 N, and 6 H on the product side. Thus this equation is correct.

Step 2: Analyze Equation (2)

The equation given is \(4 \mathrm{NH}_{3} + 2 \mathrm{NaOCl} \longrightarrow 2 \mathrm{NH}_{4} \mathrm{Cl}^{2} + 2 \mathrm{NaNH}_{2}\). On assessing, the product side seems incorrect specifically due to \(\mathrm{NH}_{4} \mathrm{Cl}^{2}\), which is not a recognized chemical formula. Instead, \(\mathrm{NH}_{4} \mathrm{Cl}\) (ammonium chloride) would be expected. Hence, this equation is incorrect.

Step 3: Analyze Equation (3)

The equation given is \(\mathrm{NH}_{3} + 3 \mathrm{Cl}_{2} \stackrel{\text { Excess }}{\text { Excess }} + \mathrm{O}_{2}^{4}\). Analyze the species involved; this suggests an incorrect format and inconsistency in the presentation of the equation. Furthermore, \(\mathrm{O}_{2}^{4}\) makes no sense. Therefore, this equation is grossly incorrect.

Step 4: Analyze Equation (4)

The equation given is \(\mathrm{NH}_{3} + 3 \mathrm{Cl}_{2}^{2} \stackrel{\text { Excess }}{\longrightarrow} \mathrm{NCl}_{3} + 3 \mathrm{HCl}\). Here, \(\mathrm{NCl}_{3}\) (nitrogen trichloride) and \(\mathrm{HCl}\) are formed. Each nitrogen requires three chlorines (correctly presented if excess chlorine is available), making the chlorine count consistent. The equation; however, shows incorrect chemical representation \(3 \mathrm{Cl}_{2}^{2}\) instead of \(3 \mathrm{Cl}_{2}\). This equation has mistakes.

Step 5: Determine Incorrect Equations

From the analysis, equations (2) and (3) are incorrect based on improper or faulty representations. Therefore, the answer is option (a) 2 and 3 only.

Key Concepts

Chemical Reactions

Chemical reactions are processes where one or more substances are transformed into new substances. These are crucial in science, particularly in chemistry, as they explain how substances interact and change.
During a chemical reaction, bonds in the reactants are broken, and new bonds are formed in the products. Reactants are the starting materials, and products are the substances formed as a result of the reaction. Understanding the concept of reactants and products is essential when analyzing or balancing chemical equations.

• Reactants: The original substances involved in a reaction.
• Products: New substances formed as a result of the reaction.

One classic example of a chemical reaction is the reaction between hydrogen and oxygen to form water, where these two gases react to create a new product, water, showing how simple elements combine to create new compounds.

Ammonia Chemistry

Ammonia, with the chemical formula \(\mathrm{NH}_{3}\), plays a significant role in various chemical reactions. It is a colorless gas with a distinct smell and is often used as a building block in the synthesis of many compounds.
In the context of the equations we're dealing with, ammonia interacts with other chemicals to form different products.

• In Reaction 1, ammonia reacts with sodium to form sodium amide \(\mathrm{NaNH}_{2}\) and hydrogen gas. This is a properly balanced and significant industrial reaction known for its use in producing ammonia derivatives.
• Reaction 2 seems to misconstrue the formation of ammonium chloride, showing \(\mathrm{NH}_{4} \mathrm{Cl}^{2}\) which is not a recognized compound, illustrating an error in understanding ammonia’s chemistry.

Understanding these interactions is essential since ammonia is widely used in fertilizers, cleaning products, and other industrial applications. Recognizing its proper chemical combinations is vital in chemical equations and real-world applications.

Equation Analysis

Analyzing chemical equations involves checking for balanced reactions and verifying that all chemical representations accurately reflect known substances.
Correctly balanced equations ensure that the number of atoms of each element is the same on both sides of the equation, respecting the Law of Conservation of Mass.

• In Step 1, equation analysis verified that the sodium and ammonia reaction produces a balanced and well-known products.
• Step 3 highlights the importance of proper data presentation. Equation 3 fails this because of an incorrect substance presentation \(\mathrm{O}_{2}^{4}\), pointing to the importance of accuracy in representation.
• Equation 4 is another example where incorrect representation, such as \(3 \mathrm{Cl}_{2}^{2}\), leads to an error.

Thus, accuracy in chemical equations is paramount for correct communication in chemistry, allowing chemists to interpret reactions and predict outcomes accurately.