Problem 38 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The conjugate acid of \(\mathrm{NH}_{2}^{-}\)is : (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{NH}_{2} \mathrm{OH}\) (c) \(\mathrm{NH}_{4}^{+}\) (d) \(\mathrm{N}_{2} \mathrm{H}_{4}\)

Step-by-Step Solution

Answer

The conjugate acid of \( \mathrm{NH}_{2}^{-} \) is \( \mathrm{NH}_{3} \).

Step 1: Identify the Base

The species given in the problem is \( \mathrm{NH}_{2}^{-} \), which is called the amide ion. We need to find the conjugate acid of this base.

Step 2: Add a Proton

In order for a base to become a conjugate acid, it must gain one proton (\( \mathrm{H}^{+} \)). Add a hydrogen to \( \mathrm{NH}_{2}^{-} \) to form \( \mathrm{NH}_{3} \).

Step 3: Verify Proton Addition

Adding the proton converts \( \mathrm{NH}_{2}^{-} \) to \( \mathrm{NH}_{3} \), which is ammonia. This transformation involves increasing the number of hydrogen atoms by one while balancing the charge.

Step 4: Match with Options

Compare the result, \( \mathrm{NH}_{3} \), with the options provided: (a) \( \mathrm{NH}_{3} \), (b) \( \mathrm{NH}_{2} \mathrm{OH} \), (c) \( \mathrm{NH}_{4}^{+} \), (d) \( \mathrm{N}_{2} \mathrm{H}_{4} \). The correct answer is option (a) \( \mathrm{NH}_{3} \).

Key Concepts

Conjugate Acids and Bases

In Acid-Base Chemistry, understanding conjugate acids and bases is essential. A conjugate pair consists of molecules or ions that differ by a single proton (\( ext{H}^{+}\)). When an acid donates a proton, it becomes a conjugate base. Conversely, when a base gains a proton, it becomes a conjugate acid.

• Acids lose a proton to become bases.
• Bases gain a proton to become acids.

For example, in the case of the amide ion \( ext{NH}_{2}^{-}\), the addition of a proton transforms it into ammonia, \( ext{NH}_{3}\). This process vividly illustrates how a base changes into its conjugate acid by accepting a proton. Identifying these transformations helps understand chemical reactions in solutions.

Proton Transfer

Proton transfer is a basic yet powerful concept in chemistry indicating the movement of a proton from one molecule to another.

• This process is central to many acid-base reactions.
• It dictates how substances interact through the gain and loss of \( ext{H}^{+}\) ions.

In simpler terms, during proton transfer, a proton is relocated from the acid to the base. For instance, when the amide ion \( ext{NH}_{2}^{-}\) accepts a proton, it turns into \( ext{NH}_{3}\), showing proton addition. Understanding proton transfer helps in predicting the outcomes of chemical reactions and balancing equations. It also highlights the dynamic nature of acid-base interactions.

Amide Ion

The amide ion, \( ext{NH}_{2}^{-}\), is a well-known anion in chemistry. It's primarily recognized for its role in forming ammonia upon protonation.

• It acts as a strong base due to its tendency to seek protons.
• It consists of one nitrogen atom bonded to two hydrogen atoms.

This ion is commonly found in various chemical reactions, particularly in organic chemistry. The negative charge on the amide ion makes it an excellent candidate for proton acceptance, leading to the formation of its conjugate acid, ammonia. This understanding of the amide ion is crucial for tackling problems in both organic synthesis and inorganic reactions.

Ammonia Formation

Ammonia (\( ext{NH}_{3}\)) is formed when the amide ion accepts a proton during a chemical reaction. This transformation is an example of how bases become conjugate acids.

• Ammonia is a weak base that can act as a building block in numerous compounds.
• It is characterized by a pyramidal shape with nitrogen at its apex.

This conversion demonstrates the principle of charge balance by neutralizing the negative charge on the amide ion. The formation of ammonia from the amide ion illustrates the practical aspects of acid-base chemistry and its relevance in chemical industries and natural processes. Ammonia's versatility in reactions makes it an important subject in the study of chemistry.