Problem 61 - A Complete Resource Book in Chemistry for JEE Main

Question

In liquid \(\mathrm{NH}_{3}\) (a) \(\mathrm{CH}_{3} \mathrm{COOH}\) behaves as strong acid (b) \(\mathrm{NaNH}_{2}\) is a base (c) \(\mathrm{NH}_{4} \mathrm{Cl}\) is an acid (d) All the above facts are true

Step-by-Step Solution

Answer

(d) All the above facts are true.

Step 1: Understanding the context

The exercise is about the behavior of certain compounds in liquid ammonia (NH_{3}). Liquid ammonia acts as a solvent similarly to water, allowing for acid-base reactions but with its own unique acid-base system.

Step 2: Analyzing CH3COOH in NH3

In liquid NH_{3}, CH_{3}COOH acts as an acid because it can donate a proton (NH_{4}^{+}) to ammonia, which behaves as a weak acid against ammonia's base properties. Thus, CH_{3}COOH behaves as a strong acid relative to the solvent.

Step 3: Examining NaNH2 in NH3

NaNH_{2} acts as a base in liquid NH_{3} because NH_{2}^{-} (amide ion) is a strong base in this solvent. It readily accepts a proton from NH_{4}^{+} that CH_{3}COOH or any ammonium compound could provide.

Step 4: Considering NH4Cl in NH3

NH_{4}Cl is an acid in liquid NH_{3} because it can donate a proton to NH_{2}^{-} (from NaNH_{2}), forming the NH_{4}^{+} ion.

Step 5: Concluding which statements are correct

Given the explanations of each compound's behavior, we can conclude that all stated behaviors in options (a), (b), and (c) are true, making (d) the correct choice.

Key Concepts

CH3COOH as acid in liquid ammonia

Acetic acid (\( \text{CH}_3\text{COOH} \)) acts as an acid when dissolved in liquid ammonia (\( \text{NH}_3 \)). This might seem surprising given that acetic acid is known as a weak acid in water. In liquid ammonia, however, the dynamics change. Acetic acid donates a proton, and in this solvent, the protons are more actively accepted by ammonia than water.

• Liquid ammonia can be considered a base, so when acetic acid donates a proton, it effectively releases \( \text{NH}_4^+ \) ions.
• This transfer of a proton from \( \text{CH}_3\text{COOH} \) to ammonia makes acetic acid function as a 'strong acid' relative to the basic nature of the ammonia environment.

Understanding this acid-base behavior helps illustrate how certain compounds can change their roles as acids or bases depending on the solvent system.

NaNH2 as base in liquid ammonia

Sodium amide (\( \text{NaNH}_2 \)) is a strong base when dissolved in liquid ammonia. Unlike water, ammonia has different interactions with both acids and bases.

• The presence of the amide ion (\( \text{NH}_2^- \)) in sodium amide readily accepts protons. This is what makes sodium amide an exceptionally strong base in liquid ammonia.
• When sodium amide is present, it can easily pick up the \( \text{NH}_4^+ \) ions released from any acidic compound in the solution, such as acetic acid or ammonium chloride.

This proton acceptance mechanism is why sodium amide plays a crucial role as a base in the ammonia solvent system.

NH4Cl in liquid ammonia

Ammonium chloride (\( \text{NH}_4\text{Cl} \)) acts as an acid when dissolved in liquid ammonia. Despite being formed from a strong acid (HCl) and weak base (NH3), in this situation, its chemistry is uniquely altered by the solvent.

• The ammonium ion (\( \text{NH}_4^+ \)) present in ammonium chloride can release a proton relatively easily in liquid ammonia, effectively increasing the acidity of the environment.
• These released protons can react with basic species like the amide ion (\( \text{NH}_2^- \)) from sodium amide to form more stable molecules.

This proton donation characterizes ammonium chloride as an acid in this setting, showing how solvent environments significantly impact chemical behavior and interactions.