Problem 48 - A Complete Resource Book in Chemistry for JEE Main

Question

Conjugate base of hydrazoic acid is (a) \(\mathrm{HN}_{3}^{-}\) (b) \(\mathrm{N}_{2}\) (c) Azide ion (d) Nitride ion

Step-by-Step Solution

Answer

The conjugate base of hydrazoic acid is the azide ion \( \text{N}_3^- \).

Step 1: Identify the Formula of Hydrazoic Acid

Hydrazoic acid is represented by the chemical formula \( ext{HN}_3 \). It consists of one hydrogen atom and the azide ion \( ext{N}_3^- \).

Step 2: Define Conjugate Base

The conjugate base of an acid is formed by removing one proton (\( ext{H}^+ \)) from the acid molecule. The conjugate base has one unit less positive charge than its parent acid.

Step 3: Remove a Proton from Hydrazoic Acid

To find the conjugate base of \( ext{HN}_3 \), we remove \( ext{H}^+ \) from the molecule. This process will result in the remaining ion being \( ext{N}_3^- \).

Step 4: Identify the Correct Answer

The ion \( ext{N}_3^- \) is known as the azide ion. Therefore, the conjugate base of hydrazoic acid is the azide ion.

Key Concepts

Hydrazoic Acid

Hydrazoic acid is a fascinating compound with the chemical formula \(\mathrm{HN}_3\). It is composed of one hydrogen atom and the azide ion \(\mathrm{N}_3^-\). Concentrated hydrazoic acid is known for being quite explosive and toxic, requiring careful handling.
In chemistry, hydrazoic acid behaves as a typical weak acid. When dissolved in water, it partially ionizes, meaning it donates a proton \(\mathrm{H}^+\) to water thereby allowing the formation of hydronium ions \(\mathrm{H}_3\mathrm{O}^+\) and azide ions \(\mathrm{N}_3^-\).
Its weak acidic behavior means that not all of the hydrazoic acid molecules dissociate in solution, which is a key characteristic differentiating weak acids from strong acids that fully dissociate. The formula \(\mathrm{HN}_3\) itself should remind us of this dual nature: containing both hydrogen and the azide structure, the latter of which forms the conjugate base when a proton is lost.

Azide Ion

The azide ion, \(\mathrm{N}_3^-\), is a negatively charged ion composed of three nitrogen atoms bonded together. When hydrazoic acid loses a proton, it transforms into its conjugate base, the azide ion.

• The azide ion is linear in structure, where the nitrogen atoms are connected in a straight line.
• It carries a negative charge distributed over the entire structure, leading to resonance stabilization.

The resonance of the azide ion is a fascinating aspect, wherein the charge is delocalized across the nitrogen atoms. This delocalization imparts extra stability to the ion.
In many reactions, the azide ion acts as a nucleophile due to its negative charge. This means it has a tendency to donate an electron pair, playing a crucial role in various chemical synthesis reactions.
Being derived from hydrazoic acid, the azide ion features prominently in the study of acid-base chemistry as an example of how acids can transform upon losing a proton.

Acid-Base Reactions

Acid-base reactions are fundamental to understanding chemical reactions and are among the most common reactions encountered in chemistry. In these reactions, an acid donates a proton \(\mathrm{H}^+\) to a base.
Hydrazoic acid serves as a classic example that illustrates this process. When it donates its proton, it transforms into the azide ion, which acts as its conjugate base.

• In the context of an acid-base reaction, the role of the conjugate base like the azide ion is crucial for maintaining chemical equilibrium.
• The relationship between the acid and its conjugate base (here, \(\mathrm{HN}_3\) and \(\mathrm{N}_3^-\)) and vice versa is governed by the Bronsted-Lowry theory of acids and bases.

This theory postulates that acids are proton donors and bases are proton acceptors. Hence, the donated proton from hydrazoic acid creates the azide ion, completing the acid-to-conjugate base transition. Understanding these reactions allows chemists to predict the behavior of substances in different chemical environments.