Problem 266 - A Complete Resource Book in Chemistry for JEE Main

Question

The conjugate base of \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)is (a) \(\mathrm{HPO}_{4}^{2-}\) (b) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (c) \(\mathrm{PO}_{4}^{3-}\) (d) \(\mathrm{P}_{2} \mathrm{O}_{5}\)

Step-by-Step Solution

Answer

The conjugate base of \\(\mathrm{H}_2 \mathrm{PO}_4^-\\) is \\(\mathrm{HPO}_4^{2-}\\).

Step 1: Understanding the Concept

To identify the conjugate base of an acid, you need to remove one hydrogen ion (H extsuperscript{+}) from the acid. This is based on the Bronsted-Lowry acid-base theory.

Step 2: Identifying the Acid

The given acid is \(\mathrm{H}_2 \mathrm{PO}_4^-\). This is a dihydrogen phosphate ion. We need to determine which ion is formed when it loses a hydrogen ion.

Step 3: Removing a Proton

The conjugate base is formed by removing a hydrogen ion (H extsuperscript{+}) from the acid. So, when one H extsuperscript{+} is removed from \(\mathrm{H}_2 \mathrm{PO}_4^-\), the resulting formula is \(\mathrm{HPO}_4^{2-}\).

Step 4: Verifying Possible Answers

Comparing with the given options: (a) \(\mathrm{HPO}_{4}^{2-}\) (b) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (c) \(\mathrm{PO}_{4}^{3-}\) (d) \(\mathrm{P}_{2} \mathrm{O}_{5}\). The formula \(\mathrm{HPO}_4^{2-}\) matches option (a).

Key Concepts

Conjugate Base

In the realm of chemistry, a conjugate base arises when an acid gives up a hydrogen ion, also referred to as a proton. This is a central concept in the Bronsted-Lowry Theory, which emphasizes the transfer of protons between reactants. By removing a proton from an acid, we obtain its conjugate base. For example, removing an \(H^+\) ion from \(H_2 \text{PO}_4^-\) results in \(HPO_4^{2-}\), making it the conjugate base of the dihydrogen phosphate ion. This principle underlines how acids and bases are interconnected in an equilibrium reaction: the base can gain a proton to revert back to the acid state.

This conjugate pairing is fundamental in gauging the strength of acids and bases in a solution, influencing pH levels and the direction of chemical reactions. It helps students understand the dynamic nature of acid-base chemistry and predict molecular behavior during reactions.

Acid-Base Reactions

Acid-base reactions are a core part of chemistry, where a proton transfer occurs between a donor (acid) and an acceptor (base). According to the Bronsted-Lowry Theory, an acid is a molecule that can donate a proton, while a base accepts a proton. This theory broadens our understanding from classical concepts, allowing the inclusion of substances that do not necessarily have hydroxide ions.

• Acids, once having donated a proton, become their conjugate bases.
• Bases, after receiving a proton, form their conjugate acids.

This interchange forms aqueous solutions, contributing to the formation of water and salts. The nature of these interactions often dictates the reaction products and equilibrium shifts.

Understanding acid-base reactions is crucial for grasping the behavior and properties of solutions in various chemical and biological systems. They are common in both laboratory settings and everyday life, affecting processes from digestion to industrial manufacturing.

Dihydrogen Phosphate Ion

The dihydrogen phosphate ion \(\mathrm{H}_2\mathrm{PO}_4^-\) is an example of a polyatomic ion prevalent in chemistry, particularly in biochemistry and environmental science. It's an intermediate ion in the conversion between phosphoric acid \(\mathrm{H}_3\mathrm{PO}_4\) and other phosphate ions such as \(\mathrm{HPO}_4^{2-}\) and \(\mathrm{PO}_4^{3-}\).

• Derived from phosphoric acid, it plays a key role in regulating pH in biological systems.
• Important for cellular energy transfer processes as it is involved in the formation of ATP (adenosine triphosphate), the energy currency of cells.

The ability of dihydrogen phosphate ions to lose or gain protons allows them to buffer solutions effectively, essential for maintaining pH stability.

It is an integral component in many systems, from nutrient cycles in ecosystems to metabolic processes in organisms. Its versatility and function demonstrate the multifaceted nature of chemical species in differing environments.