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-}\\) (Option a).

Step 1: Understanding the Concept

In chemistry, a conjugate base is formed when an acid donates a proton (H⁺). The species that remains after the acid loses its proton is the conjugate base of that acid.

Step 2: Identify the Original Acid

The acid in question is \( \mathrm{H}_{2} \mathrm{PO}_{4}^{-} \) which is known as dihydrogen phosphate.

Step 3: Remove a Proton

Since forming a conjugate base involves removing a proton (H⁺) from the acid, remove one hydrogen ion from \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\). This leaves us with \(\mathrm{HPO}_{4}^{2-}\).

Step 4: Determine the Charge

When \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) loses a proton, the charge of the base must be updated. Originally, it is -1, and after losing one H⁺, it becomes \(\mathrm{HPO}_{4}^{2-}\).

Step 5: Confirm the Conjugate Base

Now confirm the conjugate base which is \(\mathrm{HPO}_{4}^{2-}\) among the options given: (a) \(\mathrm{HPO}_{4}^{2-}\) (b) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (c) \(\mathrm{PO}_{4}^{3-}\) (d) \(\mathrm{P}_{2} \mathrm{O}_{5}\)Since \(\mathrm{HPO}_{4}^{2-}\) is derived from \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) by losing an H⁺, the correct answer is (a).

Key Concepts

Acid-Base Reactions

Acid-base reactions are a fundamental concept in chemistry and involve the transfer of protons between molecules. In these reactions, an acid donates a proton (H⁺) to a base. The original acid transforms into its conjugate base after losing the proton, while the original base becomes a conjugate acid after gaining a proton.

It's essential to remember a few key points about acid-base reactions:

• The strength of an acid is determined by its ability to donate a proton easily.
• The strength of a base is reflected in its ability to accept a proton.
• In these reactions, acids and bases always come in pairs known as conjugate acid-base pairs.
• When an acid donates a proton, the residual part is its conjugate base.
• When a base accepts a proton, the resulting species is its conjugate acid.

Thus, understanding these reactions provides insight into the behavior of molecules and ions in solution, enabling prediction and control over chemical processes.

Dihydrogen Phosphate

Dihydrogen phosphate, written chemically as \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\), is a prevalent species in buffer solutions and plays a vital role in biological systems.

Here's what you should know about dihydrogen phosphate:

• It is an anion with a -1 charge due to its extra proton.
• Functioning as an acid, it can donate a proton to become \(\mathrm{HPO}_{4}^{2-}\), which is its conjugate base.
• It's part of the larger phosphate system involved in energy transfer processes like ATP in living organisms.

This ion is versatile and widely present in both inorganic and biological chemistry, proving its immense importance.

Proton Transfer

Proton transfer is a crucial component of many chemical reactions, particularly in the context of acid-base chemistry. It involves the movement of a hydrogen ion (H⁺) from one species to another.

In more detail, the process works as follows:

• During a proton transfer, the acid donates a proton to the base.
• Proton transfer is typically rapid and often reversible, meaning the reaction can proceed both forward and backward.
• It results in changes in the charge and structure of the molecules involved.
• This mechanism is also a key part of biological systems, including enzyme activity and cellular energy management.

Understanding proton transfer is fundamental for grasping not just simple chemical reactions but complex biological mechanisms as well.