Problem 47 - A Complete Resource Book in Chemistry for JEE Main

Question

Which among the following acts as a basic buffer solution? (a) \(\mathrm{NH}_{4} \mathrm{Cl}+\mathrm{NH}_{4} \mathrm{OH}\) (b) \(\mathrm{NaCl}+\mathrm{NaOH}\) (c) \(\mathrm{NH}_{4} \mathrm{Cl}+\mathrm{CH}_{3} \mathrm{COOH}\) (d) \(\mathrm{CH}_{3} \mathrm{COONa}+\mathrm{CH}_{3} \mathrm{COOH}\)

Step-by-Step Solution

Answer

The basic buffer is (a) \(\mathrm{NH}_{4} \mathrm{Cl}+\mathrm{NH}_{4} \mathrm{OH}\).

Step 1: Understand the Basics of Buffer Solutions

A buffer solution is one that resists changes in pH when small quantities of an acid or a base are added. A basic buffer typically consists of a weak base and its salt (the salt of its conjugate acid).

Step 2: Analyze Each Option

Option (a) \(\mathrm{NH}_{4} \mathrm{Cl}\) is a salt of \(\mathrm{NH}_{3}\) (a weak base) and \(\mathrm{NH}_{4} \mathrm{OH}\) is a weak base; hence, option (a) can act as a basic buffer. Option (b) \(\mathrm{NaCl}\) is a salt of strong \(\mathrm{NaOH}\) (a strong base), not a buffer.Option (c) Both \(\mathrm{NH}_{4} \mathrm{Cl}\) and \(\mathrm{CH}_{3} \mathrm{COOH}\) are related to acids, thus forming an acidic rather than a basic buffer.Option (d) \(\mathrm{CH}_{3} \mathrm{COONa}\) is a salt of weak acid \(\mathrm{CH}_{3} \mathrm{COOH}\) and doesn’t fit the basic buffer description.

Step 3: Identify the Basic Buffer

Based on the analysis, option (a) \(\mathrm{NH}_{4} \mathrm{Cl}+\mathrm{NH}_{4} \mathrm{OH}\) includes a weak base (\(\mathrm{NH}_{4} \mathrm{OH}\)) and its salt (\(\mathrm{NH}_{4} \mathrm{Cl}\)), fitting the definition of a basic buffer solution.

Key Concepts

Buffer Solution

A buffer solution is a special type of solution that helps maintain a stable pH level, even when small amounts of acidic or basic components are added. It is like a protective shield for the pH level of a solution, allowing it to resist drastic changes. This characteristic is crucial in many chemical and biological processes where consistent pH is necessary.

Buffers typically contain a mixture of either:

• A weak acid and its conjugate base
• A weak base and its conjugate acid

In acid-base chemistry, these buffers are essential because they allow reactions to occur under controlled pH conditions, which can be critical for the proper functioning of biochemical processes.

For example, in human blood, a specific buffering system maintains the pH around 7.4, which is vital for survival.

Acid-Base Chemistry

Acid-base chemistry is a foundational area of chemistry focused on the properties and reactions of acids and bases. An acid is a substance that can donate a proton ( H^+ ), while a base is a substance that can accept a proton. When acids and bases react, they form water and a salt in a neutralization reaction.

The pH scale is used to measure how acidic or basic a solution is, ranging from 0 to 14. Lower values represent acids, 7 is neutral, and higher values indicate bases. Understanding acidity and basicity is crucial for predicting the behavior of solutions and reactions.

For buffer solutions, this knowledge informs how the buffer components will interact with added acids or bases, helping to mitigate the impact on the pH. This is why buffer solutions are so valuable in both experimental and real-life applications, such as pharmaceuticals and environmental science.

Weak Base and Conjugate Acid Pairs

In the realm of buffers, one common type is the basic buffer, which uses a weak base and its conjugate acid pair to stabilize the pH. A weak base does not fully dissociate in solution, which means it can coexist with its conjugate acid. Together, they create a buffer system that counters the addition of other acids or bases.

For example, the combination of NH_4OH (ammonium hydroxide, a weak base) with NH_4Cl (ammonium chloride, its conjugate acid's salt) once dissolved, establishes a basic buffer. The weak base NH_4OH reacts with added acids, while NH_4Cl reacts with added bases. This dual action ensures that any changes in pH are minimal.

Weak bases like NH_3, when paired with their conjugate acids, are often preferred for creating basic buffers as they provide a balance between neutralization and consistent pH maintenance.