Question

Buffer solutions have constant acidity and alkalinity because

• A. these give unionised acid or base on reaction with added acid or alkali
• B. acids and alkalies in these solutions are shielded from attack by other ions
• C. they have large excess of $ H^+ $ or $ OH^- $ ions
• D. they have fixed value of pH

Answer 1

The Correct Option is A

Buffer solutions are special solutions that resist changes in pH when small quantities of an acid or an alkali are added. Let's explore why the correct option is "these give unionised acid or base on reaction with added acid or alkali" by understanding the concept of buffer solutions:

1. Definition of Buffer Solutions: Buffer solutions consist of a weak acid and its conjugate base, or a weak base and its conjugate acid. They help maintain a consistent pH level by neutralizing small amounts of added acids or bases.
2. Mechanism of Buffer Action: When an acid (like H₂SO₄) is added to a buffer solution, the base part of the buffer reacts with the added acid. Conversely, when a base (like NaOH) is added, the acid part of the buffer reacts. In this process, the buffer components give unionised species, which prevents large scale pH variations.
3. Explanation of the Correct Option: The provided correct answer is "these give unionised acid or base on reaction with added acid or alkali". This explains that buffers neutralize added acids or bases by converting them into unionised forms, thereby stabilizing the pH.
4. Elimination of Incorrect Options:
   • Option "acids and alkalies in these solutions are shielded from attack by other ions" is incorrect because shielding from other ions is not the mechanism by which buffers stabilize pH.
   • Option "they have large excess of H^+ or OH^− ions" is incorrect. Buffers work despite not having excess of these ions; instead, they have a balance that resists change.
   • Option "they have fixed value of pH" is misleading. While buffers maintain a relatively constant pH, the pH is not absolutely fixed and can vary slightly within a narrow range.
5. Conclusion: Buffer solutions maintain constant acidity and alkalinity due to their ability to neutralize added acids or bases by forming unionised forms, thus preventing significant pH changes. This makes buffer solutions crucial in various chemical and biological systems where pH stability is essential.