Question

A solution which resists any change in pH value on the addition of a small amount of an acid or base is called

• A. amphoteric solution
• B. buffer solution
• C. acidic solution
• D. alkaline solution

Answer 1

The correct option is B

buffer solution

The explanation for the correct option (B):

• Definition of Buffer solution: It is a solution that consists of a combination of a weak acid and its conjugate base, or a weak base and its conjugate acid.
• They are resistant to changes in pH caused by the addition of small quantities of acid or alkali.
• Example: A solution of Acetic acid (CH₃COOH) and Sodium acetate (CH₃COONa).

The explanation for the incorrect options:

(A)

• Amphoteric solutions have both acidic and basic characteristics, allowing them to function as both acids and bases.
• Example: Water (H₂O) can show both acidic as well as basic behaviour. Hence, Water is an amphoteric substance.
• $$\begin{gathered} {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+\mathrm{HCl}\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}\left(\mathrm{aq}\right)+{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right) \\ \left(\mathrm{base}\right) \\ {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{NH}}_3\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{OH}}^{-}\left(\mathrm{aq}\right)+{{\mathrm{NH}}_4^{+}}^{}\left(\mathrm{aq}\right) \\ \left(\mathrm{acid}\right) \end{gathered}$$

(C)

• An acidic solution refers to a solution whose pH value is less than 7.
• Example: Lemon juice and Vinegar (CH₃COOH) are acidic solutions, as both of them have a pH value of less than 7.
• Vinegar, being an acid, dissociates in the aqueous solution to form Hydrogen ions (${\mathrm{H}}^{+}$).

${\mathrm{CH}}_3\mathrm{COOH}\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{CH}}_3{\mathrm{COO}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}^{+}\left(\mathrm{aq}\right)$

(D)

• An alkaline solution refers to a solution whose pH value is greater than 7.
• Example: Sodium hydroxide (NaOH) solution and Potassium hydroxide (KOH) solution are the basic solutions as both of them has a pH value of greater than 7.
• Sodium hydroxide, being a base, dissociates in the aqueous solution to form Hydroxide ions (${\mathrm{OH}}^{-}$).

$\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)$

Final Answer: Hence, option (B) is correct. A solution that resists any change in pH value on the addition of a small amount of an acid or base is called a buffer solution.