Question

Which of the following is a buffer
solution ?
a. CH3
COONa + NaCl in water
b. CH3
COOH + HCl in water
c. CH3
COOH+CH3
COONa in water
d. HCl + NH4
Cl in water

Answer 1

Answer:

CH₃COOH + CH₃COO⁻Na⁺ in water is a buffer solution [OPTION C].

Explanation:

What is a buffer?

A buffer is defined as a solution which resists a change in its pH when a few drops of acid or base are added to it.

Buffers are mixtures of weak acids and their salts (acidic buffer) or weak base or their salts (basic buffer).

An example of an acidic buffer is CH₃COOH + CH₃COO⁻Na⁺ (Acetic acid [weak acid] + sodium acetate [salt of acetic acid])
An example of a basic buffer is NH₄OH + NH₄Cl (Ammonium Hydroxide [weak base] + ammonium chloride [salt of ammonium hydroxide])

Mechanism of action of a buffer solution:

Let us consider CH₃COOH + CH₃COO⁻Na⁺ as the buffer solution given here.
In the solution state,
CH₃COOH dissociates into CH₃COO⁻ and H⁺ ions and CH₃COO⁻Na⁺ dissociates into CH₃COO⁻ and Na⁺ ions and these ions exist in equilibrium, i.e.,
CH₃COOH ⇄ CH₃COO⁻ + H⁺ [slight ionization]
CH₃COO⁻Na⁺ ⇄ CH₃COO⁻ + Na⁺ [complete ionization]
CH₃COOH + CH₃COO⁻Na⁺ ⇄ CH₃COO⁻ + H⁺ + CH₃COO⁻ + Na⁺

Now, if a few drops of acid are added,
The acid dissociates into its conjugate base and protons in the buffer solution. The protons released from this dissociation then combine with the acetate ions to form acetic acid. Thus, the additional H⁺ released from dissociation from this acid is consumed in the reaction and the pH remains the same.
CH₃COO⁻ + H⁺ (from new acid added) ⇄ CH₃COOH

Similarly, if a base is added,
The additional OH⁻ ions released by dissociation of the base combine with acetic acid to form acetate ions and water, i.e.,
CH₃COOH + OH⁻ (from new base added) ⇄ CH₃COO⁻ + H₂O
thus preventing an increase in the pH of the solution.

#SPJ3