Which of the following mixtures act(s) as a buffer solution?
- NaOH+CH3COOH (1:1 mole ratio)
- NH4OH+HCl (2:1 mole ratio)
- CH3COOH+NaOH (2:1 mole ratio)
- CH3COOH+NaOH (1:2 mole ratio)
The Correct Option is B, C
Solution and Explanation
Buffer Concept Recap:
An acidic buffer contains a weak acid + its salt with a strong base (e.g., CH₃COOH + CH₃COONa).
A basic buffer contains a weak base + its salt with a strong acid (e.g., NH₄OH + NH₄Cl).
Let’s analyze the options:
- (A) NaOH + HCOONa:
Not a buffer. It contains a strong base (NaOH) and the salt of a weak acid (HCOONa), but lacks the weak acid itself (formic acid). Hence, not a buffer system. - (B) NH₄OH + HCl in 2:1 mole ratio:
When NH₄OH (a weak base) reacts with HCl (a strong acid), NH₄Cl is formed. In a 2:1 mole ratio, there will be unreacted NH₄OH and formed NH₄Cl, making a basic buffer.
Correct. - (C) CH₃COOH + NaOH in 2:1 mole ratio:
CH₃COOH is a weak acid, NaOH is a strong base. In a 2:1 mole ratio, some CH₃COOH reacts to form CH₃COONa (the salt), and leftover CH₃COOH remains. This creates an acidic buffer.
Correct. - (D) NaOH + HCOONa (repeated from A):
Still not a buffer.
Correct answer: (B) and (C)
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Concepts Used:
Buffer solutions
The buffer solution is a solution that is able to maintain its Hydrogen ion concentration (pH) with only minor changes on the dilution or addition of a small amount of either acid or base. They are used in fermentation, food preservatives, drug delivery, printing, the activity of enzymes and many more.
Buffer solutions are aqueous solutions containing a weak acid and its salt - acid buffer or a weak base and its salt - base buffer.
Types of Buffer Solution
Acidic Buffers
These solutions are used to maintain acidic environments. Also, it has acidic pH and is prepared by mixing a weak acid and its salt with a strong base. An aqueous solution of an equal concentration of acetic acid and sodium acetate has a pH of 4.74.
Alkaline Buffers
These solutions are used to maintain basic conditions. It has a basic pH and is prepared by mixing a weak base and its salt with strong acid. The aqueous solution of an equal concentration of ammonium hydroxide and ammonium chloride has a pH of 9.25.