Question

\(A\) mixturc of a weak acid (say acctic acid) and its salts with a strong basc (say sodium acetate) acts as a buffcr solution. Which other pair has similar properties? (1) IICl and \(\mathrm{NaCl}\) (2) \(\mathrm{NaOII}\) and \(\mathrm{NaNO}_{3}\) (3) KOII and KCl (4) \(\mathrm{NII}_{4} \mathrm{OII}\) and \(\mathrm{NII}_{4} \mathrm{Cl}\)

Short answer

Option (4), NH4OH and NH4Cl.

Step-by-step solution

Understand the Concept of a Buffer Solution

A buffer solution is a system that minimizes changes in pH upon the addition of small amounts of an acid or a base. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

Analyze the Given Pairs

We need to identify which pair functions as a buffer system similar to the given example of acetic acid (CH3COOH) and sodium acetate (CH3COONa).

Evaluate Each Option

Option (1) includes HCl (a strong acid) and NaCl (a salt of a strong acid and strong base), which do not form a buffer system.Option (2) includes NaOH (a strong base) and NaNO3 (a salt of a strong base and strong acid), which do not form a buffer system.Option (3) includes KOH (a strong base) and KCl (a salt of a strong base and strong acid), which do not form a buffer system.Option (4) includes NH4OH (a weak base) and NH4Cl (a salt of the weak base NH4OH and a strong acid HCl), which forms a buffer system.

Conclusion

Option (4), NH4OH and NH4Cl, is the correct pair since it forms a buffer solution like the given example of acetic acid and sodium acetate.

Key concepts

weak acid

A weak acid is an acid that only partially dissociates in water. Unlike strong acids, which completely ionize, weak acids establish an equilibrium between the undissociated acid and its ions in solution. This means they don’t give up all their hydrogen ions (H+) easily.
Common examples include acetic acid (CH3COOH) and citric acid.

• Weak acids play a key role in buffer solutions.
• They typically have a higher pH than strong acids.
• Their partial dissociation makes them perfect for pH stabilization when paired with their conjugate bases.

Understanding weak acids is crucial for identifying how buffer solutions work in preventing large pH changes.

conjugate base

The conjugate base of a weak acid is the species that remains after the weak acid has donated a proton (H+). For example, when acetic acid (CH3COOH) loses a proton, it forms its conjugate base, acetate (CH3COO-).

• Conjugate bases are essential components of buffer solutions.
• They help stabilize the pH by neutralizing added acids.
• In a buffer solution, the weak acid and its conjugate base work together to minimize pH changes.

Remember, the combination of a weak acid and its conjugate base is what makes a buffer effective in pH stabilization.

pH stabilization

pH stabilization refers to the ability of a solution to resist changes in pH when acids or bases are added. Buffer solutions excel at this because they contain a weak acid and its conjugate base, or a weak base and its conjugate acid.

• When a small amount of an acid (H+) is added, the conjugate base neutralizes it.
• When a small amount of a base (OH-) is added, the weak acid neutralizes it.

This process keeps the pH relatively stable. Hence, buffer solutions are used in many biological and chemical applications to maintain a constant pH environment.

weak base

A weak base partially accepts hydrogen ions in water, unlike a strong base that fully dissociates. An example of a weak base is ammonia (NH3), which in solution forms ammonium (NH4+) and hydroxide ions (OH-).

• Weak bases, like weak acids, are crucial for buffer solutions.
• They provide a source of the conjugate acid that helps neutralize added bases.

A buffer solution containing a weak base and its conjugate acid, such as NH4OH and NH4Cl, works similarly to one with a weak acid and its conjugate base.

conjugate acid

The conjugate acid is formed when a weak base accepts a proton. For example, when ammonia (NH3) accepts an H+ ion, it forms its conjugate acid, ammonium (NH4+).

• Conjugate acids are integral to buffer systems involving weak bases.
• They counteract additions of bases by donating H+ ions.

In summary, the interaction between a weak base and its conjugate acid helps buffer solutions maintain a stable pH by balancing the concentrations of H+ and OH- ions in the solution.