Question

An example of a basic buffer is a solution of (a) \(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{NH}_{4} \mathrm{Cl}\) (b) \(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{HCl}\) (c) \(\mathrm{CH}_{3} \mathrm{COONH}_{4}\) (d) \(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{NaOH}\)

Short answer

Option (a) \(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{NH}_{4} \mathrm{Cl}\) is the basic buffer as it is composed of a weak base and its conjugate acid.

Step-by-step solution

Understanding Basic Buffer

A buffer solution is a solution that resists changes in pH when small amounts of an acid or a base are added to it. It is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid. In this case, we are focus on basic buffer, which is composed of a weak base and its conjugate acid.

Evaluating Option (a)

\(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{NH}_{4} \mathrm{Cl}\) In this case, \(\mathrm{NH}_{4} \mathrm{OH}\) is a weak base and \(\mathrm{NH}_{4} \mathrm{Cl}\) is the salt of its conjugate acid, \(\mathrm{NH}_{4}^{+}\), which makes this a basic buffer solution.

Evaluating Option (b)

\(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{HCl}\). Here, \(\mathrm{NH}_{4} \mathrm{OH}\) is a weak base, but \(\mathrm{HCl}\) is a strong acid and not the conjugate acid of the base. So, it cannot be a basic buffer.

Evaluating Option (c)

\(\mathrm{CH}_{3} \mathrm{COONH}_{4}\). Considering this option, it does not consist of a weak base and its conjugate acid. So, it is not a basic buffer.

Evaluating Option (d)

\(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{NaOH}\). In this case, \(\mathrm{NH}_{4} \mathrm{OH}\) is a weak base and \(\mathrm{NaOH}\) is a strong base, not the conjugate acid of the weak base. So, it can't be a basic buffer.

Key concepts

Buffer Solution Chemistry

A buffer solution is a specialized aqueous solution that has the remarkable ability to maintain a stable pH level even when external substances such as acids or bases are introduced. This steady-state is critical in many biochemical processes where pH can be a determining factor in the function of enzymes and the stability of molecules.

The way it works is through an equilibrium reaction between a weak acid (that can donate protons) and its conjugate base (that can accept protons), or vice versa with a weak base and its conjugate acid. This dynamic duo operates in tandem, with the weak component sacrificing a bit of itself to neutralize any excess hydrogen or hydroxide ions that come into play, thus averting any drastic shifts in pH.

pH Resistance

The term 'pH resistance' in chemistry is essentially a superpower of buffer solutions. It's their ability to resist changes in pH, standing strong against the onslaught of acids or bases that could potentially crash the pH party. This resilience is a buffer's most important feature, ensuring that the biological and chemical processes that depend on a specific pH range can continue without interruption.

Imagine adding a drop of vinegar (an acid) to a glass of pure water—the pH would change significantly. But, if you drop that same splash of vinegar to a buffer solution, the pH barely budges. This pH resistance is due to the buffer's components absorbing and neutralizing the extra hydrogen ions without causing a major shift in the overall pH level.

Weak Base and Conjugate Acid

In buffer solutions, the dynamic relationship between a weak base and its conjugate acid is the foundation of their functionality. A weak base is a hesitant proton acceptor, not all-in like its strong counterpart, which is eager to snag a proton at first sight. The conjugate acid, on the other hand, is what you get when the weak base finally decides to accept a proton.

Let's break it down with an example: ammonia (H_3) is a weak base; when it grabs a proton, it turns into its conjugate acid, ammonium (H_4^+). When you mix ammonia with ammonium chloride (H_4Cln), voila, you've got yourself a buffer! The weaker party (ammonia) and the protonated VIP (ammonium) cooperate to counteract any pH-affecting substances that come their way.

Aqueous Solution Chemistry

Aqueous solution chemistry is the realm of reactions that occur in water, the universal solvent. When substances are dissolved in water, they can break into ions (charged particles), which can then interact with each other.

Water's role in buffer chemistry is not just as a venue for the acid-base dance-off. It also contributes to the equilibrium dynamic by occasionally interacting with the weak acid or base, further affecting the concentration of hydrogen and hydroxide ions and thus the pH. This interplay is a beautiful display of give-and-take that governs the actions and stability of substances in biological systems and industrial processes.