Question

Of the following combinations, which would act as buffered solutions? a. \(\mathrm{HClO}_{2}\) and \(\mathrm{KClO}_{2}\) b. \(\mathrm{H}_{2} \mathrm{~S}\) and \(\mathrm{Na}_{2} \mathrm{~S}\) c. \(\mathrm{HCOOH}\) and \(\mathrm{NaHCO}\) d. \(\mathrm{HClO}\) and \(\mathrm{HClO}_{4}\)

Short answer

The buffered solutions are: a. \(\mathrm{HClO}_{2}\) and \(\mathrm{KClO}_{2}\) b. \(\mathrm{H}_{2} \mathrm{~S}\) and \(\mathrm{Na}_{2} \mathrm{~S}\) c. \(\mathrm{HCOOH}\) and \(\mathrm{NaHCO}\)

Step-by-step solution

Identify Weak Acids and Bases

A weak acid is an acid that does not ionize completely in solution, and a weak base is a base that does not fully dissociate in solution. The given combinations are: a. \(\mathrm{HClO_{2}}\) and \(\mathrm{KClO_{2}}\) b. \(\mathrm{H_{2}S}\) and \(\mathrm{Na_{2}S}\) c. \(\mathrm{HCOOH}\) and \(\mathrm{NaHCO}\) d. \(\mathrm{HClO}\) and \(\mathrm{HClO_{4}}\) Identifying the weak acid or base in each combination: a. \(\mathrm{HClO_{2}}\) is a weak acid. b. \(\mathrm{H_{2}S}\) is a weak acid. c. \(\mathrm{HCOOH}\) is a weak acid. d. There is no weak acid or base in this combination. \(\mathrm{HClO}\) is a weak acid, but \(\mathrm{HClO_{4}}\) is a strong acid.

Identify Conjugate Acid/Bases

A conjugate base is formed when an acid donates a proton (H+), and a conjugate acid is formed when a base accepts a proton. For each combination, let's identify the conjugate acid/base pairs. a. Conjugate base of \(\mathrm{HClO_{2}}\) is \(\mathrm{ClO_{2}^{-}}\). b. Conjugate base of \(\mathrm{H_{2}S}\) is \(\mathrm{HS^{-}}\). c. Conjugate base of \(\mathrm{HCOOH}\) is \(\mathrm{HCOO^{-}}\).

Determine Buffered Solutions

A buffered solution must contain a weak acid or base and its conjugate partner. Let's see which combinations have both a weak acid and its conjugate base or a weak base and its conjugate acid. a. \(\mathrm{HClO_{2}}\) and \(\mathrm{KClO_{2}}\): \(\mathrm{KClO_{2}}\) is the potassium salt of the conjugate base of \(\mathrm{HClO_{2}}\) (\(\mathrm{ClO_{2}^{-}}\)). So, this is a buffered solution. b. \(\mathrm{H_{2}S}\) and \(\mathrm{Na_{2}S}\): \(\mathrm{Na_{2}S}\) is the sodium salt of the conjugate base of \(\mathrm{H_{2}S}\) (\(\mathrm{HS^{-}}\)). So, this is a buffered solution. c. \(\mathrm{HCOOH}\) and \(\mathrm{NaHCO}\): \(\mathrm{NaHCO}\) is the sodium salt of the conjugate base of \(\mathrm{HCOOH}\) (\(\mathrm{HCOO^{-}}\)). So, this is a buffered solution. d. \(\mathrm{HClO}\) and \(\mathrm{HClO_{4}}\): As established in Step 1, this combination doesn't contain a weak acid/base and its conjugate partner. In conclusion, the following combinations would act as buffered solutions: a. \(\mathrm{HClO}_{2}\) and \(\mathrm{KClO}_{2}\) b. \(\mathrm{H}_{2} \mathrm{~S}\) and \(\mathrm{Na}_{2} \mathrm{~S}\) c. \(\mathrm{HCOOH}\) and \(\mathrm{NaHCO}\)

Key concepts

Weak Acids and Bases

Understanding weak acids and bases is essential for comprehending buffered solutions. A weak acid is characterized by its partial ionization in an aqueous solution. Unlike strong acids, which dissociate completely, weak acids maintain an equilibrium between their intact form and their ions. This means they donate protons to a lesser degree, leaving a considerable amount of the undissociated molecule in solution.

Weak bases also partially dissociate in water and are less proficient at accepting protons compared to strong bases. The presence of weak acids or bases is vital for the formation of a buffer system, as they help maintain a relatively stable pH when small amounts of strong acid or base are added to the solution. In applications like laboratory preparations or physiological systems, the choice of a weak acid or base is crucial to setting up an effective buffer.

Conjugate Acid-Base Pairs

Digging deeper into the topic of buffered solutions, we find that the interaction between conjugate acid-base pairs plays a pivotal role. When an acid loses a proton, it forms its conjugate base; conversely, when a base gains a proton, it forms its conjugate acid. This acid-base pair is closely related and can easily convert into one another depending on the pH of the environment.

In the context of a buffered solution, having both components of a conjugate acid-base pair is necessary. This duality allows the buffer to neutralize added acids or bases. For example, if an excess of H+ ions is introduced into the solution, the conjugate base can readily absorb these ions, preventing large swings in pH. The reversibility of this reaction is key to a buffer's ability to stabilize pH, making knowledge of conjugate acid-base pairs quintessential for students studying chemistry.

Buffer Components

The components of a buffer solution are what truly allow it to resist changes in pH. These components include a weak acid and its conjugate base or a weak base and its conjugate acid. The acid component of a buffer acts to neutralize any excess OH- ions that may be added, while the conjugate base neutralizes excess H+ ions.

To reiterate, for a solution to serve as a buffer, it must have substantial amounts of both a weak acid and its conjugate base, or a weak base and its conjugate acid. This ensures that the buffer can tackle incoming acids or bases effectively. In the exercise provided, the combinations of weak acids and their corresponding salts, which contain the conjugate base, form the desired buffered solutions. Recognizing and combining appropriate buffer components is crucial for creating a stable pH environment in a variety of biochemical and industrial processes.