Question

Name a compound that you could add to a solution of each of the compounds to make a buffer. Explain your reasoning in complete sentences. a. acetic acid b. sodium nitrite c. ammonia d. potassium formate e. \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\) (two possible answers)

Short answer

a. Add sodium acetate to acetic acid. b. Add nitrous acid to sodium nitrite. c. Add ammonium chloride to ammonia. d. Add formic acid to potassium formate. e. Add either sodium dihydrogen phosphate or trisodium phosphate to \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\).

Step-by-step solution

Identifying Acetic Acid Buffer Components

For acetic acid (CH3COOH), a weak acid, you can add its conjugate base - sodium acetate (CH3COONa) - to create a buffer. The presence of both the weak acid and its conjugate base allows the solution to resist changes in pH upon addition of small amounts of either acid or base.

Identifying Sodium Nitrite Buffer Components

Sodium nitrite (NaNO2) is a salt of a weak base (nitrous acid, HNO2). To create a buffer, you would need to add this weak acid to the solution containing sodium nitrite, which provides the conjugate acid-base pair required.

Identifying Ammonia Buffer Components

Ammonia (NH3) is a weak base. To form a buffer, you could add ammonium chloride (NH4Cl), which upon dissociation provides the conjugate acid (NH4+). Together, they establish a buffer system.

Identifying Potassium Formate Buffer Components

Potassium formate (HCOOK) is a salt of formic acid (HCOOH), which is a weak acid. By adding formic acid to the potassium formate solution, you create a buffer consisting of the weak acid and its conjugate base (formate ion).

Identifying Sodium Phosphate Buffer Components

For \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\), which is di-sodium hydrogen phosphate, you could make a buffer by adding either sodium dihydrogen phosphate (\mathrm{NaH}_2\mathrm{PO}_4), which provides additional hydrogen ions, or trisodium phosphate (\mathrm{Na}_3\mathrm{PO}_4), which can absorb hydrogen ions. Both options give you a system with a weak acid and its conjugate base.

Key concepts

Acid-Base Buffer Systems

Acid-base buffer systems are crucial in maintaining a stable pH in a solution, despite the addition of small amounts of acid or base. They do so by containing a weak acid and its conjugate base, or a weak base and its conjugate acid. When an acid (proton donor) is added to such a system, the conjugate base in the buffer solution will react with the added acid to minimize the change in pH. Conversely, when a base (proton acceptor) is added, the weak acid in the buffer system donates protons to neutralize the base, again stabilizing the pH.

For instance, acetic acid is a weak acid that can be combined with sodium acetate, its conjugate base, to create an effective buffer system. This combination is able to resist drastic changes in the pH of the solution. Understanding buffer systems is important in biological and chemical applications where maintaining a consistent pH is critical for reactions to proceed properly or for the stability of substances.

• Key Components: A buffer system is made up of a weak acid/base and its conjugate base/acid.
• Function: To resist changes in pH when small quantities of acid or base are added.
• Application: Used in a variety of settings, from laboratory experiments to biological systems.

In our textbook exercise, we see how the addition of a conjugate acid or base to a solution can form a buffer system, helping understand why it is critical for certain solutions to maintain a consistent pH.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs are two substances that transform into each other by the gain or loss of a proton (H+). A conjugate base is what is left over after an acid donates a proton, and a conjugate acid is formed when a base accepts a proton. This concept is central to buffer chemistry and plays an important role in the acid-base balance in chemical solutions.

For example, when ammonia (NH3), a weak base, accepts a proton, it becomes its conjugate acid, ammonium (NH4+). If ammonium chloride (NH4Cl) is added to ammonia, it creates a buffer that contains the conjugate acid-base pair of NH3 and NH4+. This process of proton exchange is crucial for maintaining a stable pH because it allows a buffer solution to neutralize added acids or bases effectively.

• Identifying Pairs: A substance's ability to donate or accept protons determines its role in the pair.
• Buffer Formation: Pairs are used to form buffers for controlling pH in solutions.

Conjugate acid-base pairs are directly exemplified in the textbook exercise, where the formation of a buffer from a weak acid or base with its conjugate is clearly demonstrated through multiple examples.

pH Stabilization Buffers

pH stabilization buffers are indispensable in many chemical and biochemical processes. They make it possible to maintain the pH of a solution within a narrow range, which is vital for processes that are sensitive to pH fluctuations. These buffers work on the principle of neutralizing added acids or bases, thereby preventing significant shifts in the hydrogen ion concentration of a solution.

A practical application of pH stabilization can be found in biological systems, such as human blood, which maintains a pH around 7.4. Even in industrial processes, such as fermentation or pharmaceutical manufacturing, maintaining the pH within stringent limits is necessary to ensure optimal conditions for reactions or product stability.

• Importance: Protects sensitive reactions and biological processes from pH variations.
• Ingredients: Typically made from weak acids or bases and their salts.
• Operation: They absorb excess H+ or OH– ions, thereby 'buffering' changes in pH.

By relating to the textbook exercise and considering sodium phosphate, for example, buffers can be made by using chemicals like Na2HPO4 in conjunction with its conjugates (NaH2PO4 or Na3PO4) to stabilize pH levels in a variety of scientific contexts.