Question

An example of an acid buffer is a solution of (a) ammonium acetate (b) a mixture of \(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{NH}_{4} \mathrm{Cl}\) (c) a mixture of \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{COONa}\) (d) a solution of \(\mathrm{CH}_{3} \mathrm{COONa}\)

Short answer

Therefore, the correct answer is (c) a mixture of \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{COONa}\)

Step-by-step solution

Rule out single component solutions

First, note that an acid buffer cannot consist of a single substance. This is because a buffer requires a weak acid and its conjugate base to effectively mitigate changes in pH. Therefore, choices (a) and (d) can be eliminated because they consist of ammonium acetate and sodium acetate respectively, which are single substances.

Identifying the correct mixture

Next, let's consider the remaining choices, (b) a mixture of \(\mathrm{NH}_{4} \mathrm{OH}+\mathrm{NH}_{4} \mathrm{Cl}\) and (c) a mixture of \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{COONa}\). Neither component in choice (b) is a weak acid, so it does not fit the definition of an acid buffer. Both acetate acid and sodium acetate exist in choice (c). Since acetate acid is a weak acid and sodium acetate is its conjugate base, this mixture does qualify as an acid buffer.

Key concepts

Weak Acid

In chemistry, a weak acid is a type of acid that only partially dissociates into its ions in a solution. This means that only a small fraction of the acid's molecules will release hydrogen ions when added to water.
Because of this incomplete dissociation, weak acids have higher pH levels compared to strong acids. This property makes them ideal components in acid buffer solutions, where the control of pH levels is crucial.
Common examples of weak acids include acetic acid \(\text{CH}_3\text{COOH}\), as found in vinegar, and citric acid. These acids are often used to create buffer solutions because they can donate hydrogen ions when needed but still resist changes that would shift the balance too much.

• Only partially dissociates in water
• Helps in gradual pH change instead of sudden shifts
• Frequently used in buffer solutions

Conjugate Base

A conjugate base comes from the removal of a proton (hydrogen ion) from a weak acid. When a weak acid donates a proton, what remains is the conjugate base.
Conjugate bases play an essential role in buffer solutions because they can reabsorb hydrogen ions, helping to maintain stable pH levels.
For example, when acetic acid (a weak acid) donates a proton, the leftover component is acetate ion \(\text{CH}_3\text{COO}^-\), which serves as its conjugate base. Together, acetic acid and its conjugate base, acetate, are often used to make buffer solutions that can resist pH changes effectively.

• Forms when a weak acid donates a proton
• Works with weak acids to stabilize pH
• Important component of buffer solutions

pH Mitigation

pH mitigation refers to the ability of a solution to resist changes in its pH level. This is especially important in biological and chemical systems where maintaining a specific pH is crucial for the process's efficiency or life-sustaining functions.
The presence of a weak acid and its conjugate base in a buffer solution makes it possible to add small amounts of acid or base without causing significant pH change.
For instance, in the human blood, natural buffers maintain a pH close to 7.4. Without such buffers, even small amounts of acidic or basic substances could lead to dangerous shifts in blood pH, demonstrating the importance of pH mitigation.

• Resistance against pH changes
• Essential in biological systems and chemical reactions
• Achieved with buffers containing both weak acid and its conjugate base

Buffer Solutions

Buffer solutions are special systems that help maintain a stable pH when small amounts of an acid or base are added. They are made up of a weak acid and its conjugate base, which act together to neutralize added acids or bases.
This property makes buffer solutions crucial in laboratory settings, biological systems, and industrial processes where pH balance is essential.
An ideal example of a buffer solution is the combination of acetic acid and sodium acetate. When a small amount of a strong acid is added, the acetate ions will react with the hydrogen ions to form acetic acid, thus neutralizing the effect. Similarly, when a strong base is added, the acetic acid donates protons to balance the increase in pH.

• Consists of a weak acid and its conjugate base
• Ensures stable pH levels
• Used in diverse environments from biology to industry