key term - Weak Acid

Definition

A weak acid is a type of acid that only partially dissociates into its constituent ions when dissolved in water. This means that at equilibrium, a significant portion of the acid molecules remain undissociated, unlike strong acids which completely dissociate.

5 Must Know Facts For Your Next Test

1. Weak acids have a lower degree of dissociation compared to strong acids, resulting in a higher pH value in the solution.
2. The strength of a weak acid is determined by its acid dissociation constant (Ka), with a higher Ka value indicating a stronger acid.
3. Examples of weak acids include acetic acid (CH3COOH), carbonic acid (H2CO3), and formic acid (HCOOH).
4. Weak acids can act as buffers, helping to maintain a relatively stable pH in a solution, which is important in biological systems.
5. The pH of a weak acid solution can be calculated using the Henderson-Hasselbalch equation, which relates the pH to the pKa of the acid and the ratio of the conjugate base to the acid.

Review Questions

• Explain the difference between a weak acid and a strong acid in terms of their dissociation in water.
  • The key difference between weak acids and strong acids is the extent to which they dissociate in water. Strong acids completely dissociate, producing a high concentration of hydrogen ions (H+) in the solution, while weak acids only partially dissociate, resulting in a lower concentration of H+ ions. This difference in dissociation behavior leads to significant differences in the pH and acidity of solutions containing weak acids versus strong acids.
• Describe how the acid dissociation constant (Ka) is used to determine the strength of a weak acid.
  • The acid dissociation constant (Ka) is a measure of the strength of a weak acid. A higher Ka value indicates a stronger acid, meaning the acid will dissociate to a greater extent in water. The Ka value is used in the Henderson-Hasselbalch equation to calculate the pH of a weak acid solution, which is an important factor in understanding the relative strengths of acids and their behavior in chemical systems.
• Explain the role of weak acids in maintaining pH stability in biological systems.
  • Weak acids can act as buffers, helping to maintain a relatively stable pH in a solution. This is particularly important in biological systems, where the pH must be tightly regulated for proper cellular function and metabolic processes. Weak acids, such as carbonic acid and acetic acid, can absorb or release hydrogen ions (H+) as needed to counteract changes in pH, keeping the environment within a narrow, optimal range. This buffering capacity of weak acids is crucial for the survival and proper functioning of living organisms.

Related terms

Strong Acid:

A strong acid is an acid that completely dissociates into its constituent ions when dissolved in water, producing a high concentration of hydrogen ions (H+) in the solution.

pH:

pH is a measure of the acidity or basicity of a solution, with lower pH values indicating higher acidity and higher pH values indicating higher basicity.

Acid Dissociation Constant (Ka): The acid dissociation constant (Ka) is a measure of the strength of an acid, which represents the extent to which the acid dissociates in water.