Weak acids

Definition

Weak acids are substances that partially dissociate into their ions in aqueous solutions. They have a higher pH compared to strong acids and do not completely ionize in water.

5 Must Know Facts For Your Next Test

1. Weak acids have a dissociation constant ($K_a$) less than 1, indicating partial ionization.
2. Common examples of weak acids include acetic acid (CH$_3$COOH) and formic acid (HCOOH).
3. The equilibrium expression for a weak acid is given by $HA \leftrightarrow H^+ + A^-$.
4. In titration curves, weak acids exhibit a more gradual pH change near the equivalence point compared to strong acids.
5. Buffer solutions often contain weak acids and their conjugate bases.

Review Questions

• What distinguishes a weak acid from a strong acid in terms of ionization?
• How does the $K_a$ value of a weak acid compare to that of a strong acid?
• Describe the general shape of a titration curve for a weak acid.

Related terms

Strong Acid: A substance that completely ionizes in aqueous solution, releasing all its hydrogen ions.

$K_a$ (Acid Dissociation Constant): A quantitative measure of the strength of an acid in solution; it represents the equilibrium constant for the dissociation reaction of the acid.

Buffer Solution: A solution that resists changes in pH upon addition of small amounts of an acid or base, typically composed of a weak acid and its conjugate base.