Loading subject…
Strong and Weak Acids and Bases
What Makes an Acid or Base "Strong" or "Weak"?
- Acids and bases exhibit different behaviors when dissolved in water due to their ability to ionize, or break apart into charged particles called ions.
- This ionization determines whether an acid or base is classified as "strong" or "weak."
Definitions and Ionization Behavior
Strong Acids and Bases
Definition
Strong acids and bases
Strong acids and bases ionize completely in water. All their molecules dissociate into ions, leaving no undissociated molecules in the solution.
Example
- Hydrochloric acid (HCl) dissociates fully in water:
$$\text{HCl (aq)} + \text{H}_2\text{O (l)} \rightarrow \text{H}_3\text{O}^+ \text{(aq)} + \text{Cl}^- \text{(aq)}$$ - Similarly, sodium hydroxide (NaOH), a strong base, dissociates completely:
$$\text{NaOH (aq)} \rightarrow \text{Na}^+ \text{(aq)} + \text{OH}^- \text{(aq)}$$
Weak Acids and Bases
Definition
Weak acids and bases
Weak acids and bases only partially ionize in water. At equilibrium, the solution contains both ions and undissociated molecules.
Example
- Ethanoic acid (CH₃COOH) ionizes partially:
$$\text{CH}_3\text{COOH (aq)} + \text{H}_2\text{O (l)} \rightleftharpoons \text{H}_3\text{O}^+ \text{(aq)} + \text{CH}_3\text{COO}^- \text{(aq)}$$ - Ammonia (NH₃), a weak base, also ionizes partially:
$$\text{NH}_3 \text{(aq)} + \text{H}_2\text{O (l)} \rightleftharpoons \text{NH}_4^+ \text{(aq)} + \text{OH}^- \text{(aq)}$$
Common Mistake
- Weak acids and bases are often mistaken as being dilute.
- However, "weak" refers to their partial ionization, not their concentration.
Position of Equilibrium in Strong and Weak Acids and Bases
The position of equilibrium in acid-base reactions varies depending on the strength of the acid or base.
- Strong Acids and Bases:
- Since they ionize completely in water, the equilibrium lies far to the right, favoring the formation of ions with negligible amounts of undissociated molecules remaining.
- Weak Acids and Bases:
- Weak acids and bases only partially ionize, so the equilibrium lies to the left, favoring the undissociated form.
