Overview
This lecture explains the differences between strong and weak acids, clarifies the distinction between acid strength and concentration, and describes how pH relates to hydrogen ion concentration.
Strong vs. Weak Acids
- Strong acids completely ionize in water, releasing all their hydrogen ions (e.g., hydrochloric, nitric, and sulfuric acids).
- Weak acids only partially ionize, so only some molecules release hydrogen ions (e.g., ethanoic, citric, and carbonic acids).
- Weak acid ionization is reversible, resulting in a chemical equilibrium with more undissociated molecules.
- In equilibrium for weak acids, the reaction favors the left (more undissociated acid than dissociated ions).
Acid Strength vs. Concentration
- Acid strength refers to the proportion of molecules that ionize in water (complete for strong acids, partial for weak acids).
- Concentration measures how much acid is present per unit volume in solution, regardless of strength.
- A strong acid can be dilute or concentrated, and the same is true for weak acids.
pH and Hydrogen Ion Concentration
- pH is a scale that measures the concentration of hydrogen ions in a solution.
- As hydrogen ion concentration increases, pH decreases.
- Each decrease of 1 on the pH scale means a 10-fold increase in hydrogen ion concentration.
- Moving from pH 5 to pH 3 increases hydrogen ion concentration by 100 times.
- At a given concentration, strong acids have lower pH than weak acids due to more hydrogen ions being released.
Key Terms & Definitions
- Acid — Substance that releases hydrogen ions (H⁺) in aqueous solution.
- Strong Acid — Acid that fully ionizes in solution, releasing all hydrogen ions.
- Weak Acid — Acid that only partially ionizes, establishing an equilibrium.
- Concentration — Amount of acid per unit volume of solution.
- pH — A measure of hydrogen ion concentration; lower pH means higher [H⁺].
- Equilibrium — State in reversible reactions where the rates of forward and backward reactions are equal.
Action Items / Next Steps
- Review the differences between acid strength and acid concentration.
- Practice identifying strong and weak acids and relating pH to hydrogen ion concentration.