Overview

Acids taste sour (lemon) and turn litmus red. Bases taste bitter (soap) and turn litmus blue. When mixed, they neutralize each other.

Core Idea

pH Scale: A logarithmic scale measuring acidity. pH 7 is neutral. pH < 7 is acidic. pH > 7 is basic (alkaline). $$ \text{pH} = -\log[H^+] $$

Formal Definition (if applicable)

Brønsted-Lowry Theory:

  • Acid: Proton ($H^+$) donor.
  • Base: Proton ($H^+$) acceptor.

Lewis Theory:

  • Acid: Electron pair acceptor.
  • Base: Electron pair donor.

Intuition

An acid is like a person trying to get rid of a hot potato ($H^+$). A base is a person willing to catch it. Water can act as both (amphoteric).

Examples

  • Acids: Hydrochloric acid (stomach acid), Acetic acid (vinegar), Citric acid (lemons).
  • Bases: Sodium hydroxide (drain cleaner), Ammonia (cleaner), Sodium bicarbonate (baking soda).
  • Buffer: A solution that resists changes in pH (e.g., blood).

Common Misconceptions

  • “Acids burn, bases are safe.” (Strong bases like lye are just as dangerous and corrosive as strong acids.)
  • “pH ranges from 0 to 14.” (It can actually go below 0 or above 14 for very concentrated solutions.)
  • Titration: A method to determine concentration by neutralizing.
  • Dissociation: How well an acid splits into ions (Strong vs. Weak acids).
  • Conjugate Pair: An acid and its corresponding base (e.g., $HCl$ and $Cl^-$).

Applications

  • Biology: Enzymes only work at specific pH levels.
  • Environment: Acid rain damages ecosystems.
  • Industry: Manufacturing fertilizers, dyes, and explosives.

Criticism / Limitations

The Arrhenius definition (acids produce $H^+$, bases produce $OH^-$) is too limited (doesn’t explain ammonia). Brønsted-Lowry and Lewis definitions are broader.

Further Reading

  • Zumdahl, Chemistry
  • Sorensen, Enzyme Studies (Origin of pH)