Overview
This lecture explains the concepts of pH, acidity, alkalinity, and buffers, focusing on strong vs. weak acids/bases and introduces the carbonic acid-bicarbonate buffer system.
pH, Acidity, and Alkalinity
- pH is a measure of the free hydrogen ion (proton) concentration in a solution.
- The pH scale is inverse and logarithmic, running from 0 (most acidic) to 14 (most basic).
- Lower pH means higher hydrogen ion concentration (more acidic); higher pH means lower hydrogen ion concentration (more alkaline/basic).
- Each whole number change in pH represents a tenfold change in hydrogen ion concentration.
- Pure water has a neutral pH of 7.0, where hydrogen and hydroxyl ion concentrations are equal.
- Solutions with pH < 7 are acidic; pH > 7 are alkaline/basic.
Strong vs. Weak Acids and Bases
- Strong acids/bases dissociate completely in solution, leaving no intact molecules.
- Weak acids/bases only partially dissociate, leaving some molecules intact in solution.
- Strong acid + strong base in equal amounts neutralize to form water and a salt.
Buffers and the Carbonic Acid-Bicarbonate System
- Buffers are solutions of weak acids and bases that resist large changes in pH.
- The carbonic acid-bicarbonate buffer system involves reversible reactions between carbonic acid, protons, and bicarbonate ions.
- This buffer system can absorb excess protons (from acids) or release protons (when bases are added) to stabilize pH.
- The buffer system maintains blood pH within the narrow range of 7.35 to 7.45; deviation below 6.8 or above 8.0 is fatal.
- This buffer system is critical for blood pH regulation and CO₂ transport, though detailed physiological roles will be covered next semester.
Key Terms & Definitions
- pH — a measure of free hydrogen ion concentration; indicates acidity or alkalinity.
- Acid — a substance that donates protons (hydrogen ions) in solution.
- Base — a substance that accepts protons in solution.
- Strong Acid/Base — dissociates completely into ions in solution.
- Weak Acid/Base — partially dissociates, with some molecules remaining intact.
- Buffer — a weak acid/base system that resists changes in pH when acids or bases are added.
- Carbonic Acid-Bicarbonate System — a physiological buffer system that maintains blood pH within a narrow range.
Action Items / Next Steps
- Review concepts of pH, strong/weak acids and bases, and buffer systems for upcoming assessments.
- Prepare for future lectures on classes of organic compounds and their roles.