Lecture Notes: Understanding the pH Scale

Introduction to pH Scale

• Definition of pH: A measure of how acidic or alkaline a solution is.
• Scale range: 0 to 14
  • Low numbers (0-6) = Acidic
  • High numbers (8-14) = Alkaline
  • Neutral = 7 (e.g., pure water)

Examples of pH in Everyday Substances

• Acids:
  • Stomach acid: pH ~2
  • Acid rain: pH ~4
• Alkalis:
  • Washing up liquid: pH ~9
  • Bleach: pH ~12

Measuring pH

• Indicators:
  • Chemical dyes that change color at different pH levels.
  • Universal indicator: A wide-range indicator showing a spectrum of colors across the pH scale.
    • Deep red (acidic) to blue/purple (alkaline)
• pH Probe and Meter:
  • Provides a numerical reading.
  • More accurate and precise than color indicators.

Understanding Acids and Bases

• Acids:
  • Form solutions with pH < 7.
  • Release hydrogen ions (H+) in water.
• Bases:
  • pH > 7.
  • Alkalis: Bases that are soluble in water; form hydroxide ions (OH-).

Neutralization Reactions

• Reaction between acid and base → Produces salt and water.
  • Example: Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
• Ionic equation:
  • H+ (from acid) + OH- (from base) → H2O
• Products of these reactions have a neutral pH (7).

Common Acids and Bases

• Acids:
  • Hydrochloric acid
  • Sulfuric acid
  • Nitric acid
• Bases:
  • Hydroxides (e.g., Sodium hydroxide)
  • Carbonates (e.g., Calcium carbonate)

Conclusion

• Understanding the pH scale is crucial for identifying the nature of various substances in chemistry.
• Key examples and reactions are crucial for coursework.