Understanding the pH Scale, Acids, and Alkalis

Introduction to pH Scale

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

Examples of pH in Everyday Substances

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

(Note: Specific pH values of substances are for context only, not memorization.)

Measuring pH

• Indicators
  • Chemical dyes changing color according to pH
  • Universal Indicator: Shows color range from red (acidic) to blue/purple (alkaline)
• pH Probe and Meter
  • Provides electronic and numerical pH readings
  • More accurate and precise than indicators as they eliminate human error

What Makes a Substance Acidic or Alkaline?

• Acids
  • Form aqueous solutions with pH < 7
  • Release hydrogen ions (H⁺) in water
• Bases
  • Substances with pH > 7
• Alkalis
  • Subgroup of bases, soluble in water
  • Form hydroxide ions (OH⁻) in water

Neutralization Reactions

• Definition: Reaction between an acid and a base
• Products: Always a salt and water
  • Example: Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
• Ions Perspective: H⁺ from acid and OH⁻ from base form H₂O

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 basics of the pH scale helps in identifying and dealing with substances in everyday life.
• Important to familiarize with common acids and bases as they frequently appear in studies.