Lecture on pH Scale, Acids, and Alkalis

Introduction to pH Scale

• pH measures how acidic or alkaline a solution is
• Scale ranges from 0 to 14
  • Low numbers: Most acidic
  • High numbers: Most alkaline
  • pH 7: Neutral (e.g., pure water)

Examples of pH Levels

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

Methods to Measure pH

Indicators

• Chemical dyes that change color based on pH
• Different indicators change at different pHs
• Wide range indicators (e.g., universal indicator)
  • Color changes across a wide range of pHs
  • Universal indicator shows pH range from deep red (acidic) to blue/purple (alkaline)

pH Probe and Meter

• Electronic measurement of pH
• Provides a numerical reading
• More accurate and precise
• Reduces human error in measuring color

Defining Acids and Bases

Acids

• Substances forming aqueous solutions with pH < 7
• Release hydrogen ions (H+) in water

Bases

• Substances with pH > 7
• Alkalis: Subgroup of bases, soluble in water
• Alkalis form hydroxide ions (OH-) in water

Neutralization Reactions

• Reaction between an acid and a base
• Produces salt and water
• Example: Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
  • Represented by: H+ (acid) + OH- (base) → H2O
• Products are neutral (pH 7)

Common Acids and Bases

Acids

• Hydrochloric acid
• Sulfuric acid
• Nitric acid

Bases

• Sodium hydroxide
• Calcium carbonate