Acids, Bases and Salts

• Introduction

  • Classification of substances
  • Importance in daily life

• Acids

  • Meaning & Origin
    • Derived from Latin word ‘acere’ meaning sour
  • Properties
    • Taste sour
    • Turn blue litmus to red
  • Types of Acids
    • Natural Acids (Organic)
      • Examples: Acetic acid (Vinegar), Citric acid (Citrus fruits), Lactic acid (Curd), Formic acid (Ant sting), Ascorbic acid (Amla/Vitamin C)
    • Mineral Acids (Inorganic)
      • Examples: Hydrochloric acid ($HCl$), Sulphuric acid ($H_2SO_4$), Nitric acid ($HNO_3$)
    • Strong vs. Weak Acids
      • Strong: Highly corrosive mineral acids
      • Weak: Mild organic acids, safe to consume

• Bases

  • Properties
    • Taste bitter
    • Feel soapy to touch
    • Turn red litmus to blue
  • Soluble Bases
    • Called Alkalis (e.g., Sodium hydroxide, Calcium hydroxide)
  • Examples
    • Sodium hydroxide (Soap)
    • Calcium hydroxide (Lime water)
    • Ammonium hydroxide (Window cleaner)
    • Magnesium hydroxide (Antacid)

• Indicators

  • Definition
    • Substances used to test whether a substance is acidic or basic
    • Show change in colour
  • Types of Indicators
    • Natural Indicators
      • Litmus: Extracted from lichens; Red in acid, Blue in base
      • Turmeric: Yellow in acid, Reddish-brown in basic medium
      • China Rose: Dark pink/magenta in acid, Green in base
    • Synthetic Indicators
      • Phenolphthalein: Colourless in acid, Pink in base
      • Methyl Orange: Red in acid, Yellow in base
    • Olfactory Indicators
      • Substances whose odour changes in acidic or basic media (e.g., Onion, Vanilla, Clove oil)

• Neutralisation

  • Definition
    • Reaction between an acid and a base
  • Products Formed
    • Salt and Water
    • Heat is evolved (Exothermic reaction)
  • Chemical Equation
    • $\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water} + \text{Heat}$
  • Examples in Everyday Life
    • Indigestion: Cured using an antacid (Milk of Magnesia / Magnesium hydroxide) containing base
    • Ant Sting: Neutralised by rubbing calamine solution (Zinc carbonate) or moist baking soda
    • Soil Treatment:
      • Too acidic: Treated with quicklime (Calcium oxide) or slaked lime (Calcium hydroxide)
      • Too basic: Treated with organic matter (releases acids)
    • Factory Wastes: Neutralised with basic substances before releasing into water bodies