Lecture Notes: Acids, Bases, and Salts

Acids

• Chemical compounds that are sour in taste.
• Common examples:
  • Curd: Lactic acid
  • Lemon: Citric acid
  • Vinegar: Acetic acid

Bases

• Chemical compounds that are bitter to taste and soapy to touch.
• Common examples:
  • Detergents
  • Toothpaste
  • Hair dyes

Acid-Base Indicators

Natural Indicators

• Litmus: Derived from lichens
  • Blue litmus turns red in acid
  • Red litmus turns blue in base
• Red Cabbage, Turmeric, Hibiscus: Other examples

Synthetic Indicators

• Methyl Orange
  • Acid: Turns red
  • Base: Turns yellow
• Phenolphthalein
  • Acid: No color change
  • Base: Turns pink

Olfactory Indicators

• Detect using smell
• Examples: Onion, Vanilla Essence, Clove Oil
• Experiment with Onion:
  1. Place chopped onions and a cloth in a polythene cover.
  2. Store overnight in the refrigerator.
  3. Test with dilute HCL and NaOH.
  4. HCL-treated cloth retains onion smell; NaOH-treated loses the smell.

Reactions of Acids

With Metals

• Acid + Metal → Salt + Hydrogen gas
• Example: Zn + H2SO4 → Zinc sulfate + H2 gas

With Metal Carbonates and Hydrogen Carbonates

• Acid + Metal Carbonate/Hydrogen Carbonate → Salt + Water + CO2
• Example: Na2CO3 + HCL → NaCl + CO2 + H2O
• CO2 confirms the reaction by forming a white precipitate with Ca(OH)2

Reactions of Bases

With Metals

• Base + Metal → Salt + Hydrogen gas
• Example: Zn + NaOH → Sodium zincate + H2 gas

With Non-metal Oxides

• Base + Non-metal oxide → Salt + Water
• Example: Ca(OH)2 + CO2 → CaCO3

Neutralization Reactions

• Acid + Base → Salt + Water
• Example: NaOH + HCL → NaCl + H2O

Common Properties

• Both acids and bases conduct electricity when dissolved in water, forming ions (e.g., H+ and OH-).

Dilution

• Mixing an acid or base with water reduces ion concentration.
• Highly exothermic reaction; always add acid to water slowly while stirring.

pH Scale

• Ranges from 0 to 14
  • pH 7: Neutral
  • Below 7: Acidic
  • Above 7: Basic
• Strength:
  • Closer to 0 or 14: Strong
  • Closer to 7: Weak

Importance of pH

In Daily Life

• Water bodies: Acidic water harms aquatic life.
• Soil: Farmers test soil pH for proper plant growth.

In the Human Body

• Stomach acid (HCL) aids in digestion.
• Excess acid causes acidity; antacids (e.g., Mg(OH)2) used for treatment.
• Tooth decay caused by acids produced by bacteria from sugars.

In Self-Defense

• Bee stings: Acidic; treated with baking soda.
• Nettles: Acidic; treated with dock plants.

Salts

pH of Salts

• Neutral, acidic, or basic
• Strong acid + strong base = neutral
• Strong acid + weak base = acidic
• Weak acid + strong base = basic

Common Salts and Their Uses

Sodium Chloride (Common Salt)

• Used in manufacturing several chemicals

Sodium Hydroxide (NaOH)

• Chlor-Alkali process: Produces NaOH, chlorine gas, hydrogen gas
• Uses:
  • Metal degreasing
  • Soap and detergent manufacture

Baking Soda (NaHCO3)

• Produced from common salt, water, CO2, and ammonia
• Uses:
  • Cooking
  • Antacid
  • Fire extinguishers
  • Makes food spongy and light

Washing Soda (Na2CO3)

• Produced by recrystallizing sodium carbonate
• Uses:
  • Glass, soap, and paper industries
  • Cleaning agent
  • Water softening

Bleaching Powder (CaOCl2)

• Produced by treating Ca(OH)2 with chlorine gas
• Uses:
  • Whitening fabrics
  • Oxidizing agent
  • Disinfectant

Plaster of Paris (CaSO4 · 1/2 H2O)

• Produced by heating gypsum
• Uses:
  • Bone support in medicine
  • Making toys and models

Conclusion

• Acids, bases, and salts are important in various aspects of daily life and industrial processes.