Overview
This lecture covers the properties, detection, reactions, and uses of acids, bases, and salts, including their importance in daily life and key industrial applications.
Acids and Bases: Properties and Examples
- Acids taste sour; found in curd (lactic acid), lemon (citric acid), and vinegar (acetic acid).
- Bases taste bitter and feel soapy; present in detergents, toothpaste, and hair dyes.
Indicators for Acids and Bases
- Litmus is a natural indicator: blue turns red in acid, red turns blue in base.
- Other natural indicators: red cabbage, turmeric, hibiscus.
- Synthetic indicators: methyl orange (red in acid, yellow in base), phenolphthalein (colorless in acid, pink in base).
- Olfactory indicators change smell in acids/bases (onion, vanilla, clove oil).
Chemical Reactions of Acids and Bases
- Acids + Metals → Salt + Hydrogen gas (e.g., H₂SO₄ + Zn → ZnSO₄ + H₂).
- Bases + Metals (not all) → Salt + Hydrogen gas (e.g., NaOH + Zn → Sodium zincate + H₂).
- Acids + Metal Carbonates/Hydrogen Carbonates → Salt + Water + CO₂.
- Acids + Bases (Neutralization) → Salt + Water.
- Metal Oxides + Acids → Salt + Water.
- Non-metal Oxides + Bases → Salt + Water.
Conductivity and Ionization
- Acids and bases conduct electricity in water due to formation of ions.
- HCl in water forms H⁺ (exists as H₃O⁺) and Cl⁻; NaOH in water forms Na⁺ and OH⁻.
Dilution and Strength
- Dilution lowers ion concentration; it is exothermic—add acid/base to water slowly.
- pH scale: 0-14; 7 is neutral, below 7 is acidic, above 7 is basic.
- Strength of acid/base determined by how close pH is to 0 (strong acid) or 14 (strong base).
Importance of pH in Daily Life
- Aquatic life needs specific pH; acid rain lowers water pH harming plants/animals.
- Soil pH affects plant growth; tested by farmers.
- Stomach acid helps digestion; excess causes acidity, treated with antacids.
- Tooth decay occurs if mouth pH falls below 5.5 due to acids from bacteria.
- Some animals/plants use acids/bases for defense (e.g., bee stings, nettle rashes).
Salts and Their Types
- Salts can be neutral, acidic, or basic depending on the strength of their parent acids and bases.
- Neutral salts: strong acid + strong base; Acidic salts: strong acid + weak base; Basic salts: weak acid + strong base.
Important Salts and Their Uses
- Sodium chloride (common salt): used to make caustic soda, baking soda, washing soda, and bleaching powder.
- Chlor-alkali process: produces NaOH, Cl₂, and H₂ from NaCl solution.
- NaOH used in soaps and paper; Cl₂ for disinfectants; H₂ as fuel.
- Baking soda (NaHCO₃): cooking, antacids, fire extinguishers.
- Washing soda (Na₂CO₃): glass, soap, cleaning agent, water softening.
- Bleaching powder (CaOCl₂): whitening, disinfecting, oxidizing agent.
- Plaster of Paris (CaSO₄·½H₂O): supports broken bones, used in toys/models.
Key Terms & Definitions
- Acid — compound with sour taste that releases H⁺ in water.
- Base — compound with bitter taste and soapy feel, releases OH⁻ in water.
- Indicator — substance that changes color/smell in presence of acid or base.
- Neutralization — reaction of acid with base producing salt and water.
- pH scale — numerical scale (0–14) indicating acidity/basicity.
- Chlor-alkali process — electrolysis of NaCl solution to produce NaOH, Cl₂, and H₂.
- Salt — compound formed from acid-base reaction.
Action Items / Next Steps
- Review pH values and indicator color changes.
- Practice writing reaction equations for acids, bases, and salts.
- Complete any assigned lab experiments on acid-base reactions or indicators.