Overview
This lecture covers the key concepts, definitions, reactions, and examples related to acids, bases, salts, indicators, pH scale, important laboratory chemicals, and common exam questions in chemistry.
Acids, Bases, and Their Properties
- Acids release H⁺ ions in aqueous solutions and turn blue litmus red.
- Bases release OH⁻ ions in aqueous solutions and turn red litmus blue.
- Acids taste sour, bases taste bitter and feel soapy.
- Strong acids: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Nitric acid (HNO₃).
- Weak acids: Acetic acid (CH₃COOH), Carbonic acid (H₂CO₃).
- Strong bases: Sodium hydroxide (NaOH), Potassium hydroxide (KOH).
Indicators and Their Functions
- Indicators detect whether a solution is acidic or basic by color change.
- Litmus: Blue turns red in acid, red turns blue in base.
- Turmeric: Turns red with acids, yellow with bases.
- Phenolphthalein: Colorless in acid, pink in base.
- Methyl orange: Red in acid, yellow in base.
- Olfactory (smell) indicators: Onion, clove oil, vanilla.
Reactions of Acids and Bases
- Acid + Metal → Salt + Hydrogen gas.
- Base + Metal (e.g., NaOH + Zn) → Salt (sodium zincate) + Hydrogen gas.
- Acid + Base → Salt + Water (Neutralization).
- Metal oxide + Acid → Salt + Water.
- Non-metal oxide + Base → Salt + Water.
- Metal carbonate/bicarbonate + Acid → Salt + Water + CO₂ (turns lime water milky).
pH Scale and Universal Indicator
- pH measures the concentration of H⁺ ions; lower pH = more acidic, higher pH = more basic.
- pH < 7: Acidic, pH = 7: Neutral, pH > 7: Basic.
- Universal indicator shows strength and nature of solution via color changes.
- Examples: Gastric juice pH ≈ 1.2, Lemon juice pH ≈ 2.2, Milk of magnesia pH ≈ 10, NaOH pH ≈ 14.
Uses of Important Chemicals
- Sodium hydroxide (caustic soda, NaOH): Made by chlor-alkali process; used in soaps, detergents, and paper.
- Bleaching powder (CaOCl₂): Disinfectant, used in water treatment and textile bleaching.
- Baking soda (NaHCO₃): Used in baking, as antacid, and fire extinguisher.
- Baking powder: Contains baking soda and tartaric acid; releases CO₂ during baking.
- Washing soda (Na₂CO₃·10H₂O): Used in cleaning, removes permanent hardness of water.
- Plaster of Paris (CaSO₄·½H₂O): Made by heating gypsum; used for casts and decoration.
Everyday Examples and Natural Sources
- Vinegar contains acetic acid.
- Orange/lemon: Citric acid.
- Tamarind: Tartaric acid.
- Tomato: Oxalic acid.
- Ant/nettle stings: Methanoic (formic) acid.
- Curd: Lactic acid.
Key Terms & Definitions
- Acid — Substance that gives H⁺ ions in water.
- Base — Substance that gives OH⁻ ions in water.
- Indicator — Chemical that shows pH or acidity/basicity by color.
- Salt — Product formed from acid-base neutralization.
- pH — Scale measuring acidity/basicity (0–14).
- Hydronium ion (H₃O⁺) — Ion formed by H⁺ bonding with water.
Action Items / Next Steps
- Do the assigned CBSE homework questions from the notes.
- Revise the color changes of indicators and common acid/base reactions.
- Memorize common acids found in daily life sources (vinegar, tomato, etc.).
- Practice writing chemical formulas for salts, acids, and bases.