class 12 notes

Class 12 Chemistry Notes Chapter 7 (Chemistry in Everyday Life) – Chemistry-II Book

Philoid

Philoid

— 7 min read

Chemistry-II
Alright class, let's focus our attention on Chapter 7, "Chemistry in Everyday Life". This chapter is quite important, not just for your board exams but also frequently features in various government recruitment exams because it directly connects chemical principles to tangible aspects of our daily routines – medicines, food, and cleaning. Understanding the key concepts, classifications, and especially the examples is crucial.

Here are the detailed notes structured for effective revision:

Chapter 7: Chemistry in Everyday Life - Detailed Notes

1. Introduction
Chemistry plays a vital role in meeting human needs for food, healthcare, and materials. This chapter focuses on:
* Drugs (Medicines): Chemicals used for therapeutic effect.
* Chemicals in Food: Additives like preservatives, sweeteners, antioxidants.
* Cleansing Agents: Soaps and detergents.

2. Drugs and Their Classification

  • Drugs: Chemicals of low molecular mass (~100-500 u) that interact with macromolecular targets (proteins like enzymes, receptors; carbohydrates; lipids; nucleic acids) and produce a biological response.

  • Medicines: Drugs used in diagnosis, prevention, and treatment of diseases, having a therapeutic effect.

  • Chemotherapy: Use of chemicals for therapeutic effect.

  • Classification of Drugs:

    • (a) Based on Pharmacological Effect: Based on the effect on the body. Useful for doctors.
      • Example: Analgesics (pain killing), Antiseptics (kill/arrest growth of microorganisms).
    • (b) Based on Drug Action: Based on the action on a specific biochemical process.
      • Example: Antihistamines (inhibit the action of histamine, which causes inflammation).
    • (c) Based on Chemical Structure: Drugs with common structural features often have similar pharmacological activity. Allows synthesis of new drugs based on existing ones.
      • Example: Sulphonamides (all contain the sulphonamide group).
    • (d) Based on Molecular Targets: Drugs interact with biomolecules like carbohydrates, lipids, proteins, and nucleic acids (called drug targets). Drugs with similar mechanisms of action on a target have similar structures. Most useful for medicinal chemists.
      • Example: Drugs targeting enzymes (inhibitors), receptors.

3. Drug-Target Interaction

  • Enzymes as Drug Targets:
    • Catalytic Action: Enzymes have an active site where the substrate binds. Binding involves interactions like ionic bonding, H-bonding, van der Waals forces, dipole-dipole interactions. Enzyme performs its function (chemical reaction) and releases products.
    • Drug-Enzyme Interaction (Enzyme Inhibition): Drugs can inhibit enzyme activity.
      • Competitive Inhibitors: Drugs compete with the natural substrate for binding to the active site.
      • Non-Competitive Inhibitors (Allosteric Inhibition): Drugs bind to a different site on the enzyme (called the allosteric site), changing the shape of the active site so the substrate cannot bind effectively.
  • Receptors as Drug Targets:
    • Receptors: Proteins crucial for the body's communication system, mostly embedded in cell membranes. A specific chemical messenger binds to the receptor's binding site, transmitting the message into the cell without entering it.
    • Agonists: Drugs that bind to the receptor and mimic the natural messenger, switching on the receptor.
    • Antagonists: Drugs that bind to the receptor and block its natural function, inhibiting the message. Useful when message blocking is needed.

4. Therapeutic Action of Different Classes of Drugs

  • (i) Antacids:
    • Function: Reduce or neutralize excess stomach acid, raising pH to an appropriate level.
    • Traditional: Metal hydroxides/carbonates (e.g., Sodium hydrogencarbonate, Aluminium hydroxide, Magnesium hydroxide). Problem: Carbonates cause gas; metal hydroxides can make the stomach alkaline, triggering more acid production.
    • Modern (Histamine Blockers): Excess acid release can be triggered by histamine interacting with H2 receptors in the stomach wall. Drugs were developed to prevent this interaction.
      • Examples: Cimetidine (Tagamet), Ranitidine (Zantac). These were major breakthroughs.
  • (ii) Antihistamines:
    • Function: Combat the effects of histamine (responsible for allergic reactions like rashes, nasal congestion, watery eyes, inflammation, bronchoconstriction).
    • Mechanism: Compete with histamine for binding sites on H1 receptors (different from the H2 receptors targeted by antacids like Cimetidine/Ranitidine). They act as antagonists for histamine.
    • Examples: Brompheniramine (Dimetapp), Terfenadine (Seldane).
    • Side Effect: Most antihistamines cause drowsiness.
    • Note: Antacids and anti-allergic antihistamines work on different receptors.
  • (iii) Neurologically Active Drugs: Affect the message transfer mechanism from nerve to receptor.
    • a) Tranquilizers:
      • Function: Treatment of stress, mild or severe mental diseases. Relieve anxiety, stress, irritability, or excitement by inducing a sense of well-being. Essential component of sleeping pills.
      • Mechanism: Affect neurotransmitter levels or receptor binding. Noradrenaline is a key neurotransmitter affecting mood; low levels can cause depression. Antidepressant drugs inhibit enzymes that degrade noradrenaline, or inhibit its re-uptake.
      • Examples: Chlordiazepoxide, Meprobamate (mild tranquilizers for anxiety/tension), Equanil (controls depression/hypertension), Barbiturates (derivatives of barbituric acid, hypnotic/sleep-inducing, e.g., Veronal, Amytal, Nembutal, Luminal, Seconal), Valium, Serotonin.
    • b) Analgesics:
      • Function: Reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination, paralysis, or other nervous system disturbances.
      • Classification:
        • Non-narcotic (Non-addictive):
          • Mechanism: Inhibit prostaglandin synthesis (chemicals causing inflammation/pain).
          • Uses: Antipyretic (fever reducing), pain relief (arthritis, headache), prevention of platelet coagulation (aspirin for heart attack prevention).
          • Examples: Aspirin (Acetylsalicylic acid), Paracetamol (Acetaminophen). Note: Aspirin can be toxic to the liver and cause stomach bleeding; Paracetamol is a common substitute.
        • Narcotic (Addictive):
          • Source: Opium poppy.
          • Uses: Relief from severe pain (post-operative, cardiac, terminal cancer, childbirth).
          • Examples: Morphine, Heroin (Diacetylmorphine), Codeine.
          • Side Effect: Produce sleep and unconsciousness in high doses; highly addictive.
  • (iv) Antimicrobials: Destroy or prevent the development/action of microbes (bacteria, fungi, viruses, parasites).
    • a) Antibiotics:
      • Definition: Chemical substances produced wholly or partly by chemical synthesis, which in low concentrations inhibit the growth or destroy microorganisms. Originally derived from microorganisms (bacteria, fungi, molds).
      • Discovery: Alexander Fleming (1929) - Penicillin from Penicillium notatum.
      • Classification (Effect):
        • Bactericidal: Kill bacteria (e.g., Penicillin, Aminoglycosides, Ofloxacin).
        • Bacteriostatic: Inhibit bacterial growth (e.g., Erythromycin, Tetracycline, Chloramphenicol).
      • Classification (Spectrum of Action):
        • Broad Spectrum: Effective against a wide range of Gram-positive and Gram-negative bacteria (e.g., Ampicillin, Amoxycillin, Chloramphenicol, Vancomycin, Ofloxacin). Note: Chloramphenicol requires careful administration due to potential side effects (aplastic anemia).
        • Narrow Spectrum: Effective mainly against Gram-positive OR Gram-negative bacteria (e.g., Penicillin G).
        • Limited Spectrum: Effective against a single organism or disease.
    • b) Antiseptics:
      • Function: Applied to living tissues (wounds, cuts, ulcers, diseased skin) to kill or prevent the growth of microorganisms. Not ingested.
      • Examples: Dettol (mixture of Chloroxylenol and Terpineol), Bithionol (added to soaps for antiseptic properties), Tincture of Iodine (2-3% Iodine in alcohol-water), Iodoform, Boric acid (dilute aqueous solution for eyes).
    • c) Disinfectants:
      • Function: Applied to inanimate objects (floors, drainage systems, instruments) to kill microorganisms. Harmful to living tissues.
      • Examples: Phenol (1% solution is disinfectant, 0.2% solution is antiseptic), Chlorine (0.2-0.4 ppm in aqueous solution), Sulphur dioxide (low concentrations), Formaldehyde.
  • (v) Antifertility Drugs:
    • Function: Birth control pills/oral contraceptives. Control the female menstrual cycle and ovulation.
    • Mechanism: Contain a mixture of synthetic estrogen and progesterone derivatives, which suppress ovulation.
    • Examples: Norethindrone (synthetic progesterone derivative), Ethynylestradiol (novestrol) (synthetic estrogen derivative).

5. Chemicals in Food

  • Added for: Preservation, enhancing appeal (colour, flavour, sweetness), adding nutritive value.
  • Main categories: Food colours, flavours & sweeteners, fat emulsifiers & stabilizers, antioxidants, preservatives, nutritional supplements (minerals, vitamins, amino acids).
  • (i) Artificial Sweetening Agents:
    • Provide sweetness without adding calories (useful for diabetics, weight control).
    • Examples:
      • Saccharin (ortho-sulphobenzimide): First popular sweetener, ~550 times sweeter than sucrose. Excreted unchanged.
      • Aspartame: Most successful/widely used. Methyl ester of dipeptide (aspartic acid + phenylalanine). ~100 times sweeter than sucrose. Unstable at cooking temperatures, limited to cold foods/soft drinks.
      • Alitame: High potency sweetener (~2000 times sweeter than sucrose). More stable than aspartame, but controlling sweetness is difficult.
      • Sucralose: Trichloro derivative of sucrose. ~600 times sweeter than sucrose. Stable at cooking temperatures, does not provide calories. Appearance and taste like sugar.
  • (ii) Food Preservatives:
    • Function: Prevent spoilage due to microbial growth.
    • Examples: Table salt, Sugar, Vegetable oils, Sodium benzoate (C6H5COONa - used in limited quantities, metabolised in the body), Salts of sorbic acid, Salts of propanoic acid.
  • (iii) Antioxidants in Food:
    • Function: Prevent oxidation of fats/oils (rancidity), which spoils food taste and odour. More reactive towards oxygen than the food material they protect.
    • Examples: Butylated hydroxytoluene (BHT), Butylated hydroxyanisole (BHA). Often added with citric acid for enhanced effect (synergism). Sulphur dioxide and sulphite are antioxidants for wine/beer, sugar syrups, cut/dried fruits/vegetables.

6. Cleansing Agents

  • (i) Soaps:
    • Definition: Sodium or potassium salts of long-chain fatty acids (e.g., stearic, oleic, palmitic acids).
    • Preparation (Saponification): Hydrolysis of fats or oils (esters of fatty acids with glycerol) with aqueous alkali (NaOH or KOH).
      • Fat/Oil + NaOH(aq) → Sodium Salt of Fatty Acid (Soap) + Glycerol
    • Types: Sodium soaps (hard soaps), Potassium soaps (soft soaps, shaving creams).
    • Limitations: Do not work well in hard water (containing Ca²⁺, Mg²⁺ ions). These ions precipitate the soap as insoluble calcium/magnesium salts (scum), wasting the soap.
  • (ii) Synthetic Detergents:
    • Definition: Cleansing agents with properties similar to soaps but are not salts of fatty acids. Effective in both soft and hard water.
    • Classification:
      • a) Anionic Detergents: Largest group. Anionic part involved in cleansing.
        • Types: Sodium salts of sulphonated long-chain alcohols OR hydrocarbons.
        • Examples: Sodium lauryl sulphate (from lauryl alcohol + H₂SO₄, then NaOH), Sodium dodecylbenzenesulphonate (from dodecylbenzene + H₂SO₄, then NaOH).
        • Uses: Household detergents, toothpastes.
      • b) Cationic Detergents: Quaternary ammonium salts of amines with acetates, chlorides, or bromides as anions. Cationic part has a long hydrocarbon chain and a positive charge on Nitrogen.
        • Examples: Cetyltrimethylammonium bromide.
        • Uses: Germicidal properties, expensive. Used in hair conditioners.
      • c) Non-ionic Detergents: Do not contain any ion. Formed by reaction of polyethylene glycol with stearic acid.
        • Mechanism: Ester linkage.
        • Uses: Liquid dishwashing detergents. Cleansing action similar to soaps (micelle formation).
    • Advantages over Soaps: Work in hard water because their calcium/magnesium salts are soluble.
    • Environmental Problem (Biodegradability): Detergents with highly branched hydrocarbon chains are poorly biodegradable, causing water pollution. Straight-chain hydrocarbons are preferred as they are more easily degraded by bacteria.

Multiple Choice Questions (MCQs)

  1. Which of the following is classified as a non-narcotic analgesic?
    (a) Morphine
    (b) Heroin
    (c) Aspirin
    (d) Codeine

  2. Ranitidine (Zantac) is primarily used as:
    (a) An antiseptic
    (b) An antacid
    (c) An antihistamine (for allergies)
    (d) A tranquilizer

  3. Dettol, a common antiseptic, is a mixture of:
    (a) Phenol and Cresol
    (b) Chloroxylenol and Terpineol
    (c) Bithionol and Iodine
    (d) Formaldehyde and Boric acid

  4. Which type of antibiotic is effective against a wide range of Gram-positive and Gram-negative bacteria?
    (a) Narrow spectrum antibiotic
    (b) Limited spectrum antibiotic
    (c) Broad spectrum antibiotic
    (d) Bacteriostatic antibiotic (only)

  5. Aspartame, an artificial sweetener, is unstable under which condition?
    (a) Cold temperatures
    (b) Acidic conditions
    (c) Basic conditions
    (d) Cooking temperatures

  6. Which of the following acts as a food preservative?
    (a) Saccharin
    (b) Sodium benzoate
    (c) BHT (Butylated hydroxytoluene)
    (d) Aspartame

  7. Soaps are chemically:
    (a) Sodium/Potassium salts of long-chain fatty acids
    (b) Sodium salts of sulphonated hydrocarbons
    (c) Quaternary ammonium salts
    (d) Esters of polyethylene glycol

  8. Which class of drugs is used for treating stress and mental diseases?
    (a) Analgesics
    (b) Antiseptics
    (c) Tranquilizers
    (d) Antihistamines

  9. The primary reason synthetic detergents are preferred over soaps for washing clothes in hard water is:
    (a) They are cheaper than soaps.
    (b) They form soluble salts with Ca²⁺ and Mg²⁺ ions.
    (c) They have better germicidal properties.
    (d) They are more biodegradable than soaps.

  10. Bithionol is often added to soaps to impart:
    (a) Softening properties
    (b) Antiseptic properties
    (c) Sweet fragrance
    (d) Better lathering

Answer Key:

  1. (c)
  2. (b)
  3. (b)
  4. (c)
  5. (d)
  6. (b)
  7. (a)
  8. (c)
  9. (b)
  10. (b)

Make sure you revise these concepts thoroughly, paying close attention to the specific examples given for each category, as questions often test your ability to recall and classify these common chemicals. Good luck with your preparation!

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