Comprehensive Study Notes: Science - Chemical Reactions, Life Processes, and Light and Environment

CHEMICAL REACTIONS AND EQUATIONS

• Initial Substances and Changes: In situations such as leaving milk at room temperature in summer, exposing iron to humid atmospheres, fermentation of grapes, cooking food, digestion, and respiration, the identity and nature of initial substances change. A chemical reaction is said to occur whenever a chemical change takes place.

• Observation Factors: A chemical reaction can be determined by observing:

  • Change in state.

  • Change in colour.

  • Evolution of a gas.

  • Change in temperature.

• Activity 1.1 (Magnesium Burning):

  • Procedure: Clean a magnesium ribbon (roughly $3-4\,cm$ long) with sandpaper. Hold with tongs and burn using a spirit lamp. Collect the ash ($MgO$) in a watch-glass.

  • Observation: The ribbon burns with a dazzling white flame and converts into a white powder ($Magnesium\,oxide$) due to reaction with oxygen in the air.

• Chemical Equations:

  • Word Equation: $\text{Magnesium} + \text{Oxygen} \rightarrow \text{Magnesium\,oxide}$.

  • Definitions: Reactants (substances undergoing change, on the LHS) and Products (new substances formed, on the RHS).

  • Skeletal Equations: Equations where the number of atoms of each element is not the same on both sides (unbalanced), such as $Mg + O_2 \rightarrow MgO$.

• Balanced Chemical Equations:

  • Law of Conservation of Mass: Mass can neither be created nor destroyed in a chemical reaction. Total mass of elements in products must equal total mass of elements in reactants.

  • Balancing Process (Hit-and-Trial):

    1. Draw boxes around formulas; do not change contents.

    2. List the number of atoms per element on LHS and RHS.

    3. Start balancing with the compound containing the maximum number of atoms (e.g., oxygen in $Fe_3O_4$).

    4. Adjust coefficients ($4H_2O$ makes $8H$ atoms, requiring $4H_2$ on the RHS).

    5. Balance remaining elements ($3Fe$ on LHS).

    6. Final balanced equation: $3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)$.

• Physical States: Symbols used are $(s)$ for solid, $(l)$ for liquid, $(g)$ for gas, and $(aq)$ for aqueous (solution in water). Special conditions like pressure ($340\,atm$) or catalysts (Chlorophyll/Sunlight) are written above/below the arrow.

• Types of Reactions:

  • Combination Reaction: Two or more reactants form a single product. Example: $CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + \text{Heat}$.

    • Whitewashing Note: Slaked lime ($Ca(OH)_2$) reacts with atmospheric $CO_2$ to form a thin layer of calcium carbonate ($CaCO_3$), giving a shiny finish after $2-3$ days.

  • Exothermic Reactions: Heat is released. Examples: Burning natural gas ($CH_4$), Respiration ($C_6H_{12}O_6(aq) + 6O_2(aq) \rightarrow 6CO_2(aq) + 6H_2O(l) + \text{energy}$), and decomposition of vegetable matter.

  • Decomposition Reaction: A single reactant breaks down into simpler products.

    • Thermal Decomposition: Caused by heating. Example: $CaCO_3(s) \xrightarrow{\text{Heat}} CaO(s) + CO_2(g)$ (Limestone to Quick lime, used in cement manufacture).

    • Ferrous Sulphate: $2FeSO_4(s) \xrightarrow{\text{Heat}} Fe_2O_3(s) + SO_2(g) + SO_3(g)$. Green crystals turn to reddish-brown ferric oxide.

    • Lead Nitrate: $2Pb(NO_3)_2(s) \xrightarrow{\text{Heat}} 2PbO(s) + 4NO_2(g) + O_2(g)$. Emits brown fumes of nitrogen dioxide.

    • Electrolytic Decomposition: Example: Electrolysis of water ($2H_2O \rightarrow 2H_2 + O_2$).

    • Photolytic Decomposition: Caused by light. $2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$. Silver bromide behaves similarly ($2AgBr \rightarrow 2Ag + Br_2$); both are used in black and white photography.

  • Displacement Reaction: A more reactive element displaces a less reactive one. Example: $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$. Iron nails turn brownish, and the blue copper sulphate solution fades.

  • Double Displacement Reaction: Exchange of ions between reactants. Example: $Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)$. The white insoluble $BaSO_4$ is called a precipitate.

• Oxidation and Reduction (Redox):

  • Oxidation: Gain of oxygen or loss of hydrogen.

  • Reduction: Loss of oxygen or gain of hydrogen.

  • Example: $CuO + H_2 \xrightarrow{\text{Heat}} Cu + H_2O$. $CuO$ is reduced to $Cu$; $H_2$ is oxidised to $H_2O$.

• Everyday Effects of Oxidation:

  • Corrosion: Metals attacked by moisture/acids. Rusting of iron (reddish-brown), black coating on silver, green coating on copper.

  • Rancidity: Oxidation of fats/oils changes smell/taste. Prevented by antioxidants, airtight containers, or flushing bags with Nitrogen.

ACIDS, BASES AND SALTS

• General Properties: Acids are sour and turn blue litmus red. Bases are bitter, soapy, and turn red litmus blue.

• Indicators:

  • Natural: Litmus (purple dye from lichen), turmeric (turns reddish-brown with soap), red cabbage, flowers like Hydrangea, Petunia, and Geranium.

  • Synthetic: Methyl orange, Phenolphthalein.

  • Olfactory: Odour changes in acidic/basic media; examples include Onion, Vanilla essence, and Clove oil.

• Chemical Properties:

  • Reaction with Metals: $\text{Acid} + \text{Metal} \rightarrow \text{Salt} + H_2(g)$. Example: $Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2$. Test for $H_2$: the gas burns with a 'pop' sound.

  • Bases with Metals: Only some metals react. $2NaOH + Zn \rightarrow Na_2ZnO_2 + H_2$ (Sodium zincate).

  • Metal Carbonates/Bicarbonates: React with acids to produce salt, $CO_2$, and water. Example: $Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2$. Test for $CO_2$: turns lime water milky ($Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$).

  • Neutralisation: $\text{Base} + \text{Acid} \rightarrow \text{Salt} + \text{Water}$. Example: $NaOH + HCl \rightarrow NaCl + H_2O$.

  • Metallic Oxides: Basic in nature; react with acids to form salt and water.

  • Non-metallic Oxides: Acidic in nature; react with bases to form salt and water.

• Commonalities: All acids produce $H^+(aq)$ or $H_3O^+$ (hydronium) ions in water. All bases/alkalis produce $OH^-(aq)$ (hydroxide) ions. Distilled water doesn't conduct electricity, but acidic/basic solutions do.

• Dilution Warning: Dissolving acid/base in water is highly exothermic. Always add acid slowly to water with stirring, never water to acid, to prevent splashing or container breakage.

• pH Scale:

  • Measures $H^+$ concentration ($0-14$). 'p' stands for potenz (power).

  • $pH < 7$: Acidic. $pH = 7$: Neutral. $pH > 7$: Basic.

  • Importance:

    • Body: Works within $7.0 - 7.8$.

    • Acid Rain: $pH < 5.6$.

    • Stomach: Produces $HCl$; excess causes indigestion, treated with antacids (Milk of Magnesia).

    • Tooth Decay: Starts when mouth $pH < 5.5$.

    • Self-Defence: Bee-stings (acidic) and nettle leaves (methanoic acid) cause pain; treated with mild bases like baking soda or leaves of the dock plant.

• Chemicals from Sodium Chloride:

  • Sodium Hydroxide: Produced via Chlor-alkali process ($2NaCl + 2H_2O \rightarrow 2NaOH + Cl_2 + H_2$).

  • Bleaching Powder ($Ca(ClO)_2$): Produced by action of $Cl_2$ on dry slaked lime. Used in textiles, paper factories, and as a disinfectant.

  • Baking Soda ($NaHCO_3$): Produced using $NaCl$, $H_2O$, $CO_2$, and $NH_3$. Used for crispy pakoras, baking powder (mixture with tartaric acid), and soda-acid fire extinguishers.

  • Washing Soda ($Na_2CO_3 \cdot 10H_2O$): Produced by recrystallisation of sodium carbonate. Used in glass, soap, and paper industries, and for removing permanent hardness of water.

  • Plaster of Paris ($CaSO_4 \cdot \frac{1}{2}H_2O$): Formed by heating gypsum ($CaSO_4 \cdot 2H_2O$) at $373\,K$. Used for surgical plasters, toys, and smooth surfaces.

METALS AND NON-METALS

• Physical Properties of Metals:

  • Shining surface (Metallic Lustre).

  • Generally hard (Alkali metals like $Li$, $Na$, $K$ are exceptions; can be cut with a knife).

  • Malleability: Can be beaten into thin sheets (Gold and Silver are most malleable).

  • Ductility: Can be drawn into thin wires (Gold is most ductile; $1\,g$ can yield a $2\,km$ wire).

  • Good conductors of heat (Best: Silver, Copper; Poor: Lead, Mercury).

  • High melting points (Gallium and Caesium melt on the palm).

  • Good conductors of electricity (Coated with PVC/rubber).

  • Sonorous: Produce sound on striking hard surfaces.

• Properties of Non-metals:

  • Exist as solids or gases (Bromine is a liquid).

  • Iodine: Lustrous non-metal.

  • Carbon Allotropes: Diamond (hardest natural substance, high MP) and Graphite (electrical conductor).

• Chemical Properties of Metals:

  • Reaction with Oxygen: Form basic oxides ($4Al + 3O_2 \rightarrow 2Al_2O_3$).

    • Amphoteric Oxides: React with both acids and bases ($Al_2O_3$, $ZnO$).

    • Anodising: Forming a thick oxide layer on aluminum to resist corrosion.

  • Reaction with Water:

    • $Na$ and $K$ react violently with cold water.

    • $Ca$ and $Mg$ start floating due to $H_2$ bubbles sticking to surface.

    • $Al$, $Fe$, $Zn$ react with steam only.

    • $Pb$, $Cu$, $Ag$, $Au$ do not react with water.

  • Reaction with Acids: Metal + Acid $\rightarrow$ Salt + $H_2$. $H_2$ is not evolved with $HNO_3$ (it's a strong oxidising agent), except with $Mg$ and $Mn$.

  • Aqua Regia: $3:1$ mixture of conc. $HCl$ and conc. $HNO_3$; dissolves Gold and Platinum.

• The Reactivity Series: Order from most reactive to least: $K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au$.

• Ionic Compounds:

  • Formed by transfer of electrons from metal to non-metal (e.g., $NaCl$, $MgCl_2$).

  • Properties: Solid, hard, brittle. High MP/BP. Soluble in water, insoluble in petrol. Conduct electricity only in molten or aqueous state.

• Extraction of Metals:

  • Minerals: Naturally occurring elements/compounds in earth's crust.

  • Ores: Minerals from which metals can be profitably extracted.

  • Gangue: Impurities like soil/sand in ores.

  • Metallurgy Processes:

    • Low Reactivity: Reduction by heating alone (e.g., Cinnabar $HgS \rightarrow Hg$).

    • Medium Reactivity: Roasting (sulphide ores in excess air) or Calcination (carbonate ores in limited air) to form oxides, then reduced using Carbon or aluminum (Thermit reaction: $Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3 + \text{Heat}$).

    • High Reactivity: Electrolytic reduction (e.g., Sodium from molten $NaCl$).

  • Electrolytic Refining: Anode is impure metal, cathode is pure metal strip. Pure metal transfers from anode to cathode through electrolyte.

• Corrosion Prevention: Painting, oiling, galvanisation (zinc coating), chrome plating, or alloying (e.g., Stainless steel = $Fe + Ni + Cr$).

• Alloys: Homogeneous mixtures of metals/non-metals. Amalgam: Alloy containing Mercury. Brass: $Cu + Zn$. Bronze: $Cu + Sn$. Solder: $Pb + Sn$.

LIFE PROCESSES

• Criteria for Life: Visible movement (growth-related or not) and invisible molecular movements.

• Nutrition:

  • Autotrophic: Organisms (plants, some bacteria) use $CO_2$ and water to synthesise carbohydrates via photosynthesis.

    • Photosynthesis Equation: $6CO_2 + 12H_2O \xrightarrow{\text{Chlorophyll/Sunlight}} C_6H_{12}O_6 + 6O_2 + 6H_2O$.

    • Events: Absorption of light by chlorophyll, conversion to chemical energy, splitting of water, reduction of $CO_2$ to carbohydrates.

    • Stomata: Tiny pores for gas exchange; opening/closing controlled by guard cells.

  • Heterotrophic: Fungi (Saprophytic), Cuscuta (Parasitic), or Holozoic (Amoeba, Humans).

    • Amoeba: Uses pseudopodia to form food vacuoles.

  • Human Digestion:

    • Mouth: Salivary amylase breaks starch into sugar.

    • Stomach: Pepsin (proteins), $HCl$ (acidic medium), and mucus (lining protection).

    • Small Intestine: Site of complete digestion. Receives bile (fats emulsification) from liver and pancreatic juice (trypsin, lipase) from pancreas. Villi increase surface area for absorption.

• Respiration:

  • Six-carbon glucose breaks down into three-carbon pyruvate in the cytoplasm.

  • Anaerobic: In yeast ($\rightarrow$ Ethanol + $CO_2$) or muscles during cramps ($\rightarrow$ Lactic acid).

  • Aerobic: In mitochondria ($\rightarrow CO_2 + H_2O$). Releases significant energy.

  • ATP: Energy currency ($30.5\,kJ/mol$ per terminal phosphate linkage).

  • Human System: Nostrils $\rightarrow$ Pharynx $\rightarrow$ Larynx $\rightarrow$ Trachea $\rightarrow$ Alveoli (gas exchange site, $80\,m^2$ surface).

• Transportation:

  • Humans: Heart (muscular organ). Double circulation: blood passes through heart twice per cycle. High pressure in arteries (thick walls); low pressure in veins (valves).

    • Blood Pressure: Measured by sphygmomanometer; normal $120/80\,mm\,Hg$.

    • Components: RBCs (carry oxygen via haemoglobin), WBCs, Plasma, Platelets (blood clotting).

    • Lymph: Tissue fluid; drains excess fluid and carries digested fats.

  • Plants: Xylem (water/minerals via root pressure and transpiration pull) and Phloem (Translocation of sucrose using ATP).

• Excretion:

  • Humans: Kidneys $\rightarrow$ Ureters $\rightarrow$ Urinary Bladder $\rightarrow$ Urethra.

  • Nephron: Functional unit. Bowman's capsule collects filtrate; selective re-absorption of glucose/salts occurs along the tube.

  • Artificial Kidney: Hemodialysis used in case of kidney failure.

  • Plants: Get rid of gases via stomata, excess water via transpiration, and store wastes in vacuoles, leaves that fall, or resins/gums.

CONTROL AND COORDINATION

• Nervous System:

  • Neuron: Cell body, dendrites (acquire info), axon (transmits info). Synapse is the gap between neurons where chemical signals cross.

  • Reflex Action: Sudden, unconscious response to stimuli. Reflex Arc: path comprises Receptor $\rightarrow$ Sensory neuron $\rightarrow$ Spinal cord $\rightarrow$ Motor neuron $\rightarrow$ Effector (muscle).

  • Human Brain:

    • Fore-brain: Cerebrum; main thinking centre, controls voluntary actions, interprets sensory info, hunger centre.

    • Mid-brain & Hind-brain: Control involuntary actions (salivation, blood pressure, vomiting via Medulla).

    • Cerebellum: Controls posture, balance, and precision of voluntary movements.

• Plant Coordination:

  • Immediate Response: Not growth-dependent (e.g., Mimosa pudica folding leaves via water movement).

  • Tropic Movements: Growth-dependent. Phototropism (light), Geotropism (gravity), Hydrotropism (water), Chemotropism (pollen tube growth).

  • Hormones: Auxin (shoot growth, bends toward light), Gibberellins (stem growth), Cytokinins (cell division), Abscisic Acid (growth inhibitor, wilting).

• Animal Hormones:

  • Adrenaline: 'Fight or flight' hormone from adrenal glands; increases heart rate and breathing.

  • Thyroxin: From thyroid (requires Iodine); regulates metabolism. Deficiency causes Goitre.

  • Growth Hormone: From Pituitary; deficiency causes dwarfism.

  • Insulin: From Pancreas; regulates blood sugar. Deficiency causes Diabetes.

  • Testosterone/Oestrogen: Control puberty changes.

LIGHT – REFLECTION AND REFRACTION

• Reflection:

  • Laws: $\angle i = \angle r$; incident ray, normal, and reflected ray lie in the same plane.

  • Spherical Mirrors: Concave (converging) and Convex (diverging).

  • Terms: Pole ($P$), Centre of curvature ($C$), Radius of curvature ($R$), Principal focus ($F$), Focal length ($f$). Relationship: $R = 2f$.

  • Mirror Formula: $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$.

  • Magnification: $m = \frac{h'}{h} = -\frac{v}{u}$.

• Refraction: Bending of light when entering different media.

  • Laws: Incident, refracted, and normal rays in same plane; Snell's Law: $\frac{\sin(i)}{\sin(r)} = \text{constant} (n)$.

  • Refractive Index: $n_{21} = \frac{v_1}{v_2}$. Absolute refractive index: $n_m = \frac{c}{v}$. ($c = 3 \times 10^8\,m/s$).

  • Lenses: Convex (converging) and Concave (diverging).

  • Lens Formula: $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$.

  • Magnification: $m = \frac{h'}{h} = \frac{v}{u}$.

  • Power of Lens ($P$): $P = \frac{1}{f}$ (in metres). Unit: Dioptre ($D$).

HUMAN EYE AND COLOURFUL WORLD

• Eye Structure: Cornea, Iris (controls pupil size), Pupil (regulates light), Crystalline lens (adjusts focus), Retina (light-sensitive screen, forms inverted real image), Optic nerve.

• Accommodation: Ability to adjust focal length.

  • Near point: $25\,cm$. Far point: Infinity.

• Defects of Vision:

  • Myopia (Near-sightedness): Image forms in front of retina; corrected by concave lens.

  • Hypermetropia (Far-sightedness): Image forms behind retina; corrected by convex lens.

  • Presbyopia: Aging causing loss of accommodation; often requires bifocal lenses.

• Natural Phenomena:

  • Refraction through Prism: Causes dispersion (splitting white light into VIBGYOR spectrum).

  • Rainbow: Caused by dispersion, internal reflection, and refraction in water droplets.

  • Atmospheric Refraction: Twinkling of stars, advance sunrise ($2$ mins), delayed sunset ($2$ mins).

  • Scattering: Tyndall Effect; sky is blue because fine particles scatter shorter (blue) wavelengths more strongly. Red is least scattered (used for danger signals).

OUR ENVIRONMENT

• Ecosystem: Interacting biotic (living) and abiotic (physical) components.

• Trophic Levels: Producers $\rightarrow$ Herbivores $\rightarrow$ Small Carnivores $\rightarrow$ Large Carnivores.

  • $10\%$ Law: Only $10\%$ of organic matter/energy transfers to the next level.

• Energy Flow: Unidirectional and diminishes at each level.

• Biological Magnification: Accumulation of non-degradable chemicals (pesticides) in the food chain; highest concentration in humans at the top.

• Ozone Layer ($O_3$): Forms at higher atmosphere by UV acting on $O_2$. Protects from UV-induced skin cancer. Depleted by CFCs.

• Waste Management: Biodegradable vs. Non-biodegradable waste. Issues with plastic and shift toward paper cups in trains. Recycling and sewage treatment are vital.