Assam ASSEB HSLC General Science cheat sheet

Three states: solid (fixed shape and volume, particles closely packed, vibrate in place), liquid (fixed volume, takes container shape, particles slide), gas (no fixed shape or volume, particles move fast and far apart).

Interconversion: melting (solid→liquid), freezing (liquid→solid), evaporation/boiling (liquid→gas), condensation (gas→liquid), sublimation (solid→gas directly, e.g. camphor, naphthalene, iodine), deposition (gas→solid).

Physical change alters only state, shape or size and is usually reversible (ice melting, dissolving sugar); chemical change forms new substances, is usually irreversible, and shows gas, precipitate, colour change or heat (burning, rusting).

Element: one kind of atom, cannot be split chemically (Na, O2). Compound: two or more elements chemically combined in fixed ratio (H2O, CO2). Mixture: components in any ratio, separable physically (air, salt water).

Solution = solute + solvent; homogeneous. Concentration terms: mass percent = (mass solute / mass solution) x 100; parts per million for very dilute solutions. Solubility rises with temperature for most solids, falls for gases.

Separation rules: filtration for insoluble solid from liquid; evaporation/crystallisation for dissolved solid; distillation for liquid from dissolved solid or two liquids with different boiling points; fractional distillation for miscible liquids (petroleum, liquid air); separating funnel for immiscible liquids; sublimation for camphor/salt; chromatography for dyes and pigments.

Tyndall effect distinguishes colloid from true solution; colloid particles are 1-1000 nm and scatter a light beam.

Law of conservation of mass: total mass of reactants equals total mass of products in a closed system.

Atom: protons (+1, mass 1 u) and neutrons (0, mass 1 u) in nucleus; electrons (-1, negligible mass) in shells. Atomic number Z = protons; mass number A = protons + neutrons; isotopes differ in neutrons.

Shell capacity 2n²: K=2, L=8, M=18 (filled to 8 before N starts), N=32. Valence electrons decide chemical behaviour.

Valency: number of electrons lost, gained or shared to reach the nearest noble-gas configuration (octet). Group 1 → valency 1; group 2 → 2; group 13 → 3; group 17 → 1; group 16 → 2; group 15 → 3.

Ion: charged particle from loss of electrons (cation, e.g. Na+) or gain (anion, e.g. Cl-). Ionic bond = transfer of electrons between metal and non-metal (NaCl, MgO); covalent bond = sharing between non-metals (H2O, CH4, O2).

Molecule: smallest particle of an element or compound with independent existence; formula unit for ionic solids.

Criss-cross rule for formulae: write symbols, write valencies above, exchange them as subscripts, simplify (Al³⁺ + O²⁻ → Al2O3; Ca²⁺ + Cl⁻ → CaCl2).

Balanced chemical equation: same number of each kind of atom on both sides; add state symbols (s), (l), (g), (aq) and conditions (heat, catalyst) above the arrow.

Mole concept: 1 mole = 6.022 x 10^23 particles = molar mass in grams; molar volume of any gas at STP = 22.4 L.

Acid: gives H+ (H3O+) in water, sour, turns blue litmus red, pH < 7, reacts with metals to give H2 and with carbonates to give CO2. Base: gives OH- in water, bitter, soapy, turns red litmus blue, pH > 7.

Strong acids (HCl, H2SO4, HNO3) ionise completely; weak acids (CH3COOH, H2CO3) ionise partly. Same for bases: NaOH strong, NH4OH weak.

Indicators: litmus (red/blue), methyl orange (red in acid, yellow in base), phenolphthalein (colourless in acid, pink in base), turmeric (yellow → red in base). pH scale 0-14; pH 7 neutral.

Neutralisation: acid + base → salt + water, e.g. HCl + NaOH → NaCl + H2O; heat is released. Acid + metal oxide → salt + water; acid + carbonate/bicarbonate → salt + water + CO2.

pH of a solution measures H+ concentration: pH = -log[H+]; each drop of 1 unit means tenfold change in H+.

Common salts: NaCl (common salt, food, chlorine and NaOH manufacture), NaHCO3 (baking soda, antacid, fire extinguisher), Na2CO3.10H2O (washing soda, water softening), CaOCl2 (bleaching powder, disinfectant), CaSO4.1/2H2O (plaster of Paris, casts), CuSO4.5H2O (blue vitriol, fungicide).

Water of crystallisation gives colour and shape to crystals; heating gypsum (CaSO4.2H2O) at 373 K gives plaster of Paris.

Acid rain: pH below 5.6 from SO2 and NOx; harms crops, aquatic life and corrodes marble (CaCO3).

Metals: lustrous, malleable, ductile, sonorous, good conductors, mostly solid (Hg is liquid). Non-metals: dull, brittle, poor conductors (graphite conducts; iodine is lustrous).

Reactivity series (decreasing): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au. A metal above another displaces it from its salt solution (Zn + CuSO4 → ZnSO4 + Cu).

Metals above H displace H2 from dilute acids; Cu, Ag, Au do not.

Occurrence: reactive metals as compounds (Na as NaCl, Al as bauxite Al2O3.2H2O), unreactive metals native (Au, Ag, Pt).

Extraction: concentration of ore → roasting (sulphide ores heated in air) or calcination (carbonate ores heated without air) → reduction (carbon for Zn, Fe; electrolysis for Na, Al; thermite for Fe) → refining (electrolysis).

Corrosion: rusting of iron needs both oxygen and moisture; prevented by painting, oiling, galvanising (zinc coat), alloying (stainless steel with Cr and Ni) and electroplating.

Alloys: brass (Cu + Zn), bronze (Cu + Sn), solder (Pb + Sn, low melting), steel (Fe + C).

Reaction with oxygen: metal + O2 → metal oxide; amphoteric oxides (Al2O3, ZnO) react with both acids and bases.

Carbon forms four covalent bonds (tetravalency) and catenates, giving millions of compounds. Saturated = only single bonds (alkanes CnH2n+2); unsaturated = double (alkenes CnH2n) or triple (alkynes CnH2n-2) bonds.

Homologous series: same functional group, successive members differ by CH2 and 14 u (CH4, C2H6, C3H8).

Functional groups: alcohol -OH (ethanol), aldehyde -CHO, ketone -CO-, carboxylic acid -COOH (ethanoic acid), halo -X, amine -NH2.

Ethanol: fermentation of sugar by yeast; burns with blue flame to CO2 and H2O; oxidised to ethanoic acid. Ethanoic acid (vinegar) is a weak acid that reacts with NaHCO3 giving brisk CO2 effervescence.

Soap: sodium/potassium salt of long-chain fatty acid; has a hydrophilic head and hydrophobic tail, forms micelles that trap oil in water. Detergent: ammonium/sulphonate salt, works in hard water; soap forms scum with hard water.

Combustion: rapid oxidation releasing heat and light. Fuels: coal, petroleum, natural gas, LPG, CNG, biogas. Calorific value in kJ/kg ranks hydrogen > LPG > CNG > coal.

Incomplete combustion gives CO (poisonous, binds haemoglobin) and soot; CO2 is the main greenhouse gas.

Fossil fuels are non-renewable; burning them releases SO2 and NOx causing acid rain.

Cell theory: all living things are made of cells; the cell is the basic unit of life; new cells arise from pre-existing cells.

Plant cell has cell wall (cellulose), large central vacuole, chloroplasts and plasmodesmata; animal cell has no wall or chloroplast, has centrioles and small vacuoles. Both have plasma membrane, nucleus, mitochondria, ribosomes, ER, Golgi, lysosomes.

Organelles: nucleus (DNA, control), mitochondrion (ATP, powerhouse), ribosome (protein synthesis), ER (transport; rough has ribosomes), Golgi (packaging and secretion), lysosome (digestion), chloroplast (photosynthesis), vacuole (storage and turgor).

Prokaryote: no true nucleus or membrane-bound organelles (bacteria); eukaryote: true nucleus with membrane (plants, animals, fungi, protists).

Plastids: chloroplast (green, photosynthesis), chromoplast (colour), leucoplast (storage).

Plant tissues: meristematic (apical, lateral, intercalary - dividing) and permanent (parenchyma, collenchyma, sclerenchyma; xylem and phloem; epidermis; cork).

Animal tissues: epithelial, connective (blood, bone, cartilage, tendon, adipose), muscular (striated, smooth, cardiac) and nervous.

Cell division: mitosis gives two identical diploid cells for growth and repair; meiosis gives four haploid gametes with crossing over and variation.

Nutrition: autotrophic (photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 in chloroplasts using light and chlorophyll) and heterotrophic (holozoic, saprophytic, parasitic).

Human digestion: mouth (salivary amylase, starch) → stomach (HCl, pepsin, protein) → small intestine (bile emulsifies fat, pancreatic and intestinal enzymes; absorption via villi) → large intestine (water absorption).

Respiration: aerobic (glucose + O2 → CO2 + H2O + 38 ATP) in mitochondria; anaerobic in muscle gives lactic acid, in yeast gives ethanol + CO2. Breathing uses diaphragm and ribs; alveoli give large surface area.

Transport in humans: double circulation; arteries carry blood away (thick, elastic), veins toward heart (valves), capillaries allow exchange. Blood: plasma, RBC (haemoglobin, O2), WBC (immunity), platelets (clotting).

Transport in plants: xylem carries water and minerals upward (transpiration pull); phloem carries food in both directions (translocation). Stomata regulate transpiration and gas exchange.

Excretion: kidneys filter blood into nephrons, forming urine (urea, water, salts); nephron = glomerulus + tubule. Dialysis replaces failed kidney function. Plants excrete via stomata, lenticels and leaf fall.

Photosynthesis needs light, chlorophyll, CO2 and water; rate rises with light intensity and CO2 up to a limit.

Ammonia (aquatic animals) and urea/uric acid (land animals) are the main nitrogenous wastes.

Neuron: dendrite receives, cell body, axon conducts, synapse releases neurotransmitters. Reflex action is a fast, involuntary response through the spinal cord without brain involvement.

Brain parts: cerebrum (thinking, memory), cerebellum (balance and coordination), medulla (involuntary functions such as breathing).

Endocrine glands and hormones: pituitary (growth hormone), thyroid (thyroxine, needs iodine), pancreas (insulin lowers blood glucose), adrenal (adrenaline, fight or flight), testes/ovaries (sex hormones).

Plant hormones: auxin (phototropism, apical dominance), gibberellin (growth), cytokinin (cell division), abscisic acid (dormancy, closes stomata). Tropisms: phototropism, geotropism, hydrotropism, thigmotropism.

Asexual reproduction: binary fission, budding, fragmentation, regeneration, vegetative propagation, spore formation. Sexual reproduction involves gamete fusion and gives variation.

Human male: testes produce sperm and testosterone; female: ovaries produce ova, oviduct is the site of fertilisation, uterus for development, placenta for exchange.

Heredity: genes on chromosomes carry traits; dominant and recessive alleles; genotype vs phenotype; monohybrid cross 3:1 phenotypic ratio. Sex in humans determined by X and Y chromosomes.

Evolution: variations arise in reproduction; natural selection favours useful traits (Darwin); fossils and homologous organs give evidence.

Pathogen types: bacteria (TB, cholera, typhoid), virus (influenza, polio, dengue, AIDS), protozoa (malaria by Plasmodium via female Anopheles), fungi (ringworm).

Disease transmission: air (TB, cold), water and food (cholera, typhoid), vectors (mosquito: malaria, dengue; housefly: typhoid), contact and blood. Prevention: sanitation, safe water, vaccination, vector control.

Immunity: innate (non-specific barriers) and acquired (specific, from antibodies after infection or vaccination). Vaccines contain weakened or killed pathogens or toxoids to trigger antibody production.

Health is physical, mental and social well-being, not merely absence of disease.

Ecosystem: biotic (producers, consumers, decomposers) and abiotic (light, temperature, water, soil) components; food chain and food web; 10 percent energy transfer between trophic levels; pyramids of number, biomass and energy.

Biogeochemical cycles: carbon, nitrogen (fixation by Rhizobium and lightning, nitrification, denitrification), oxygen and water cycles.

Natural resources: renewable (solar, wind, water, biomass) and non-renewable (coal, petroleum, minerals).

Biodiversity loss causes: habitat destruction, pollution, overexploitation, invasive species. Conservation: national parks, sanctuaries, biosphere reserves, seed banks, recycling and reduced use of CFCs.

Distance is scalar (total path); displacement is vector (straight line from start to finish) and can be zero while distance is not.

Speed = distance/time (scalar); velocity = displacement/time (vector). Average speed = total distance / total time.

Acceleration a = (v - u)/t, unit m/s²; negative acceleration is retardation. Uniform circular motion has constant speed but changing velocity, so it is accelerated.

Equations of motion (uniform a): v = u + at; s = ut + ½at²; v² = u² + 2as.

Newton's first law: a body stays at rest or in uniform motion unless a net external force acts (inertia). Second law: F = ma, force in newtons. Third law: every action has an equal and opposite reaction on a different body.

Momentum p = mv (kg m/s); impulse = F x t = change in momentum; total momentum is conserved when no external force acts.

Friction opposes relative motion; static friction exceeds sliding friction; rolling friction is least.

Weight W = mg (g ≈ 9.8 m/s² on Earth); mass is constant, weight varies with location.

Universal law: F = G m1 m2 / r², G = 6.67 x 10^-11 N m²/kg²; gravity is always attractive and acts along the line joining centres.

g = GM/R²; on Earth ≈ 9.8 m/s². Weight = mg. Free fall: v = gt, h = ½gt².

Pressure P = F/A (pascal); liquid pressure P = hρg, increases with depth and density and is independent of container shape.

Buoyancy: upthrust equals weight of displaced fluid (Archimedes). Object floats if its density is less than the fluid's; sinks if greater.

Work W = F s cosθ, unit joule; work is zero when force is perpendicular to displacement (circular motion) or displacement is zero.

Kinetic energy KE = ½mv²; potential energy PE = mgh; work-energy theorem: net work = change in kinetic energy.

Power P = W/t (watt); 1 kW h = 3.6 x 10^6 J. Commercial unit of electricity is the kilowatt-hour.

Simple machines: lever, pulley, inclined plane, wheel and axle, screw, wedge. Mechanical advantage = load/effort; efficiency = useful work / total energy x 100; no machine gives more work out than in.

Reflection: angle of incidence = angle of reflection; image in a plane mirror is virtual, erect, laterally inverted, same size, as far behind as the object is in front.

Spherical mirrors: concave mirror converges (real image when object beyond focus; concave used in torches, dentist); convex diverges (virtual, diminished image; used as rear-view mirror). Mirror formula 1/v + 1/u = 1/f; magnification m = -v/u.

Refraction: light bends toward the normal when going from rarer to denser medium. Snell's law n = sin i / sin r; refractive index n = c/v.

Lenses: convex converges (real images for object beyond f, used as magnifying glass when object inside f); concave diverges. Lens formula 1/v - 1/u = 1/f; power P = 1/f in dioptres (f in metres).

Human eye: cornea and lens focus on retina; myopia corrected by concave lens, hypermetropia by convex lens; dispersion by prism gives the spectrum VIBGYOR.

Sound needs a material medium; speed is highest in solids and lowest in gases; audible range 20 Hz to 20 kHz; frequency determines pitch, amplitude determines loudness.

Electric current I = Q/t (ampere); Ohm's law V = IR; resistance R = ρL/A, increases with length and temperature, decreases with area.

Series: R = R1 + R2 + ...; same current, voltage divides. Parallel: 1/R = 1/R1 + 1/R2 + ...; same voltage, current divides. Power P = VI = I²R = V²/R; energy = P x t.

Heating effect: H = I²Rt (Joule's law), used in heaters, fuses and bulbs. Magnetic effect: a current-carrying conductor has a magnetic field; solenoid acts as an electromagnet; electric motor uses this, generator uses electromagnetic induction.