Fundamentals
The core facts every aspirant should own — each a titled nugget with a real-world story, the concept in plain words, and a memory trick. Works even when the internet doesn't.
1,200 fundamentals
“A fertilizer plant’s bright platinum-rhodium gauze ignites ammonia, turning it stepwise into nitric acid – the heart of the Ostwald process.”
NH₃ is first oxidised to NO over a Pt–Rh gauze at ~900 °C, then NO is oxidised to NO₂ and absorbed in water to give HNO₃. The high temperature and catalyst make the otherwise slow oxidation feasible. Trap: NO forms first, not HNO₃ directly.
Memory trick: Pt-Rh spark → NH₃ → NO → HNO₃
“When you clean a kitchen countertop, the fizz you see is H₂O₂ breaking into water and oxygen.”
Hydrogen peroxide is a pale-blue liquid and a strong oxidising agent used as bleach and antiseptic. It readily decomposes: 2 H₂O₂ → 2 H₂O + O₂, releasing oxygen. In redox questions remember H₂O₂ can act as oxidiser or reducer; overlooking this flips the half-reaction.
H₂O₂
Memory trick: H2O2 = H2O + extra O → oxidiser
“Rinsing a glass bottle and seeing a cloudy ring shows Ca²⁺/Mg²⁺ deposits – the same ions that make tap water hard.”
Hard water contains high Ca²⁺ and Mg²⁺; they react with soap to form insoluble salts, so lather drops. Hardness is expressed as mg CaCO₃ per litre: 1 mmol Ca²⁺ (or Mg²⁺) = 100 mg CaCO₃, and 1 meq L⁻¹ = 50 mg CaCO₃ L⁻¹. Remember CaCO₃’s equivalent weight (50 g eq⁻¹) – confusing mmol with mg or ignoring the valence factor gives wrong hardness values.
Memory trick: Hardness → CaCO₃: 1 mmol =100 mg, 1 meq =50 mg.
“ICl behaves like a mixed-flavor ice-cream, two different halogens blend to give a polar molecule that reacts more readily than pure iodine.”
Interhalogen molecules contain two different halogens (e.g., ICl, BrF₅). The bond is polar because of the electronegativity difference, making them often more reactive than the heavier parent halogen. Their reactivity depends on the specific pair; they readily hydrolyze, giving HX and halogen oxides. A common trap: assuming all interhalogens are stronger oxidizers than Cl₂ – check the actual reaction conditions.
Memory trick: Inter-halogen = INter-different → polarity ↑ reactivity ↑
“The vivid blue of a copper(II) sulfate solution comes from d-orbital splitting of Cu²⁺ by water ligands.”
In an octahedral field ligands split the five d-orbitals into lower-energy t₂g and higher-energy e_g sets; tetrahedral complexes reverse the order (e lower, t₂ higher) and the splitting Δ_t is only 4/9 of Δ₀. Remember that Δ and pairing energy together decide high- or low-spin – a common exam slip is to ignore Δ_t’s smaller size.
Memory trick: Octa: t₂g<e_g; Tet: e<t₂; Δ_t=4/9Δ₀
“Just as spices are ranked from mild to hot, ligands are ordered from weak to strong field in the spectrochemical series.”
The spectrochemical series orders ligands by the crystal-field strength they generate, affecting Δ₀. Weak-field ligands (I⁻, Br⁻) give small Δ, strong-field ligands (CN⁻, CO) give large Δ. Exam trap: remember the series follows observed Δ values, not alphabetical order.
Memory trick: I⁻<Br⁻<Cl⁻<F⁻<H₂O<NH₃<NO₂⁻<CN⁻
“Identical sauce bottles on a rack, one holding ketchup, another mustard, illustrate how complexes with the same formula can have different ligands attached.”
Complexes exhibit structural isomerism (ionization, coordination, solvate/hydrate, linkage) where connectivity changes, and stereoisomerism (geometrical, optical) where spatial arrangement changes. Optical activity demands true chirality – no mirror plane, inversion centre or improper rotation axis. A frequent trap is to mention only geometrical, optical and linkage isomers, omitting the other structural types.
Memory trick: I C S L G O – Ionization, Coordination, Solvate, Linkage, Geometrical, Optical
“Like a Lego brick snapping onto a carbonyl’s ‘sticky’ carbon, a Grignard adds its R group, later giving an alcohol after acid work-up.”
Grignard reagents (R–MgX) attack the electrophilic carbon of aldehydes and ketones, giving after H⁺ work-up a secondary or tertiary alcohol. They do NOT react with carboxylic acids (protonate MgX) and with esters they add twice, yielding a tertiary alcohol. The exam trap is to assume every carbonyl gives a single-addition product.
Memory trick: Grignard + COOH = NO; + Ester = 2-additions; + Ald/Ket = 1-addition
“When ozone passes over a double-bonded rubber band, it snaps the bond, leaving two separate ends that become carbonyl groups.”
Ozonolysis adds O₃ across a C=C bond, forming an unstable ozonide that, after reductive or oxidative work-up, splits into carbonyl compounds (aldehydes or ketones) at each former double-bond carbon. It reveals the position of unsaturation.
Memory trick: Cuts at the C=C.
“When you dip a clean silver spoon into an aldehyde solution, the surface shines back like a mirror.”
In Tollens’ test Ag(NH₃)₂⁺ is reduced to metallic Ag, depositing a silver mirror. Aldehydes do this readily; α-hydroxy ketones, some sugars and enediols also reduce the reagent, while most ketones do not. The common mistake is to mark any silver mirror as proof of an aldehyde only.
Memory trick: Ag⁺↓ with aldehyde or α-OH carbonyl → mirror
“Adding iodine to a bottle of rubbing alcohol makes a yellow, fluffy precipitate – the classic iodoform cloud.”
The iodoform test is positive for compounds containing a CH₃-CO- group. Ethanol and secondary alcohols of type CH₃-CH(OH)-R are first oxidised to a methyl ketone, then three iodinations and base-induced cleavage give yellow CHI₃. Assuming only methyl ketones work misses ethanol and oxidisable secondary alcohols.
Memory trick: CH₃CO- or CH₃CH(OH)- → CHI₃ yellow
“Esterification is like a seesaw: acid + alcohol on one side, ester + water on the other; removing water tips it toward ester.”
Acid-catalyzed esterification protonates the carbonyl, alcohol attacks, and water is eliminated, giving ester. The reaction is an equilibrium; Le Chatelier’s principle says removing water or using excess alcohol drives it forward. Forgetting to shift the balance yields low ester yield.
Memory trick: Ester ⇌ acid+alcohol; pull by removing H₂O
“In a swimming pool, chlorine gas dissolves and splits into salty chloride and bleaching hypochlorite.”
Disproportionation is a redox where the same element is simultaneously oxidised and reduced. In cold dilute alkali: Cl₂ + 2OH⁻ → Cl⁻ + ClO⁻ + H₂O. In hot or concentrated alkali the main product is chlorate: 3Cl₂ + 6OH⁻ → 5Cl⁻ + ClO₃⁻ + 3H₂O. The common exam trap is confusing the cold-alkali (hypochlorite) and hot-alkali (chlorate) equations or omitting the water on the right side.
Memory trick: Cold Cl: 2OH⁻ → Cl⁻ + ClO⁻ + H₂O; Hot Cl → ClO₃⁻
“Forming water from H₂ gas and O₂ gas at 1 atm is the reference ΔH_f⁰ you see in tables.”
Standard enthalpy of formation ΔH_f⁰ is the enthalpy change when one mole of a compound forms from its elements in their standard states (1 atm, 298 K). Elements in their stable form have ΔH_f⁰ = 0. A frequent error is forgetting this zero reference when calculating reaction ΔH.
Memory trick: Elements → 0; compound → ΔH_f⁰
“Ice melting on a warm kitchen counter shows a +ΔH, +ΔS process that only runs when T is high enough.”
ΔG = ΔH – TΔS. If ΔH and ΔS are both positive, high T makes ΔG negative; if both are negative, low T makes ΔG negative. When ΔH and ΔS have opposite signs, ΔG keeps the sign of ΔH, so temperature cannot flip spontaneity. Beware the trap that any opposite-sign pair can be reversed by temperature.
Memory trick: Same sign → T decides; opposite sign → T irrelevant.
“In a copper refinery, impure copper anode dissolves and pure copper plates the cathode like a mirror in a bathtub.”
Electrolytic refining uses an impure metal anode, an electrolyte of its ions, and a pure cathode. Under DC, the anode metal dissolves, metal ions travel to the cathode and deposit as pure metal; less-reactive impurities fall as anode mud, more-reactive stay in solution. The common trap is to think the impurity plates out – only the cathode gets pure metal.
Memory trick: Anode → dissolve; Cathode → pure.
“When you ride a bike, the rubber tire stays firm because sulfur-cross-linked vulcanisation holds the polymer chains together.”
Heating natural rubber with sulfur creates S-bridges between polyisoprene chains, turning a sticky gum into a tough, elastic material. The cross-links restrict chain sliding, increasing tensile strength and reducing tack. Excess sulfur or too high temperature makes the rubber brittle, lowering its elasticity.
Memory trick: S = Strong cross-links; heat + S → firm rubber.
“A compost heap turning a PHBV bag into soil is like a fruit peel disappearing after a few weeks.”
Biodegradable polymers like poly(3-hydroxybutyrate-co-3-hydroxyvalerate) are made by microbes and contain hydrolyzable ester bonds that microorganisms cleave, converting the material to CO₂, H₂O and biomass. In JEE/NEET, remember that true biodegradability requires microbial action on ester linkages, not just photodegradation.
Memory trick: Ester bonds → microbes → CO₂ + H₂O.
“You apply iodine on a cut (antiseptic) but use bleach on the kitchen floor (disinfectant).”
Antiseptics are antimicrobial agents safe for living tissue and are used on skin or wounds; disinfectants are stronger chemicals intended for inanimate surfaces and are toxic to cells. Both lower microbial load but differ in concentration and allowed use. Trap: assuming a substance is safe on skin just because it kills microbes; check the label.
Memory trick: Skin-safe = antiseptic; Surface-only = disinfectant
“When you sip a diet soda, the same sweetness you get from a spoonful of sugar comes from just a few grains of aspartame.”
Artificial sweeteners are high-intensity (200–600× sucrose) so only milligram amounts are needed, making their net caloric contribution negligible. Some (e.g., aspartame) are metabolised to phenylalanine, aspartic acid and methanol, while others (e.g., saccharin, sucralose) pass unchanged. The exam trap is to assume all sweeteners are non-metabolizable or provide zero calories per gram.
Memory trick: 200-600× sweeter → mg dose → ≈0 kcal
“Sodium benzoate stops mold from growing in your citrus soda when the drink’s pH stays below 4.5.”
Sodium benzoate (NaC7H5O2) is an antimicrobial preservative. In acidic media (pH < 4.5) it exists as benzoic acid, which penetrates microbial cells and disrupts metabolism, inhibiting yeasts, molds and some bacteria. At neutral pH it is ineffective, and it does not act as an antioxidant.
Memory trick: Benzoate Banishes Bugs Below pH 4.5
“Aspirin quiets a headache by silencing the COX-enzyme fire alarm in your brain.”
Aspirin (acetylsalicylic acid) irreversibly blocks COX-1 and COX-2, lowering prostaglandin synthesis → reduces pain, fever, inflammation. Paracetamol mainly acts in the CNS, lowering fever and pain but little anti-inflammatory effect. Trap: don’t assume both have the same peripheral action; aspirin can cause gastric irritation.
Memory trick: A-spirin = A-voids inflammation; P-ara = P-ain relief
“A helium balloon filled with 1 mol of gas at STP expands to exactly 22.4 L, the same volume any ideal gas would occupy.”
At standard temperature and pressure (0 °C, 1 atm) one mole of any ideal gas occupies 22.4 L, derived from PV=nRT. This molar volume applies only under STP conditions; at other T or P the volume changes proportionally. Remember the condition when using the value.
22.4 L/mol
Memory trick: STP → 22.4 L per mole
“One mole of electrons carries enough charge to light a 1 W LED for about 26 hours, equal to ~96 500 C.”
The Faraday constant F = N_A·e ≈ 96 485 C mol⁻¹ (≈96 500 C). It links amount of substance to electric charge: Q = n·F in electrolysis. Do not mix F with Avogadro’s number alone; use F when converting moles of electrons to coulombs.
F ≈ 96500 C
Memory trick: F ≈ 96 500 C per mole e⁻