ChemistryRedox Reactions· Class 11
Oxidation number rules
“A quick bookkeeping system for tracking electron transfer.”
Free elements are 0, oxygen is usually −2, hydrogen +1, and the sum equals the ion's charge.
Memory trick: Sum = overall charge.
Fundamentals
1,200 must-knows for NEET & JEE
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
ChemistrySome Basic Concepts (Mole Concept)· Class 11
Percentage yield
“Real reactions rarely give 100% — side reactions and losses eat into the total.”
Actual yield divided by theoretical yield, times 100.
Memory trick: Real ÷ theoretical × 100.
ChemistrySolutions· Class 12
Concentration: ppm
“Safe drinking-water limits for metals are quoted in ppm.”
Parts per million expresses very dilute concentrations.
Memory trick: 1 ppm = 1 mg per litre.
ChemistrySome Basic Concepts (Mole Concept)· Class 11
Law of conservation of mass
“Whatever mass goes into a sealed reaction comes back out.”
Mass is neither created nor destroyed in a chemical reaction.
Memory trick: Reactant mass = product mass.
ChemistrySome Basic Concepts (Mole Concept)· Class 11
Law of definite proportions
“Water is always 8:1 oxygen to hydrogen by mass, from any source.”
A pure compound always contains its elements in the same fixed mass ratio.
Memory trick: Fixed ratio, always.
ChemistrySome Basic Concepts (Mole Concept)· Class 11
Accuracy vs precision
“A dartboard can be precise but off-target — tight but inaccurate.”
Accuracy is closeness to the true value; precision is repeatability.
Memory trick: Close vs consistent.
ChemistrySome Basic Concepts (Mole Concept)· Class 11
Stoichiometry
“It's the recipe maths of chemistry — how much yields how much.”
Using balanced equations to relate amounts of reactants and products.
Memory trick: Balance first, then ratio.
ChemistrySolutions· Class 12
Osmosis
“Plant roots drink water by osmosis, and it's why salted slugs shrivel.”
Solvent flows through a semipermeable membrane from dilute to concentrated.
Memory trick: Solvent moves to the saltier side.
ChemistrySolutions· Class 12
Osmotic pressure
“Reverse osmosis purifies seawater by overpowering this pressure.”
The pressure needed to stop osmosis; a colligative property.
π = CRT
Memory trick: Depends on particle count.
ChemistrySolutions· Class 12
Van't Hoff factor
“One mole of NaCl gives two particles, doubling its colligative effect.”
Accounts for particles formed when a solute dissociates or associates.
Memory trick: Counts actual particles.
ChemistryElectrochemistry· Class 12
Molar conductivity
“Spread ions farther apart and each carries current more freely.”
Conductivity per mole of electrolyte; it rises on dilution.
Memory trick: Increases with dilution.
ChemistryElectrochemistry· Class 12
Standard hydrogen electrode
“Every electrode potential is measured against this agreed zero.”
The reference electrode assigned a potential of exactly zero volts.
Memory trick: Reference = 0 V.
ChemistryChemical Kinetics· Class 12
Collision theory
“Most collisions bounce off harmlessly; only the right ones react.”
Reactions occur when particles collide with enough energy and correct orientation.
Memory trick: Energy + orientation.
ChemistryChemical Kinetics· Class 12
Pseudo first-order reaction
“Sugar hydrolysis looks first-order because water is overwhelmingly abundant.”
A higher-order reaction that behaves as first-order because one reactant is in large excess.
Memory trick: Excess reactant hides its order.
ChemistryChemical Kinetics· Class 12
Rate-determining step
“A reaction is only as fast as its slowest bottleneck.”
The slowest step in a mechanism sets the overall reaction rate.
Memory trick: Slowest step rules the rate.
ChemistryStates of Matter· Class 11
Critical temperature
“You can't squeeze oxygen into liquid at room temperature — you must cool it first.”
Above it, a gas cannot be liquefied by pressure alone.
Memory trick: Above it, no liquefaction.
ChemistryChemical Bonding & Molecular Structure· Class 11
Formal charge
“It helps pick which Lewis structure nature actually prefers.”
Bookkeeping charge on an atom in a Lewis structure, guiding the best structure.
Memory trick: Lowest formal charges win.
ChemistryChemical Bonding & Molecular Structure· Class 11
Fajans' rules
“They explain why some 'ionic' compounds behave partly covalent.”
Small, highly charged ions give bonds more covalent character.
Memory trick: Small + high charge → covalent.
ChemistryChemical Bonding & Molecular Structure· Class 11
Molecular orbital theory: O₂ is paramagnetic
“The theory that finally explained why oxygen sticks to a magnet.”
MOT correctly predicts O₂ has two unpaired electrons, so liquid oxygen is attracted to a magnet.
Memory trick: O₂ has unpaired electrons.
ChemistryOrganic Chemistry — Basic Concepts· Class 11
Hyperconjugation
“The 'no-bond resonance' that steadies carbocations and alkenes.”
Stabilisation from overlap of a σ-bond with an adjacent empty or partly filled orbital.
Memory trick: σ-electrons lend stability.
ChemistryOrganic Chemistry — Basic Concepts· Class 12
Chirality
“One mirror-form of a drug can heal while the other harms.”
A molecule that can't be superimposed on its mirror image is chiral, like your hands.
Memory trick: Non-superimposable mirror images.
ChemistryAldehydes, Ketones & Carboxylic Acids· Class 12
Tautomerism
“Keto and enol forms flip back and forth in many carbonyl compounds.”
A molecule rapidly interconverts between structural isomers, usually by shifting an H.
Memory trick: H hops between two forms.
ChemistryThe p-Block Elements· Class 12
Haber process
“This reaction feeds roughly half the world's population.”
N₂ + 3H₂ ⇌ 2NH₃ over an iron catalyst makes ammonia for fertilisers.
N₂+3H₂⇌2NH₃
Memory trick: Iron catalyst, high pressure.
ChemistryThe p-Block Elements· Class 12
Contact process
“Sulphuric acid is the most-produced industrial chemical on Earth.”
Industrial sulphuric acid is made by oxidising SO₂ to SO₃ over a V₂O₅ catalyst.
Memory trick: V₂O₅ catalyst.