Chemistry

Exam focus: NCERT's current STP is 1 bar, giving an ideal gas a molar volume of 22.7 L — not the older 22.4 L (at 1 atm) many default to by habit. NTP (25°C, 1 atm) gives yet a third value, 24.45 L, so match the number to whichever condition the question actually states.

3 topics · 3 lectures · 11 questions · 3 with exam focus

Exam focus: Bohr's energy and radius formulas are exact only for one-electron species (H, He⁺, Li²⁺) — applying them to a multi-electron atom without adjustment is the usual overreach. Only the Balmer series (transitions down to n=2) falls in the visible range; Lyman is UV and the rest are infrared.

3 topics · 3 lectures · 13 questions · 3 with exam focus

Exam focus: The modern periodic law orders elements by atomic number, not atomic mass — the switch from Mendeleev's basis that fixed anomalies like the Co/Ni and Ar/K ordering. Hydrogen's dual placement (loses one electron like an alkali metal, needs one like a halogen) is a recurring "which group" trap.

2 topics · 2 lectures · 7 questions · 2 with exam focus

Exam focus: Fajans' rules explain why some "ionic" compounds behave covalently: a small, highly charged cation next to a large, polarisable anion pulls electron density back toward itself, which is why AlCl₃ and BeCl₂ don't act like typical ionic solids. Octet exceptions — BF₃ incomplete, PCl₅/SF₆ expanded, NO odd-electron — are tested directly, not as a footnote.

5 topics · 5 lectures · 19 questions · 5 with exam focus

Exam focus: NCERT's sign convention is ΔU = q + w with w the work done ON the system — mix that up with the older "w = work done BY the system" convention and every work term flips sign. For gas-phase reactions, ΔH and ΔU differ by Δn(gas)×RT, a correction it's easy to forget even when Δn(gas) isn't zero.

3 topics · 3 lectures · 15 questions · 3 with exam focus

Exam focus: Kp and Kc are related by a factor of (RT) raised to the power Δn — moles of gaseous product minus reactant — and getting that exponent's sign backwards inverts the whole conversion. Separately, adding an inert gas at constant volume leaves equilibrium untouched, but adding it at constant pressure shifts it toward the side with more gas moles, because the container must expand to keep pressure fixed.

3 topics · 3 lectures · 14 questions · 3 with exam focus

Exam focus: Oxygen isn't always −2: it's −1 in peroxides (H₂O₂), −1/2 in superoxides (KO₂), and +2 in OF₂, where fluorine is the more electronegative atom — NEET tests exactly these exceptions, not the default. Also watch for disproportionation, where the same element is simultaneously oxidised and reduced in one reaction, such as Cl₂ with cold dilute NaOH.

2 topics · 2 lectures · 6 questions · 2 with exam focus

Exam focus: When two numbering directions both give substituents low locants, the tie breaks at the first point of difference, not the lowest sum — a frequent numbering slip. The functional-group seniority order (roughly: acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine) decides which group becomes the suffix and which get demoted to prefixes like oxo- or hydroxy-.

4 topics · 4 lectures · 11 questions · 4 with exam focus

Exam focus: Ethane's anti-staggered conformation is the most stable (zero torsional strain) and the fully eclipsed one the least — tested via potential-energy-vs-dihedral-angle graphs, not just the word "staggered." In free-radical halogenation, bromination is far more selective for 3° C–H than chlorination — "both give the same product ratio" is the trap.

3 topics · 3 lectures · 20 questions · 3 with exam focus

Exam focus: Steam distillation only works for a substance that's virtually insoluble in water and has some vapour pressure at 373 K — it lets something like aniline distil below its own, much higher, boiling point instead of decomposing there. In chromatography, Rf is the distance moved by the compound divided by the distance moved by the solvent front, always less than 1 — a value NEET expects you to compute, not just define.

2 topics · 2 lectures · 6 questions · 2 with exam focus

Exam focus: A higher Henry's law constant means lower gas solubility, not higher — an inverse relationship (p = KH·x) that's easy to flip under pressure. For non-ideal solutions, positive deviation from Raoult's law (weaker A–B interactions, e.g. ethanol–acetone) gives a minimum-boiling azeotrope, while negative deviation (stronger A–B interactions from H-bonding, e.g. chloroform–acetone) gives a maximum-boiling one — a pairing students often reverse.

3 topics · 3 lectures · 12 questions · 3 with exam focus

Exam focus: At equilibrium, E(cell) = 0, not E°(cell) = 0 — that's the condition linking E°(cell) to K through 0 = E° − (0.0591/n)log K. In the standard cell notation, oxidation (anode) is written on the left and reduction (cathode) on the right — reverse that and every EMF you calculate flips sign.

3 topics · 3 lectures · 14 questions · 3 with exam focus

Exam focus: Order is an experimentally determined exponent in the rate law — it can be zero, fractional, even negative — while molecularity is a theoretical count of colliding species in one elementary step and must be a positive integer; the two coincide only for a genuine single-step reaction. You cannot read a complex, multi-step reaction's rate law off its balanced equation the way you can for an elementary step.

3 topics · 3 lectures · 15 questions · 3 with exam focus

Exam focus: The inert pair effect makes the lower oxidation state more stable going down groups 13 and 14 — Tl⁺ is more stable than Tl³⁺, Pb²⁺ more stable than Pb⁴⁺ — the reverse of what "higher group, higher favoured state" intuition suggests. Diborane is the other signature trap: B₂H₆ has too few electrons for conventional 2-electron bonds at every position, forcing two 3-centre-2-electron bridge bonds at the bridging hydrogens.

3 topics · 3 lectures · 22 questions · 3 with exam focus

Exam focus: Zn, Cd and Hg are d-block elements but not true transition elements — their d-subshell is completely filled (d¹⁰) in both the metal and its common ions, so they miss the defining traits: variable oxidation states, coloured ions, catalytic activity. Also, second- and third-row transition metals in the same group (Zr and Hf, for instance) have almost identical atomic radii, because lanthanoid contraction cancels out the increase you'd otherwise expect going down a group.

3 topics · 3 lectures · 14 questions · 3 with exam focus

Exam focus: Werner's key distinction is primary valence (ionisable, the oxidation state) versus secondary valence (non-ionisable, the fixed coordination number and geometry) — a complex's conductivity in solution tests exactly this, since only ions outside the coordination sphere carry current. In naming, ligands are listed alphabetically by name regardless of charge or multiplying prefix (bis, tris), and an anionic complex ion always ends in "-ate."

3 topics · 3 lectures · 15 questions · 3 with exam focus

Exam focus: SN2 is a single backside attack that gives complete inversion of configuration (Walden inversion) at the stereocentre; SN1 goes through a planar carbocation attacked from either face, giving near-racemisation instead — "inversion versus racemisation" is the fastest way to tell the two mechanisms apart in a question stem. SN1 favours 3° substrates and polar protic solvents that stabilise the carbocation; SN2 favours 1° substrates and is blocked by bulky groups at the reacting carbon.

2 topics · 2 lectures · 9 questions · 2 with exam focus

Exam focus: The Lucas test tells 1°, 2° and 3° alcohols apart by how fast turbidity appears with ZnCl₂/HCl — instantly for 3° (via a stable carbocation), within minutes for 2°, not at all at room temperature for 1°. Acidity among simple alcohols runs 1° > 2° > 3°, the opposite of carbocation stability, because the same electron-donating alkyl groups that stabilise a cation destabilise the alkoxide anion instead.

3 topics · 3 lectures · 11 questions · 3 with exam focus

Exam focus: Reactivity toward nucleophilic addition runs aldehydes above ketones, and an aryl group directly on the carbonyl carbon lowers it further still, since the ring donates electron density into the C=O by resonance and makes that carbon less electrophilic. That steric-plus-electronic combination is what "arrange by reactivity toward HCN/NaHSO₃" questions are actually testing, not a memorised list.

3 topics · 3 lectures · 19 questions · 3 with exam focus

Exam focus: In water, aliphatic amine basicity doesn't rise monotonically with substitution — the usual order is 2° > 1° > 3° > NH₃, because a 3° amine's extra alkyl groups add electron density but also add steric hindrance that weakens solvation of the resulting ammonium ion, and that loss outweighs the electronic gain. Aniline is far less basic than ammonia for a different reason: its nitrogen lone pair delocalises into the ring by resonance, and a ring nitro group weakens it further still.

2 topics · 2 lectures · 11 questions · 2 with exam focus

Exam focus: Sucrose is the classic non-reducing sugar because its glycosidic bond ties up both anomeric carbons — C1 of glucose and C2 of fructose — leaving no free anomeric OH to open into a reactive aldehyde or ketone, unlike maltose and lactose, which keep one free and do reduce Fehling's or Tollens'. This is also why sucrose shows no mutarotation, while glucose's optical rotation visibly drifts as its α and β anomers interconvert through the open-chain form.

3 topics · 3 lectures · 11 questions · 3 with exam focus

Exam focus: The iodoform test isn't exclusive to methyl ketones — any compound with a CH₃–CH(OH)– group, such as ethanol or isopropanol, also gives it, because it oxidises to the methyl ketone or aldehyde in situ under the test conditions. A positive iodoform test on an unknown alcohol therefore doesn't by itself prove a ketone is present — that's the standard trap.

2 topics · 2 lectures · 3 questions · 2 with exam focus