Complete Chemistry Revision for NEET Exam: Core Concepts and PYQs

Chemistry is one of the most scoring sections in NEET, and NEET 2027 Chemistry revision works best when concepts, reactions and formulas are revised together. Organic Chemistry rewards recall of named reactions, reagents and electronic effects. Physical Chemistry depends on a compact set of formulas. Inorganic Chemistry depends on periodic trends, exceptions and test observations.

This chemistry revision covers the high-yield topics from all three branches, along with important questions and key tips for the final weeks. PW’s NEET resources, including PYQs, MCQs, mind maps and formula sheets, can support each topic as you revise.

Organic Chemistry: High-Yield Concepts and Named Reactions

Organic Chemistry questions are mostly reagent-, product- and condition-based. Learn each reaction as a single package of reactant, reagent, condition and product.

Aromaticity, Amines and Diazonium Salts

• Huckel’s rule: A planar, cyclic molecule with a continuous ring of p-orbitals is aromatic if it has (4n + 2) π electrons. Six π electrons (n = 1) is the most common NEET case.

• Carbylamine test: Primary amines (aliphatic or aromatic) react with CHCl3 and KOH or NaOH to give a foul-smelling isocyanide (RNC). It is specific to primary amines.

• Bromination of aniline: Aniline with Br2/H2O gives a white precipitate of 2,4,6-tribromoaniline, because -NH2 is strongly activating (+M effect).

• Nitrile reduction: RCN is reduced to RCH2NH2 using H2/Ni, Na/C2H5OH or LiAlH4.

• Diazotisation: Aliphatic primary amines form unstable diazonium salts that convert to alcohols. Aromatic diazonium salts are stable at 0-5 °C.

• Hofmann bromamide degradation: A primary amide with Br2/NaOH gives a primary amine with one carbon less.

• AgCN vs KCN: AgCN with R-X gives an isonitrile (reduction gives RNHCH3). KCN with R-X gives a nitrile (reduction gives RCH2NH2). The products are functional isomers.

• Amine basicity: A delocalised lone pair on nitrogen lowers basicity, while electron-donating groups increase it.

• -I effect order: -NO2 > -F > -OH > -NH2.

Phenols, Carbonyls and Carboxylic Acids

• Reimer-Tiemann reaction: Phenol with CHCl3 and NaOH gives salicylaldehyde. The electrophile is dichlorocarbene (:CCl2).

• Hell-Volhard-Zelinsky (HVZ) reaction: A carboxylic acid with at least one alpha-hydrogen reacts with Br2 or Cl2 and red phosphorus to give an alpha-halo acid.

• Gattermann-Koch reaction: Benzene with CO, HCl, anhydrous AlCl3 and CuCl gives benzaldehyde.

• Haloform reaction: X2 with NaOH works for compounds with a -COCH3 group, secondary alcohols oxidisable to methyl ketones, ethanol (the only primary alcohol) and acetaldehyde. Benzaldehyde does not respond.

• Esterification: Acid and alcohol with H2SO4. The acid loses -OH and the alcohol loses -H.

• Williamson ether synthesis: An SN2 reaction between an alkoxide and a primary alkyl halide. Tertiary halides give elimination, and aryl halides do not undergo SN2.

• Acidity order: Carboxylic acid > phenol > alcohol. Formic acid is stronger than benzoic acid.

Reduction Reactions

• Rosenmund reduction: Acid chloride to aldehyde using H2/Pd-BaSO4.

• LiAlH(OtBu)3: A mild, bulky reducing agent that converts acid chloride to aldehyde.

• R2Cd: Converts acid chloride to ketone.

• Wolff-Kishner reduction: C=O to CH2 using N2H4 and KOH in basic medium.

• Clemmensen reduction: C=O to CH2 using Zn-Hg and HCl in acidic medium.

Other Important Named Reactions

Revise named reactions in comparison tables so that similar ones are not confused.

• Wurtz-Fittig: Aryl halide + alkyl halide + Na gives an alkylbenzene.

• Fittig: Two aryl halides + Na give a biaryl.

• Sandmeyer: A diazonium salt with a Cu(I) salt gives Ar-Cl, Ar-Br or Ar-CN.

• Finkelstein: Alkyl halide + NaI in acetone gives an alkyl iodide (SN2).

• Benzene sequence: Friedel-Crafts acylation gives acetophenone, Clemmensen reduction gives ethylbenzene, Cl2/UV gives (1-chloroethyl)benzene, and aqueous KOH gives 1-phenylethanol.

Stereoisomerism and Hydrocarbons

• Geometrical isomerism: Needs restricted rotation and two different groups on each carbon of the C=C bond or ring. Trans isomers are usually more stable. 2-Pentene shows it, while 1-butene does not.

• Optical isomerism: Needs a chiral centre (four different groups) and no symmetry element. Enantiomers are non-superimposable mirror images.

• Alkene stability: Heat of hydrogenation (HOH) is inversely related to stability. HOH order: anti-aromatic > cumulative > isolated > resonance-stabilised.

• Boiling and melting points of alkanes: Boiling point falls with branching. Melting point rises with symmetry, so neopentane has the highest melting point but the lowest boiling point among the pentane isomers.

• Electrophilic aromatic substitution: Activating groups direct ortho/para. Deactivating groups direct meta, except halogens, which are ortho/para-directing but deactivating.

• Ozonolysis: Cleaves C=C to carbonyls. Join the carbonyl carbons with a double bond to find the original alkene.

• Free radical monochlorination: Count unique hydrogen environments. Cyclopentane gives only one product.

Biomolecules, Tests and Separation

• Sugars: Sucrose is non-reducing and hydrolyses to alpha-D-glucose and beta-D-fructose. Maltose is reducing and gives two alpha-D-glucose units.

• Polysaccharides: Amylose is linear (alpha-1,4). Amylopectin and glycogen are branched (alpha-1,4 and alpha-1,6). Cellulose is linear (beta-1,4).

• Protein denaturation: Secondary, tertiary and quaternary structures are lost, but the primary structure and peptide bonds remain intact.

• Qualitative tests: Schiff’s test detects aldehydes. Baeyer’s reagent (cold, dilute, alkaline KMnO4) detects unsaturation by decolourisation, while benzene and alkanes do not react.

• Elemental analysis: %C = (12/44) × (mass of CO2 / mass of compound) × 100. %H = (2/18) × (mass of H2O / mass of compound) × 100.

• Kjeldahl method: %N = 1.4 × milliequivalents of N / mass of compound in grams.

• Separation techniques: Sublimation for benzoic acid, simple distillation for ether and toluene, vacuum distillation for glycerol and steam distillation for ortho-nitrophenol.

Physical Chemistry: Essential Formulas

Physical Chemistry rewards accurate formula recall and careful unit handling.

Thermodynamics

• ΔU = ΔH - Δng RT, and ΔU = Q + W with W = -PΔV.

• 1 L.atm is approximately 101.3 J.

• State functions (ΔG, ΔS, ΔH, ΔU) show zero net change in a cyclic process, while heat and work do not.

• Isothermal reversible process (ideal gas): ΔU = 0, ΔH = 0, so Q = -W.

• Adiabatic process: Q = 0, ΔU = W = n Cv ΔT, and PV^γ = constant.

• ΔS = Qrev / T, and ΔS = n Cp ln(T2/T1) at constant pressure.

• At equilibrium ΔG = 0, so T = ΔH / ΔS.

• The Born-Haber cycle applies Hess’s law to find lattice energy.

Chemical Equilibrium

Chemical equilibrium combines formulas with direction-based reasoning.

• Ksp: MX = s², MX2 or M2X = 4s³, MX3 or M3X = 27s⁴. Precipitation occurs when Qsp > Ksp.

• Kp = Kc (RT)^Δng.

• Reversing a reaction gives K’ = 1/K, multiplying coefficients by n gives K’ = K^n, and adding reactions gives K = K1 × K2.

• Weak acid: [H+] = √(Ka × C). Weak base: [OH-] = √(Kb × C).

• Ka × Kb = Kw. At neutrality, pH = pKw/2, and Kw increases with temperature.

• Salt pH: strong acid + weak base is below 7, weak acid + strong base is above 7, and strong acid + strong base is 7.

• Buffer capacity is maximum when pH = pKa.

• Le Chatelier’s principle: raising pressure shifts equilibrium towards fewer gas moles, and there is no effect when Δng = 0.

Electrochemistry

Electrochemistry questions are mostly direct formula applications.

• Nernst equation: Ecell = E°cell - (0.059/n) log Q at 298 K.

• ΔG° = -nFE°cell, and E°cell = (0.059/n) log Kc.

• 1 Faraday = 96485 C. Equivalent mass = molar mass / n-factor.

• Cell constant = R × K, and molar conductivity = (K × 1000) / C.

• Kohlrausch’s law gives the molar conductivity of a weak electrolyte from strong electrolytes.

• A more negative reduction potential means a stronger reducing agent.

• Lead-acid battery: Pb and PbO2 convert to PbSO4 on discharge. Nickel-cadmium is a rechargeable secondary cell.

Solutions and Colligative Properties

• Raoult’s law: (P° - P) / P° = X(solute).

• ΔTb = i Kb m, and ΔTf = i Kf m. A higher i means a lower freezing point.

• Osmotic pressure: π = i C R T.

• Positive deviation: A-B forces are weaker than A-A and B-B, with ΔVmix > 0.

• Henry’s law does not apply when the gas reacts with the solvent, such as NH3 in water.

• Molality does not change with temperature, but molarity decreases as temperature rises.

Chemical Kinetics

• The slope of ln k vs 1/T is -Ea/R, and the slope of log k vs 1/T is -Ea/(2.303 R).

• log(k2/k1) = (Ea / 2.303 R) × (1/T1 - 1/T2). Always convert temperature to Kelvin.

• Zero order: [R]t = [R]0 - kt. First order: α = 1 - e^(-kt).

• As T tends to infinity, k tends to A.

• Molecularity comes from the elementary step, while the rate law depends on the slowest step.

• At [A] = 1 M, the rates of all orders are equal if k is numerically the same.

Inorganic Chemistry: Periodic Table, Bonding and Coordination Compounds

Inorganic Chemistry rewards revision of exceptions and observations.

Periodic Trends

• Down a group, atomic radius and metallic character increase while ionisation energy decreases.

• IE order in the second period: Li < B < Be < C < O < N < F < Ne. Helium has the highest ionisation energy.

• A large jump in successive ionisation energies shows removal from an inner shell.

• The second electron gain enthalpy is always positive.

• Cl, S and P have higher electron gain enthalpy than F, O and N respectively, due to electron repulsion in small atoms.

• Isoelectronic size order: N3- > O2- > F- > Na+ > Mg2+.

• Amphoteric oxides and hydroxides include Zn, Al, Sb, As, Pb, Sn, Ga, Cr, Be and V2O5.

• Basic character of oxides decreases left to right and increases down a group.

Chemical Bonding

• BCl3 and AlCl3 are electron deficient, while PCl3 and BH4- follow the octet rule.

• Lattice energy rises with charge and falls with ionic size, so KF > KCl > KBr > KI.

• Fluorine forms only single bonds. Oxygen’s maximum covalency is 3, so OF4 does not exist.

• Increasing s-character raises bond angle and bond strength and lowers bond length.

• NH3 has a higher dipole moment than NF3, because bond dipoles reinforce in NH3 and oppose in NF3.

• Hydrogen bond strength: F-H > O-H > N-H.

• Fajan’s rule: small cation, large anion and high charges increase covalent character.

• MO theory: N2 has bond order 3 and is diamagnetic. O2 has bond order 2 and is paramagnetic. N2+ is weaker than N2, while O2+ is stronger than O2.

• Hybridisation = sigma bonds + lone pairs. IF5 is sp3d2 and I3- is sp3d.

Coordination Compounds

Coordination compounds are a high-weightage topic that combines theory with application.

• Werner’s theory: Primary valency is the oxidation state (ionisable) and secondary valency is the coordination number (non-ionisable).

• Stability: Increases with metal charge, chelation and ligand strength. Chelating ligands include oxalate, EDTA and en, but not pyridine.

• CFSE (octahedral): t2g gives -0.4 Δo and eg gives +0.6 Δo. Weak field d5 and d10 have zero CFSE.

• Spin states: Low spin occurs only in octahedral complexes. Tetrahedral complexes are never low spin.

• Hybridisation: sp3d2 is outer orbital (weak field) and d2sp3 is inner orbital (strong field).

• Geometry from magnetism: Four-coordinate Mn2+ with 5 unpaired electrons is tetrahedral. Pairing suggests square planar, as in PtCl4(2-), which is dsp2 and diamagnetic.

• Colour: d0 and d10 complexes are colourless, since d-d transitions are not possible.

• Isomerism: Hydrate, ionisation, geometrical, optical and linkage. Linkage needs an ambidentate ligand such as NO2-.

• Conductivity: Molar conductance is proportional to the number of ions produced.

• Biological importance: Chlorophyll contains magnesium.

• Nomenclature: NH3 is “ammine” with a double m, and amine derivatives use a single m.

d-Block Elements

• Zn, Cd and Hg (d10) do not show variable valency.

• Cu+ disproportionates in water to Cu and Cu2+, due to the high hydration energy of Cu2+.

• Paramagnetism peaks at d5. Melting points rise from Sc to Cr and drop at Mn.

• Higher oxidation state means more acidic oxide. Cr(+2) is basic, Cr(+3) amphoteric and Cr(+6) acidic.

• Cr2O7(2-) is orange in acid, and CrO4(2-) is yellow in base. K2Cr2O7 is the preferred primary standard.

• Chrome yellow is PbCrO4.

Salt Analysis

• Chromyl chloride test: Confirms Cl- (reddish-brown CrO2Cl2 vapours), only for ionic chlorides.

• Brown ring test: Confirms NO3- through [Fe(H2O)5(NO)]SO4.

• Sodium nitroprusside: Gives a purple colour with S2-.

• Lead acetate paper: Turns black with H2S (PbS).

• Nessler’s reagent: Gives a brown precipitate with NH4+.

• DMG test: Gives a rosy red precipitate with Ni2+.

• Flame test: Copper gives a green flame with a blue centre.

• Borax bead (oxidising flame): Cu(+2) gives blue-green.

• Group separation: H2S in acidic medium precipitates Group II, and in alkaline medium precipitates Group IV (NiS, CoS, ZnS, MnS).

Final Revision Strategy for NEET Chemistry

A focused revision plan can help you recall important concepts, improve accuracy and manage time effectively during NEET 2027.

• Physical Chemistry: Revise important formulas and practise numerical questions.

• Organic Chemistry: Review reaction conversions, named reactions and reagents.

• Inorganic Chemistry: Focus on salt analysis, chemical bonding and coordination compounds.

• Follow a Revision Plan: Read How to Study Chemistry for NEET 2027 for more preparation tips.

• Avoid Silly Mistakes: Read each question carefully and attempt it calmly on exam day.

• Fill the OMR Sheet Carefully: Mark the correct options and check that your responses are recorded properly.

Important Questions for NEET 2027 Chemistry

Practise these questions to check formula recall and reaction knowledge.

1. Which test is specific for primary amines?

2. What is the product when aniline reacts with bromine water at room temperature?

3. Find the pH of a 0.01 M weak acid with Ka = 1 × 10^-6.

4. Write the Ksp expression for MX2 in terms of molar solubility s.

5. Calculate ΔG° for a cell with E°cell = 1.1 V and n = 2.

6. The slope of a log k vs 1/T graph is -5000 K. Find Ea.

7. Which solution has the lowest freezing point among equimolal glucose, NaCl, CaCl2 and K3[Fe(CN)6]?

8. Which of these will not give the iodoform test: ethanol, acetone, benzaldehyde, propan-2-ol?

Key Tips for NEET 2027 Chemistry Revision

These tips help you avoid common errors and revise efficiently.

• Revise reactions as complete packages. Note the reactant, reagent, condition and product together, and compare similar reactions such as Wolff-Kishner and Clemmensen in one table.

• Memorise exceptions. Examples are IE of Be vs B, positive electron gain enthalpy of noble gases and Cl having a higher electron gain enthalpy than F.

• Check units and temperature in numericals. Convert temperature to Kelvin, and convert mass to moles before using rate or concentration formulas.

• Use shortcuts for coordination compounds. Link ligand strength, spin state, hybridisation and magnetic moment (μ = √n(n+2) BM) in a single chain.

• Practise PYQs by chapter. Previous year questions show repeated patterns, especially in electrochemistry, kinetics and coordination compounds.

NEET 2027 Chemistry revision is most effective when named reactions, core formulas and inorganic exceptions are revised in short, regular cycles. Combine this with chapter-wise PYQs, MCQs and mind maps, and take mock tests to build speed and accuracy. Consistent practice in the final weeks turns revision into marks. You can also check the PW NEET Batches for more efficient practice

Related Resources

• Chemistry Chemical Kinetics

• Chemical Kinetics NEET Formulae

• Chemical Kinetics NEET PYQs

• Coordination Compounds NEET Notes

• Coordination Compounds NEET PYQs