CBSE Class 12 Chemistry

Chapters: 11

1. Solutions

Types and concentration · Vapour pressure and ideal solutions · Colligative properties

Solutions: Types, Concentration and Henry's Law – A solution is an even mix of two or more substances. The part in bigger amount is the solvent, the smaller part is the solute. We tell 'how strong' a solution is with concentration terms: mass %, volume %, ppm, mole fraction, molarity (per litre of solution) and molality (per kg of solvent). Solids usually dissolve more when hot. Gases dissolve more when their pressure is high (Henry's law, p = KH·x) and less when it is hot.
Raoult's Law: Vapour Pressure, Ideal and Non-Ideal Solutions – In a closed jar, some molecules of a liquid escape and push on the walls: that push is the vapour pressure. Raoult's law says each volatile part of a solution gives a vapour pressure equal to its own pure vapour pressure times its mole fraction: pA = xA·pA°. Solutions that obey this at every mix are ideal (ΔmixH = 0, ΔmixV = 0). Others deviate: positive deviation (weaker A–B pull, more vapour, forms minimum-boiling azeotropes) or negative deviation (stronger A–B pull, less vapour, forms maximum-boiling azeotropes).
Colligative Properties: Counting Particles, Not Their Type – Colligative properties depend only on HOW MANY solute particles are in the solution, not on what they are. There are four: relative lowering of vapour pressure (Δp/p° = x₂), elevation of boiling point (ΔTb = Kb·m), depression of freezing point (ΔTf = Kf·m) and osmotic pressure (π = CRT). We use them to find molar mass. Salts that split into ions (NaCl) or molecules that pair up (acetic acid in benzene) give abnormal molar masses, fixed with the van 't Hoff factor i.

2. Electrochemistry

Galvanic cells and Nernst equation · Conductance of electrolytic solutions · Electrolysis, batteries, fuel cells, corrosion

Galvanic Cells and the Nernst Equation – A galvanic cell turns the energy of a redox reaction into electricity. Oxidation happens at the anode (−) and reduction at the cathode (+). Each electrode has a potential measured against the standard hydrogen electrode (0 V). E°cell = E°cathode − E°anode. The Nernst equation, E = E° − (0.059/n) log Q at 298 K, gives the cell voltage at any concentration, and ΔG = −nFE links voltage to energy.
Conductance of Electrolytic Solutions – In a solution, ions carry the current. Resistance R depends on the cell shape through the cell constant G* = l/A, so conductivity κ = G*/R. Molar conductivity Λm = κ × 1000/c tells how well one mole of the solute conducts. On dilution κ falls but Λm rises: a little for strong electrolytes (Λm = Λ°m − A√c) and a lot for weak ones. Kohlrausch's law says Λ°m = sum of the ion values, which gives Λ°m of weak electrolytes and their degree of dissociation.
Electrolysis, Batteries, Fuel Cells and Corrosion – In an electrolytic cell an outside source of electricity forces a non-spontaneous reaction: cations are reduced at the cathode (−) and anions oxidised at the anode (+). Faraday's laws link the mass changed to the charge: m = (M/nF) × I × t. Which product forms depends on electrode potentials and overpotential. Batteries are galvanic cells: primary (dry cell, mercury cell) cannot be recharged; secondary (lead storage, Ni–Cd) can. Fuel cells burn H₂ with O₂ to give electricity directly. Corrosion (rusting) is an unwanted galvanic cell on the metal surface.

3. Chemical Kinetics

Rate of reaction · Integrated rate equations · Temperature and collision theory

Rate of a Chemical Reaction – The rate of a reaction tells how fast a reactant is used up or a product is made, per unit time. Rate = −Δ[R]/Δt = +Δ[P]/Δt (unit mol L⁻¹ s⁻¹). The rate law, rate = k[A]^x[B]^y, is found by experiment; x + y is the order. Molecularity is the number of particles that collide in one elementary step.
Integrated Rate Equations: Zero and First Order – Integrated rate equations link concentration with time. Zero order: [R] = [R]₀ − kt (straight line), t½ = [R]₀/2k. First order: k = (2.303/t) log([R]₀/[R]), ln[R] falls in a straight line with slope −k, and t½ = 0.693/k, which does not depend on the starting amount.
Temperature, Activation Energy, Catalysts and Collision Theory – Reactant molecules must climb an energy hill, the activation energy Ea, to become products. The Arrhenius equation k = A e^(−Ea/RT) shows that a small rise in temperature lets many more molecules cross, so k rises fast. A catalyst gives a lower hill without changing ΔH. Collision theory: molecules react only when they collide with enough energy and the right orientation.

4. d- and f-Block Elements

Transition elements · Important compounds · Lanthanoids and actinoids

Transition Elements (d-Block) – Transition elements are the d-block metals of groups 3 to 12. Their last electron goes into an inner (n−1)d orbital. Because the d-orbitals are only partly filled, they show many oxidation states, coloured ions, magnetism (μ = √(n(n+2)) BM), good catalytic power and easy alloy formation.
Potassium Dichromate and Potassium Permanganate – K₂Cr₂O₇ (orange, Cr +6) is made from chromite ore; in water it exists as dichromate in acid and yellow chromate in base. KMnO₄ (purple, Mn +7) is made from pyrolusite (MnO₂). Both are strong oxidising agents: acidified dichromate takes 6 electrons per ion (→ green Cr³⁺); permanganate takes 5 in acid (→ Mn²⁺), 3 in neutral/weak base (→ MnO₂) and 1 in strong alkali (→ MnO₄²⁻).
Lanthanoids and Actinoids (f-Block) – The f-block has two rows kept below the periodic table: the lanthanoids (Ce to Lu, filling 4f) and the actinoids (Th to Lr, filling 5f). Lanthanoids mostly show +3; actinoids show many more states (up to +7) and are all radioactive. Poor shielding by f-electrons makes the size shrink steadily across the row: the lanthanoid contraction, which makes 4d and 5d elements (like Zr and Hf) almost the same size.

5. Coordination Compounds

Werner's theory and terms · Isomerism · Bonding

Coordination Compounds: Werner's Theory, Terms and IUPAC Names – A coordination compound has a central metal atom or ion joined to a fixed number of ions or molecules called ligands. Each ligand gives one pair of electrons to the metal. The metal and its ligands sit together inside square brackets, the coordination sphere. The number of donor atoms bonded to the metal is the coordination number. Werner said a metal shows two kinds of valence: primary (ionisable, outside the bracket) and secondary (fixed, inside the bracket).
Isomerism in Coordination Compounds – Isomers have the same formula but a different arrangement of atoms. In structural isomers the bonds themselves are different: ionisation, linkage, coordination and solvate isomers. In stereoisomers the bonds are the same but the positions in space differ: geometrical (cis-trans, fac-mer) and optical (mirror images that cannot overlap).
Bonding in Coordination Compounds: VBT, Crystal Field Theory and Metal Carbonyls – Valence bond theory (VBT) says the metal mixes its empty orbitals into hybrid orbitals (like d²sp³ or sp³d²) that accept the ligand electron pairs; it predicts shape and magnetism. Crystal field theory (CFT) treats ligands as negative charges that raise some d orbitals more than others: in an octahedron the 5 d orbitals split into t₂g (lower) and e_g (higher) by Δo. Strong ligands make Δo big and electrons pair (low spin). An electron jumping across Δo by absorbing light gives colour. In metal carbonyls, CO gives a σ pair and takes back π electrons (synergic bonding).

6. Haloalkanes and Haloarenes

Haloalkanes · Haloarenes · Polyhalogen compounds

Haloalkanes – A haloalkane is an alkane in which a hydrogen is replaced by a halogen (R–X). The C–X bond is polar: carbon is slightly positive, so nucleophiles attack it. Haloalkanes react by SN2 (one step, backside attack, inversion; best for 1°), SN1 (two steps, flat carbocation, racemic product; best for 3°) or elimination (strong base in alcohol gives an alkene).
Haloarenes – A haloarene has a halogen joined straight to a benzene ring (Ar–X), like chlorobenzene C₆H₅Cl. Resonance gives the C–X bond part double-bond character, so haloarenes resist nucleophilic substitution unless –NO₂ groups sit at ortho/para. With electrophiles, the halogen slows the ring slightly but sends new groups to ortho and para positions.
Polyhalogen Compounds – Polyhalogen compounds have more than one halogen on carbon. Dichloromethane is a solvent and paint remover; chloroform is a solvent that turns into poisonous phosgene in air and light; iodoform is a yellow antiseptic; carbon tetrachloride was a solvent and fire extinguisher; freons were coolants that destroy ozone; DDT is an insecticide that builds up in food chains.

7. Alcohols, Phenols and Ethers

Alcohols · Phenols · Ethers

Alcohols – An alcohol is a carbon compound with an –OH group on an sp³ carbon (R–OH). Count the carbons joined to the C–OH carbon to classify it as primary (1°), secondary (2°) or tertiary (3°). Name it as alkan-n-ol, giving –OH the lowest number. Make alcohols from alkenes (acid-catalysed hydration or hydroboration–oxidation), by reducing aldehydes, ketones and acids, or from Grignard reagents. H-bonding gives them high boiling points and water solubility. Reactions break either the O–H bond (acidic: Na, esterification) or the C–O bond (HX, dehydration), and 1°/2° alcohols can be oxidised. Methanol and ethanol are the key commercial alcohols.
Phenols – A phenol has –OH joined straight to a benzene ring carbon. It is made from chlorobenzene (NaOH, 623 K, 300 atm), benzenesulphonic acid, diazonium salts or cumene. Phenol is more acidic than alcohols and water because the phenoxide ion spreads its negative charge over the ring; electron-pulling groups like –NO₂ (at ortho/para) raise acidity, electron-pushing groups like –CH₃ lower it. The –OH group activates the ring at ortho and para positions: bromine water gives 2,4,6-tribromophenol, dilute HNO₃ gives o- and p-nitrophenol, NaOH + CO₂ gives salicylic acid (Kolbe) and CHCl₃ + NaOH gives salicylaldehyde (Reimer–Tiemann).
Ethers – An ether has one oxygen joining two carbon groups: R–O–R′. Name it as alkoxyalkane (the smaller group becomes the alkoxy part). Make ethers by dehydrating primary alcohols with conc. H₂SO₄ at 413 K (symmetrical ethers) or by Williamson synthesis: sodium alkoxide + primary alkyl halide (SN2). Ethers cannot H-bond with each other, so their boiling points are low, close to alkanes, but they H-bond with water and small ones dissolve slightly. HI breaks the C–O bond: the smaller group becomes the alkyl iodide (SN2), a tertiary group does so by SN1, and anisole gives phenol + CH₃I. The –OCH₃ group in anisole directs ring substitution to ortho and para.

8. Aldehydes, Ketones and Carboxylic Acids

Aldehydes and ketones · Carboxylic acids

Aldehydes and Ketones: Structure, Preparation and Reactions – Aldehydes and ketones both have a carbonyl group, C=O. In an aldehyde the carbonyl carbon has at least one H on it (−CHO). In a ketone it has two carbon groups (−CO−). The C=O bond is polar: carbon is slightly positive, oxygen slightly negative. So electron-rich particles (nucleophiles) attack the carbon. This one idea explains most of their reactions: addition of HCN, NaHSO₃, alcohols and ammonia derivatives. Aldehydes are easy to oxidise (Tollens and Fehling tests), ketones are not. A hydrogen on the carbon next to C=O (α-H) is slightly acidic, which gives aldol condensation. Aldehydes with no α-H give the Cannizzaro reaction instead.
Carboxylic Acids: Carboxyl Group, Acidity and Reactions – A carboxylic acid has the carboxyl group, −COOH: a C=O and an O−H on the same carbon. It can give away H⁺, and the ion left behind (carboxylate, −COO⁻) is stable because its negative charge is shared equally by two oxygen atoms. That is why these acids are stronger than phenols and alcohols (but weaker than mineral acids like HCl). Groups that pull electrons (Cl, F, NO₂) make the acid stronger; groups that push electrons (alkyl) make it weaker. We make carboxylic acids by oxidising alcohols, aldehydes or alkylbenzenes, by hydrolysing nitriles, esters and amides, or from Grignard reagents and CO₂. Their key reactions: salt formation with NaHCO₃ (CO₂ fizz), esterification, acid chloride and anhydride formation, reduction to alcohols, decarboxylation and the HVZ reaction.

9. Amines

Amines · Diazonium salts

Amines: Structure, Naming, Preparation, Basicity and Reactions – An amine is ammonia with one, two or three H atoms swapped for carbon groups. The N keeps a lone pair, so amines are bases and nucleophiles. Count the C atoms on N to get 1°, 2° or 3°. Make them by reducing nitro compounds, nitriles or amides, from alkyl halides + NH₃, by Gabriel (1° only) or Hofmann bromamide (one C fewer). Alkyl groups push electrons and raise basicity; the ring in aniline pulls the pair away and lowers it. Key reactions: salts with acids, acylation, carbylamine test (1°), Hinsberg test (1°/2°/3°), nitrous acid and ring substitution in aniline.
Diazonium Salts: Preparation, Properties and Use in Making Aromatic Compounds – A diazonium salt is Ar–N₂⁺X⁻, e.g. benzenediazonium chloride C₆H₅N₂⁺Cl⁻. It is made by diazotisation: aniline + NaNO₂ + HCl at 273–278 K. It is stable only in the cold and is used at once. On warming, N₂ gas (a great leaving group) escapes. Two kinds of reactions: (1) N₂ is replaced by Cl, Br, CN (Sandmeyer/Gattermann), I (KI), F (HBF₄), H (H₃PO₂) or OH (warm water); (2) N₂ is kept and the ion couples with phenol or aniline to give coloured azo dyes. This lets us put groups on a benzene ring that cannot be added directly.

10. Biomolecules

Carbohydrates · Proteins and enzymes · Vitamins, nucleic acids, hormones

Carbohydrates: Classification, Glucose, Disaccharides and Polysaccharides – Carbohydrates are sugars and the big molecules made from sugars. Chemically they are polyhydroxy aldehydes or ketones (many –OH groups plus one C=O), or things that give these on hydrolysis. We sort them by how many sugar units they have: one (monosaccharide), two to ten (oligosaccharide) or many (polysaccharide). Glucose is an aldose with six carbons; fructose is a ketose. Two units join by a glycosidic (–O–) bond to give disaccharides like sucrose, maltose and lactose. Hundreds join to give starch, cellulose and glycogen.
Proteins and Enzymes: Amino Acids, Peptide Bond, Structure and Denaturation – Proteins are long chains of amino acids. Each amino acid has an amino group (–NH₂), an acid group (–COOH), a hydrogen and a side group R on one carbon. The –COOH of one amino acid joins the –NH₂ of the next, losing water, to make a peptide bond (–CO–NH–). The order of amino acids is the primary structure; coils and sheets are the secondary structure; the full 3D fold is the tertiary structure; several chains together make the quaternary structure. Heat, acid or alcohol can undo the folds (denaturation). Enzymes are mostly proteins that speed up reactions in the body.
Vitamins, Nucleic Acids and Hormones: Types, Roles, DNA and RNA – Vitamins are small organic compounds we need in tiny amounts from food; A, D, E, K dissolve in fat and B, C dissolve in water, and a lack of each causes a known disease. Nucleic acids (DNA and RNA) are long chains of nucleotides. Each nucleotide = a pentose sugar + a phosphate + a nitrogen base. DNA has deoxyribose, bases A, G, C, T and two strands in a double helix, where A pairs with T and G with C. RNA has ribose, U instead of T and usually one strand. Hormones are chemical messengers made by glands, and can be steroids, proteins/peptides or amino acid derivatives.

11. Formative-only topics

Surface chemistry · Isolation of elements · Polymers · Chemistry in everyday life

Colloids and Dispersed Systems – A dispersed system is one substance spread as small bits (the dispersed phase) through another (the dispersion medium). By particle size it is a true solution (below about 1 nm), a colloid (about 1–100 nm) or a suspension (above about 100 nm). Colloid particles are too small to see or to settle, but big enough to scatter light, so a beam passing through shows its path: the Tyndall effect. Colloids are grouped by the states of the two phases (fog, smoke, milk, foam, gel). Colloid particles often carry the same charge and repel each other; adding an electrolyte cancels the charge, so they clump and settle: coagulation.
Metallurgy: From Metallic Bond to Getting Metals Out of Ores – Metals are made of positive ions held in a sea of free electrons. This metallic bond explains why they shine, conduct and bend. Most metals are found in rocks as compounds called ores. Metallurgy is the science of getting a pure metal out of its ore: first concentrate the ore, then turn the compound into metal by heat (pyrometallurgy), by solutions (hydrometallurgy) or by electricity (electrometallurgy), then refine it. The more reactive a metal is, the harder it is to extract and the faster it corrodes.
Polymers – A polymer is a giant molecule made by joining many small molecules (monomers) into a long chain. In addition polymerisation, monomers with a C=C double bond open up and link with nothing lost (ethene → poly(ethene)). In condensation polymerisation, two kinds of monomer with reactive groups at both ends join and give off a small molecule such as water at every link (nylon, polyester). Nature makes polymers too: starch, cellulose, proteins, DNA, rubber. Separate chains give thermoplastics that melt and can be recycled; cross-linked chains give thermosets that never melt. Most plastics do not rot, so we must reduce, reuse and recycle them.
Chemistry in Everyday Life: Medicines, Food, Cleaning and Soil – Chemistry is at work in your home every day. Antacids are weak bases that calm extra stomach acid. Medicines are grouped by what they do: painkillers, antibiotics, antiseptics, antihistamines, tranquilisers. Food chemicals keep food safe and tasty: preservatives, antioxidants and sweeteners. Soap cleans because one end of its molecule loves water and the other loves oil. Farmers add lime to acid soil and fertilisers to feed crops. Some metal ions are needed by the body, others are toxic, which is one reason we recycle.