CBSE Chemistry — Class 12 Chemistry Board Complete Chapter Guide

Chapter Overview & Weightage

Class 12 Chemistry is one of the most scoring subjects in CBSE boards — if you know where the marks are hiding. The syllabus has 16 chapters grouped into physical, inorganic, and organic chemistry. Total: 70 marks theory + 30 marks practical.

The 70-mark theory paper follows a predictable pattern. Physical chemistry (Solutions, Electrochemistry, Chemical Kinetics, Surface Chemistry) carries roughly 23 marks. Inorganic chemistry (d-f block, Coordination Compounds, p-block) carries around 19 marks. Organic chemistry (Haloalkanes, Alcohols, Aldehydes/Ketones, Amines, Biomolecules, Polymers, Chemistry in Everyday Life) takes the remaining 28 marks.

Unit	Topics	Approx. Marks
Unit 1	Solutions	5
Unit 2	Electrochemistry	9
Unit 3	Chemical Kinetics	5
Unit 4	d and f Block + Coordination	9
Unit 5	Haloalkanes & Haloarenes	6
Unit 6	Alcohols, Phenols, Ethers	4
Unit 7	Aldehydes, Ketones, Carboxylic Acids	6
Unit 8	Amines	4
Unit 9	Biomolecules + Polymers + Everyday Life	8

Year-by-year, CBSE has been remarkably consistent — Electrochemistry and Coordination Compounds are the two chapters that never disappoint in terms of high-weightage questions. Organic reactions (especially name reactions) appear every single year without fail.

Key Concepts You Must Know

Ranked by frequency — the first five are near-guaranteed to appear.

Physical Chemistry

Colligative properties — depression of freezing point, elevation of boiling point, osmotic pressure. Van’t Hoff factor for electrolytes is the twist CBSE loves.
Nernst equation — cell EMF calculation under non-standard conditions. Must know how to substitute and interpret sign of EMF.
Rate law and order of reaction — half-life formulas for first order and zero order. Pseudo-first order reactions come up regularly.
Kohlrausch’s law — molar conductivity at infinite dilution, especially for weak electrolytes.

Inorganic Chemistry

Coordination compounds — IUPAC naming (both complex and simple), EAN rule, isomerism (geometric and optical). Crystal Field Theory is asked every year.
d-block chemistry — why transition metals show variable oxidation states, magnetic properties (paramagnetism calculation), catalytic properties.
p-block — interhalogen compounds, oxoacids of sulphur and phosphorus (structures), anomalous behaviour of first elements (N, O, F).

Organic Chemistry

Name reactions — Aldol condensation, Cannizzaro reaction, Reimer-Tiemann, Kolbe’s reaction, Gabriel phthalimide synthesis, Hoffmann bromamide degradation. Make a dedicated list and memorise conditions.
Mechanism types — SN1 vs SN2, electrophilic addition, electrophilic aromatic substitution. Know which substrate favours which.
Distinction tests — Lucas test, Tollens’ test, Fehling’s test, Victor Meyer test. These appear as 2-3 mark questions repeatedly.
Polymers and Biomolecules — classification, monomers, linkage types. Pure memory — score these quickly.

Important Formulas

Relative lowering of vapour pressure:

\frac{P^\circ - P_s}{P^\circ} = x_2 = \frac{n_2}{n_1 + n_2}

Elevation of boiling point:

\Delta T_b = K_b \cdot m \cdot i

Depression of freezing point:

\Delta T_f = K_f \cdot m \cdot i

Osmotic pressure:

\pi = iCRT

When to use: Whenever a solute is dissolved in a solvent and you need to find any of the four colligative properties. The van’t Hoff factor $i$ = 1 for non-electrolytes, and $i > 1$ for electrolytes (use degree of dissociation to find exact $i$ ).

Nernst equation:

E_{cell} = E^\circ_{cell} - \frac{0.0591}{n} \log Q \quad \text{(at 298 K)}

Relationship between ΔG and EMF:

\Delta G^\circ = -nFE^\circ_{cell}

Kohlrausch’s law:

\Lambda^\circ_m = \nu_+ \lambda^\circ_+ + \nu_- \lambda^\circ_-

When to use: Nernst equation applies when concentrations are NOT 1 M (non-standard conditions). For equilibrium constant from EMF: use $\log K = \frac{nE^\circ}{0.0591}$ .

Integrated rate law (first order):

k = \frac{2.303}{t} \log \frac{[A]_0}{[A]_t}

Half-life (first order):

t_{1/2} = \frac{0.693}{k}

Half-life (zero order):

t_{1/2} = \frac{[A]_0}{2k}

Arrhenius equation:

k = Ae^{-E_a/RT} \quad \Rightarrow \quad \log\frac{k_2}{k_1} = \frac{E_a}{2.303R}\left(\frac{T_2 - T_1}{T_1 T_2}\right)

When to use: First-order half-life is independent of initial concentration — this is the key property CBSE uses in MCQs. When two rate constants at different temperatures are given, use the log form of Arrhenius.

For octahedral complexes:

Strong field ligands → large $\Delta_o$ → low spin → paired electrons → diamagnetic
Weak field ligands → small $\Delta_o$ → high spin → unpaired electrons → paramagnetic

Magnetic moment:

\mu = \sqrt{n(n+2)} \text{ BM}

where $n$ = number of unpaired electrons.

When to use: Any question asking about magnetic properties of a complex ion — first find oxidation state, write electronic configuration, apply ligand field strength, count unpaired $d$ -electrons.

Solved Previous Year Questions

PYQ 1 — Solutions (CBSE Board 2023, 3 marks)

Question: Calculate the boiling point of a solution of 18 g of glucose (M = 180 g/mol) dissolved in 1 kg of water. $K_b$ for water = 0.52 K·kg/mol.

Solution:

Moles of glucose = $\frac{18}{180} = 0.1$ mol

Molality = $\frac{0.1 \text{ mol}}{1 \text{ kg}} = 0.1$ m

\Delta T_b = K_b \times m = 0.52 \times 0.1 = 0.052 \text{ K}

Boiling point of solution = $100 + 0.052 = \mathbf{100.052°C}$

Glucose does not dissociate — it’s a non-electrolyte. So $i = 1$ and we don’t multiply by any van’t Hoff factor. If the solute were NaCl, we’d use $i = 2$ . This distinction trips up many students.

PYQ 2 — Electrochemistry (CBSE Board 2024, 5 marks)

Question: The standard electrode potentials of $\text{Zn}^{2+}/\text{Zn}$ and $\text{Cu}^{2+}/\text{Cu}$ are −0.76 V and +0.34 V respectively. (i) Write the cell reaction for the Daniell cell. (ii) Calculate $E^\circ_{cell}$ . (iii) Calculate $\Delta G^\circ$ (F = 96500 C/mol).

Solution:

(i) At anode (oxidation): $\text{Zn} \rightarrow \text{Zn}^{2+} + 2e^-$

At cathode (reduction): $\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}$

Overall: $\text{Zn} + \text{Cu}^{2+} \rightarrow \text{Zn}^{2+} + \text{Cu}$

(ii) $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode} = 0.34 - (-0.76) = \mathbf{+1.10 \text{ V}}$

(iii) $n = 2$ electrons transferred

\Delta G^\circ = -nFE^\circ = -2 \times 96500 \times 1.10 = \mathbf{-212300 \text{ J} = -212.3 \text{ kJ}}

The negative value confirms the reaction is spontaneous — which makes sense because $E^\circ_{cell}$ is positive.

PYQ 3 — Organic Chemistry: Name Reaction (CBSE Board 2022, 3 marks)

Question: Give the IUPAC name of the product formed when benzaldehyde undergoes Cannizzaro reaction. Also write the mechanism type.

Solution:

Cannizzaro reaction involves disproportionation — one molecule of benzaldehyde gets oxidised, another gets reduced.

2\text{C}_6\text{H}_5\text{CHO} \xrightarrow{\text{conc. NaOH}} \text{C}_6\text{H}_5\text{COONa} + \text{C}_6\text{H}_5\text{CH}_2\text{OH}

Products: sodium benzoate + benzyl alcohol (phenylmethanol).

IUPAC name of benzyl alcohol = phenylmethanol

Mechanism type = nucleophilic addition (hydride transfer)

Cannizzaro reaction occurs only with aldehydes that have NO alpha-hydrogen. Benzaldehyde, formaldehyde, trimethylacetaldehyde — these qualify. If alpha-H is present, Aldol condensation happens instead. CBSE has asked this distinction multiple times.

Difficulty Distribution

Difficulty	Questions	Marks	Examples
Easy	~40%	28 marks	Colligative properties calculation, polymer classification, distinction tests, name reactions
Medium	~40%	28 marks	Nernst equation, coordination compound naming + isomerism, organic synthesis 1-step
Hard	~20%	14 marks	Multi-step organic problems, Arrhenius calculation, CFT + magnetic moment combined

The 5-mark questions in Section D are usually either: (a) an electrochemistry numerical, or (b) an organic chemistry synthesis/conversion involving 2-3 steps. These are predictable. Practice 10 each from PYQs and you’ll be ready for anything they throw.

The “hard” 20% is mostly in the organic chemistry section — multi-step conversions. If you can’t crack those in the exam, don’t panic. The easy and medium questions will already give you 56+ marks.

Expert Strategy

How toppers approach this paper:

First, attempt inorganic chemistry (d-f block, coordination compounds, p-block) in the first 20 minutes — these are memory-based and give quick, clean marks. Don’t burn time here.

Physical chemistry numericals come next. Electrochemistry and kinetics questions have standard templates. If you’ve solved 15-20 PYQs from each, you’ll recognise the question type in seconds and know exactly which formula applies.

Make a “name reaction flashcard deck” — one side has the reaction name and conditions, other side has the substrate → product. Spend 10 minutes daily for the last 2 weeks before boards. Name reactions alone are worth 6-8 marks reliably.

Organic chemistry synthesis questions have a limited set of transformations tested at Class 12 level. The key conversions to master: alcohol → aldehyde → carboxylic acid → ester → amine (via Hoffmann degradation), and benzene → various substituted products. Build a “conversion map” on paper and pin it to your study table.

Time management in the exam:

Section A (MCQ/assertion-reason): 20 minutes max
Section B (2-mark short answers): 25 minutes
Section C (3-mark questions): 30 minutes
Section D (5-mark): 30 minutes
Section E (case-based): 15 minutes
Buffer: 10 minutes for revision

Common Traps

Trap 1 — Van’t Hoff factor confusion. For NaCl, $i = 2$ (dissociates into Na $^+$ and Cl $^-$ ). For BaCl $_2$ , $i = 3$ . For a weak acid like CH $_3$ COOH with 50% dissociation, $i = 1 + \alpha = 1.5$ . Many students use $i = 2$ for all electrolytes.

Trap 2 — Cell EMF formula. $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$ , NOT addition. The anode is where oxidation happens — the more negative standard potential. Students sometimes add both values and get a wrong answer.

Trap 3 — IUPAC naming of coordination compounds. The ligands are named in alphabetical order (ignoring “di”, “tri” prefixes). The metal’s oxidation state goes in Roman numerals in parentheses AFTER the metal name. Anionic complexes end in “-ate”. Example: $[\text{CoCl}_2(\text{en})_2]^+$ = dichlorobis(ethylenediamine)cobalt(III) ion — note “bis” not “di” because ethylenediamine is already a complex name.

Trap 4 — SN1 vs SN2. Tertiary carbons favour SN1 (stable carbocation, racemisation). Primary carbons favour SN2 (backside attack, inversion = Walden inversion). Secondary can go either way depending on solvent polarity. CBSE frequently gives a substrate and asks “which mechanism” — always look at carbon substitution first.

Trap 5 — Pseudo-first order reaction. When one reactant is in large excess, its concentration barely changes during the reaction. The rate law simplifies to first order in the other reactant. The classic example: hydrolysis of ester in excess water. If CBSE gives you rate = k[A][B] but [B] is very large and constant, you must write $k' = k[B]$ and call it pseudo-first order.

One last pointer: In organic chemistry, whenever a question says “write the mechanism”, show the curved arrows explicitly. CBSE marking schemes award marks for each step — a complete mechanism with arrow-pushing gets full marks even if you write nothing else. Practice drawing mechanisms, not just writing equations.