π NEB Science | Grade 12
Complete Class 12 Chemistry Notes
NEB Syllabus 2082/2083
The most comprehensive, exam-ready chemistry notes for Nepal’s NEB Class 12 Science students β covering Physical, Inorganic, Organic, and Applied Chemistry with formulas, examples, and past-paper focus points.
Looking for the best Class 12 Chemistry Notes for the NEB board exam in Nepal? This guide covers the complete NEB Grade 12 Chemistry syllabus β from Physical Chemistry topics like Volumetric Analysis, Titration, Gravimetric Analysis, Acid-Base Theory, Ionization, and Solubility Product, to Inorganic and Organic Chemistry chapters β structured for maximum exam performance.
Whether you are preparing for your NEB Class 12 final exam, doing quick revision, or need a chapter-wise breakdown with formulas and key definitions, this page is your complete resource.
π NEB Class 12 Chemistry β Chapter Coverage
Physical Chemistry
11 chapters
Inorganic Chemistry
6 chapters
Organic Chemistry
10 chapters
Applied Chemistry
4 chapters
βοΈ Physical Chemistry
Physical Chemistry is the most formula-heavy section of the NEB Class 12 Chemistry syllabus and is consistently tested in board exams. It deals with the quantitative and thermodynamic aspects of chemical reactions.
01 Volumetric Analysis
02 Titration
03 Gravimetric Analysis
04 Acid & Base
05 Ionization
06 Solubility Product
07 Thermodynamics
08 Chemical Kinetics
09 Electrochemistry
Volumetric Analysis & Concentration of Solution
High WeightageVolumetric analysis is a quantitative analytical technique that determines the concentration of an unknown substance by measuring the volume of a known-concentration solution (standard solution) required to completely react with it.
Key Concepts: Equivalent Weight
The equivalent weight of an element is the number of parts by weight that combines with or displaces 1.008 parts of hydrogen, 8 parts of oxygen, or 35.5 parts of chlorine.
// Gram Equivalent Formula
No. of gram equivalents = Weight of substance / Equivalent weight
// Equivalent Weight of Acid = Molecular weight / Basicity
// Equivalent Weight of Base = Molecular weight / Acidity
// Equivalent Weight of Salt = Molecular weight / Total +ve valence
Concentration Units β Complete Summary
| Unit | Definition | Formula |
|---|---|---|
| Molarity (M) | Moles of solute per litre of solution | M = n/V(L) |
| Normality (N) | Gram equivalents per litre of solution | N = Eq/V(L) |
| Molality (m) | Moles of solute per kg of solvent | m = n/W(kg) |
| Mole Fraction (Ο) | Ratio of moles of one component to total moles | Ο = nβ/(nβ+n_b) |
| % by mass (w/w) | Grams of solute per 100 g of solution | (w_solute/w_solution)Γ100 |
| % by volume (v/v) | mL solute per 100 mL solution | (v_solute/v_solution)Γ100 |
// Relation: Normality β Molarity
N = M Γ n-factor
// Law of Equivalence (used in titration)
NβVβ = NβVβ
// Dilution Formula
MβVβ = MβVβ
β NEB Exam Tip
Questions on molarity, normality, and gram equivalents appear in every NEB board exam. Master the interconversion formula: N = M Γ n-factor. For acids, n-factor = basicity; for bases, n-factor = acidity; for salts, n-factor = total charge change.
Titration
NEB PracticalTitration is the process of determining the unknown concentration of a solution by reacting it with a standard solution until the equivalence point is reached, as indicated by a colour change at the endpoint.
Types of Titration
| Type | Reaction | Indicator Used | Example |
|---|---|---|---|
| Acid-Base | Neutralisation | Phenolphthalein, Methyl orange | HCl vs NaOH |
| Redox | Oxidation-Reduction | Self-indicating (KMnOβ) | KMnOβ vs FeSOβ |
| Precipitation | Precipitate formation | Potassium chromate | AgNOβ vs NaCl |
| Complexometric | Complex formation | Eriochrome Black T | EDTA vs CaΒ²βΊ |
Common Indicators & pH Ranges
| Indicator | pH Range | Colour Change (Acid β Base) | Used For |
|---|---|---|---|
| Phenolphthalein | 8.3 β 10.0 | Colourless β Pink | Strong acid vs Strong/Weak base |
| Methyl Orange | 3.1 β 4.4 | Red β Yellow | Strong acid vs Strong base |
| Methyl Red | 4.4 β 6.2 | Red β Yellow | Weak acid/base systems |
| Litmus | 5.0 β 8.0 | Red β Blue | General indicator |
// Core Titration Formula
NβVβ = NβVβ
// Example: Find concentration of HCl if 25 mL of 0.1N NaOH neutralises 20 mL HCl
N_HCl = (0.1 Γ 25) / 20 = 0.125 N
- Equivalence point: When moles of titrant exactly equal moles of analyte.
- Endpoint: The observed point (colour change) approximating the equivalence point.
- Primary standard: A pure, stable substance used to prepare standard solutions (e.g., oxalic acid, NaβCOβ).
- Back titration: Used when direct titration is impractical β excess reagent is added, then the excess is titrated.
β
Quick Revision Tip
In KMnOβ titrations, KMnOβ acts as its own indicator (purple β colourless β faint pink at endpoint). No external indicator is needed.
Gravimetric Analysis
NEB TheoryGravimetric analysis determines the amount of an analyte by measuring the mass of a precipitate or residue formed during a chemical reaction.
Steps in Gravimetric Analysis
- Preparation: Dissolve the sample in a suitable solvent.
- Precipitation: Add precipitating agent to convert analyte to insoluble form.
- Digestion: Heat the precipitate to make it filterable (Ostwald ripening).
- Filtration: Filter through fine filter paper or sintered glass crucible.
- Washing: Remove impurities from the precipitate.
- Drying/Ignition: Remove moisture; convert to a stable weighable form.
- Weighing: Determine the mass and calculate the analyte’s percentage.
// Gravimetric Factor (Chemical Factor)
Gravimetric Factor = Molar mass of analyte / Molar mass of precipitate
// Amount of analyte
Mass of analyte = Mass of precipitate Γ Gravimetric Factor
// Percentage of analyte
% analyte = (Mass of analyte / Mass of sample) Γ 100
π Key Difference
Volumetric analysis measures the volume of solutions. Gravimetric analysis measures the mass of a precipitate. Both are forms of quantitative analysis under the NEB Class 12 Chemistry syllabus.
Concept of Acid and Base
Very ImportantThe NEB Class 12 Chemistry syllabus covers three major theories of acid-base, essential for understanding ionisation, pH, buffers, and titrations.
Three Major Theories
| Theory | Acid | Base | Limitation |
|---|---|---|---|
| Arrhenius | Produces HβΊ in water | Produces OHβ» in water | Only aqueous; can’t explain NHβ as base |
| BrΓΈnsted-Lowry | Proton donor (HβΊ) | Proton acceptor | Doesn’t cover Lewis acid-base reactions |
| Lewis | Electron pair acceptor | Electron pair donor | Most general; no HβΊ concept needed |
pH Scale and Calculations
// pH Definition
pH = -log[HβΊ] pOH = -log[OHβ»]
pH + pOH = 14 (at 25Β°C)
// For Strong Acids
pH = -log(C) where C = concentration of acid
// For Weak Acids (using Ka)
[HβΊ] = β(Ka Γ C) pH = Β½(pKa – log C)
// Henderson-Hasselbalch (Buffer)
pH = pKa + log([Aβ»]/[HA])
Strong vs Weak Acids
| Property | Strong Acid | Weak Acid |
|---|---|---|
| Dissociation | Complete (100%) | Partial (Ξ± < 1) |
| Example | HCl, HβSOβ, HNOβ | CHβCOOH, HβCOβ, HF |
| Ka value | Very large | Small (e.g., 1.8Γ10β»β΅) |
| pH formula | pH = -log[C] | pH = Β½(pKa - log C) |
β οΈ Common Exam Mistake
Don’t confuse concentration with strength. A concentrated weak acid still has a higher pH than an equally concentrated strong acid. Strength = degree of dissociation, NOT concentration.
Ionization
NEB TheoryIonization refers to the process by which an electrolyte splits into its constituent ions in solution. The degree determines whether an electrolyte is strong or weak.
Ostwald’s Dilution Law
// For weak electrolyte AB β AβΊ + Bβ» (concentration C, degree Ξ±)
Ka = CΞ±Β² / (1 – Ξ±)
// For weak electrolytes (Ξ± << 1): Ka β CΞ±Β²
Ξ± = β(Ka/C)
// Degree of ionization INCREASES with dilution
Factors Affecting Degree of Ionization
- Nature of electrolyte: Strong electrolytes ionise completely; weak electrolytes partially.
- Dilution: Increasing dilution increases ionization (Ostwald’s Dilution Law).
- Temperature: Higher temperature generally increases ionization.
- Nature of solvent: Higher dielectric constant β greater ionization.
- Common ion effect: Adding a common ion decreases the degree of ionization.
// Ionic Product of Water
Kw = [HβΊ][OHβ»] = 1 Γ 10β»ΒΉβ΄ (at 25Β°C)
// In pure water: [HβΊ] = [OHβ»] = 1Γ10β»β· mol/L β pH = 7
// Conjugate pair relation: Ka Γ Kb = Kw
β Board Exam Focus
NEB frequently asks: (1) derivation of Ostwald’s Dilution Law, (2) degree of dissociation calculations given Ka and C, and (3) the conjugate acid-base pair relation: Ka Γ Kb = Kw.
Solubility Product (Ksp) & Buffer Solution
High WeightageThe solubility product (Ksp) is the equilibrium constant for the dissolution of a sparingly soluble ionic compound, quantifying the extent to which a compound dissolves in water.
Ksp Expressions
// AgCl(s) β AgβΊ(aq) + Clβ»(aq)
Ksp = [AgβΊ][Clβ»]
// Caβ(POβ)β β 3CaΒ²βΊ + 2POβΒ³β»
Ksp = [CaΒ²βΊ]Β³[POβΒ³β»]Β²
// Ksp β Molar Solubility (s)
AB type: Ksp = sΒ² ABβ type: Ksp = 4sΒ³ AβBβ type: Ksp = 108sβ΅
Precipitation Conditions
[AβΊ][Bβ»] > Ksp β Precipitation occurs
[AβΊ][Bβ»] = Ksp β Saturated (equilibrium)
[AβΊ][Bβ»] < Ksp β Unsaturated (no precipitation)
Buffer Solutions
A buffer solution resists pH changes when small amounts of acid or base are added. It consists of a weak acid and its conjugate base.
// Henderson-Hasselbalch Equation
pH = pKa + log([Salt]/[Acid])
// Buffer capacity is maximum when [Salt] = [Acid], i.e., pH = pKa
// Example: CHβCOOH/CHβCOONa β both 0.1M, pKa = 4.74
pH = 4.74 + log(1) = 4.74
- Acidic buffer: Weak acid + its sodium salt (e.g., CHβCOOH + CHβCOONa; pH < 7)
- Basic buffer: Weak base + its chloride salt (e.g., NHβOH + NHβCl; pH > 7)
- Blood buffer: HβCOβ/HCOββ» maintains blood pH between 7.35β7.45
Thermodynamics, Enthalpy & Chemical Kinetics
NEB Theory
// First Law of Thermodynamics
ΞU = q + w
// Enthalpy (constant pressure)
ΞH = ΞU + PΞV ΞH = qp
// Hess’s Law
ΞHrxn = Ξ£ΞHf(products) – Ξ£ΞHf(reactants)
// Gibbs Free Energy
ΞG = ΞH – TΞS
// ΞG < 0 β Spontaneous ΞG > 0 β Non-spontaneous
// Arrhenius Equation (Chemical Kinetics)
k = A Γ e^(-Ea/RT) ln(kβ/kβ) = (Ea/R)(1/Tβ – 1/Tβ)
π¬ Inorganic Chemistry
The Inorganic Chemistry section covers transition metals and heavy metals β commonly tested through short-answer and diagram-based questions in NEB board exams.
Transition Metals β Key Properties
- Variable oxidation states: Due to involvement of d-electrons (e.g., Fe: +2 or +3; Cu: +1 or +2).
- Coloured compounds: d-d electron transitions absorb visible light, giving transition metals their characteristic colours.
- Catalytic activity: Fe (Haber process), Pt (Contact process), VβOβ (HβSOβ manufacture).
- Complex formation: Available d-orbitals allow complex formation with ligands.
- Paramagnetic nature: Unpaired d-electrons make transition metals paramagnetic.
π§ͺ Organic Chemistry
Organic Chemistry is the largest section of NEB Class 12 Chemistry. Conversion reactions are heavily tested in every NEB board exam.
01 Haloalkanes
02 Haloarenes
03 Alcohols
04 Phenol
05 Ethers
06 Aldehydes & Ketones
07 Carboxylic Acid
08 Nitro Compounds
09 Amines & Aniline
10 Organometallic
Important Organic Reactions for NEB
Exam Critical| Reaction | Reactant | Product | Condition |
|---|---|---|---|
| Nucleophilic Substitution (SN2) | Haloalkane + OHβ» | Alcohol | Aq. KOH |
| Elimination (E2) | Haloalkane + OHβ» | Alkene | Alc. KOH, heat |
| Lucas Test | Alcohol + ZnClβ/HCl | Turbidity (speed varies) | Room temp |
| Fehling’s Test | Aldehyde + Fehling sol. | Brick-red precipitate | Heat |
| Tollens’ Test | Aldehyde + AgNOβ/NHβ | Silver mirror | Mild heat |
| Iodoform Test | Methyl ketone + Iβ/NaOH | CHIβ (yellow ppt) | Room temp |
| Diazotisation | ArNHβ + NaNOβ/HCl | Diazonium salt | 0β5Β°C |
β NEB Conversion Questions
NEB board exams frequently ask 5β10 mark conversion questions. Common examples: Benzene β Aniline β Chlorobenzene, Ethanol β Acetic Acid β Acetaldehyde, Methane β CHβCl β Methanol.
π Applied Chemistry
Nuclear Chemistry β Key Points
// Radioactive Decay Law
N = Nβ Γ e^(-Ξ»t)
// Half-Life Formula
tΒ½ = 0.693 / Ξ»
// Mass-Energy Equivalence
E = mcΒ²
// Ξ± decay: A β A-4, Z β Z-2
// Ξ² decay: A unchanged, Z β Z+1
// Ξ³ emission: No change in A or Z (energy release only)
NEB Class 12 Chemistry β Exam Strategy
High-Priority Topics (Maximum NEB Marks)
| Topic | Expected Marks | Priority |
|---|---|---|
| Volumetric Analysis + Titration (calculations) | 10β15 | π΄ Must |
| Organic Chemistry Conversions | 10β15 | π΄ Must |
| Acid-Base + pH Calculations | 8β10 | π΄ Must |
| Solubility Product + Buffer | 6β8 | π High |
| Thermodynamics + Kinetics | 6β8 | π High |
| Transition Metals + Heavy Metals | 8β10 | π‘ Medium |
| Ionization + Ostwald’s Law | 4β6 | π‘ Medium |
| Nuclear Chemistry | 4β5 | π’ Standard |
β
Study Plan Recommendation
Spend 40% of your time on Physical Chemistry (especially calculations), 35% on Organic (conversions + reactions), and 25% on Inorganic + Applied. Revise formulas daily using flashcards.
Frequently Asked Questions (FAQ)
Common questions from NEB Class 12 Chemistry students in Nepal:
What are the main topics in NEB Class 12 Chemistry?
NEB Class 12 Chemistry covers four main units: Physical Chemistry (Volumetric Analysis, Titration, Gravimetric Analysis, Acid-Base, Ionization, Solubility Product, Thermodynamics, Kinetics, Electrochemistry), Inorganic Chemistry (Transition Metals and Heavy Metals), Organic Chemistry (Haloalkanes, Alcohols, Aldehydes, Amines, etc.), and Applied Chemistry (Cement, Paper, Nuclear Chemistry).
What is the difference between molarity and normality in Class 12 Chemistry?
Molarity (M) is the number of moles of solute per litre of solution, while Normality (N) is the number of gram equivalents of solute per litre of solution. They are related by: N = M Γ n-factor, where n-factor is basicity for acids and acidity for bases.
What is Ksp in NEB Class 12 Chemistry?
Ksp (solubility product) is the equilibrium constant for the dissolution of a sparingly soluble ionic compound. It is used to predict whether precipitation will occur and is important for topics like the common ion effect and buffer solutions.
Which chapters are most important for the NEB Class 12 Chemistry board exam?
The highest-weightage topics are: Volumetric Analysis and Titration (numerical calculations), Organic Chemistry Conversions, Acid-Base and pH calculations, and Solubility Product. These typically carry 40β50% of the total marks.
What is a buffer solution and its formula?
A buffer solution resists pH change upon addition of small amounts of acid or base. It is made from a weak acid and its conjugate base. The pH is calculated using the Henderson-Hasselbalch equation: pH = pKa + log([Salt]/[Acid]).
What is Ostwald’s Dilution Law?
Ostwald’s Dilution Law states that the degree of dissociation (Ξ±) of a weak electrolyte increases with dilution. Mathematically: Ka = CΞ±Β²/(1-Ξ±), which simplifies to Ξ± = β(Ka/C) for weak electrolytes where Ξ± is small.
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