Curriculum
Chemistry
Chapter 1 - Transition Elements and Iron Metallurgy
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1.1Where they are in the periodic table1.2The main transition elements (d-block)1.3The four transition series1.4Economic importance of the first-series elements1.5Electron configurations of the first series1.6Rules for filling1.7Configurations of the common ions1.8Why Fe(II) is easily oxidized to Fe(III) but Mn(II) is not1.9Oxidation-state rules for the series1.10Calculating oxidation states in compounds1.11Definition of a transition element
Chapter 2 - Chemical Analysis
0/221.1Revision of concepts and laws needed in this chapter1.2Importance1.3Kinds of analysis1.4Qualitative analysis1.5A. Identification of acid radicals (anions)1.6(1) Dilute hydrochloric acid group1.7(2) Concentrated sulphuric acid group1.8(3) Barium chloride group1.9Practical differentiation between pairs of salts (typical exam type)1.10Reasoning questions1.11Detailed Comparison Matrix: Diagnostic Silver Nitrate (AgNO3) Confirmatory Matrix
Chapter 3 - Chemical Equilibrium
0/221.1The equilibrium system1.2Types of chemical reactions1.3Chemical equilibrium1.4Rate of reaction1.5Factors affecting the rate of a reaction1.6Nature of the reactants1.7Concentration and the law of mass action1.8Temperature — collision theory1.9Pressure1.10Le Chatelier's principle1.11Catalysts1.12Light
2.1Strong and weak electrolytes2.2Hydronium ion2.3Definitions2.4Ostwald's dilution law2.5Hydronium ion concentration of a weak acid2.6Hydroxide ion concentration of a weak base2.7Ionization of water and the ionic product Kw2.8pH and pOH2.9Solubility and solubility product2.10Summary of key relations
Chapter 4 - Electrochemistry
0/331.1The starting experiment: zinc in copper sulphate1.2The idea behind the galvanic cell1.3Construction of the Daniell cell1.4What happens at each electrode1.5When does the current stop?1.6The salt bridge — what it is and why it is needed1.7Why we need a reference1.8The standard hydrogen electrode1.9Standard electrode potentials1.10Measuring an electrode potential (idea of the experiment)1.11Definition1.12What the series tells us (the conclusions to know)1.13Calculating the cell emf1.14Cell notation (cell diagram)
3.1The electrolytic cell3.2Example: electrolysis of copper(II) chloride solution3.3First law3.4Second law3.5The faraday3.6The working formula3.7Worked examples3.8Electroplating3.9Extraction of aluminium3.10Electrorefining of copper3.11Galvanic cells versus electrolytic cells3.12Scientists and the value of electrochemistry
Chapter 5 - Organic Chemistry
0/721.1Historical background1.2Modern definition1.3Why are there so many organic compounds?1.4Comparison: organic and inorganic compounds1.5Molecular formula1.6Structural formula1.7Isomerism1.8Detecting carbon and hydrogen in an organic compound1.9Classification of hydrocarbons1.10Structure and the homologous series1.11Alkyl radicals (R–)1.12IUPAC nomenclature of alkanes1.13Methane — occurrence and preparation1.14Physical properties1.15Chemical properties of alkanes
5.1Functional groups5.2Alcohols and phenols — the difference5.3Nomenclature of alcohols5.4Classification of alcohols5.5Ethanol — preparation5.6Denatured (methylated) alcohol — "red spirit"5.7Physical properties5.8Chemical properties of ethanol5.9Uses of alcohols5.10Phenols5.11Preparation5.12Physical properties5.13Chemical properties5.14Tests for phenol
6.1The carboxyl group6.2Types6.3Nomenclature6.4Preparation of acetic acid6.5Physical properties6.6Chemical properties6.7Aromatic acids: benzoic acid6.8Important acids and their uses6.9Definition and formation6.10Nomenclature6.11Preparation6.12Physical properties6.13Chemical properties6.14Applications of esters6.15Aspirin6.16Types of organic reactions (summary)6.17Revision key points for Part B
7.1The birth of organic chemistry and the vital-force theory7.2Why organic compounds are so abundant7.3Organic versus inorganic compounds7.4Molecular formula, structural formula and isomers7.5Detecting carbon and hydrogen in an organic compound7.6Hydrocarbons and the alkane series7.7The alkyl radical and IUPAC naming7.8Methane, physical and chemical properties of alkanes7.9Practice with answers7.10Ministry exam traps
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Text lesson
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins)
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins)
Overview
Overview
🌳 Concept tree
- Unsaturated Hydrocarbons – Alkenes (Olefins)
- ├── Structure
- ├── Nomenclature
- ├── Laboratory preparation of ethene
- ├── Physical properties
- └── Chemical properties of alkenes
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins) · 1 / 7
Structure
Structure
- Alkenes are unsaturated open-chain hydrocarbons containing at least one C=C double bond.
- The double bond consists of one strong sigma (σ) bond and one weaker pi (π) bond, which is easily broken — this is why alkenes are much more reactive than alkanes.
- They may be considered alkanes minus two hydrogen atoms; general formula CₙH₂ₙ (n ≥ 2).
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins) · 2 / 7
Nomenclature
Nomenclature
- Take the longest chain containing the double bond; replace -ane by -ene.
- Number from the end nearer the double bond (whatever other groups there are), and put the number of the first carbon of the double bond before the name.
- Substituents are named and numbered as for alkanes.
Examples: CH₂=CH–CH₃ propene; CH₃–CH=CH–CH₂–CH₃ 2-pentene; CH₂=CH–CH(CH₃)–CH₂–CH₃ 3-methyl-1-pentene; CH₂=CH–CH₂–CH₂Cl is 4-chloro-1-butene; (CH₃)₂C=CH₂ 2-methylpropene (isobutene). The common name of ethene is ethylene.
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins) · 3 / 7
Laboratory preparation of ethene
Laboratory preparation of ethene
By dehydration of ethanol→heat ethanol with concentrated sulphuric acid at about 180 °C:
C₂H₅OH —(conc. H₂SO₄, 180 °C)→ CH₂=CH₂ + H₂O
- It occurs in two steps:
- CH₃CH₂OH + HOSO₃H → CH₃CH₂–OSO₃H (ethyl hydrogen sulphate) + H₂O
- CH₃CH₂–OSO₃H (heat) → CH₂=CH₂ + H₂SO₄ (the acid is regenerated, so it acts as a catalyst/dehydrating agent)
Apparatus→flask with ethanol/acid mixture (sand or pumice stones added to prevent bumping) → delivery tube → wash bottle with NaOH solution (removes SO₂ and CO₂ formed in side reactions) → collect ethene over water. If the temperature is only 140 °C the product is diethyl ether instead (see alcohols).
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins) · 4 / 7
Physical properties
Physical properties
- The first alkenes (C₂–C₄) are gases; C₅–C₁₅ are liquids; above C₁₅ solids.
- They are non-polar, insoluble in water, soluble in organic solvents such as ether, benzene and CCl₄.
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins) · 5 / 7
Chemical properties of alkenes
Chemical properties of alkenes
- (exothermic): C₂H₄ + 3O₂ → 2CO₂ + 2H₂O + energy. (Alkenes burn with a smokier flame than alkanes because of the higher carbon percentage.)
- The weak π bond breaks, and each carbon of the double bond picks up one atom or group; the product is saturated.
- CH₂=CH₂ + H₂ → CH₃–CH₃ (ethane). Each π bond needs one mole of H₂.
- CH₂=CH₂ + Br₂ (in CCl₄) → CH₂Br–CH₂Br (1,2-dibromoethane). The red-brown colour of bromine disappears, so this is a test for unsaturation.
- CH₂=CH₂ + HBr → CH₃CH₂Br (bromoethane).
- For a symmetrical alkene (e.g. ethene) H may go to either carbon — one product.
- For an unsymmetrical alkene (e.g. propene) there are two possible products; Markovnikov’s rule decides: when an unsymmetrical reagent (HX or H–OSO₃H) adds to an unsymmetrical alkene, the positive part (H) adds to the double-bond carbon that already carries more hydrogen atoms and the negative part adds to the carbon with fewer hydrogens.
CH₃–CH=CH₂ + HBr → CH₃–CHBr–CH₃ (2-bromopropane, the major product). - water alone is not able to add (its H–OH bond is too weakly polar to attack the double bond), so a strong acid is needed:
- CH₂=CH₂ + H–OSO₃H → CH₃CH₂–OSO₃H (ethyl hydrogen sulphate)
- CH₃CH₂OSO₃H + H₂O → CH₃CH₂OH + H₂SO₄
- CH₂=CH₂ + H₂O —(H₃PO₄ or H₂SO₄)→ CH₃CH₂OH. Industrially, ethene is hydrated with steam in the presence of phosphoric acid (catalyst) at high temperature and pressure.
- Cold dilute alkaline potassium permanganate (KMnO₄ + Na₂CO₃) oxidises alkenes to glycols (diols): the purple colour disappears (a brown MnO₂ precipitate appears). This is used to detect a double bond.
- CH₂=CH₂ + [O] + H₂O → HOCH₂–CH₂OH (ethylene glycol, 1,2-ethanediol)
- it forms hydrogen bonds with water molecules and prevents them from joining into ice crystals, lowering the freezing point.
- Polymerisation. A polymer (Greek: "many parts") is a very large molecule built from many small repeating units called monomers.
- is the joining of many unsaturated monomer molecules without losing any atoms.
- When ethene is heated under very high pressure (about 1000 atm) with a peroxide initiator, its π bonds open, each carbon gets a free electron, and the molecules join in a long chain: n CH₂=CH₂ → –(CH₂–CH₂)ₙ– polyethylene (polythene). Though ethene has M = 28, polyethylene may have a molecular mass of tens of thousands.
- PVC (polyvinyl chloride) from chloroethene CH₂=CHCl; Teflon (polytetrafluoroethene, PTFE) from CF₂=CF₂, non-stick and chemically very resistant; polypropene from propene CH₃CH=CH₂.
- A copolymer is formed from two different monomers (the copolymer unit then continues the polymerisation).
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins) · 6 / 7
Part 7
Part 7
- 📖
🔍 In-Depth Explanations, Deductions & Multi-Book Insights:
Chemistry Thanaweya Amma (2026/2027)
- Lesson 2 – Unsaturated Hydrocarbons – Alkenes (Olefins)
- Detailed Academic Lesson Overview:
- Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond (C=C, consisting of one strong σ bond and one weak π bond, general formula CnH2n).
- They undergo characteristic addition reactions governed by Markovnikov's rule.
🌳 Hierarchy Classification & Conceptual Roadmap
Alkenes (Olefins – CnH2n)
├── 1. Laboratory Preparation of Ethene (C2H4)
- │ └── Dehydration of Ethanol (C2H5OH) using conc. H2SO4 at 180°C via ethyl hydrogen sulfate
├── 2. Addition Reactions across Double Bond
| Comparison aspect | Main idea | Keywords |
|---|---|---|
| │ ├── Hydrogenation (Ni catalyst at 150-300°C) | C2H4 + H2 → C2H6 (Hardening of vegetable oils) | C2H4C2H6Hardeningvegetable |
| │ ├── Halogenation | Addition of Br2 dissolved in CCl4 (Red color of bromine discharges) | AdditiondissolvedCCl4color |
| • | │ ├── Hydrohalogenation (HX addition) | Hydrohalogenationaddition |
| │ │ ├── Symmetrical alkenes | Any carbon receives H | carbonreceives |
| │ │ └── Unsymmetrical alkenes |
| MarkovnikovRuleaddsrich |
| │ └── Catalytic Hydration | C2H4 + H2O (dil. H2SO4 at 110°C) → C2H5OH | C2H4H2SO4C2H5OH |
| • | └── 3. Oxidation & Baeyer's Test and Polymerization | OxidationBaeyerTestPolymerization |
| ├── Baeyer's Test | Ethene + alkaline KMnO4 → Ethylene glycol (turns purple KMnO4 colorless) | EthenealkalineKMnO4Ethylene |
| └── Addition Polymerization |
| C2H4HighcatalystPolyethylene |
| • | 📋 Master Teacher's Blackboard Rules & Exam Secrets | MasterTeacherBlackboardRules |
| RULE 1 |
| Markovnikovasymmetricreagentlike |
| RULE 2 |
| BaeyertestalkalineKMnO4 |
| RULE 3 |
| Ethyleneglycolethanediolused |
| 📊 Detailed Comparison Matrix | Diagnostic Tests for Carbon-Carbon Double Bonds | DiagnosticTestsCarbonDouble |
| Reagent Used | Condition | Observation with Alkene (Ethene) | Observation with Alkane (Ethane) |
|---|---|---|---|
| Bromine in Carbon Tetrachloride (Br2 / CCl4) | Room temp, dark | Red bromine color discharges completely | Red color persists (No reaction) |
| Alkaline Potassium Permanganate (Baeyer's) | Aqueous alkaline solution |
|
Purple color persists |
| Acidic Hydration (H2O + H2SO4) | 110°C | Forms ethanol | No reaction |
Lesson 2: Unsaturated Hydrocarbons – Alkenes (Olefins) · 7 / 7
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