Class 10 ICSE – Organic Chemistry: ALKYNES The Metal Mayur Gupta скачать в хорошем качестве

Class 10 ICSE – Organic Chemistry: ALKYNES The Metal Mayur Gupta

Class 10 ICSE – Organic Chemistry: ALKYNES (Metal Mayur Gupta style: topic-wise, exam-oriented description) ALKYNES – Topic per Description 1. Definition Alkynes are unsaturated hydrocarbons which contain at least one triple bond (–C≡C–) between two carbon atoms. 👉 General formula: CₙH₂ₙ₋₂ Example: Ethyne (Acetylene): C₂H₂ Propyne: C₃H₄ 2. Homologous Series Alkynes form a homologous series where: Successive members differ by –CH₂– They have similar chemical properties Physical properties show a gradual change 3. Nomenclature (ICSE level) Longest carbon chain containing triple bond is selected Suffix “-yne” is used Numbering starts from the end nearest to the triple bond Example: CH≡C–CH₃ → Propyne 4. Structure of Ethyne Each carbon atom is sp hybridised Bond angle = 180° (linear molecule) Contains: 1 σ bond 2 π bonds (in triple bond) 5. Preparation of Ethyne (Very Important) From Calcium Carbide Reaction: CaC₂ + 2H₂O → Ca(OH)₂ + C₂H₂ ↑ 📌 Lab method & industrial method – same reaction 6. Physical Properties Lower members are colourless gases Insoluble in water Soluble in organic solvents Highly inflammable 7. Chemical Properties of Alkynes (a) Combustion Ethyne burns with sooty flame due to high carbon content. 2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O (b) Addition Reactions (Key Property) Because of triple bond, alkynes undergo addition reactions. 1. Hydrogenation C₂H₂ + H₂ → C₂H₄ → C₂H₆ (Nickel catalyst) 2. Halogenation C₂H₂ + Br₂ → C₂H₂Br₂ 🔹 Bromine water is decolourised 3. Hydrohalogenation C₂H₂ + HCl → Vinyl chloride 8. Acidic Nature of Ethyne Ethyne is weakly acidic due to presence of terminal hydrogen. With Ammoniacal AgNO₃: Forms white precipitate of silver acetylide 📌 This test is used to distinguish ethyne from ethene & ethane 9. Uses of Ethyne Oxy-acetylene welding Artificial ripening of fruits Manufacture of plastics & synthetic rubber 10. Difference Based Questions (ICSE Favourite) Property Alkane Alkene Alkyne Saturation Saturated Unsaturated Unsaturated Bond Single Double Triple Formula CₙH₂ₙ₊₂ CₙH₂ₙ CₙH₂ₙ₋₂ Bromine water No effect Decolourises Decolour ALKYNES – Topic per Description 1. Definition Alkynes are unsaturated hydrocarbons which contain at least one triple bond (–C≡C–) between two carbon atoms. 👉 General formula: CₙH₂ₙ₋₂ Example: Ethyne (Acetylene): C₂H₂ Propyne: C₃H₄ 2. Homologous Series Alkynes form a homologous series where: Successive members differ by –CH₂– They have similar chemical properties Physical properties show a gradual change 3. Nomenclature (ICSE level) Longest carbon chain containing triple bond is selected Suffix “-yne” is used Numbering starts from the end nearest to the triple bond Example: CH≡C–CH₃ → Propyne 4. Structure of Ethyne Each carbon atom is sp hybridised Bond angle = 180° (linear molecule) Contains: 1 σ bond 2 π bonds (in triple bond) 5. Preparation of Ethyne (Very Important) From Calcium Carbide Reaction: CaC₂ + 2H₂O → Ca(OH)₂ + C₂H₂ ↑ 📌 Lab method & industrial method – same reaction 6. Physical Properties Lower members are colourless gases Insoluble in water Soluble in organic solvents Highly inflammable 7. Chemical Properties of Alkynes (a) Combustion Ethyne burns with sooty flame due to high carbon content. 2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O (b) Addition Reactions (Key Property) Because of triple bond, alkynes undergo addition reactions. 1. Hydrogenation C₂H₂ + H₂ → C₂H₄ → C₂H₆ (Nickel catalyst) 2. Halogenation C₂H₂ + Br₂ → C₂H₂Br₂ 🔹 Bromine water is decolourised 3. Hydrohalogenation C₂H₂ + HCl → Vinyl chloride 8. Acidic Nature of Ethyne Ethyne is weakly acidic due to presence of terminal hydrogen. With Ammoniacal AgNO₃: Forms white precipitate of silver acetylide 📌 This test is used to distinguish ethyne from ethene & ethane 9. Uses of Ethyne Oxy-acetylene welding Artificial ripening of fruits Manufacture of plastics & synthetic rubber 10. Difference Based Questions (ICSE Favourite) Property Alkane Alkene Alkyne Saturation Saturated Unsaturated Unsaturated Bond Single Double Triple Formula CₙH₂ₙ₊₂ CₙH₂ₙ CₙH₂ₙ₋₂ Bromine water No effect Decolourises Decolour