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  • Writer's pictureTerence Pang

Key points to take note for O Level Chemistry - Alkanes and Alkenes



Here are some important points to take note for O Levels chemistry Alkanes and Alkenes:


1. Alkanes are saturated hydrocarbons, while alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond. They are examples of what we term as homologous series (families of organic compounds that have the same general formula and functional group)


2. Alkanes and Alkenes have similar trend in physical properties. Their boiling and melting points increases as the molecular size increases. How about the viscosity and flammability?


3. The nomenclature rules for naming alkanes and alkenes are important to understand, including the use of prefixes and suffixes to indicate the number of carbon atoms and the presence of functional groups. 1 carbon hydrocarbon starts with meth- prefix, 2 carbon hydrocarbon starts with eth-prefix and so on.


4. Alkanes and Alkenes undergo complete combustion reactions with oxygen to produce carbon dioxide and water, releasing a large amount of energy. This process is used in engines and power generation. Incomplete combustion would produce carbon, and/or carbon monoxide (usually question would provide).


5. Alkenes can undergo addition reactions with hydrogen (hydrogenation), halogens (halogenation), and water (hydration) to form different types of organic compounds. What are the conditions? How do we make margarine from the process of hydrogenation?


6. The isomerism of alkanes and alkenes is important to understand, as it affects the physical and chemical properties of the compounds. Naming is important. For example, 2-3 dimethylbutane indicates 2 methyl groups bonded to the 2nd and 3rd carbon atom respectively in a main chain consisting of 4 carbon atoms.


7. The reactivity of alkanes and alkenes can be explained by the type of bonding present, with alkanes having strong single bonds and alkenes having a weaker double bond that is more reactive. Due to this property, alkenes are able to decolorise bromine water readily (bromination) while alkanes require UV light to do so and the reaction is slow.


8. The study of alkanes and alkenes is essential for understanding the basic principles of organic chemistry and provides a foundation for more complex organic compounds and reactions.


9. Alkenes can form alcohols due to hydration with conditions - 300 Deg Celcius, Phosphoric Acid, 60 atm. This process is much faster than fermentation of glucose.


10. Alkenes can also form polymers. The most common polymer is poly(ethene). Understanding of monomer and repeating unit is important.



Overall, it is important to have a strong understanding of the properties, nomenclature, reactivity (including conditions), and isomerism of alkanes and alkenes for success in the O Levels chemistry exam.


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