Topic 6: Global Challenges - Subtopic 2: Organic Chemistry
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What are alkanes?
• Saturated hydrocarbons • Only single bonds • C-C Functional Group
What is the general formula of the alkanes?
CₙH₂ₙ₊₂
How do physical properties change across alkanes?
• All colourless compounds • Gradual change as number of carbon atoms in chain increases
How reactive are alkanes and what reactions do they undergo?
• Generally unreactive compounds • Combustion reactions • Cracked into smaller more useful molecules
What are the alkanes and their molecular formulas?
• Methane: CH₄ • Ethane: C₂H₆ • Propane: C₃H₈ • Butane: C₄H₁₀ • Pentane: C₅H₁₂
When do hydrocarbons undergo combustion?
Presence of air
What does complete combustion in hydrocarbons occur to form?
• Excess Oxygen • Water and Carbon Dioxide Gas
Why do car engines lead to environmental factors?
• Not efficient, not all gasoline burns • Small amounts of unburnt hydrocarbons and CO and soot • CO₂, global warning contributor • Replacing with electric vehicles on-going challenge
What are alkenes?
• Unsaturated hydrocarbons • Contain double carbon bond • C=C Functional Group
What are the alkenes and their molecular formulas?
• Ethene: C₂H₄ • Propene: C₃H₆ • But-1-ene: C₄H₈ • Pent-1-ene: C₅H₁₀
What does being an unsaturated compound allow?
• Can make more bonds with other atoms • Opening up C=C bond and allowing incoming atoms to from another single bond with each carbon atom of functional group • Now form 4 single bonds instead of one double two single • Makes them much more reactive than alkanes
What occurs during incomplete combustion?
• More common for alkenes due to higher carbon to hydrogen ratio • Insufficient oxygen • Carbon Monoxide and Water Products or Carbon (C, soot) and Water • Smoky yellow flame
What are addition reactions?
• Atoms of a simple molecule add across the C=C double bond • Bond opens up, forming a single bond
What are hydrogenation reactions?
• When alkenes undergo addition reactions with hydrogen • Alkane formed • Occur at 150ºC, nickel catalyst • Used to manufacture margarine from vegetable oils • Polysaturated molecules partially hydrogenated to increase MR and turn oils into solid fats
What are halogenation reactions?
• When alkenes undergo addition reactions with halogens • Works for any halogen or alkene in which the halogen atom always add to the carbon atoms involved in the double bond • Occurs readily at room temp.
How can we tell alkenes and alkanes apart?
• Bromine Water Test • Alkane no change to water • Alkene orange to colourless • Due to presence of C=C, reacts in ways alkanes can’t
What are alcohols?
• Contain hydroxyl (-OH) functional group • Part of molecule responsible for their characteristic reactions • General formula CₙH₂ₙ₊₁OH
What are the first four alcohols?
• Methanol: CH₃OH • Ethanol: CH₃CH₂OH • Propanol: CH₃CH₂CH₂OH • Butanol: CH₃CH₂CH₂CH₂OH
What are physical properties of alcohols?
• Colourless Liquids • Dissolve in water to form neutral solutions
What are the first four alcohols commonly used as?
• Fuels • School labs use ethanol in spirit burners as it burns cleanly and without strong odours • Methanol and ethanol used extensively as solvents • Can dissolve many substance water cannot e.g. fats and oils
What do alcohols undergo combustion to form?
Carbon Dioxide and Water
What do alcohols undergo oxidation to produce?
• Carboxylic Acids, an organic acid • Achieved by heating alcohols with acidified potassium manganate
Why is [O] used?
Symbolic representation of an oxidising agent which simplifies equation
What are carboxylic acids?
• Homologous series of compounds with general formula CₙH₂ₙ₊₁COOH