Chemistry - C3.5 - Organic Chemistry

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C3.5.1 - Structure of Alcohols, Carboxylic Acids a

  • Organic molecules - form basic living of things, all contain carbon - carbon atoms covalently bond to each other forming the backbone of many organic molecule series
  • Homologous series: series of molecules with general formula
  • Alcohols - function group: -O-H - one hydrogen atom from an alkane replaced with -O-H = alcohol, structure formula: CH3OH, CH3CH2OH, CH3CH2CH2OH
  • Carboxylic acids - function group: -COOH, structure formula: HCOOH, CH3COOH, CH3CH2COOH
  • Esters - function group: -COO-, stucture formula: CHOOCH3 (methyl methanoate), CH3COOCH2CH3 (ethyl ethanoate), CH3COOCH3 (methyl ethanoate)
  • Acid + alcohol Equilibrium symbol ( ester + water - acid = -oate, alcohol = -yl
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C3.5.2 - Properties and Uses of Alcohols

  • Alcohols with smaller molecules dissolve in water producing neutral solutions - many organic substances dissolve in alcohols: useful solvents - ethanol in alcoholic drinks
  • Alcohols burn in air - oroduce CO2 and H2O when burnt completely - useful fuels, eg. spirit burners or combustion engines or can be mixed with petrol
  • Sodium reacts with alcohols producing H2(g) - more vigarous with water
  • Acohols oxidised by addind chemical oxidising agents eg. potassium dichromate producing carboxylic acids - some microbes in air can oxidise solutions of ethanol producing ethanoic acid - turns alcoholic drinks sour and is main acid in vinegar
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C3.5.3 - Carboxylic Acids and Esters

  • Carboxylic acids - dissolve in water producing solutions of <pH7 - properties of typical acids, eg. fizz when added to carbonate, as CO2 forms, as well as a salt and H2O
  • Different from acids: react with alcohols to form esters, in presence of acid catalyst - eg. ethanol and ethanoic acid react when mixed with sulfuric acid as a catalyst, forming ethyl ethanoate and H2O
  • Esters - volatile compounds with distinctive smells - some have pleasant, fruity smells and are used as flavourings and in perfume
  • Carboxylic acids are weak acids: in aqueous solution, hydrochloric acid ionises (HCl(aq) -> H+(aq) + Cl-(aq)): strong acids - ethanoic acid doesn't ionise completely in aqueous solution (CH3COOH(aq) Equilibrium symbol ( CH3COO-(aq) + H+(aq)): weak acid - in aqueous solutions of equal concentration, have higher pH and react slower
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C3.5.4 - Organic Issues

  • Alcohols, carboxylic acids and esters are important organic chemicals used in foods, drinks as solvents and fuel for societies benefit
  • Can be disadvantages: alcoholic drinks and solvents can be abused, leading to health and social problems
  • Biofuel is a fossil fuel alternaive - may help with diminishing resources and climate change problems - crops grown for biofuels take up land that could be used to grow food
  • Advantages and disadvantages change over time or when new developments happen - monitoring and careful research required
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