AQA Chem4: Carboxylic acids and Esters

Revision notes on carboxylic acids and esters from the organic section of AQA Chem4

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  • Created by: anna
  • Created on: 04-06-13 13:54

Carboxylic Acids

  • The functional group of carboxylic acids are -COOH and their ending is -oic acid
  • They are weak acids R-COOH <--> R-COO-  +  H+
  • To test for carboxylic acids use sodium carbonate or calcium carbonate
  • If a carboxylic acid is present effervescence (bubbles) is produced
  • Example: ethanoic acid + sodium carbonate --> sodium ethanoate + water + carbon dioxide
  • When dissolved in solution carboxylic acids form hydrogen bonds with water
  • Smaller carboxylic acids e.g. methanoic acid are more soluble as they have less carbon which isn't soluble in water
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Formation of esters:

  • carboxylic acid + alcohol --> ester + water
  • catalysed by H+ ions from concentrated H2SO4

Use of esters:

  • have characteristic sweet smells and are used as food flavourings
  • used as solvents
  • used as plasticisers - to increase plasticity of materials

Hydrolysis of esters:

  • can take place in acidic or alkaline solution (hot alkaline preferred)
  • esters are hydrolysed to alcohol and sodium salt of acid
  • RCOOR1 + NaOH --> RCOO-Na + R1OH
  • if you add dilute H2SO4 or HCl you can regenerate the carboxylic acid
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More about esters

Fats and Oils:

  • Fats and oils are esters of the alcohol propan-1,2,3-triol (glycerol)
  • They are triglycerides made of glycerol and 3 fatty acids
  • They are hydrolysed using hot NaOH to produce 3 moles of long chain acid and 1 mole of glycerol
  • Sodium stearate (C17H35COO-Na+) is produced which is used in the manufacture of soap
  • Rapeseed oil (a triglyceride ester) is used to make biodiesel
  • It is reacted with  methanol with a strong alkali catalyst to form glycerol and a mixture of methyl esters
  • The methyl esters are the biodiesel
  • Carbon Neutral: a process or series of processes in which as much CO2 from the air is taken in as given out
  • The advantage of biodiesel is that it is a renewable source of energy
  • The disadvantages of biodiesel are that it is expensive and uses large areas which could be used for food production
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