AQA Chem4: Carboxylic acids and Esters

• 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

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

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