BY MOHAMED ALKHARUSI
GRADE 12 BIL
Esters have a very sweet fruity smell. Naturally occurring esters are found in fruits. An ester is a product of the reaction of an acid (usually organic) and an alcohol (the hydrogen of the acid R-COOH is replaced by an alkyl group R'). Esters mainly result from the condensation (a reaction that produces water) of a carboxylic acid and an alcohol. The process is called esterification. This reaction can be catalyzed by the presence of H+ ions. Sulphuric acid, H2SO4, is often used as a catalyst for this reaction. Esters have the general formula R-COOR.
Produce three different esters by using a range of carboxylic acids and alcohols. Determine the ester formed by using the smell given off by the products and the chemical equations for the three different reactions.
Ethanoic acid was used as the carboxylic acid for all three reactions. The alcohols used were ethanol, methanol and propanol. The reaction of ethanoic acid with ethanol will be discussed in detail and results and equations will be given for all three reactions.
1. Place 1 drop of concentrated sulphuric acid in a test tube 2.Add 10 drops of ethanoic acid (or propanoic acid) to the sulfuric acid in the tube. 3. Add 10 drops of ethanol (or other alcohol) to the mixture. 4. Put about 10 cm3 of water into the 250 cm3 beaker. Carefully lower the tube into the beaker so that it stands upright. 5. Heat the beaker gently on a tripod and gauze until the water begins to boil, then stop heating. 6. Stand for 1 minute in the hot water. If the mixture in the tube boils, use the tongs to lift it out of the water until boiling stops, then return it to the hot water. 7. After 1 minute, carefully remove the tube and allow it to cool. 8. When cool, pour the mixture into a test-tube half-full of 0.5 M sodium carbonate solution. There will be some effervescence. Mix well by pouring back into the specimen tube â€“ repeat if necessary. A layer of ester will separate and float on top of the aqueous layer. 9. Smell the product by gently wafting the odour towards your nose with your hand â€“ do not put your nose near the top of the tube! 10. Repeat this procedure for up to three more different esters. Compare the odours of the different esters prepared by your group and by other groups. Write word equations for each reaction, and (for advanced students) chemical equations using structural formulae.
Equipment Safety glasses test tubes dropping pipettes 250mL beaker test tube rack Bunsen burner heat resistant mat tripod gauze retort stand chemicals.
An ester is formed whenever a carboxylic acid reacts with an alcohol. In this first reaction, the alcohol used was ethanol and the carboxylic acid used was Ethanoic Acid. A small amount of concentrated H2 SO4 (Sulphuric Acid) was used as a catalyst. H2 SO4 is a dehydrating agent and removes water from the products. The alcohol (ethanol) loses OH and the carboxylic acid (ethanoic acid) loses a H. The method used for this reaction is only suitable for preparing small amounts and the ester formed in this reaction could only be characterised by odour.
Prior to mixing the solutions an equation was written for the reaction and ethyl ethanoate was predicted as being the ester that would be formed.
Once this reaction was complete, the ester could not be determined as the strong odour given off by unreacted ethanol made it impossible to smell the actual ester. The experiment was performed again with much care given to the accuracy of measurements. This time the ester formed could easily be smelt and group members agreed that the odour was very similar to nail polish remover. After some investigation, it was confirmed that the aroma given off by ethyl ethanoate is of nail polish remover (although some believe it to smell like pear)....