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Investigations FolioPreparation of an EsterReport
ResultsDistillation range:128 - 135CEster has a sweet odour.DiscussionReaction equation:Reflux procedureThe reactants must be heated for an extended period. This is a problem because the liquidsare volatile and so will evaporate and this will mean that not much product will form. Safetywill also be a problem. By heating under reflux conditions the vapours condense on the sidesof the water-cooled condenser so that the liquids fall back into the pear-shaped flask so thatno reactants or products are lost during the heating process.Isolation procedures1. Initial washing with waterAt the end of the heating period all reactants and products are present in the mixture.This is because the system reaches a state of chemical equilibrium and theconcentrations of all species remain unchanged. Washing with water will remove most ofthe water-soluble substances.The aqueous layer was identified by adding some distilled water and seeing which layerincreased in volume. This layer was removed and the ester layer left in the separatingfunnel.2. Washing with Na2CO3solutionAfter the washing with water there will still be traces of acid left in the ester layer. Thesecan be removed by reaction with Na2CO3.2H++ CO32-CO2+ H2O3. Final washing with waterThis removes any traces of water-soluble materials (such as the salts formed in the lastwashing) from the separating funnel.CH3COOH +pentyl ethanoateCH3CH2CH2CH2CH2-OH+ H2OCH3COOCH2CH2CH2CH2CH3
4. Stand over CaCl2CaCl2is a dehydrating agent and so removes any traces of water trapped in the esterlayer. There was so much water that it formed a new layer.5. DistillationDistillation allows the separation of liquids that have different boiling points as each liquidhas its own boiling point and the temperature only rises when that liquid has beencompletely boiled off. The ester had the highest boiling point and so was collected last.Poor YieldThis method results in a poor yield of ester because:the reaction was not refluxed for long enoughthe reaction reaches an equilibrium so that 100% product yield cannot be obtained –the concentrations of all species, reactants and products, will remain constanta little bit of ester is lost at every washing – some is let through the tap of theseparating funnel, with the aqueous layer.Modifications to improve yield of ester1.Reflux the reaction mixture for longer so that more reactants are converted intoproducts.2.An increased concentration of one of the reactants (eg, the acid) could be used topush the equilibrium to the right and so improve the yield of ester.3.The separating funnel could be used more carefully so that less ester gets throughwith the aqueous layers.Modifications to improve purity of esterThe preparation could be carried out more carefully to get a better boiling point and a clearerester.Safety hazards/precautions1.Safety glasses, and plastic apron were worn and any heating was done with a tinyflame and constant observation.2.When the mixture was shaken with Na2CO3solution a gas (CO2) formed in theseparating funnel and could have caused the tap or stopper to burst out and spill theliquids. The tap of the funnel was opened often to allow the gas to escape before itbuilt up badly. When the tap was opened it was turned away from people so that noliquids got onto their faces.