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(solved) Investigations Folio
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Added on 2020-06-05
(solved) Investigations Folio
Added on 2020-06-05
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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 liquids are volatile and so will evaporate and this will mean that not much product will form. Safety will 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 that no 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 the concentrations of all species remain unchanged. Washing with water will remove most of the water-soluble substances. The aqueous layer was identified by adding some distilled water and seeing which layer increased in volume. This layer was removed and the ester layer left in the separating funnel.2. Washing with Na2CO3 solutionAfter the washing with water there will still be traces of acid left in the ester layer. These can 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 last washing) from the separating funnel.CH3COOH + pentyl ethanoateCH3CH2CH2CH2CH2-OH+ H2OCH3COOCH2CH2CH2CH2CH3
4. Stand over CaCl2CaCl2 is a dehydrating agent and so removes any traces of water trapped in the ester layer. 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 liquid has its own boiling point and the temperature only rises when that liquid has been completely 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 enough the 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 the separating funnel, with the aqueous layer.Modifications to improve yield of ester1.Reflux the reaction mixture for longer so that more reactants are converted into products.2.An increased concentration of one of the reactants (eg, the acid) could be used to push 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 through with 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 tiny flame and constant observation.2.When the mixture was shaken with Na2CO3 solution a gas (CO2) formed in the separating funnel and could have caused the tap or stopper to burst out and spill the liquids. The tap of the funnel was opened often to allow the gas to escape before it built up badly. When the tap was opened it was turned away from people so that no liquids got onto their faces.
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