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Determination of the equilibrium constant for esterification of ethanoic acid and propan-1-ol by using the method of titration.

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Introduction

IMMANUEL LUTHERAN COLLEGE S6 Chemistry Name: Lam Kong Lan ( 7 ) Experiment 12 : Determination of the equilibrium constant for esterification: ethanoic acid and propan-1-ol Title: Determination of the equilibrium constant for esterification of ethanoic acid and propan-1-ol by using the method of titration. Theory : In this experiment, we have to find out the equilibrium constant for esterfication by using the method of titration. The specific esterification reaction studied in this experiment is that between ethanoic acid (acetic acid) and propan-1-ol: CH3COOH (l) + CH3CH2CH2OH (l) CH3COOCH2CH2CH3 (l) + H2O (l) It is a homogeneous reaction with the same number of moles of reactants and products in the same phase (liquid phase). Moreover, it is a reversible and acid-catalyzed reaction. Since the reaction is slow at room temperature, the reaction is speeded up by the acid catalyst. The acid catalyst protonates the carbonyl group of the ethanoic acid making it more readily attacked by the nucleophilic oxygen of the alcohol. A molecule of water is then eliminated and the ester is formed. In this experiment, we use conc. H2SO4 as the acid catalyt and it doesn't take part in the overall reaction. And also, since it is a conc. acid, the water found in it was assumed to be small and thus can be neglected. In order to determine the equilibrium constant for this reaction, we should first find out the initial number of moles of the reactants and products, then carry out the reaction, until the equilibrium condition is reached and find the final number of moles of the reactants and products in the equilibrium position at last. At first, we have to titrate 1.00 cm3 of the mixture of the 0.2 mole of glacial ethanoic acid and 0.2 mole of ...read more.

Middle

of moles of ethanoic acid present in 1 cm3 of mixture at the beginning = no. of moles of NaOH = 0.0078 mole Relative molecular mass of ethanoic acid = 12�2 + 1�4 + 16�2 = 60 Volume of ethanoic acid in 1 cm3 mixture = 0.0078 X 60 /1.05 = 0.4457 cm3 Volume of propan-1-ol in 1 cm3 mixture = 1 - 0.4457 = 0.5543 cm3 No. of moles of propan-1-ol in 1 cm3 mixture = 0.5543 X 0.8/60 = 0.00739 mol From the second titration, No. of moles of NaOH added = 19.75 / 1000 � 0.4 = 0.0079 mole No. of moles of NaOH reacted with H2SO4 = ( 0.0079 - 0.0078 ) mole = 0.0001 mole ? the amount of of H2SO4 present in 1 cm3 of mixture is 0.0001 mole From the third titration, No. of moles of NaOH added = 6.85 / 1000 � 0.4 = 0.00274 mole No. of moles of NaOH reacted with CH3COOH = ( 0.00274 - 0.0001 ) mole = 0.00264 mole From equation (2), no. of moles of ethanoic acid remained unreacted in 1 cm3 of mixture at the end of reflux = no. of moles of NaOH = 0.00264 mole From equation (1), no. of moles of ester formed = no. of moles of water formed = no. of moles of ethanoic acid reacted = (0.0078 -0.00264 ) mole = 0.00516 mole From equation (1), no. of moles of propan-1-ol reacted = no. of moles of ethanoic acid reacted = 0.00516 mol CH3COOH (l) CH3CH2CH2OH(l) CH3COOC3H7 (l) H2O (l) Initial no. of moles 0.00780 0.00739 -- -- No. of moles at equil 0.00264 0.00223 0.00516 0.00516 Concentrations at equil 0.00217 � 1000 /1 = 2.64 M 0.00223 �1000 / 1 = 2.23 M 0.00516 �1000 / 1 = 5.16 M 0.00516 �1000 / 1 = 5.16 M Equilibrium expression for the reaction: ? ...read more.

Conclusion

Secondly, the flask should always be stoppered unless there is transferring of the reaction mixture. The transferring process should be done quickly and the flask should be stoppered at once after transferring. B. As the percentage of deviation would be smaller when using larger collected volumes of sample, we should use a larger volume of sample each time for titration, say 5 cm3, so that the results are far more reliable. At the same time, the initial volume of the reactants used should also be increased. C. As solidification may occur during cooling in an ice bath, the flask should be cooled by running water. However, sometimes solidification may still occur due to rapid cooling. Therefore, in order to cool down the flask as well as maintain the temperature of the reacture mixture back to the room temperature, the best method is to leave the flask behind until it is cooled down. Although it can ensure that it is at room temperature, it is time consuming. D. Instead of carrying out two titration to find out the amount of H2SO4 added, the volume of H2SO4 can be measured before adding to the reaction mixture. This can prevent the errors that have mentioned before which existed in making two titrations. In short conclusion, the experiment is not reliable and modification of the experiment is needed to obtain a more precise result. Modification of the experiment: 1. Use another method to determine the equilibrium constant for the reaction A. Gas Chromatography We can obtain the ester product by the method of distillation and usually the product isolated from the distillation is not 100% pure ester. Contaminants can include unreacted alcohol, water, and solvent. A gas chromatograph of the product will tell the actual percent ester in the distillation mixture. The concentration of the different species can then be known, thus the equilibrium constant can be found. ...read more.

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