EQ3 Determination of the Equilibrium Constant for Esterification -

it wasattach to a water cooled reflux condenser. The condenser was then heatunder reflux for 1 hour. The flask and its contents was cooled in aniced water bath. Then 1.00 cm3 sample was pipetted out from the flaskand was titrated with the 0.5M NaOH.The flask was continuous heated under reflux for an additional 1/2hour, and was cooled after 1/2 hour. 1.00 cm3 sample was againpipetted out to go under titration with 0.5M NaOH. The refluxingprocess was repeated until the two titrations results’ different waswithin 0.2 cm3.Results and CalculationsVolume of ethanoic acid used:0.25 x 60.05 / 1.05 = 14.3 cm3Volume of propan-1-ol used:0.25 x 60.1 / 0.8 = 18.8 cm31st titration2ndtitration3rd titration4th titrationInitial volume of NaOH (cm3)1.6517.4033.7539.5Final volume of NaOH (cm3)17.4033.7539.545.1Volume used15.7616.355.755.6Evaluate the equilibrium constant for the esterification, assumingthat all solutions are ideal.(i) Give the equation for the esterification reaction betweenethanoic acid and propan-1ol.(ii) How many moles of unreacted CH3COOH remain at the end of therefluxing?(iii) Calculate the concentrations of the other species present atequilibrium.(iv) Give the equilibrium expression for the reaction.(v) Calculate the equilibrium constant for the reaction.Ans.:(i). CH3COOH (aq) + CH3CH2CH2OH (aq)  H2O (l) + CH3COOCH2CH2CH3 (aq)(ii). CH3COOH (aq) + NaOH (aq)  CH3COONa (aq) + H2O (l)The average volume of NaOH used = (5.75+5.6)/2= 5.675 cm3No. of moles NaOH = 0.504 x 5.675 /1000= 2.8602 x 10-3 mol= No. of moles of CH3COOH remains(iii).CH3COOH (aq) + CH3CH2CH2OH (aq) H2O(l) + CH3COOCH2CH2CH3(aq)Start: 6.552 x 10-3 6.552 x 10-3 0 0At eqm:2.8602 x 10-3 2.8602 x 10-3 3.6918 x 10-3 3.6918 x 10-3[CH3COOH] at equilibrium = 2.8602 / 1 x 10-3= 2.8602 mol dm-3= [CH3CH2CH2OH][CH3COOH] at start = (0.504 x 13/1000) / 1 x 10-3= 6.552 mol dm-3[CH3COOCH2CH2CH3 (aq)] at equilibrium = 6.552 - 2.8602= 3.6918 mol dm-3(iv). Kc = [CH3COOCH2CH2CH3][H2O] / [CH3COOH] [CH3CH2CH2OH](v). Kc =3.6918 /2.8602 x 2.8602 = 0.4513 dm3 mol-1Questions1. What is the purpose of adding a small amount of concentrated H2SO4to the reaction mixture at the beginning of the experiment?It also acts as a positive catalyst to speed up the reaction byproviding an alternate pathway with lower activation energy. It wasused to correct the volume of CH3COOH.2. Why do we need to add anti-bumping granules to the reactantmixtures before refluxing?It is used to prevent the solution from boiling vigorously duringheating. Also propan-1-ol is a volatile solution; it will easily catchfire if it is boiled vigorously.3. Why should we keep on refluxing until the volume of the NaOH neededfor complete titration is constant (or more or less constant)?It can help us to make sure that the reaction has reached theequilibrium position. If the volume of NaOH needed is not constant, itmeans the concentration of ethanoic acid is still decreasing and,instant of the same; the forward rate is larger than the backwardrate. We need to keep on refluxing so the forward and backward ratesbecome the same.4. Explain what effect, if any, each of the following would have onyour determination of the equilibrium constant for the esterificationreaction:(i). The concentration of the sodium hydroxide solution is not knownexactly.The remained CH3COOH is then cannot be calculated as the NaOH is usedto titrate with it, and we cannot find the concentration, so that theequilibrium constant cannot be determined without the concentration ofSodium Hydroxide.(ii). 100 cm3 of ethanoic acid and 100 cm3 of propan-1-ol yield 190 cm3of solution, which yields 190 cm3 of product at equilibrium.The equilibrium constant remains unchanged. It is because the volumeof the ethanoic acid and propan-1-ol are used to calculate theconcentration of ethanoic acid and propan-1-ol respectively. When theconcentration of the ethanoic acid and propan-1-ol are increased, theconcentration of propyl ethanoate and water will also be increased. Asa result, there will have no change to the equilibrium constant.DiscussionsA summary of the main result============================The results of the 1st and the 2nd titration are not accurate. Thevolume of NaOH used to react with the reaction mixture is too largebecause it is at the beginning of the reaction. As the volume is usedto calculate the concentration of CH3COOH and CH3CH2CH2OH, the largerthe volume of NaOH, the larger the concentration of CH3COOH and CH3CH2CH2OHwill be calculated. Although the volume of NaOH used in the 1st andthe 2nd titration is larger than literature volume, both values arestill sensible. This is because the volume of the 2nd titration isslightly larger than that of the 1st titration. As about 8 drops ofconcentrated sulphuric acid was added to the reaction mixture afterthe 1st titration and before the 2nd, the concentration of acidcontent in the mixture is larger. So a larger amount of NaOH was usedto react with the acid.The results in the 3rd and the 4th titration are also reliable becausethe volume of NaOH used in the 4th titration is slightly larger thanthat in the 3rd titration and the different between two values arewithin 0.2 cm3. There exists a small difference because the mixturethat was titrated with NaOH in the 4th titration which had beenrefluxed for 1/2 hour is more than that in the 3rd titration. Thereflux condenser used to reduce the loss of mixture due to evaporationthrough condensation however the loss still existed. Besides, CH3COOHwould further react with CH3CH2CH2OH in the above 1/2 hour. Then theconcentration of acid content in the mixture would decrease; so asmaller amount of NaOH was used for the titration.An examination of the errors in the results===========================================The errors in the 1st and the 2nd titration were known by the changein colour of the solution. The colour changed from colourless to deeppink (nearly purple in colour). In this case, we knew that thereaction was further away from the equivalence point and too much NaOHsolution was added. Therefore the results of two titrations were notaccurate.Comparison of results with available literature value=====================================================The equilibrium constant in this experiment is different from theliterature value. This is because the results in the 3rd and the 4thtitrations are not accurate and the volume of NaOH used in bothtitrations is not accurate. And these inaccurate values are used tocalculate the concentration of the species in the mixture. And theconcentration values are used to calculate the equilibrium constant.When the concentrations of the species are inaccurate, the value ofthe equilibrium constant will also be inaccurate.Defects in the experiment and suggested improvements====================================================When we process the titration in this experiment, the NaOH solutionshould be added slowly to the reaction mixture. If there was a largeproportion of area of the solution turned to pink colour when the NaOHsolution is added and then back to colourless, the NaOH should beadded slowly by adding half drop of it.The end of the report