BACH 2114 KINETICS, MECHANISM, AND STEREOCHEMISTRYName : 1. Amirah Chan (15WAR08520) 2. Chey Sze Ying (15WAR09194) 3. Chong Khai En (15WAR08702) Group : RBS 2- Group 1 Date : 20-5-2015 Title: Experiment 1- Kinetics study of the hydrolysis of methyl acetate by acid-base titration. Aim : To determine the activation energy of the hydrolysis of methyl acetate by acid-base titration. Introduction: Hydrolysis occurs when the bond in a molecule is being broken down after addition of water. Acid – base – catalyzed hydrolyses is very common and it is used in the hydrolysis of ester such as methyl acetate. Hydrolysis occurs in a very low rate in pure water. Activation energy of the hydrolysis of methy acetate is required to be overcome by the reactants in order to complete the reaction. Thus, acid which produces hydrogen ion such as hydrochloric acid is used as a catalyst to increase the rate of reaction. As the rate of reaction is being increased, the activation energy is now being overcome. When methyl acetate reacts with water molecules, acetic acid and methyl alcohol will be formed as the products. The reaction is reversible and the rate constant, k of this reaction is relatively small. A large amount of water is present during the reaction so that there is a complete reaction towards the end of the experiment. In the hydrolysis of methyl acetate, the methyl acetate will take a hydrogen ion and the hydrogen ion will attached to one of the lone pairs on the oxygen which formed a double bond to the carbon. The carbon will then become electrophile and one of the lone pairs on the oxygen of water molecules will attack the electrophilic carbon. Then, the oxygen atom from the water molecule will be deprotonated. Methanol is now being produced. The hydrogen is being removed from the oxygen which attached to the electrophilic carbon. The products which are acetic acid and alcohol are then being produced. Schematic mechanism of hydrolysis of methyl acetate . 2481 71 39.50 6 32.Vt) 0 Titrant volume Vt (ml) 32.6225 31 37.91 2.81 2.10 32.00 15.60 9.60 15. 40oC 1 Titrant volume Vt (ml) 30.30 14.2481 t (min) .30 13.80 16.70 11.37 2.20 2 32.77 2.35 15.47 2.6225 21 35.60 9.11 2.20 Titration B) 1 – Room temperature V ∞ .47 2.7893 11 34.90 16.2481 51 39.Results: A) Standardization of sodium hydroxide solution Average volume used (ml) 1 Volume of NaOH used (ml) 32.17 3 32.30 14.27 2.60 9.20 15.7669 30 33.00 16.77 2.7606 40 34.50 15.6469 V∞ .57 2.Vt (ml) ln (V∞ .77 2.51 2.7979 20 33.7350 50 34.41 2.7220 60 34.8040 10 33.41 2.7120 80 35.47 2.21 2.Vt (ml) ln (V∞ .4310 41 39.9215 t (min) 2 – Water bath.30 13.6926 16 35.Vt) 18.06 2. 9141 at 35oC) M2 = molecular weight (74. 0.Calculation of V∞ : V∞ = Final volume per 5 ml aliquot of the reaction mixture at time t = Volume of NaOH required to neutralize HCl in 5 ml of the reaction mixture + volume of NaOH required to neutralize the acetic acid produced by complete hydrolysis of 1 mol of methyl acetate in 5 ml of the reaction mixture Volume required to neutralize HCl in 5 ml of reaction mixture at any time: 100 V x Vs Where Vs = volume of solution initially formed by mixing 100 ml of 1 M HCl with 5 ml methyl acetate (104.6 ml) Vx = Volume of NaOH required to neutralize a 5 ml aliquot of the original 1 M HCl No. of moles of methyl acetate initially present in any 5 ml aliquot of the reaction mixture: 5 d2 5 25 d2 x = M2 V S M2V S Where d2 = density of methyl acetate (0.9273 at 25oC.08) Since 1000/N ml of NaOH of molarity N is required to titrate the CH 3COOH produced by hydrolysis of 1 mol of CH3COOCH3: 1000 25 d 2 25000 d 2 x = N M 2 V S NM 2 V s . y = -0.920 Density of methyl acetate.905 0. T = 27oC.9252 At T = 40oC.0013(27) + 0.9603 50 .0x + 0. V∞ required to titrate both the HCl and CH3COOH produced by complete hydrolysis of the CH3COOCH3 in a 5 ml sample of the reaction mixture: V ∞= 100V X 25000 d 2 + VS NM 2 V S Graph of density of methyl acetate against temperature 0.96 0.910 0. d2 0.0013(40) + 0.Therefore.930 f(x) = .900 20 30 40 Temperature (oC) Graph 1 From Graph 1: At room temperature. y = -0.9603 = 0.925 0.915 0. 17) 25000(0.9083 To find molarity of NaOH N1V1 = N2V2 Where N2 = the molarity of NaOH (1.6 (0.= 0.9252) + 104.16 M Therefore for the reaction at room temperature.17 ml) ∴ N2 = 0.08)(104.6) ∴V ∞=¿ 49.16)(74. V ∞= 100V X 25000 d 2 + VS NM 2 V S V ∞= 100(32.0 M)(5 ml) = N2 (32.41 . Vt) 2.65 2.Graph of ln (V∞ .80 f(x) = .6 (0.Vt) against time for reaction at room temperature 2.8116 ∴ k1 = 0.0019 M min-1 Therefore for the reaction at 40oC.k1t + c y = -0.Vt) = .9083) + 104.16)(74.0x + 2.0019x + 2. V ∞= 100V X 25000 d 2 + VS NM 2 V S V ∞= 100(32.08)(104.k1t + c ln (V∞ .81 2.60 2.75 ln (V∞ .6) 60 70 80 90 .85 2.70 2. ln C = .17) 25000(0.55 0 10 20 30 40 50 Time (min) Graph 2 From Graph 2. Vt) against time for reaction at 40oC 3.0019 8.k2t + c y = -0.30 2.50 2.40 2.k2t + c ln (V∞ .70 2.Vt) = .07 Graph of ln (V∞ .10 2.90 2.00 0 10 20 30 40 Time (min) Graph 3 From Graph 3.00 2. ln C = .0.0099x + 2.80 f(x) = .7886 ∴ k2 = 0.79 2.0099 313−300 = 0.0099 M min-1 ln k 2 E a T 2−T 1 = k1 R T 1 T 2 ln Ea 0.3145 ( 313 ) ( 300 ) ( ) ( ) 50 60 70 80 .20 2.60 ln (V∞ .∴V ∞=¿ 49.01x + 2.Vt) 2. Hydrolysis occurs slowly in pure water. For the room temperature. If this reaction is carried out in a dilute solution with the presence of a known concentration of strong acid. This can determine the specific rate constants. then at 20 minutes for half an hour. but with this reaction can be considered as a complete reaction with the presence of excess water. with acid as catalyst. only it recorded at 5 minutes intervals for 20 minutes. room temperature and 40 oC. at 10 minutes intervals for half an hour and then 20 minutes intervals for half an hour. The time between titrations is increased due to the molecules ability . In this experiment. is proportional to the concentration of acid. the rate and order of the reaction depends only on the concentration of methyl acetate. In the second set of experiment in 40oC.Ea =99 133. it creates a higher temperature and therefore higher activation energy. Phenolphthalein is used as the indicator for this experiment.74 J ∴ E a=99. This is thought to be due to the concentration of water which is considered to be constant throughout the experiment and the concentration of acid does not change. This allows determining how it affects the reaction rate and thus the activation energy of the experiment after the concentration has settled. The methyl acetate is hydrolyzed and separated into acetic acid and methanol by addition of water. the hydrolysis of methyl acetate was carried out in two temperature variables. however. The rate of reaction. The resulted acetic acid is what was being titrated in this experiment.13 kJ mol-1 mol-1 Discussion: When esters such as methyl acetate react with water. and the reaction can be explained as: CH3COOCH3 + H2O + H2 ↔ CH3COOH + CH3OH + H2 This is a reversible reaction. As we carry out this experiment. Both temperatures are titrated where the time intervals are fixed. some are converted to alcohol and acid. it is titrated at 10 minutes intervals for an hour. methyl acetate is not directly titrated with sodium hydroxide. thus more of the collisions are successful. The air bubble in the nozzle of burette was removed before taking the initial reading as it can be the reason for altering the results. the activation energy of hydrolysis of methyl acetate is calculated as 99. Some other reasons may include the different judgment of human on the end-point of titration and also related to the environment factors. In addition. all the equipments like burette. The National University of Singapore.0019 min-1. the rate of reaction increases. According to the results we obtained.0019 M min-1 from which the second order rate constant. 2003. The temperatures played an important role in the rate of reaction. When temperature increases. They have more energy and the particles collide more often. which is 60. In order to initiate a reaction. The minimum energy with which molecules must have in order for a collision to occur chemical reaction is known as the activation energy. calculated result has a slope equal to –k 1. This errors may caused by the incorrect concentration of the solutions prepared by the lab. The hydrochloric acid was handled carefully by wearing glove and rinse with plenty of water if acid contact with eyes or hands. This means that the apparent first order rate constant. It is a source of energy in order to have a chemical reaction occurs.0099 M min-1.13kJ mol -1. beaker and pipette were rinsed properly with the solution to be filled in it before taking them in use as the presence of any other chemical can be the reason for wrong measurement. The slope of the best straight line through the data was calculated using linear regression to be 0.62kJ mol -1. The experimental value we obtained is higher than the theoretical value published by Department of Chemical and Environmental Engineering. Subsequently. the reactants must be moving fast enough and have enough kinetic energy so that they collide with sufficient force for bonds to break. k 2 is calculated to be 0.to achieve the activation barrier at a higher rate compared to the room temperature. the flask was swirl well right after adding the . The data were used to construct a plot of ln [V∞-Vt] versus time (Graph 2) which according to equation: ln C = -k1t + constant Thus. During the experiment. the reactant particles move more quickly. The proportion of collisions that can overcome the activation energy increases with temperature. There are some precautions in this experiment. k 1 for the reaction is 0. References: 1. 4. Volumetric Analysis.com/2013/01/09/determination-ofreaction-rate-and-reaction-rate-constant/> 3.com/analytical-chemistry/volumetricanalysis. viewed on 30th May 2015.ca/200901/chem27403/15)AppendC. The experimental value we obtained is higher than the theoretical value published by Department of Chemical and Environmental Engineering. which is 60.tutorvista. Year 1.62kJ mol-1. Determination of Reaction Rate and Reaction Rate Constant Practical Report.edu.html> 5. On the other hand. Laboratory Report.uk/physical/catalysis/hydrolyse. The titration was carried out slowly as the end point was approached and the flask was removed immediately when the end point of reaction was achieved. <https://dissa4ict. viewed on 30 th May 2015. < http://www. viewed on 30th May 2015. Conclusion: The experimental activation energy for the hydrolysis of methyl acetate by acid-base titration is 99. The National University of Singapore. 2003.kimia.chemguide. Physical Chemistry.pdf> 2.pdf> 2015. The Mechanism for the Acid Catalysed Hydrolysis of Esters. <http://www.html> .um.uleth.13kJ mol-1. pipetting has to be accurate in order to avoid excess addition of the solution and thus give an inaccurate result.wordpress. <http://chemistry. viewed on 30th May <http://classes.indicator and also the titration flask with addition of each drop of solution from burette to ensure complete mixing of reagents. Laboratory Manual.co. The burette reading was taken with placing the eyes parallel to the bottom meniscus of solution to avoid parallax error. viewed on 31st May 2015.my/images/kimia/lab %20manual/level1/Physical%20/Expt%203%20Manual.
Report "Experiment 1- Kinetics study of the hydrolysis of methyl acetate by acid-base titration."