Hydrolysis of methyl acetate by acid-base titration
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EXPERIMENT 1- KINETICS STUDY OF THE HYDROLYSIS OF METHYL ACETATE BY ACID-BASE TITRATION.
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BACH 2114 KINETICS, MECHANISM, AND STEREOCHEMISTRY
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BACH 2114 KINETICS, MECHANISM, AND STEREOCHEMISTRYName: 1. Amirah Chan (15WAR08520) 2. Chey Sze Ying (15WAR09194) 3. Chong Khai En (15WAR08702)Group: RBS 2- Group 1Date: 20-5-2015Title: 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
Results:A) Standardization of sodium hydroxide solutionTitrationVolume of NaOH used (ml)Average volume used (ml)
132.2032.17
232.10
332.20
B) 1 Room temperaturet (min)Titrant volume Vt (ml)V- Vt (ml)ln (V - Vt)
032.9016.512.8040
1033.0016.412.7979
2033.5015.912.7669
3033.6015.812.7606
4034.0015.412.7350
5034.2015.212.7220
6034.3515.062.7120
8035.3014.112.6469
2 Water bath, 40oC t (min)Titrant volume Vt (ml)V - Vt (ml)ln (V - Vt)
130.5018.572.9215
632.8016.272.7893
1134.3014.772.6926
1635.3013.772.6225
2135.3013.772.6225
3137.7011.372.4310
4139.609.472.2481
5139.609.472.2481
7139.609.472.2481
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:
Where Vs = volume of solution initially formed by mixing 100 ml of 1 M HCl with5 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:
Where d2 = density of methyl acetate (0.9273 at 25oC; 0.9141 at 35oC)M2 = molecular weight (74.08)
Since 1000/N ml of NaOH of molarity N is required to titrate the CH3COOH produced by hydrolysis of 1 mol of CH3COOCH3:
Therefore, 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