- Experiment 3 Rate Constant For The Saponification Of Ethyl Acetate 1 Objective 1 1 To Measure The Rate Constant For Th 1 (215.17 KiB) Viewed 97 times
QUESTION SECTION 2nd question please make it short pointful and do
it quick please!uprate!
as recording answers guide i am giving one question which is
QUESTION SECTION 2nd question please make it short pointful and do
it quick please!uprate!
as recording answers guide i am giving one question which is
QUESTION SECTION 2nd question please make it short pointful and do
it quick please! uprate!
Experiment 3 Rate Constant for the Saponification of Ethyl Acetate 1. Objective 1.1. To measure the rate constant for the saponification of ethyl acetate by conductometric method. 1.2. To learn how to evaluate the rate constant of a second-order reaction by a graphic method. 1.3. To be familiarized with the operation of a digital conductometer. 2. Introduction The saponification reaction of ethyl acetate with sodium hydroxide is a second-order reaction, and its equation is: CH,COOC,H, + NaOH +CH,COONa +C,H,OH t = 0 со со 0 0 t=1 Сх Сх t = 00 CO CO CO-CX CO-CX 0 0 co is the initial concentration of ethyl acetate and NaOH solution; Cx is the concentration reacted at the time t, so the rate equation for the above second-order reaction can be expressed as: dcx = k(Co- - cx)2 dt k is the reaction rate constant. After integrating the above formula, we get: Сх = kt CoCo - Cx) From the concentrations of the reactant and product in the reaction vessel and time of reaction, the rate constant can be calculated. In the saponification reaction of ethyl acetate, OH, Nat, and CH3C00 are electric in the solution. Since the reactants are dilute aqueous solution, it can be considered that CH3COONa is completely ionized. There is no change in the concentration of the Nat before and after the reaction. As the reaction progresses, OH ions with strong conductivity are gradually replaced by CH3COO ions with weak conductivity, resulting in the gradual decrease of the conductivity of the solution (The conductivity of solvent water, ethyl acetate and ethanol is negligible). Therefore, the change of the conductivity with time in saponification reaction can be measured by conductometer, so as to track the change of reactant concentration with time. Let Go be the conductance of the solution at t = 0, G be the conductance at t, and Go be the conductance at t = oo (complete reaction). In the dilute solution, the decrease of conductance is proportional to the concentration of CH3COO . Set K as the proportionality constant, then: 1 = 1, Cx = Cx, Cx = K(Go-Gt) t = 0, Cx = co, co = K(Go-G.) Therefore: Co- Cx = KG-G) So, co- Cx and Cx can be represented by the corresponding conductivity of the solution
= and substituted into equation to obtain: 1 (Go - Gt) = kt Co (Gt - G.) Rewrite the above equation as: 1 Go - Gt Gt + GO cok t So, as long as you measure the conductance of the solution at different times and the conductance of the initial solution, then plot Go against (Go - Gt)/t to get a straight line. The slope of the line is 1/(cok), so the reaction rate constant k at the corresponding temperature is obtained. The relationship G = KA/l between conductance and conductivity K is substituted into equation (3), and the following equation can be obtained: 1 Ko - Kt Kt = + Ko By measuring the conductivity K of the solution at different times and the conductivity of the initial solution as ko. Plot the graph with Kt versus (Ko - Kt)/t, a straight line can also be obtained, and the reaction rate constant k can also be obtained from the slope of the line. If the reaction rate constant k at another temperature is measured, the activation energy Ea of the reaction can be obtained according to Arrhenius formula: In k2 Ea(T2-T) k1 RT T2 3. Apparatus and Reagent DDS-11A conductometer; conductance pool; thermostat water baths; stopwatch; pipette (50ml); volumetric flask (100ml); microsyringe (100uL); NaOH (0.0100mol. L'); ethyl acetate (A.R.). cok t = 4. Procedure 4.1. Adjust the thermostat and set the temperature to (25.0 + 0.1) °C [or (30.0 0.1) °C]. 4.2. Turn on and adjust the conductometer for standby. 4.3. Determination of initial conductivity Ko of solution Remove 100ml NaOH solution (0.0100 mol·L"') from the pipette into the conductivity cell. Put the conductance tank into the thermostat for about 15 minutes at a constant temperature, and gently shake it several times. After the temperature is steady, insert the electrode into the solution (cover the upper edge of the electrode and exceed about 1 cm). The conductivity is measured until it is constant, which is Ko. 4.4. Determination of conductivity Kt during reaction Use a microsyringe to extract 0.001mol of ethyl acetate (at 25°C is about 98.54 uL). Inject it quickly into the conductivity cell, and meanwhile press the stopwatch to time it as the starting time of the reaction. And sway immediately to make the solution mix even. Determine the conductivity of the solution Kt, measure the conductivity once in 5 min, 7 min, 9 min, 12 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min. Record Kt and the corresponding time t. At the end of the experiment, the power is turned off, the electrode is taken out and washed with distilled water. 5. Data Analysis
5.1. Present the results in the table 3-1. Table 3-1. Conductivities for the solution in saponification of ethyl acetate ; K= t/min K/Sm! Ko-K/S.m-1 KO= 5.2. (Ko-K)/t is plotted by Ki, and the rate constant k is obtained from the slope of the straight line. 5.3. Calculation of half-life of reaction by reaction rate constant k and initial concentration Co. 6. Notes 6.1. Boiled conductive water is used. Since the ethyl acetate solution is slowly hydrolyzed and the hydrolyzed product consumes a part of NaOH, the test solution must be freshly prepared. 6.2. The volume of ethyl acetate at different temperatures can be calculated by density and molar mass. The density of ethyl acetate p can be expressed as: p/(kg m-?) = 924.54 – 1.168 * (t/°C) -1.95x10-3 x (t/°C)2 The molar mass of ethyl acetate is 88.11kg.mol-'. 7. Exercises 7.2. How to determine the activation energy of this reaction?