On the rate constant of the saponification of ethyl acetate

I. INTRODUCTION The rate constant of the chemical reaction is a very critical parameter in chemical kinetics, which reflects the rate characteristics of the reaction. In many chemical reaction systems, the saponification of ethyl acetate has become an important object for the study of reaction kinetics because of its typical and representative nature. The precise investigation of the rate constant of the saponification of ethyl acetate not only helps to deeply understand the mechanism of the reaction, but also has important significance for the theoretical development and practical application in related fields.

Second, Experimental Principle
The saponification of ethyl acetate is a typical second-order reaction, and its reaction equation is: $CH_3COOC_2H_5 + NaOH\ longrightarrow CH_3COONa + C_2H_5OH $. During the reaction, the conductivity of the solution will change as the reaction proceeds. Since the conductivity of $OH ^ - $ions is much greater than that of $CH_3COO ^ - $ions, as the reaction proceeds, the concentration of $OH ^ - $ions gradually decreases, and the conductivity of the solution also gradually decreases. By measuring the conductivity of the solution at different times and combining the kinetic equation of the reaction, the expression of the rate constant of the saponification reaction of ethyl acetate can be deduced.

Let the initial concentration of ethyl acetate and sodium hydroxide at the beginning of the reaction be $a $, and the concentration of $CH_3COONa $and $C_2H_5OH $generated by the reaction at $t $is $x $, then the concentration of $CH_3COOC_2H_5 $and $NaOH $at this time is $a - x $. According to the second-order kinetic equation, the reaction rate $v = k (a - x) ^ 2 $, and the integral can be obtained: $\ frac {1} {a - x} -\ frac {1} {a} = kt $.

Because there is a linear relationship between conductivity and concentration, let the conductivity of the solution at the initial time be $\ kappa_0 $, the conductivity of the solution at the time of $t $is $\ kappa_t $, and the conductivity of the solution at the end of the reaction is $\ kappa_ {\ infty} $, then: $\ kappa_0 = A_1a $, $\ kappa_ {\ infty} = A_2a $, $\ kappa_t = A_1 (a - x) + A_2x $, where $A_1 $, $A_2 $are proportional constants. By sorting: $a - x =\ frac {\ kappa_t -\ kappa_ {\ infty}} {\ kappa_0 -\ kappa_ {\ infty}} a $, which is substituted into the above kinetic equation to obtain the ethyl acetate saponification reaction rate constant expressed in conductivity: $k =\ frac {1} {ta}\ frac {\ kappa_0 -\ kappa_t} {\ kappa_t -\ kappa_ {\ infty}} $.

III. Experimental Methods
1. ** Experimental Instruments and Reagents **
Instruments: conductivity meter, constant temperature water bath pot, double tube saponification tank, pipette, stopwatch, etc.
Reagents: ethyl acetate (analytically pure), sodium hydroxide (analytically pure), distilled water.
2. ** EXPERIMENTAL STEP **
(1) Prepare different concentrations of sodium hydroxide solution and ethyl acetate solution.
(2) Adjust the constant temperature water bath to the desired temperature, such as 25 dollars ^ {\ circ} C $, 35 dollars ^ {\ circ} C $, etc.
(3) Calibrate the conductivity meter and preheat it.
(4) Use a pipette to accurately measure a certain volume of sodium hydroxide solution and inject it into one side of the double-tube saponification cell, and then measure the same volume of ethyl acetate solution and inject it into the other side.
(5) Quickly mix the two solutions, start the stopwatch timer at the same time, and start measuring the conductivity of the solution at different times.
(6) Record the conductivity $\ kappa_t $corresponding to $t $at different times until the conductivity change tends to stabilize, resulting in $\ kappa_ {\ infty} $.
(7) Change the temperature and repeat the above steps to measure the conductivity data at different temperatures.

IV. Experimental Data Processing and Analysis of Results
1. ** Data Processing **
Draw a straight line with $\ frac {\ kappa_0 -\ kappa_t} {\ kappa_t -\ kappa_ {\ infty}} $as the ordinate and $t $as the abscissa. According to the slope of the straight line $m $, the rate constant $k $of the saponification reaction of ethyl acetate at different temperatures is calculated from $k =\ frac {m} {a} $.
2. ** RESULTS ANALYSIS **
(1) Analyze the change law of the rate constant at different temperatures. According to the Arrhenius formula $k = A e ^ {-\ frac {E_a} {RT}} $, plotted with $\ ln k $to $\ frac {1} {T} $, a straight line can be obtained, and the activation energy of the reaction can be calculated from the slope of the straight line $E_a $.
(2) Discuss the possible sources of errors in the experimental process, such as uneven solution mixing, temperature fluctuations, measurement errors of conductivity meter, etc. on the measurement results of the rate constant, and propose corresponding improvement measures.

V. CONCLUSION
Through the experimental study of the rate constant of ethyl acetate saponification reaction, we successfully obtained the rate constant of the reaction at different temperatures, and conducted an in-depth analysis of its change law and influencing factors. The experimental results show that temperature has a significant impact on the rate constant of ethyl acetate saponification reaction. With the increase of temperature, the rate constant increases. At the same time, the analysis of the experimental error provides a direction for further improving the experimental accuracy. This study has important reference value for in-depth understanding of chemical reaction kinetics and related practical applications.