Experimental Report on the Saponification Reaction of Ethyl Acetate
I. Purpose of the experiment
1. Master the principle and method of determining the rate constant of the saponification reaction of ethyl acetate by conductance method.
2. Understand the characteristics of the secondary reaction and learn to find the rate constant of the secondary reaction by diagramming.
3. Be familiar with the use of conductivity meter.
II. Experimental Principle
The saponification reaction of ethyl acetate is a secondary reaction. The reaction formula is:
\ [CH_3COOC_2H_5 + NaOH\ longrightarrow CH_3COONa + C_2H_5OH\]
During the reaction, the concentration of each substance changes with time. If the starting concentration of ethyl acetate and sodium hydroxide is the same, both are\ (a\), and if the reaction proceeds to a certain time\ (t\), the concentration of sodium acetate and ethanol produced is\ (x\), then the concentration of ethyl acetate and sodium hydroxide at this time is\ (a - x\). The rate equation for this reaction is:
\ [\ frac {dx} {dt} = k (a - x) ^ 2\]
Integrating the above equation yields:
\ [\ frac {x} {a (a - x) } = kt\]
For dilute solutions, the conductivity of a strong electrolyte\ (\ kappa\) is proportional to its concentration, and the total conductivity of the solution is equal to the sum of the conductivities of the electrolytes that make up the solution. In this experiment,\ (NaOH\) and\ (CH_3COONa\) are strong electrolytes, and\ (CH_3COOC_2H_5\) and\ (C_2H_5OH\) are non-electrolytes. As the reaction proceeds,\ (OH ^ -\) continues to decrease,\ (CH_3COO ^ -\) continues to increase, because the conductivity of\ (OH ^ -\) is much larger than that of\ (CH_3COO ^ -\), so the conductivity of the solution decreases over time. Let the initial conductivity of the solution at the beginning of the reaction be\ (\ kappa_0\), which is proportional to the initial concentration\ (a\) of\ (NaOH\), that is,\ (\ kappa_0 = A_1a\); the conductivity of the solution at the time of\ (t\) is\ (\ kappa_t\), at this time\ (\ kappa_t = A_1 (a - x) + A_2x\); when the reaction is complete, the conductivity of the solution is\ (\ kappa_ {\ infty}\), which is proportional to the concentration\ (CH_3COONa\) \ (a\), that is,\ (\ kappa_ {\ infty} = A_2a\). Combined with the above three formulas, eliminating\ (A_1\),\ (A_2\) and\ (x\), we can get:
\ [\ frac {\ kappa_0 -\ kappa_t} {\ kappa_t -\ kappa_ {\ infty}} = akt\]
with\ (\ frac {\ kappa_0 -\ kappa_t} {\ kappa_t -\ kappa_ {\ infty}}\) to\ (t\) plot, a straight line can be obtained, the slope\ (m = ak\), from which the reaction rate constant\ (k\) can be obtained.
III. Experimental instruments and reagents
1. ** Instruments **: Conductivity meter, thermostatic tank, double tube saponification cell, pipette, volumetric bottle, stopwatch, etc.
2. ** Reagents **:\ (0.0200mol/L\) \ (NaOH\) solution,\ (0.0200mol/L\) ethyl acetate solution (freshly prepared).
IV. Experimental steps
1. ** Thermostatic tank adjustment **
Adjust the thermostatic tank temperature to\ ((25.00\ pm 0.1) ^ {\ circ} C\).
2. ** Calibration of conductivity meter **
Calibrate according to the instruction manual of conductivity meter. Determination of
3 . **\(\ kappa_0\) **
Accurately pipette the\ (25mL\) \ (0.0200mol/L\) \ (NaOH\) solution in the A tube of the dry double-tube saponification cell, and then pipette the\ (25mL\) distilled water with another pipette into the B tube, insert the conductivity electrode, and place the double-tube saponification cell in the constant temperature tank for 10min. Then quickly pour the distilled water in the B tube into the A tube, start the stopwatch at the same time, and keep stirring. Record the conductivity value every certain time (such as 1min) until the conductivity does not change much. This conductivity value is\ (\ kappa_0\).
4 . **\(\ kappa_t\) **
accurate pipette with a pipette\ (25mL\) \ (0.0200mol/L\) \ (NaOH\) solution in a dry double tube saponification cell A tube, and then pipette with another pipette\ (25mL\) \ (0.0200mol/L\) ethyl acetate solution was added to the B tube, the conductive electrode is inserted, the double tube saponification cell was placed in a constant temperature tank constant temperature 10min. Then quickly pour the ethyl acetate solution in tube B into tube A, start the stopwatch at the same time, stir continuously, record the conductivity value every 1 min until the conductivity does not change much, and record the conductivity\ (\ kappa_t\) corresponding to different times\ (t\).
5 . **\(\ kappa_ {\ infty}\) Determination **
After the experiment, place the reaction mixture in a water bath of\ (50 - 60 ^ {\ circ} C\) for 30 minutes to complete the reaction. Then cool to the experimental temperature and measure its conductivity. This conductivity value is\ (\ kappa_ {\ infty}\).
V. Data recording and processing
1. ** DATA RECORD **
Record experimental temperature\ (T = \)______ \(^{\ circ} C\),\ (\ kappa_0 = \)______ \( S/m\),\ (\ kappa_ {\ inft y } = \)______ \( S/m\), the conductivity\ (\ kappa_t\) corresponding to different times\ (t\) is as follows:
|\ (t/min\) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| --- - | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
|\ (\ kappa_t/(S/m )\) | | | | | | | | | | |
2. ** Data Processing **
Based on experimental data, calculate the value of\ (\ frac {\ kappa_0 -\ kappa_t} {\ kappa_t -\ kappa_ {\ infty}}\) and plot\ (\ frac {\ kappa_0 -\ kappa_t} {\ kappa_t -\ kappa_ {\ infty}}\) against\ (t\) to obtain a straight line. From the slope of the line\ (m\), calculate the reaction rate constant\ (k\) according to\ (m = ak\) (\ (a = 0.0100mol/L\)).
6. Precautions
1. The ethyl acetate solution needs to be freshly prepared, because ethyl acetate is volatile and hydrolyzed easily.
2. When mixing the solution, the action should be rapid to ensure that the reaction starts timing in the shortest possible time.
3. The constant temperature should be maintained during the experiment, the conductivity meter needs to be accurately calibrated, and the electrode should be completely immersed in the solution and not contact the container wall during the measurement.
7. Results and discussion
1. In this experiment, the rate constant of ethyl acetate saponification reaction was measured at a temperature of ______ \(^{\ circ} C\) \ (k = \)______ \( L/(mol\ cdot min) \).
2. Analyze the differences between the experimental results and the theoretical values, and discuss the possible reasons for the errors, such as temperature fluctuations, uneven solution mixing, and measurement errors of conductivity meter.
VIII. CONCLUSION
Through this experiment, the rate constant of ethyl acetate saponification reaction was successfully determined by conductivity method, and the kinetic characteristics of the second-order reaction were understood. The use of conductivity meter and related data processing methods were mastered. At the same time, the possible sources of errors in the experimental process are analyzed, which provides a reference for further improving the experimental accuracy.
