UAH - Department of Chemical and Material Engineering

CHE440 - Unit Operations

Batch Kinetics Saponification Experiment

 

Location – Unit Opertaions Biotechnology Room EB256

 

Chemicals Used – Ethyl Acetate, Sodium Hydroxide, Sodium Acetate

                    

Objectives 

To determine equation(s) that demonstrate the kinetics of a known reaction.  Possible objectives may include the derivation of a rate law, its reaction order and rate constants, the activation energy, and equilibrium constants

 

Theory

Kinetic rate laws can be derived either by the differential method, the integral method, the method of initial rates, the method of excess, and/or the method of half-lives as demonstrated in Fogler, Ch. 5.  The Arrhenius Law is needed to determine the activation energy as shown in Fogler, Ch. 3.

 

Apparatus

The stirred tank is located in Room 256 of the Engineering Building. It contains a heat jacket, which is connected via tubing to a water bath, to provide a constant temperature. It also contains a stirring impeller and a rotary magnet to assist in mixing.

Adjacent to the reactor is a pH meter, which is interfaced with an IBM-compatable computer via an RS-232 cable. Before use every day, the pH-meter needs to be calibrated using two different pH-standard buffers.  Select two from among this list: pH= 4, 7, or 10.  BE CAREFUL WITH THE pH ELECTRODE!  You must be certain to return the pH electrode to its standard solution when not in use.  The computer software will allow pH and temperature readings to be taken and stored as a function of time using a time interval selected by the user. The data can be easily transferred/converted into a spreadsheet. Detailed instructions are given below.

 

 

 

 

 

 

 

 

 

 

Reaction Theory

The reaction to be investigated here is known as a saponification reaction:

Ethyl Acetate + Sodium Hydroxide <-----> Ethanol + Sodium Acetate


Some notes about this reaction:

 

Experimental Notes

Start the reaction by combining aqueous NAOH solution and aqueous ethyl acetate solution, not by adding pure ethyl acetate to the NaOH solution.

After the pH meter is calibrated and the computer "booted up", data acquisition can begin. Follow these instructions:

At this point, the data: time, pH and temperature, will transfer to the screen, as can be observed.

Press the "Setup" key twice (to arrive at Menu #2)

The pH electrode is very fragile. Be careful! Never use the pH electrode as a stirring rod. Also take care in placing the electrode inside of the reactor. Make sure that the impeller does not harm the electrode. If you suspect that the electrode is not functioning properly, see the TA or lab instructor.

 

References

Fogler, H.S., Elements of Chemical Reaction Engineering, 2nd ed., Prentice-Hall, 1992.