The Hydrolysis of Methyl Acetate

620 words | 3 page(s)

The hydrolysis of methyl acetate experiment involves the determination of the rate constant in the hydrolysis of methyl acetate reaction. In the hydrolysis, an aliquot of the reaction mixture is titrated with a sodium hydroxide solution in various intervals. The reaction is quenched using ice cold distilled water immediately before the reaction. The sum of the moles of the resultant acetic acid and the moles of the HCl which was added before the reaction gives the moles of NaOH necessary to neutralize the reaction mixture. Apart from the rate constant, the activation energy, entropy and free energy of the reaction are also obtained.

The experiment was undertaken in accordance to the procedure given by the JCP221 lab manual, found in page 5. However, there were some changes in the experiment which were not in accordance with lab manual where the concentration of HCl and NaOH were not the same as the ones given in the Lab manual. Another change was that the experiment was not repeated in three different temperatures by a single group, however, different groups were tasked to do the experiment at different temperatures.

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The enthalpy of the reaction, rate constant, entropy of the reaction and free energy of the reaction are as given in Table 1. The three different rate constants are obtained using Figure 1, Figure 2 and Figure 3. Figure 4 gives the graph from which the enthalpy of the reaction and entropy of the reaction were obtained (1). From the experimental data, the relationship between ln⁡〖[((V_∞-V_t))/((V_∞-V_0))]〗 and time was graphed as shown by the figures. From the gradient of each of the relationship in the different temperatures, the rate constants were obtained. A sample calculation is given showing how the graphical points were obtained. From the gradient of each graph, the rate constants were obtained as 0.025 min-1, 0.027 min-1, and 0.037 min-1.

The relationship between ln⁡[k_f/T] and [1/T] were graphed using the rate constant obtained above. Steps 4A to 4B give the steps taken to obtained the graph in Figure 4. The linear equation in the graph in Figure 4 was necessary to obtain the enthalpy of the reaction, as given by 4C, which was found to be 27,866.754J (1). From Figure 4, the entropy of the reaction and the free energy of the reaction were also found. Using the y-intercept of the linear equation, the entropy of the reaction was calculated, the calculation process is shown in Step 5 (2). Once the entropy of the reaction was obtained, the equation indicated in section 6B of the Appendix was used to calculate the free energy of the reaction was also obtained. The equation gives the free energy of the reaction and relates it to the entropy of the reaction and the enthalpy of the reaction (2).

An error analysis was conducted for the sample calculations in the Appendix. As it can be seen, the errors were in most cases very small with an insignificant effect to the main values. As it is common with errors, they always show their effect in the preceding calculations worsening the accuracy of the final figures. This was taken into account by including previous errors in the calculation of the current errors.
The objective of the experiment was therefore achieved as the rate constant of the hydrolysis of methyl acetate was obtained at the three different temperatures required: 250C, 31.10C and 350C. The enthalpy of reaction, entropy of the reaction and the free energy of the reaction were also obtained following the three rate constants.  

  • The engineering toolbox. The Universal Gas Constant – Ru – in alternative Units. http://www.engineeringtoolbox.com/individual-universal-gas-constant-d_588.html (accessed March, 27th 2017)
  • Encyclopedia Britannica. Planck’s constant. http://www.britannica.com/EBchecked/topic/462917/Plancks-constant (accessed March, 27th 2017)

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