Objective To find out the equilibrium constant, Kc, for the reaction below, using acid hydrolysis:

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Determining an Equilibrium Constant

           To find out the equilibrium constant, Kc, for the reaction below, using acid hydrolysis:

           Although the hydrolysis of ethyl ethanoate is very slow, by using dilute hydrochloric acid as catalyst, the above equilibrium can be attained in 48 hours. After 48 hours, the reaction mixture can then be titrated with standard sodium hydroxide solution. Finally, the equilibrium concentrations of four components below and hence, Kc of hydrolysis of CH3COOCH2CH3 can then be calculated:

          2M HCl, 1.0335M NaOH, ethyl ethanoate, phenolphthalein indicator

          5 small reagent bottles, 5ml pipette & filler, burette, measuring cylinder, conical flask, electronic balance, stand, white tile

Procedure ── Preparation, allow reaching equilibrium position
         1.> Label 5 reagent bottles & their stoppers as 1A, 1B, 2, 3 and 4.
         2.> Weigh each reagent bottles with their stoppers and record their corresponding masses in
Table 3.
         3.> Pipette 2M HCl into each bottles, using measuring cylinders to transfer ethyl ethanoate into bottles 2,3,4 and water into bottles 3,4 according to the
               amount shown in
Table 1.

Table 1 shows the amount of chemicals added:

         4.> Record the total mass before and after each addition of chemical into Table 3.
         5.> Set them aside for at least 48 hours and shake the bottles occasionally.

Procedure ── Titration (48 hours later)
         1.> Rinse and fill a burette with standardized NaOH solution.
         2.> Pour the contents of bottle 1A into a conical flask and rinse the bottle with deionized water.
         3.> Add 2 - 3 drops of phenolphthalein indicator and titrate the mixture with standardized NaOH solution.
         4.> Repeat steps 2 - 3 for other regent bottles. The results are recorded in
Table 2.

Table 2 shows the results of titration:

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Calculation & Results
         Below, it shows how the values in individual items in Table 3 can be obtained:
                   1.> Since HCl
(aq) and NaOH(aq) react in equimolar amounts, so,

2.> Total amount of acid at equilibrium in bottles 2,3 & 4
                         = no. of moles of HCl
(aq) added + CH3COOH(l) formed
                         = concentration of NaOH
(aq) x volume of NaOH(aq) added
                   3.> Equilibrium amount of CH
                         = total amount of acid at equilibrium - amount of HCl(aq) added
                         = the value obtained in
(2) - that in (1)
                   4.> Equilibrium amount of CH3CH2OH(l)
                         = equilibrium amount of CH3COOH(l)
                         = the value obtained in (3).
                   5.> Mass of pure HCl in ...

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This is a very descriptive, well through out practical. It contains advanced mathematical analysis for an A2 course and draws good conclusions This piece of work is 5 stars out of 5