Determining an Equilibrium constant

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Ho Ka Wing (9) Group: 4B Date: 21/12/09

Determining an Equilibrium constant


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


although the hydolysis of ethyl ethanoate is very slow, by using dilute hydrochloric acid as catalyst which can be used to alter the time required to reach the equilibrium as the catalyst increases both the forward and backward reaction to the same extent,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 concentration of four components below and hence, Kc,, of hydrolysis of CH3COOC2H5 can then be calculated by the equilibrium law:

Kc =

The experiment can be divided into two parts:

In part A: mixtures containing different proportions of the two reactants are added with a fixed amount of dilute hydrochloric acid as a catalyst.
In part B: after the mixtures have reached equilibrium at room temperature, each one is titrated with sodium hydroxide.

Safety Precautions

Ethyl ethanoate –General Hazards

Hydrochloric acid –General Hazards

Sodium hydroxide –General Hazards

Special Handling Information

  • Eye protection (safety goggles) must be worn at all times.
  • Wear gloves
  • Avoid skin contact with the chemicals

Apparatus and Reagents Used (Part A)

  • Safety spectacles
  • 10 specimen tubes with well-fitting caps
  • Labels for tubes and stoppers
  • Access to a balance
  • Pipette, 5 cm3, and safety filler
  • Dilute hydrochloric acid, 2M HCl
  • 2 measuring cylinders, 10 cm3
  • Distilled water
  • Ethyl ethanoate, CH3COOC2H5

Procedures :( PART A)

  1. Ten specimen tubes were labeled with 1a, 1b, 1c, 1d, 2a, 2b, 3a, 3b, 4a, 4b. the stoppers were labeled too, so that they do not get misplaced.
  2. each tube is weight, with its stopper, and the masses are recorded in a copy of Results table 1
  3. A pipette and safety filler are used, 5 cm3 of 2Mhydrochloric acid is carefully added to each tube, the stoppers are replaced.
  4. Each stoppered tube is weight and the masses are recorded.
  5. A dry measuring cylinder is selected, and is used to add to tubes 2a,2b,3a,3b,4a,4b the volumes of ethyl ethanoate shown in results table 1, the stoppers are replaced.
  6. The stoppered tubes 2a,2b,3a,3b,4a,4b. The masses are recorded.
  7. a second measuring cylinder is used to add to tubes 3a,3b,4a,4b the volumes of distilled water shown in results table 1, the stoppers are replaced.
  8. The stoppered tubes 3a,3b,4a,4b is weight. The masses are recorded.
  9. the tubes are shaken gently and are set aside for at least 48 hours.during this time, the tubes are shaken occasionally.
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Results Table 1

Apparatus and Reagents Used (Part B)

  • Safety spectacles
  • 5 conical flasks,250 cm3
  • Wash-bottle of distilled water
  • Phenolphthalein indicator
  • Burette, stand and white tile
  • Small funnel
  • Sodium hydroxide solution,1M NaOH(standardised)

Procedures :(PART B)

  1. A burette is rinsed and filled with standardized sodium hydroxide solution.
  2. The contents of tube 1a into a conical flask. The tube is rinsed into the flask three times with distilled water.
  3. two to three drops of phenolphthalein indicator solution is added and the acid is titrated against sodium hydroxide solution. ...

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