The equilibrium constant for the acid hydrolysis of ethyl ethanoate can be found by experiment.
CH3COOC2H5(l)+H2O(l)⇌CH3COOH(l)+C2H5OH(l)
A reaction mixture is set up in a sealed flask and left for 48 hours at 25 °C to reach equilibrium. Samples can then be taken from the flask and titrated with alkali to find the concentration of ethanoic acid present at equilibrium.
Diagram showing three stages of the experiment: 1. A conical flask containing a reaction mixture is placed in a beaker of water with a thermometer, labeled 'mixtures allowed to equilibrate in a water bath (25 °C)'. 2. A pipette is shown drawing a sample from the flask and dispensing it into another flask containing ice and water, labeled 'a 25 cm³ sample is run into a flask containing ice and water'. 3. A burette is shown titrating the sample in the second flask, labeled 'ethanoic acid in the reaction mixture is titrated with alkali'.
44.0 g of ethyl ethanoate was mixed with 36.0 g of water (acidified with a small amount of hydrochloric acid to act as a homogeneous catalyst) and allowed to reach equilibrium. The equilibrium mixture was then made up to 250 cm3 (3 s.f.) with distilled water.
A 25.0 cm3 sample of the diluted mixture was titrated with 1.00 mol dm-3 sodium hydroxide solution. After allowing for the acid catalyst present, the ethanoic acid in the equilibrium mixture required 29.5 cm3 of alkali to neutralize it.
Determine the equilibrium constant, K, for the reaction by working through the following stages of calculation: