The Determination of an Equilibrium Constant

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The Determination of an Equilibrium Constant

I will be determining the equilibrium constant - Kc; of ethanoic acid reacting

with ethanol producing an equilibrium to form ethyl ethanoate and

water.

CH3COOH(aq) + C2H5OH(aq) ó CH3COOC2H5(aq) + H2O(l)

Following the method as detailed, I conducted experiment 4 and these

results were obtained:

Titration Trial

Volume of Sodium Hydroxide Neutralised (cm3)

1

7.65

2

7.75

3

7.80

4

7.70

5

7.75

μ

7.75

To calculate Kc, the concentrations of each reactant must be

calculated from the point of equilibrium at which the titration was

taken.

Therefore, using 7.75cm3 as the average titre,

Moles = 0.2M x (7.75cm3 / 1000 cm3) = 1.55 x 10-3.

However, this represents the total amount of acid in the system which

included ethanoic acid but also the acid catalyst: hydrochloric acid.

Therefore this must be taken away from the number of moles of acid to

calculate number of moles of ethanoic acid.

Since 25 cm3 of 1.0M HCl was included in the initial 250 cm3 mixture,

Moles = 1 x (25 / 250) = 0.1 moles.

But 1cm3 samples were taken at a time, therefore:

Moles = 0.1 x (1 cm3 / 1000 cm3) = 1 x 10-4.

Taking this away from the total amount of acid = 1.55 x 10-3 - 0.1 x

10-3 = 1.45 x 10-3 (moles of ethanoic acid).

Considering the stoichiometry of the equation, there is equal amounts

of ethanol as there is ethanoic acid, therefore there is 1.45 x 10-3

moles of ethanol at equilibrium also. This is because the total amount

of acid reacted is equal to the amount of acid, even though it is a

weak acid. Because it reacts with a strong base, it means that the

acid dissociates completely.

Now to calculate the number of moles of products;

The number of moles is calculated from multiplying volume by density

to calculate mass (which is provided on the enclosed sheet), and then

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