Question

Hello. In the class, we did the experiment to calculate the value of Kc for the following reaction:

CH3COOH+CH3CH2OH ÌCH3COOCH2CH3+H2O


we measured the mass for 5 cm^3 of all 5 compound above:

CH3COOH 5.236 g
CH3CH2OH 4.021 g
CH3COOCH2CH3 5.020 g
H2O 5.020 g
HCl 5.098 g

when we titrate 2 mol dm^-3 HCl with the 1 mol dm-^3,10 cm^3 NaOH, the result was 4.85 cm^3.

we used the following mixtures in order to find Kc. We titrated with 1 mol dm^-3 NaOH using phenolphthalein as the indicator.

1) 5 cm^3 HCl, 5 cm^3 CH3COOCH2CH3. titration result 38.8 cm^3
2) 5 cm^3 HCl, 1cm^3 H20, 4 cm^ CH3COOCH2CH3.
titration result 35.7 cm^3
3) 5 cm^3 HCl, 2 cm^3 H2O, 3 cm^3 CH3COOCH2CH3.
titration result 30.2 cm^3
4) 5 cm^3 HCl,3 cm^3 H2O, 2 cm^3 CH3COOCH2CH3.
titration result 37.1 cm^3
5) 5 cm^3 HCl, 4 cm^3 CH3COOCH2CH3, 1 cm^3 CH3CH2OH.
titration result 31.5 cm^3
6) 5 cm^3 HCl, 4 cm^3 CH3COOCH2CH3, 1 cm^3 CH3COOH.
titration result 47.4 cm^3
7) 5 cm^3 HCl, 4 cm^3 CH3CH2OH, 1 cm^3 CH3COOH.
titration result 15.1 cm^3
8) 5 cm^3 HCl, 3 cm^3 CH3CH2OH, 2 cm^3 CH3COOH.
titration result 27.3 cm^3


How do we calculate the value of Kc ?
My teacher told us that the literature value is about 4, but I cannot get the correct/nearly correct answer.

Answer 1

I assume the masses measured were before the experiment started; i.e., what you started with. If so, then change each of these to mols/dm^3.
The titrations were to find the equilibrium concentrations of the components. Use M x dm^3 = #mols,
convert # mols per whatever volume was in the equilibrium mixture, and substitute this value into the Kc expression.