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.
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.
To calculate the value of Kc for the given reaction, you need to use the titration results and the initial concentrations of the reactants.
The balanced equation for the reaction is:
CH3COOH + CH3CH2OH ⇌ CH3COOCH2CH3 + H2O
Step 1: Calculate the initial concentration of HCl in mol dm^-3:
Given that you used 5 cm^3 of HCl and its molarity is 2 mol dm^-3, you can use the formula:
Concentration (mol dm^-3) = (mass / molar mass) / volume (dm^3)
HCl:
Mass = 5.098 g
Molar mass = 36.461 g/mol
Volume = 5 cm^3 = 0.005 dm^3
Step 2: Calculate the initial concentration of CH3COOCH2CH3 in mol dm^-3:
Given that you used 5 cm^3 of CH3COOCH2CH3 and its molar mass is 88.106 g/mol, you can use the same formula as in Step 1.
Step 3: Calculate the initial concentration of H2O in mol dm^-3:
H2O is a liquid, so its concentration is constant and does not need to be calculated.
Step 4: Use the titration results to calculate the final concentration of the reactants:
For each mixture, subtract the titration result from the initial volume to obtain the volume of reactants consumed during the reaction.
Let's consider mixture 1 as an example:
HCl:
Initial volume = 5 cm^3
Titration result = 38.8 cm^3
Final volume = Initial volume - Titration result = 5 cm^3 - 38.8 cm^3 = -33.8 cm^3
Since the final volume is negative, there was an excess of HCl, and no CH3COOCH2CH3 was consumed.
Calculate the final concentrations of CH3COOCH2CH3, H2O, and HCl for each mixture using the same method.
Step 5: Calculate the value of Kc using the following equation:
Kc = ([CH3COOCH2CH3] x [H2O]) / ([HCl] x [CH3COOH])
Now that you have the final concentrations of the reactants, substitute them into the equation and calculate Kc for each mixture.
Compare the calculated values of Kc with the literature value to evaluate the accuracy of your results.
Note: Make sure to convert the volumes from cm^3 to dm^3 and check for any errors or inconsistencies in the given data before performing the calculations.