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Determination of the equilibrium constant for an Esterification reaction.

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Introduction

Determination of the equilibrium constant for an Esterification reaction Evaluation of the Experiment (Skill E) Overall, I feel that the accuracy of the result was quite good. Because the equilibrium constant is a constant, the value of Kc should be the same for each experiment. All of the Kc values calculated for the four experiments came to approximately 6 (no units). The results are summarised below. INITIAL VOLUMES (in cm3) Experiment Ethanoic acid Ethanol Ester Water Kc 1 75 75 75 25 3.07 2 75 75 0 100 6.36 3 35 0 35 180 6.47 4 0 75 75 100 6.15 We can see from these results that although the value of Kc is roughly the same for all of them it is quite small for experiment one. I believe that this is an anomalous result. There were two main areas of limitation in this experiment. The first concerns the fact that the temperature of the experiment was not reliably regulated. ...read more.

Middle

1 18.40 0.54 2 15.47 0.65 3 18.09 0.55 4 6.80 1.47 The percentage uncertainties for the individual volumes are shown below: As we can see clearly from the above data, experiments 1, 2, and 3 have quite high volumes of NaOH. These give low percentage uncertainties ranging between 0.54 and 0.65 percent. However for experiment four the volume is much lower, only 6.8cm3. This gives a percentage uncertainty just less than a percent more than the large volumes. The conclusion is that for larger collected volumes the results are far more reliable, in fact they are nearly 170% more reliable using the burette. The second source of error in measurement was in the use of the pipette. This was used to gather a 1cm3 sample of the equilibrium mixture. The pipette is accurate to � 0.01cm3 giving an overall accuracy of 0.02cm3. Using the same formula as before the percentage of uncertainty is: 0.02/1 x 100 = 2% In conclusion, we can see from the two calculations that using the burette and titrating gives a much lower percentage of uncertainty than using the pipette. ...read more.

Conclusion

The temperature of an ice bath at this temperature is very easy to regulate. If the temperature rises slightly then more ice can be added to lower it again. In this way the temperature is kept constant for all of the experiments. The fact that the experiment is not conducted in a closed environment means that the equilibrium shift cannot be completely stopped but it can be minimised by using the ice-bath. If we cool the experiment from room temperature quickly to the temperature of the ice then the reaction will be frozen at the equilibrium at room temperature - it will still be moving but at a much reduced rate which can be considered negligible. This means that titrating with the sodium hydroxide will still neutralise the acid but because the reaction is moving so slowly it will not have time to move towards producing more acid and so the concentrations will be the same as those of the equilibrium at room temperature giving a more reliable value for Kc ...read more.

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