Investigation of Some of the Properties of a Pair of Cis-Trans Isomers

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Experiment18

Aim

To determination the partition coefficient of ethanoic acid between water and butan-2-ol.

Procedure

  1. The room temperature was recorded.
  2. 15cm3 of the given aqueous ethanoic acid and 15cm3 of butan-2-ol were poured into a 100cm3 separating funnel, using suitable apparatus. The funnel was stoppered and was shook vigorously for 1 to 2 minutes. (The pressure in the funnel was released by occasionally opening the tap.)
  3. 10cm3 of each layer was separated approximately. (The fraction near the junction of the two layers was discarded.)
  4. 10.0cm3 of the aqueous layer was pipetted into a conical flask and was titrated with 0.1 M sodium hydroxide solution using phenolphthalein.
  5. Using another pipette, 10.0 cm3 of the alcohol layer was delivered into a conical flask and was titrated with 0.1 M sodium hydroxide solution.
  6. Steps (2) to (5) was repeated with another separating funnel using the following volume:
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25cm3 of aqueous ethanoic acid and 15cm3 of butan-2-ol

  1. For each experiment, the ratio of the concentration of ethanoic acid in the aqueous layer to that in the butan-2-ol layer was calculated.

Result

Room temperature: 29

Volume of butan-2-ol: 15 cm3 

Conclusion

The partition coefficient of ethanoic acid between water and butan-2-ol is :

=

=0.786

Discussion

  1. Shaking is necessary in step (2) because it made it faster to attain equilibrium state.
  2. When temperature increases, the solubility of the two solvents increase. But the rate of the increase in solubility are not the same, it is expected that ...

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The grammar is wrong in the aim, 'to determination' should be 'To determine.' There are also other minor grammatical errors that can be found in the discussion. Otherwise spelling, grammar and punctuation are fine. The layout is well done as each fine point is split into relevant sections.

The method used is very clearly presented and the text used is clear and easy to read so other students would easily be able to follow this method. The experiment was only repeated twice, and this should ideally have been done three times because one result could have been anonymous leading to incorrect results overall, but this could also have been avoided by the use of a 'trial' experiment first and then followed by two accurate titrations. The number of decimal places used in the table are not consistent and should be so that when calculations are being worked out there is less margin for error. The conclusion is adequate and clearly presents the working out and what the partition co-efficient is. The discussion is good and addresses a number of points in the experiment and why they were done, explaining this well. I would also have included improvements to the discussion for the experiment as this shows a higher level of understanding about what might affect the experiment and the results.

The experiment is performed and reported well. The partition co-efficient is worked out accurately, but to improve the experiment the candidate should have repeated the experiment one more time, the reason for this is pointed out below. The discussion at times is hard to read due to the minor grammatical errors present in places, but overall the discussion is done well. A discussion is important to include for an experiment because this shows a higher understanding of different components of the experiment, how things can go wrong and what there is to improve upon.