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

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Introduction

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: 25cm3 of aqueous ethanoic acid and 15cm3 of butan-2-ol 7. ...read more.

Middle

Therefore, the volumes of the aqueous and alcohol solution used in the titration must be known as accurately as possible in order to find accurately concentration. The aim of adding aqueous ethanoic acid and 2-methypropan-1-ol is only to leave the mixture to equilibrium and provide enough solvent for the titration. Therefore the amounts of aqueous ethanoic acid and 2-methypropan-1-ol need not be measured out accurately. 4. The following assumptions are made: a) The temperature of the mixture remained constant throughout the experiment. This assumption was valid as it was felt (by hand) that the temperature of the separating funnel did not changed throughout the experiment. b) Ethanoic acid, water and butan-2-ol are non-volatile and do not evaporate slowly. This assumption is not valid because there is a smell of alcohol over the separating funnel. That means that there are particles coming out from the mixture in the separating funnel. ...read more.

Conclusion

+ I2(aq) + 6H2O(l) 8OH-(aq) + 4Mn2+(aq) + O2(aq) + 2H2O(l) --> 4Mn(OH)3(s) No. of mole of sodium thiosulphate used: 6 ? 10-6 ? 0.0125 = 7.5 ? 10-8 No. of mole of I2 in 100cm3 sample: 7.5 ? 10-8 �2 = 3.75 ? 10-8 No. of mole of Mn(OH)3 in 100cm3 sample: 3.75 ? 10-8 ? 2 = 7.5 ? 10-8 No. of mole of dissolved O2 in 100cm3 sample: 7.5 ? 10-8 �4 = 1.875 ? 10-8 No. of mole of dissolved O2 per dm3 : 1.875 ? 10-8 �100 ? 106 = 1.875 ? 10-4 Mass of dissolved O2 per dm3 : 1.875 ? 10-4 ? 16 ? 2 = 0.006g DO value of the water sample is: 0.006 ? 103 = 6mg dm-3 Conclusion The Do value of the water sample is 6mg dm-3. Discussion 1. No air bubble should be trapped as the oxygen in the bubbles may dissolve in the water sample and affect the result. 2. During titration, starch solution is added as indicator. Starch solution should not be added too early as it may react with the iodine. ...read more.

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The candidate has written up a logical and well-presented piece of coursework. The work is methodical and there is a clear order throughout, with the aims being immediately presented. The method section is easy to follow, and the results/calculations seem ...

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Response to the question

The candidate has written up a logical and well-presented piece of coursework. The work is methodical and there is a clear order throughout, with the aims being immediately presented. The method section is easy to follow, and the results/calculations seem to be correct. A good level of depth is used to show the working-out behind the calculations, with full formulas being written out when necessary.

Level of analysis

The level of depth is good, and there is plenty of discussion into the science behind the results. Wider knowledge is demonstrated as the student mentions what assumptions have to be made and why certain experimental features, such as shaking, are carried out. One improvement that could be made is more content on potential errors. For example, with the second set of the results, the candidate mentions that the first experiment encountered error, but doesn't provide any additional information about what the error was or any methods by which the error could have been prevented.

Quality of writing

Overall, the use of spelling, punctuation and grammar is very good. There are a few mistakes, such as in the title which are just typos, but could be easily removed with a thorough proof-read. The student uses technical language when necessary and demonstrates a strong understanding of the subject.


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