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equilibrium constant

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Introduction

Experiment 13 Aim: To determine the equilibrium constant for esterification from ethanoic acid and propan-1-ol. Procedure: 1. 0.25 mole (equals to 14.3 cm3) of glacial ethanoic acid (density = 1.05 g cm-3) and 0.25 mole (equals to 18.8 cm3) of propan-1-ol (density = 0.8 g cm-3) was put into a clean, dry pear-shaped flask. It was mixed thoroughly. 2. 1.0 cm3 of the mixture was transferred by pipette to a 250 cm3 conical flask containing about 25cm3 deionized water and 2 drops of phenolphthalein indicator. It was titrated to end point with 0.50 M sodium hydroxide solution. The titre (V1 cm3)was recorded. 3. 8 drops of concentrated sulphuric(VI) acid was added to the remainder of the acid-alcohol solutions while continuously swirling the flask. Another 1.0 cm3 sample was titrated immediately. The titre (V2 cm3)was recorded. The difference between V1 and V2 Represents the volume to be subtracted from subsequent titration to correct for the amount of sulphuric (VI) ...read more.

Middle

As the time is not enough, step 5 was not performed. Result V1 (cm3) V2 (cm3) V3 (cm3) Initial 1.3 17.6 3.4 Final 17.6 32.6 9.5 Net 16.3 15.6 6.1 Calculation 1. A small amount of concentrated sulphuric(VI) acid was added to the reaction mixture at the beginning of the experiment in order to act as a catalyst to speed up the reaction. 2. During refluxing, the mixture may become gases bubbles. Anti-bumping granules were added to the reaction mixture before refluxing in order to prevent the splitting out of the reaction mixture. 3. The refluxing was continued in step 5 until the titre of sodium hydroxide used approaching constant in order to make sure that the reaction had reached equilibrium stage. 4. The equation for the esterification reaction between ethanoic acid and propan-1-ol is: H2SO4(l) CH3COOH(aq) + CH3CH2CH2OH(aq) ? CH3COOCH2CH2CH3(aq) + H2O(l) 5. The equation of the reaction between ethanoic acid and sodium hydroxide is: CH3COOH(aq) ...read more.

Conclusion

2.575) = 4.687 mole-1 dm3 9. If the concentration of the sodium hydroxide solution is not known exactly, there will be no effect on the determination of the equilibrium constant for the esterification reaction. The initial concentration of CH3COOH can be found {0.25 / (14.3 + 18.8) ? 1000 = 7.55}. The concentration of NaOH can also be found { 7.55 / (1/1000) / (16.3/1000) = 0.46M ??????? Conclusion The equilibrium constant for the reaction (esterification) between ethanoic acid and propan-1-ol is 4.687 mole-1 dm3 Discussion 1. It is assumed that the volume of 8 drops of concentrated sulphuric(VI) acid is very small which could not greatly affected the volume of the original mixture. 2. It is assumed that the volume of 8 drops of concentrated sulphuric(VI) acid added by Joe is same as that of me. 3. It is assumed that the rate of reaction was slow that when the reaction mixture is cooled down by ice water, KC did not change. 4. After adding of 8 drops of concentrated sulphuric(VI) acid, V2 should be found out immediately. Otherwise, the reaction may have started and the result became incorrect. ...read more.

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Response to the question

The focus of the question is done very well. The experiment is set out well and succinctly with accurate calculations. Improvements would be to include diagrams of the experiment to aid the candidates method to show how exactly the equipment ...

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Response to the question

The focus of the question is done very well. The experiment is set out well and succinctly with accurate calculations. Improvements would be to include diagrams of the experiment to aid the candidates method to show how exactly the equipment should be set out.

Level of analysis

The method is set out very accurately which enables the candidate to perform the experiment very precisely. The candidate also shows modification to the experiment in hindsight which shows their understanding of the experiment and also makes their results more reliable. The calculations are performed very well although decimal places are sometimes inconsistent which may mean calculation results are not as accurate. The conclusion and discussion are to a succinct and high level as improvements to the experiment are also suggested at the end.

Quality of writing

Punctuation, grammar and spelling all to an good level. Format of the experiment is very neatly set out.


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