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the partition coef of ethanoic acid between water and 2-methylpropan-1-ol

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Introduction

Determination of the distribution coef. of ethanoic acid between water and 2-methylpropan-1-ol Aim To determine the distribution (partition) coefficient for the equilibrium that exists when ethanoic acid is distributed between water and 2-methylpropan-1-ol. Principle By shaking ethanoic acid solution with 2-methylpropan-1-ol, the concentration of ethanoic acid in each solvent is determined by titration. The partition coefficient, Kd, can be obtained due to different solubility of solute in 2 solvents. Apparatus titration apparatus, separating funnel, 10ml pipettes, beakers, measuring cylinders Procedure 1. 15cm3 of the given aqueous ethanoic acid and 25cm3 of 2-methylpropan-1-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.) 2. 10cm3 of each layer was separated approximately. (The fraction near the junction of the two layers was discarded.) 3. 10.0cm3 of the aqueous layer was pipetted into a conical flask and was titrated with 0.1 M sodium hydroxide solution using phenolphthalein. ...read more.

Middle

is independent of masses of the 2 solvents used in the 3 trails of different volumes of solvents used but only temperature dependent. Hence, the distribution law does not hold when temperature is changed since the equilibrium constant is changed. 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 the partition coefficient varies with temperature. 3. The aim of titration is to find the concentration of the solvent, but not the total number of mole in the solvent. 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. ...read more.

Conclusion

5. The distribution law does not seem to hold in partially miscible solvents (e.g. hexan-1-ol & water). But the basic strength of NaOH is not strong enough to neutralize 2-methylpropan-1-ol and only reacts with ethanoic acid in the experiment. Actually, Pure 2-methylpropan-1-ol (or methylpropan-1-ol) can act as an acid only when it reacts with a very reactive metal (e.g. Na). However, the reaction rate is slow. 6. Two successive extractions by using 25cm3 make a better interaction between two kinds of solutions; than one extraction during shaking. A better equilibrium is thus set up, resulting a higher extraction efficient. 7. In practice, we add little solvent to extract several times in order to obtain a higher yield. Partition can be also applied in chromatography to separate a mixture of solutes. In laboratory, we often use partition applied to solvent extraction to purify a substance instead of by fractional distillation, since the boiling point for both substance and impurities may be so high that the substance may decompose at this temperature. ?? ?? ?? ?? Subject: Chemistry TAS Experiment13 msn: eric0927hk@hotmail.com Name: Eric LI [18/5/2007] 1 ...read more.

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