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Determination of the Partition Coefficient of Ethanoic Acid between Water and Butan-1-ol

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Introduction

Experiment 03 (16-10-09) Determination of the Partition Coefficient of Ethanoic Acid between Water and Butan-1-ol Objective To determine the partition coefficient of ethanoic acid between water and butan-1-ol by titration. Theory When a solute(X) is added into two immiscible liquids A and B, it can dissolve in both liquids with different solubilities. After shaking, solutions of X in A and X in B can be obtained. X is said to distribute between immiscible liquids A and B. This phenomenon is called the distribution or partition of the solute in two immiscible liquids. The two liquid layers can then be separated by a separating funnel. At constant temperature, the concentrations of solute X in these two liquids are governed by the distribution or partition law: Kd = Concentration of solute in solvent A / Concentration of solute in solvent B, where Kd is the distribution coefficient or partition coefficient. Procedures 1. Room temperature was recorded. 2. 25 cm3 of 0.2000 M aqueous Ethanoic acid and 25 cm3 of butan-1-ol was poured into a 250 cm3 separating funnel by using a 100 cm3 measuring cylinder. 3. ...read more.

Middle

The shaking process of the separating funnel will increase the kinetic energy of the solutions' molecules and thus will increases the temperature. Also, when touching the funnel, warmth of human palms may increase the temperature of the solutions as well. As the partition coefficient is temperature dependent, increasing the temperature will increase the partition coefficient. - Butan-1-ol and water are not completely immiscible. Butan-1-ol is slightly soluble in water. - Ethanoic acid dissociates in water. Ethanoic acid ionizes to some extent in water, so the concentration of free ethanoic acid in water is lowered, leaving less ethanoic acid molecules in butan-1-ol. Suggestion for the improvement - Avoid holding the separating funnel with palms which greatly affects the partition coefficient. - Two totally immiscible solvents should be used instead, e.g. water and ether. - It's hard to prevent the dissociation of ethanoic acid in water. But this error can be minimized by shaking the separating funnel again to force some ethanoic acid molecules back to butan-1-ol before running the solution to the beaker. ...read more.

Conclusion

8. Solvent extraction is more efficient if the extraction solvent is added in small portions several times instead of all at once. One portion of 50 cm3 butan-1-ol: No. of moles of ethanoic acid originally = 25 x 10-3 x 0.2000 = 5 x 10-3 mol Let x be the no. of moles of ethanoic acid extracted in butan-1-ol: = 0.8040 x = 3.57 x 10-3 mol Two portions of 25 cm3 butan-1-ol: No. of moles of ethanoic acid originally = 25 x 10-3 x 0.2000 = 5 x 10-3 mol Let y be the no. of moles of ethanoic acid extracted in butan-1-ol in the first 25 cm3 butan-1-ol: = 0.8040 y = 2.77 x 10-3 mol Let z be the no. of moles of ethanoic acid extracted in butan-1-ol in the second 25 cm3 butan-1-ol: = 0.8040 z = 1.24 x 10-3 mol ?Total no. of moles extracted = 2.77 x 10-3 + 1.24 x 10-3 = 4.01 x 10-3 mol, which is more than that extracted in one portion of 50 cm3 butan-1-ol. 9. Paper chromatography and solvent extraction. Practical Report (Experiment 03) F.7A Angel Chan (4) Page 1 of 5 ...read more.

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