Anonymous
Anonymous asked in 科學及數學化學 · 1 decade ago

ChemExp about partition coeff

Topic: Determination of the partition coefficient of ethanoic acid between water and 2-methylpropan-1-ol.

1. Why is shaking necessary when aqueous ethanoic acid and 2-methylpropan-1-ol were added into a separating funnel?

2. Would you expect the Partition Coefficient to vary with temperature? Explain briefly.

3. Explain why the amounts of aqueous ethanoic acid and 2-methylpropan-1-ol placed in the funnel need not be measured out accurately, whereas the volumes of the aqueous and alcohol solution used in the titration must be know as accurately as possible.

4. What assumptions are made in the above experiment? Based on experimental evidence,are these assumptions vaild? Explain your answer.

5. Why is it more efficient to extract a solute with two 25cm3 portions of solvent rather than with a single 50cm3 extration?

6. Give two applications of the partition law.

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  • 1 decade ago
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    1. Shaking is necessary 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 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.

    2009-04-24 01:40:39 補充:

    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.

    2009-04-24 01:40:56 補充:

    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.

    2009-04-24 01:41:14 補充:

    5. Solvent extraction is more efficient if the extraction solvent is added in small portions several times instead of all at once. Therefore it is more efficient to extract a solute with two 25cm3 portions of solvent rather than with a single 50cm3 extraction.

    2009-04-24 01:42:26 補充:

    6. The applications of the partition law:

    a) By partition law, the KD can be found experimentally. The amount of the solute that can be extracted using solvent extraction can be predicted, instead of using other complex method.

    2009-04-24 01:42:35 補充:

    b) By partition law, we know that the amount of solute extracted is more when the extracting solvent is added in several small portions instead of all at once.

    Source(s): , i'm working on this too ... add oil! =)
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