Determination of partition co-efficient of Acetic acid between n-butanol and water at room temperature

Principle:

Nernst distribution law states that at constant temperature, when a solute are allowed to distribute  between two immiscible solvents in contact with each other, then at equilibrium  the ratio of the concentration of the solute in two solvent  layers is constant.

When a solute is shaken in two immiscible liquids, then the solute is found to be distributed between the liquids in a definite manner, if the solute is soluble in each of the solvent.

According to distribution law, the distribution co-efficient at a particular temperature is given by

Kd = C1 / C2, where

C1 and C2 represent the concentration of solute in solvent 1 and 2 respectively. When the solute molecules in each solution phase are in same state of association.

Chemicals:   n-butanol, acetic acid, distilled water, NaOH Solution.

Apparatus:

Burette, pipette, 100 ml conical flask, 250 ml Stoppered bottle, Wash bottle, Dropper

Procedure:

  •  A 250 ml stoppered bottle is taken and washed properly with distilled water.
  • This bottle is filled up with 20 ml of n-butanol, 25 ml distilled water and 5 ml of acetic acid.
  • Then it is allowed to shake in a mechanical shaker for about an hour. After shaking, it is kept aside for about 5 minutes so that two layers separate out clearly.
  • 5ml of aqueous layer is pipette out in a 100 ml conical flask. 2 -3 drops of phenolphthalein indicator is added and titrated against standard NaOH solution until colour changes from colourless to pink.
  • 5ml of organic layer is pipette out in a 100 ml conical flask. 2 -3 drops of phenolphthalein indicator is added and titrated against standard NaOH solution until colour changes from colourless to pink.
  • The experiments are repeated to get concordant values.

Observation Table:  

Record the Room temperature =……… °C

Layers TakenPipette Reading (ml)Burette ReadingVolume of NaOH consumed (ml)(Mean Vol.)(V)Kd= C1 / C2
Initial (ml)Final (ml)Difference (ml)
Aqueous Layeri)

ii)

Organic Layeri)

ii)


Calculation
:  

Aqueous Layer (C1): 

Vol. of aqueous layer x C1 = Vol. of NaOH required x strength of NaO

5 ml x C= V x S

C1   = (V x S) / 5

Organic Layer (C2): 

Vol. of Organic layer x C2 = Vol. of NaOH required x strength of NaOH(S)

5 ml x  C= V x S

C2   = (V x S) / 5

Hence,Kd  =  C1 / C2

Conclusion: 

Partition Coefficient of Acetic acid between water & n-butanol is ……..

Precautions:      

  1. Stoppered bottle should be thoroughly cleared & dried.
  2. During withdrawing of liquid for titration, one layer must not be contaminated with other layer.

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