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BACKGROUND
When a solute is shaken with 2 immiscible solvents it gets partitioned between the solvents. This distribution of solute in 2 solvents depends upon the solubility of the solute in two solvents. At the distribution equilibrium, the ratio of concentrations of solute in both solvents is constant at a given temperature. The constant is called the partition coefficient (K) or the distribution coefficient of the solute between the two solvents.1
Aim: To establish the partition co-efficient of iodine in distilled water (d.w.) and carbon tetrachloride.
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REQUIREMENTS
Chemicals: Distilled water
Iodine crystals
Carbon tetrachloride
0.01N Na2S2O3
0.1N Na2S2O3
Starch indicators
Apparatus: Separating funnels
Conical flask
Pipette
Burette
Reagent bottles
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PROCEDURE
Approximately prepare 110 ml of saturated solution of iodine in carbon tetrachloride for use as stock solution.
Prepare the following mixtures in separating funnels:
Set I: 50 ml water + 40ml stock solution + 10 ml of CCl4
Set II: 50 ml water + 30ml stock solution + 20 ml of CCl4
Set III: 50 ml water + 20ml stock solution + 30 ml of CCl4
Set IV: 50 ml water + 10ml stock solution + 40 ml of CCl4
Shake the mixture in separating funnel forcefully for about 30 minutes for the iodine to get distributed between the two solvents and to reach the distribution equilibrium. Let the flasks to stand for about 10 minutes so that two clear layers are separated. Now remove stopper of the separating funnel and keep its mouth open during this period to facilitate the separation. Release the lower layer which is aqueous into 4 different stoppered dry bottles. (Discard the intermediate layer between both the phases). Organic layer stays in the separating funnels. Using a dry pipette withdraw 10 ml of organic layer to a conical flask. Titrate it against 0.1N Na2S2O3. Starch is used as an indicator. End point: Blue color will disappear. Withdraw 10 ml of the aqueous layer using a dry pipette and titrate it against 0.01N Na2S2O3 solution using starch as an indicator. End point: Blue color will disappear. Repeat the process for all the mixtures.
Observation table:
|
Set No. |
Vorg |
Vaq |
Norg =Corg |
Naq =Caq |
K=Caq/Corg |
log Corg |
log Caq |
|
I |
|||||||
|
II |
|||||||
|
III |
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|
IV |
Mean Partition coefficient K =
Where,
Vorg= Volume in ml of 0.1N Na2S2O3 per 10ml of the organic layer
Vaq= Volume in ml of 0.01N Na2S2O3 per 10ml of the aqueous layer
Norg= Normality of the organic layer
Naq= Normality of the aqueous layer
Corg= Concentration of the organic layer in g mole/lit = Normality (Norg)
Caq= Concentration of the aqueous layer in g mole/lit = Normality (Naq)
K= Caq/Corg= Partition coefficient of the iodine in water and carbon tetrachloride
Calculations:
Set I
-
For Organic layer
Normality of Na2S2O3 (N1= 0.1N)
Volume of organic layer pipetted (V2) = 10ml
N1V1 (Na2S2O3) = N2V2 (Organic layer)
Similarly calculate concentration of iodine in organic layer of all other sets.
2. For aqueous layer
Normality of Na2S2O3 (N1= 0.01N)
Volume of organic layer pipetted (V2) = 10 ml
N1V1 (Na2S2O3) = N2V2 (Aqueous layer)
Similarly calculate concentration of iodine in of all other sets..
Graph: Plot the graph of log CaqVs log Corg
Above equation, is equation of straight line which is y = mx+c)
Result from the graph
Slope (m) = =
Therefore n is nearly =
Substituting the value of slope of line in the equation
Log (1/n) Caq = (1/n) log Corg + log K
Therefore,
log K=
K = __________
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CONCLUSION
Partition co-efficient of iodine in distilled water and carbon tetrachloride ____________ by calculation and ____________ by graph ____________.
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REFERENCES
1. More HN, HAjare AA. Practical Physical Pharmacy, Career publications; 2010: 70-73.
