Determination of Partition Coefficient Of benzoic acid between Benzene and water

 

Aim: To determine partition  Coefficient of Benzoic acid between Benzeen and water.

Requirements:

• Separating funnel(250ml)
• Conical flask
• Pipette
• Burette
• Stoppered bottle
• Saturated solution of Benzoic acid in Benzene 
•  Benzene
• 0.1N NaOH
• Distilled water

Principle:

Prepared the following mixtures in separating funnels: 

Set I: 25ml water+25ml of saturated solution of benzoic acid in benzene.  

Set II: 25ml water+ 20ml saturated solution of benzoic acid in benzene +5ml benzene.

Set III: 25ml water+15ml saturated solution of benzoic acid in benzene + 10ml benzene.

Shaken the mixture in the separating funnel vigorously for about 30minutes so that the benzoic acid gets distributed between the two solvents and the distribution equilibrium is reached. Allowed the flasks to stand for 10 minutes to separate into two clear layers (removable stopper of the separating funnel and keep its mouth open during this period to facilitate the separation). Drain off the lower aqueous layers in 3 different stoppered by bottles(Discard the intermediate layer between  the two phases). Benzene layer remains in the separating funnels using a dry pipette take 5ml of organic layer (Benzene into a conical flask containing 10ml of water and titrate against 0.1N NaOH using phenolphthalein as an indicator. The end point is indicated by the color change from colorless to pink. Pipette out 10ml of the aqueous layer using dry pipette and titrate it against NaOH solution using Phenolphathalein as an indicator. End point is indicated by the color change from colorless to pink.

Observation: 

Set no	Vorg	Vaq	Norg =Corg	Naq =Caq	K	log Corg	log Caq

Mean partition coeficient (K) =

V_org = Volume in ml of 0.1N sodium hydroxide per 5ml of organic layer.

V_aq = Volume in ml pf 0.1 N sodium hydroxide per 5ml of aqueous layer.

N_org = Normality of organic layer.

N_aq = Normality of aqueous layer.

C_org = Concentration of organic layer in g mole/lit.

C_aq = Concentration of aqueous layer in g mole/lit.

K =C_aq/(C_org)^1/2 =Partition coefficient of benzoic acid in water and benzene

 

Calculations:

Set 1: 

 For organic layer

Normality of NaOH (N₁=0.1N)

    Volume of organic layer pipetted (V₂) =5ml 

N₁V₁Sodium hydroxide =N₂V₂ (organic layer)

Similarly calculate concentration of benzoic acid in organic layer of sets  II and III

For aqueous layer

Normality of NaOH (N₁=0.01N)

    Volume of organic layer pipetted (V₂) =5ml 

N₁V₁ Sodium hydroxide =N₂V₂ (Aqueous layer)

Similarly calculate concentration of benzoic zcid in aqueous layer of sets II and III 

Graph

Polt the graph of log C_aq VS Log C_aq

 partition coefficient (k) = C_aq

                                                           C_aq^1/2

log C_aq =1/n log C_org +log k         

 Above eqution is eqution of a straight line (y-mx+c)

Result from graph

Slope(m) = 1/n

Therefore, n is nearly = substituting the value of slope of line in the equation log

 log C_aq =1/n log C_org +log k  

 log C_aq =log C_org +log k

log k =  

Report: 

1. Partition coefficient of benzoic acid between distilled water and benzene is _________by calculation and_______by graph.
2. Since C_aq/C_org^1/2 is practically constant benzoic acid exists as a dimer (n=2) in benzene. 
3. Molecular condition of benzoic acid associate in benzene is 1 slope =n =_______molecules of benzoic acid associate in benzene.