HETEROGENOUS EQUILIBRIUM || B.TECH FIRST YEAR CHEMISTRY PRACTICAL

       HETEROGENIOUS  EQUILIBRIUM

TITLE=HETEROGENOUS EQUILIBRIUM

 

OBJECT=  Determination of partition co-efficient of Acetic acid between n- butanol and water.

Theory= Thermodynamic derivation of the distribution law.

       We know Gibbs free energy equation.

The thermodynamic derivation of the distribution law is based  upon the principle that if there are two phase in equilibrium the chemical potential of a substance present in them must be in both th phases.

From thermodynamics ,we know that the chemical potential of a substance is a solution given by 

μ=μº+ RTlna

where μ0 is the standard chemical potential and 'a' is the activity of the substance in the solution.

Thus for the solute in liquid A,we have

μA=μºB+RT lnaB

But as already stated ,since the liquid A and B are in equilibrium

μA=μn

μ1+RT lnan=μºB-μºA

or ln aA/aB=(μºB-μºA)/RT

Further at a given temperature μºA and μºB are constant for given substancein the particular solvents .Hence at constant temperarure,we have from equation

ln (an/aB)=constant

And therefore

aA/aB=constant

This is the exact expression of the distribution law.However ,if the solution are dilute,the activates are equal to the concentrations so that the expression is modified to CA/CB=constant

Which is the original form of the distribution law when a system consist of parts which have different  physical properties and which are seperated by bounding surfaces ,the system is said to be a homogenous one.Consider a liquid system ,say water and n-butanol,to which little quantity of acetic acid is added .Acetic acid will dissolve partly in water and partly in n- butanlo.The two solutions of acetic acid will seperate into two layers at equilibrium .The concentrations in the two layers are different but their ratio is fixed at a constant temperature provided there is neither association nor dissociation of the solute in solvents and the ratio is independent of the amount of acetic acidadded or the volume of the two liquids present.

"The concentration of a solute distrubuted between two phases at a constant temperature bear a fixed ratio".

This is the Nernst Distribution law.

This is mathematically expressed as : C1/C2=Kd

Where,C1 is the concentration of the solute in one solvent and C2 is that in another solvent Kd is called the distribution coefficient.

OBSERVATION TABLE

Determination of partition co - efficient of Acetic acid between n-butanol &water

For Homogenous equilibrium system 1&2

CALCULATION :

Determination of partition co-efficient of Acetic acid between n-butanol and water.

1. For heterogenous equilibrium system 1 

 Calculation of C1:

Volume of aqueous layer taken ×C1(strength of aqueous layer)=volume of NaoH required ×strength of Naoh 

  5ml×C1= 4×0.5

C1= 0.4

   

   Calculation of C2:

Volume of organic layer taken ×C2(strength of organic layer)=volume of Naoh required×strength of Naoh

  5 ml ×C2 = volume of Naoh required ×S2

C2 = 0.5

Kd1 = 0.8

2.For Heterogenous Equilibrium system 2:

 Calculation of C3 :

Volume of aqueous layer ×(strength of aqueous layer)=volume of Naoh required ×strength of Naoh 

    5ml×C3=volume of Naoh required ×S2

  C3 = 0.8

Calculation of C4:

Volume of organic layer taken ×C4(strength of organic layer)=volume of Naoh required ×strength of Naoh

     5ml×C4=volume of Naoh required ×S2

 C4=0.95

   Determination of Kd2:

Partition co-efficient for the heterogenous equilibrium system 2

     

 Kd2 =C3/C4=0.84

 Kd1≈Kd2≈1