Distribution Coefficient and Le Chatliers Principle Lab For Chemical Equilibrium Partition Coefficient

Lab Chemical Equilibrium – Distribution Coefficient and Le Chatliers Principle – Partition Coefficient

This activity is based on the following equilibrium

I2(aq) ==     I2(Varsol)

Brown   Pink

Iodine distributes itself between an aqueous solution and a non-aqueous solution like varsol. When a solution of iodine is distributed the color of the two solutions will appropriately indicate the concentrations of iodine in the respective solutions. There exists constancy in the macroscopic property. In this case the color of the two solutions, this demonstrates that the system has attained equilibrium. The equilibrium constant in this case is called distribution coefficient or partition coefficient.

I2 does not dissolve in water  I2 is dissolved in KI solution when it forms a complex ion

I2 + I(aq) « I3(aq)

Procedure

Label 6 clean dry test tubes 1 to 6

· In each of the test tubes place 2 mL of aqueous Iodine solution and 2 mL of Varsol to each of the test tube.

· Perform this one at a time in the fume cupboard; stopper the test tube as soon as you have mixed to two solutions.

· Repeat this for the remaining 5 test tubes.

· The non-aqueous solutions will float over the aqueous solution.

· Use test tube 1 as a reference.

Procedure

Predictions

Observations

1

Control mixture

2 mL of I2/KI solution + 2 mL Varsol

Retain this mixture for color reference

Varsol

Varsol

Aqueous

Aqueous

2

Add 4 mL of Varsol to above composition

Varsol

Varsol

Aqueous

Aqueous

3

Add 4 mL of water

Varsol

Varsol

Aqueous

Aqueous

4

Add 2 drops of saturated I2/KI

Varsol

Varsol

Aqueous

Aqueous

5

Add saturated Na2S2O3

Varsol

Varsol

Aqueous

Aqueous

6

Add saturated KI

Varsol

Varsol

Aqueous

Aqueous

Report

· Using equilibrium equations and Le Chatliers principle to rationalize observations made for activity 2 to 6. Write an equilibrium equation, answers should include equilibrium shifts left or right because … and explain in terms of what causes the equilibrium to shift, give formulas of the reactants and products that may have formed. Give a complete equation for experiment part 5.

Teacher notes:

Reagents:

Lugol, dilute it to obtain a 10 % solution 1 mL Lugols iodine solution and 9 mL distilled water. Make sure the color of the mixture is pale pink and pale yellow. If the colors are too deep, color changes cannot be noticed.

10 % KI solution add 5 drops at a time shake the solution well followed by the next 5 drops, continue until you see noticeable change in color of the solutions.

10 % Na2 S2O3 add 1 drop at a time shake the solution well and add the second drop

Reaction between Iodine and Thiosulfate

2Na2S2O3 + I2 ® Na2S4O6 + 2NaI

© Stan Vincent