Determination of Critical Solution Temperature - Thermolab

DETERMINATION OF CRITICAL SOLUTION TEMPERATURE AIM:

To determine the critical solution temperature for Phenol-water system. APPARATUS REQUIRED:

Beaker, Water bath, Graduated pipette, Measuring Cylinder etc. THEORY:

The phase rule expresses the condition of equilibrium by the relation between the no. of the coexisting phases and the components and is is given as F = C + 2 –  P  P When two partially miscible liquids are mixed and shaken together, we get two solutions of different compositions. For example, on shaking phenol and water, we get two layers. The upper layer is a solution of water in phenol & the lower layer is a solution of phenol in water. At a fixed temperature, the composition of each solution is fixed and solutions are in equilibrium. Two solutions of different composition existing in equilibrium with one another are known as conjugate solutions. Above a particular temperature, such solutions are completely miscible in all  proportions; such temperature is known as critical solution temperature. The mutual solubility increases with temperature. In this experiment, mixtures of phenol and water of varying compositions are taken and their miscibility temperatures are determined. The miscibility temperatures are plotted against their compositions. The maximum temperature point on the curve obtained is the critical solution temperature. PROCEDURE: 1. Add 1 ml of water to 5 ml of phenol in a test tube and heat th e contents by inserting the test tube in hot water beaker. 2. On heating the two solutions will become a single layer so that turbidity disappears. Note down that miscibility temperature. 3. Take the test tube outside then allow it to cool slowly till the turbidity reappears. Note down that temperature also. 4. Repeat the same procedure by adding one more ml to the mixture of phenol water taken already upto 6-7 ml of water addition. 5. Note down different turbidity disappearing and appearing temperatures for each 1 ml addition of water to phenol. 6. Plot a graph of miscibility temperature versus % of Phenol. The maximum temperature is the Critical Solution Ttemperature of the system.

Tabular Column for the Determination of miscibility temperature

S NO

1 2 3 4 5 6 7 8

Volume of Phenol (Va) 5 5 5 5 5 5 5 5

Volume of Water (Vb) 1 2 3 4 5 6 7 8

% of Phenol Va/Va+Vb

Miscibility Temperature °C Turbidity Turbidity Mean disappears appears Value

MODEL GRAPH: Miscibility temperature Vs Vol. % of phenol

RESULT: The critical solution temperature for Phenol water system is found to be __ °C