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When small quantity of phenol is mixed with water and the mixture is shaken, phenol dissolves, forming a single layer. On adding larger quantities of phenol, however, two kinds of compositions (layers) of liquid are formed. The lower layer consists of small amounts of water dissolved in phenol (phenol saturated with water) and upper layer of phenol dissolved in water (water saturated with phenol).1
Aim: To determine the critical solution temperature or upper consolute temperature of phenol-water system.
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Chemicals: Phenol in liquid state
Apparatus: Hard glass tube
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Weigh accurately 4 gms (w1 gm) of phenol in a glass tube. (Do not touch phenol, it is corrosive). Introduce glass rod and thermometer (with 0.1◦C accuracy) into it. Fix the tube in a vertical position in a water bath (beaker containing water). Set up the apparatus as shown in the figure. Add 2 ml of distilled water to phenol and heat the test tube in a water bath, whose temperature is initially raised to about 30◦C on low flame with constant stirring. Note the temperature (T1) of solution at which a clear and transparent solution is obtained. It is the solution of water in phenol. Remove the tube outside the water bath and with constant stirring note the transition temperature t◦ C at which the turbidity reappears (this is because water separates out as a different layer.). Add 2 ml more of distilled water and record the transition temperature. Continue the addition of 2 ml distilled water and record the transition temperature till the temperature goes through a maximum value (CST) and comes down to about 40◦C.
Weight of phenol = w1 gm (about 4 gms)
Density of water d = 1.0 gm/ml
W2 = V.d
V = ml of water added
W2 = weight of water
P = % Phenol = 100W1
W1 + W2
Graph: Plot a graph of transition temperature vs Percent by weight of phenol (P) and read the critical solution temperature. (Maximum temperature)
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The critical solution temperature for phenol water system is ___◦C at___% by weight of phenol.
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1. More HN, Hajare AA. Practical Physical Pharmacy, Career publications; 2010: 86-87.