MINIMUM AND MAXIMUM BOILING NEGETIVE OR POSITIVE AZEOTROPES

 AZEOTROPES:- THE MIXTURE OF LIQUID WHICH BOIL AT CONSTANT TEMPERATURE LIKE A PURE LIQUID AND POSSESS SAME COMPOSITION OF COMPONENT IN LIQUID AS WELL AS VAPOUR PHASE ARE CALLED CONSTANT BIOLING MIXTURE OR AZEOTROPIC MIXTURE.

MINIMUM BOILING AZEOTROPES:-

THEY FORMED BY THOSE LIQUID PAIRS WHICH SHOW POSITIVE DEVIATION FROM IDEAL BEHAVIOUR Eg., ETHANOL -WATER MIXTURE.

1. Minimum Boiling Azeotropes or Negative Azeotrope

Azeotropic mixtures with a higher boiling point in their constitutions are maximum boiling azeotropes. Water boils at 373 K and hydrochloric acid boil at about 188 K,  while azeotropes boil at around 383 K which is a boiling point greater than its constituents. Consider, for example, hydrochloric acid Consider, for example, hydrochloric acid consisting of a weight concentration of approximately twenty per cent and 79 per cent of water.

Examples:

• Separation of water and isobutaol
• Dehydration of ethanol.
• Separation of cyclohexane and benzene

2. Maximum Boiling Azeotropes or Positive Azeotrope

Similarly, an azeotropic mixture that has a boiling point lesser than its constituents is known as minimum boiling azeotropes. Consider, for example, ethanol consisting of a weight concentration of approximately ninety-five per cent and four per cent of water. Water boils at 373 K, and ethanol boils at about 351.5K, while azeotropes boil at around 351.15 K, suggesting a boiling point lower than its constituentsisting of a weight concentration of approximately twenty per cent and 79 per cent of water.

COLLIGATIVE PROPERTIES:

A colligative property is a property of a solution that is dependent on the ratio between the total number of solute particles (in the solution) to the total number of solvent particles. Colligative properties are not dependent on the chemical nature of the solution’s components. Thus, colligative properties can be linked to several quantities that express the concentration of a solution, such as molarity, normality, and molality. The four colligative properties that can be exhibited by a solution are:

RELATIVE LOWERING OF VAPOUR PRESSURE:

Vapour pressure is the pressure exerted by the vapours over the liquid under the equilibrium conditions at a given temperature. Now let us take an example of a pure liquid, the surface of the liquid is occupied by the molecules of the liquid. Suppose a non-volatile solute is now added to this pure liquid. Since the solute molecules are non-volatile, the vapour above the solution consists of only solvent (pure liquid) molecules. After adding the solute, the vapour pressure of the solution is found to be lower than that of the pure liquid at a given temperature.