Question

On the basis of information given below mark the correct option.
Information: On adding acetone to methanol some of the hydrogen bonds between methanol molecules break.
A. At specific composition methanol acetone mixture will form a minimum boiling azeotrope and will show positive deviation from Raoult’s law.
B. At specific composition methanol acetone mixture will form maximum boiling azeotrope and will show positive deviation from Raoult’s law.
C. At specific composition methanol acetone mixture will form a minimum boiling azeotrope and will show negative deviation from Raoult’s law.
D. At specific composition methanol acetone mixture will form maximum boiling azeotrope and will show negative deviation from Raoult’s law.

Answer 1

Hint:Azeotrope mixture is the mixture in which the vapor and the fluid have the same concentration. This mixture is made up of two or more liquids. It is basically defined as a constant or same boiling point and the mixture vapor will also have the same composition as the liquid. The components of the mixture can be separated by the process of distillation.

Complete answer:
There are two types of azeotrope mixtures, the first is minimum azeotrope mixture in which the boiling point of the mixture is low so they are known as negative azeotrope also. Generally the boiling point of water is hundred degree Celsius and for hydrochloric acid is about minus eight degree Celsius. But the boiling point of azeotropic mixture is around seventy eight degree Celsius showing that the boiling point of the mixture is greater than the components. Example - separation of water and isobutanol, dehydration of ethanol and the separation of benzene and cyclohexane. The other type of azeotrope mixture is maximum azeotrope in which the boiling point of the mixture is higher than the constituents. For example- separation of water from ethanol.
The Raoult’s law states that the vapor pressure of the solvent above the solution is equal to the vapor pressure of the pure solvent at the same temperature scaled by the mole fraction of the solvent present. The solutions which obey Raoult law are ideal solutions and those which do not show Raoult law are called non- ideal solutions. The positive deviation from Raoult’s law shows that if the vapor pressure of constituents is higher than the solution and if the vapor pressure of the constituents is lower than the solution then it shows negative deviation.
When acetone is added to methanol the intermolecular forces of attraction between the particles get weaker so the vapor pressure of the solution increases thereby decreasing the boiling point of the solution. When the boiling point of solution gets decreased it shows a minimum azeotrope mixture. As the vapor pressure of solution increases due to breakage of hydrogen bonding, it shows positive deviation from Raoult's law.

So the correct answer to this question is option ‘A’.

Note:
The Raoult’s Law for non volatile solute is equal to the vapor pressure of pure solvent at the temperature multiplied by its mole fraction. The limitations for the law are that the intermolecular force of attraction between solvent and solute particles should be the same as that of individual molecules. It is valid when the liquid phase is almost pure .