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Mass Transfer - Engineering

Q1:

On addition of solute in the solvent, the __________ of the solution decreases.

A boiling point

B freezing point

C vapour pressure

D both (b) and (c)

ANS:D - both (b) and (c)

The correct answer is: "both (b) and (c)" Explanation:

  1. Freezing Point Depression:
    • When a solute is added to a solvent, it disrupts the orderly arrangement of solvent molecules in the liquid phase, making it more difficult for the solvent to form a crystalline solid structure.
    • As a result, the freezing point of the solution decreases compared to that of the pure solvent. This phenomenon is known as freezing point depression.
  2. Vapor Pressure Lowering:
    • Addition of a non-volatile solute to a solvent reduces the vapor pressure of the solution compared to that of the pure solvent.
    • This is because the presence of the solute reduces the number of solvent molecules available to escape into the vapor phase, resulting in a lower vapor pressure.
    • Consequently, the boiling point of the solution increases compared to that of the pure solvent due to vapor pressure lowering.
In summary, upon addition of a solute in a solvent, both the freezing point of the solution decreases and the vapor pressure of the solution decreases. Therefore, the correct answer is "both (b) and (c)".