Lowering of vapor pressure is directly proportional to:
a) Temperature
b) Mole fraction of Solute
c) Mole fraction of Solvent
d) Amount of solution
The correct answer is b) Mole fraction of Solute.
Lowering of vapor pressure is a colligative property, which means it depends on the number of solute particles in a solution rather than their nature. According to Raoult's law, the vapor pressure of a solution is directly proportional to the mole fraction of the solvent and inversely proportional to the mole fraction of the solute.
Thus, the more solute particles there are in the solution (higher mole fraction of solute), the lower the vapor pressure will be compared to the pure solvent. Similarly, if the mole fraction of the solute is low, the vapor pressure will be closer to that of the pure solvent.
Temperature (option a) can also affect vapor pressure, but it is not the direct factor responsible for the lowering of vapor pressure in a solution. The other options, c) Mole fraction of Solvent and d) Amount of solution, are not directly linked to the change in vapor pressure.
To determine which factor directly affects the lowering of vapor pressure, we need to understand the concept of Raoult's law, which explains the behavior of ideal solutions.
According to Raoult's law, the vapor pressure of an ideal solution is directly proportional to the mole fraction of the solvent present. This means that as the mole fraction of solvent increases, the vapor pressure of the solution decreases.
On the other hand, the vapor pressure of a solution is not affected by the temperature or the amount of solution. Temperature affects the boiling point but does not directly influence the vapor pressure. The amount of solution (i.e., the volume or mass) does not directly impact the vapor pressure either.
Therefore, the correct answer is:
c) Mole fraction of Solvent