Question

If P₀​ and P are the vapor pressures of a solvent and its solution, respectively, and n₁​ and n₂​ are the mole fractions of the solvent and non-volatile solute, respectively, then the correct relation is:

a. P=P0​(n₁​−n₂​)
b. P=P0​(n₁​+n₂​)
c. P=P0​n₁​−P0​n₂​
d. P=P0​(n₁​/n₂​)

Answer 1

The correct relation is represented by P = P0n1 - P0n2, which is derived from Raoult's Law and reflects that the vapor pressure of a solution is the product of the mole fraction of the solvent and the vapor pressure of the pure solvent.

Step-by-step explanation:

The correct relation between vapor pressure of a solvent (P0), vapor pressure of a solution (P), mole fraction of the solvent (n1), and mole fraction of the non-volatile solute (n2) is given by Raoult's law. According to Raoult's law, the vapor pressure of the solution is directly proportional to the mole fraction of the solvent. Therefore:

P = P0 × n1

Since n1 + n2 = 1, we can express n1 as (1 - n2). Substituting this into the equation gives us:

P = P0 × (1 - n2)

Therefore, the relationship between the decrease in vapor pressure (ΔPA) and the mole fraction of nonvolatile solute (n2) is:

P = P0 - P0 × n2

So the correct answer to the student's question is P = P0n1 - P0n2, which resembles answer option (c).