At 50 °C, the vapour pressure of pure benzene is 268 torr. The number of moles of non-volatile solute per mole of benzene required to prepare a solution having a vapour pressure of 167 torr at the same temperature is
0.505
0.705
0.605
0.405
The correct option is: (C): 0.605.
The decrease in vapor pressure when a non-volatile solute is added to a solvent follows Raoult's law. According to Raoult's law, the vapor pressure of a solvent in a solution is proportional to its mole fraction in the solution.
The formula for Raoult's law is:
P_solvent = x_solvent * P°_solvent
Where:
In this case, you want to find the mole fraction of benzene (the solvent) that results in a vapor pressure of 167 torr at 50 °C. You're given the vapor pressure of pure benzene as 268 torr at the same temperature.
Rearranging the Raoult's law equation to solve for x_solvent:
x_solvent = P_solvent / P°_solvent
Plug in the values:
x_solvent = 167 torr / 268 torr ≈ 0.6231
Now, the mole fraction of the solute (non-volatile solute) can be calculated as:
x_solute = 1 - x_solvent ≈ 1 - 0.6231 ≈ 0.3769
The number of moles of non-volatile solute per mole of benzene can be calculated using the mole fractions:
Moles of solute / Moles of benzene = x_solute / x_solvent
Moles of solute / 1 = 0.3769 / 0.6231
Moles of solute ≈ 0.605
So, the answer is approximately 0.605
A solution is a homogeneous mixture of two or more components in which the particle size is smaller than 1 nm.
For example, salt and sugar is a good illustration of a solution. A solution can be categorized into several components.
The solutions can be classified into three types:
On the basis of the amount of solute dissolved in a solvent, solutions are divided into the following types: