Find molality of a solution containing non - volatile solute if its vapour pressure is 2% below the vapour pressure of pure water

1.134molal

6.173 molal

1.134

To find the molality of a solution containing a non-volatile solute where its vapor pressure is 2% below the vapor pressure of pure water, we need to use Raoult's law.

Raoult's law states that the vapor pressure of a solvent in a solution is directly proportional to the mole fraction of the solvent. In this case, the solvent is water.

Given that the vapor pressure of the solution is 2% below the vapor pressure of pure water, we can write the equation as:

P_solution = (1 - 0.02) * P_water

Where P_solution is the vapor pressure of the solution and P_water is the vapor pressure of pure water.

Now, let's denote the molality of the solution as 'm' and the molality of the solvent (water) as 'm0'. Molality is defined as the number of moles of solute per kilogram of solvent.

Since the solute is non-volatile, its vapor pressure is negligible, and we can assume that the vapor pressure of the solution is equivalent to the solvent's vapor pressure.

Therefore, we can rewrite Raoult's law equation as:

P_solution = (1 - 0.02) * P_water = P_water = m0 * R * T

Where R is the gas constant and T is the temperature in Kelvin.

Since we are given the vapor pressure of water, we can find the corresponding molality by rearranging the equation as follows:

m0 = P_water / (R * T)

To determine the molality, we need to know the temperature at which the solution is being measured and the vapor pressure of water at that temperature. Then, we can substitute those values into the equation to calculate the molality.