Question

. 11.94g of a non-volatile solute is dissolved in 100g water.
The vapour pressure of the resulting solution is 740.9 mm
Hg at 373K. Calculate the molar mass of the solute. pls give me the procidure ​

Answer 1

The molar mass of the solute is 11.94 g/mol.

To calculate the molar mass of the solute, we can use the concept of Raoult's law and the equation relating vapor pressure and mole fraction.

Raoult's law states that the vapor pressure of a solution is directly proportional to the mole fraction of the solvent. The equation for Raoult's law is as follows:

P = X_solvent * P_solvent

where P is the vapor pressure of the solution, X_solvent is the mole fraction of the solvent, and P_solvent is the vapor pressure of the pure solvent.

In this case, we are given that the vapor pressure of the solution (P) is 740.9 mmHg, and we need to calculate the molar mass of the solute.

To proceed, we need to determine the mole fraction of the solvent (X_solvent) in the solution. The mole fraction can be calculated as follows:

X_solvent = moles of solvent / total moles of solution

Since the solute is non-volatile, its contribution to the vapor pressure is negligible, and we can assume that the total moles of solution are equal to the moles of solvent.

Given that 11.94g of solute is dissolved in 100g of water, the total mass of the solution is 100g + 11.94g = 111.94g.

Now, let's calculate the moles of solvent:

moles of solvent = mass of solvent / molar mass of solvent

The mass of the solvent is 100g, and the molar mass of water is 18.015 g/mol.

moles of solvent = 100g / 18.015 g/mol = 5.548 mol

Since the total moles of solution are equal to the moles of solvent, the mole fraction of the solvent is:

X_solvent = 5.548 mol / 5.548 mol = 1

Now, we can use Raoult's law to determine the vapor pressure of the pure solvent, P_solvent:

P_solvent = P / X_solvent = 740.9 mmHg / 1 = 740.9 mmHg

At this point, we have all the necessary information to calculate the molar mass of the solute. The equation for Raoult's law can be rearranged as follows:

Molar mass of solute = P_solvent * mass of solute / (P - P_solvent)

Plugging in the values:

Molar mass of solute = 740.9 mmHg * 11.94g / (740.9 mmHg - 740.9 mmHg)

= 11.94g

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