"an aqueous cacl2 solution has a vapor pressure of 83.1mmhg at 50 ∘c. the vapor pressure of pure water at this temperature is 92.6 mmhg. what is the concentration of cacl2 in mass percent? "

Answer : The the concentration of in mass percent is, 41.18 %

Solution : Given,

Molar mass of water = 18 g/mole

Molar mass of = 110.98 g/mole

First we have to calculate the mole fraction of solute.

According to the relative lowering of vapor pressure, the vapor pressure of a component at a given temperature is equal to the mole fraction of that component of the solution multiplied by the vapor pressure of that component in the pure state.

where,

= vapor pressure of the pure component (water) = 92.6 mmHg

= vapor pressure of the solution = 83.1 mmHg

= mole fraction of solute,

Now put all the given values in this formula, we get the mole fraction of solute.

Now we have to calculate the mole fraction of solvent (water).

As we know that,

The number of moles of solute and solvent will be, 0.102 and 0.898 moles respectively.

Now we have to calculate the mass of solute, and solvent, .

Mass of solution = Mass of solute + Mass of solvent

Mass of solution = 11.32 + 16.164 = 27.484 g

Now we have to calculate the mass percent of

Therefore, the the concentration of in mass percent is, 41.18 %