The question is incomplete, here is the complete question:
A solution contains 0.115 mol and an unknown number of moles of sodium chloride. The vapor pressure of the solution at 30°C is 25.7 torr. The vapor pressure of pure water at this temperature is 31.8 torr. Calculate the number of grams of sodium chloride in the solution. (Hint: Remember that sodium chloride is a strong electrolyte.)
<u>Answer:</u> The mass of sodium chloride in the solution is 0.714 grams
<u>Explanation:</u>
The formula for relative lowering of vapor pressure will be:
where,
= vapor pressure of solvent (water) = 31.8 torr
= vapor pressure of the solution = 25.7 torr
i = Van't Hoff factor = 2
= mole fraction of solute (sodium chloride) = ?
Putting values in above equation, we get:
Mole fraction of a substance is calculated by using the equation:
We are given:
Moles of water = 0.115 moles
To calculate the mass for given number of moles, we use the equation:
Moles of NaCl = 0.0122 moles
Molar mass of NaCl = 58.5 g/mol
Putting values in above equation, we get:
Hence, the mass of sodium chloride in the solution is 0.714 grams