We’re being asked to determine the molar mass of the unknown solute in the ethanol solution.
We’re given the vapor pressure of the solution, 7.40×102 torr, and the vapor pressure of pure ethanol, 760 torr. The vapor pressure of a solution can be given by Raoult’s Law:
where P˚ = vapor pressure of solvent and χ = mole fraction of solvent.
We shall follow these steps to determine the molar mass of the unknown solute:
Step 1: Calculate the mole fraction of ethanol
Step 2: Calculate the mole of unknown solute.
Step 3: Calculate the molar mass of the unknown solute.
Step1. The mole fraction of ethanol is:
χsolvent = 0.97
The normal boiling point of ethanol, CH3CH2OH, is 78.4 C. When 8.65 g of a soluble nonelectrolyte is dissolved in 100.0 g of ethanol at that temperature, the vapor pressure of the solution is 7.40 x 102 torr. What is the molar mass of the solute?
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