If of a non-electrolyte solute is dissolved in of n-octane to reduce its vapour pressure to , the molar mass (in ) of the solute is [Given that molar mass of n-octane is ]

Question

If  of a non-electrolyte solute is dissolved in  of n-octane to reduce its vapour pressure to , the molar mass (in ) of the solute is [Given that molar mass of n-octane is ]

Canvas Classes · Accepted Answer

🧠 Deciphering the Vapour Pressure Drop
We are looking at "Relative Lowering of Vapour Pressure," a colligative property. The examiner says the pressure reduces to , which is a fancy way of saying the pressure of the solution is  times the pressure of the pure solvent. This gives us the mole fraction of the solute directly if we are careful!

🗺️ The Rigorous Calculation
According to Raoult's Law for a non-volatile solute:

where  is pure solvent pressure and  is solution pressure.

1. Find the

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