Mole Fraction Formula:
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Definition: Mole fraction is the ratio of the number of moles of solute to the total number of moles of solute and solvent in a solution.
Purpose: It's a way to express the concentration of a solution and is particularly useful in studying colligative properties like vapour pressure lowering.
The calculator uses the formula:
Where:
Explanation: The difference in vapour pressures is divided by the pure solvent's vapour pressure to determine the solute's mole fraction.
Details: Mole fraction helps predict how much a solute will affect the solvent's properties, particularly its vapour pressure, boiling point, and freezing point.
Tips: Enter the vapour pressure of pure solvent and the vapour pressure of the solution. Both values must be in Pascals, and solution pressure must be ≤ pure solvent pressure.
Q1: What does a mole fraction of 0.05 mean?
A: It means 5% of all molecules in the solution are solute molecules (5 solute molecules per 100 total molecules).
Q2: Why does adding solute lower vapour pressure?
A: Solute molecules occupy space at the surface, reducing solvent molecules that can escape into the vapour phase.
Q3: What's the range of possible mole fraction values?
A: Mole fraction ranges from 0 (pure solvent) to 1 (pure solute), but typically much less than 1 in real solutions.
Q4: How accurate is this calculation?
A: It's exact for ideal solutions and a good approximation for dilute real solutions.
Q5: Can I use different pressure units?
A: Yes, as long as both pressures are in the same units (mmHg, atm, etc.), the mole fraction will be correct.