Molality Formula:
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Definition: This calculator determines the molality of a solution based on the relative lowering of vapour pressure when a solute is added to a solvent.
Purpose: It helps chemists and students calculate solution concentration (molality) using vapour pressure measurements.
The calculator uses the formula:
Where:
Explanation: The difference in vapour pressures is multiplied by 1000 (for kg conversion) and divided by the product of molecular mass and pure solvent vapour pressure.
Details: Molality is a temperature-independent concentration measure crucial for colligative property calculations and precise solution preparation.
Tips: Enter the vapour pressures in Pascals and molecular mass in kg (default 0.018 kg for water). Ensure pure solvent pressure > solution pressure.
Q1: Why use molality instead of molarity?
A: Molality is temperature-independent since it's based on mass, not volume which changes with temperature.
Q2: What's a typical molecular mass for water?
A: Water has a molecular mass of 0.018 kg/mol (18 g/mol).
Q3: Can vapour pressure of solution be higher than pure solvent?
A: No, adding non-volatile solute always lowers vapour pressure.
Q4: What units should I use for vapour pressure?
A: Pascals (Pa) are recommended, though any consistent pressure unit would work.
Q5: How precise should my measurements be?
A: For accurate results, measure vapour pressures to at least 3 significant figures.