1. What is Molality using Relative Lowering of Vapour Pressure?

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.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( m \) — Molality of the solution (mol/kg)
• \( p_o \) — Vapour pressure of pure solvent (Pa)
• \( p \) — Vapour pressure of solvent in solution (Pa)
• \( M \) — Molecular mass of solvent (kg)

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.

3. Importance of Molality Calculation

Details: Molality is a temperature-independent concentration measure crucial for colligative property calculations and precise solution preparation.

4. Using the Calculator

Tips: Enter the vapour pressures in Pascals and molecular mass in kg (default 0.018 kg for water). Ensure pure solvent pressure > solution pressure.

5. Frequently Asked Questions (FAQ)

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.