1. What is Van't Hoff Relative Lowering of Vapour Pressure?

Definition: This calculator determines the colligative pressure (lowering of vapour pressure) based on the Van't Hoff factor, molality, and molecular mass of the solvent.

Purpose: It helps chemists and students understand how solutes affect the vapour pressure of solvents in solutions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \Delta p \) — Colligative pressure (lowering of vapour pressure)
• \( i \) — Van't Hoff factor (dimensionless)
• \( m \) — Molality of the solution (mol/kg)
• \( M \) — Molecular mass of the solvent (kg)

Explanation: The formula accounts for the number of particles in solution (i), the concentration (m), and the molecular mass of the solvent.

3. Importance of Vapour Pressure Calculation

Details: Understanding vapour pressure lowering is crucial for predicting boiling point elevation, freezing point depression, and osmotic pressure in solutions.

4. Using the Calculator

Tips: Enter the Van't Hoff factor (default 1.008), molality (default 1.79 mol/kg), and molecular mass of solvent (default 0.018 kg for water). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is the Van't Hoff factor?
A: It's a measure of the effect of solute on colligative properties, equal to 1 for non-electrolytes and greater for electrolytes.

Q2: Why is molality used instead of molarity?
A: Molality (moles solute/kg solvent) is temperature-independent, making it more reliable for colligative property calculations.

Q3: What's a typical molecular mass for water?
A: Water has a molecular mass of 0.018 kg/mol (18 g/mol).

Q4: What units does the result have?
A: The result is unitless, representing the relative lowering of vapour pressure.

Q5: How accurate is this calculation?
A: It's accurate for ideal solutions. For real solutions, activity coefficients should be considered.