Relative Lowering of Vapour Pressure given Number of Moles for Concentrated Solution Calculator

Relative Lowering of Vapour Pressure Formula:

\[ \Delta p = \frac{n}{n + N} \]

Relative Lowering of Vapour Pressure (Δp):

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1. What is Relative Lowering of Vapour Pressure?

Definition: The Relative Lowering of Vapour Pressure is the ratio of the lowering of vapour pressure of the solvent to the vapour pressure of the pure solvent when a non-volatile solute is added.

Purpose: This calculation is important in colligative properties studies and helps determine molecular weights of solutes and understand solution behavior.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \Delta p = \frac{n}{n + N} \]

Where:

\( \Delta p \) — Relative Lowering of Vapour Pressure (unitless)
\( n \) — Number of Moles of Solute (mol)
\( N \) — Number of Moles of Solvent (mol)

Explanation: The formula shows that the relative lowering of vapour pressure is equal to the mole fraction of the solute in the solution.

3. Importance of This Calculation

Details: Understanding vapour pressure lowering is crucial for:

Determining molecular weights of unknown solutes
Studying colligative properties of solutions
Predicting boiling point elevation and freezing point depression
Industrial applications like antifreeze solutions and food preservation

4. Using the Calculator

Tips:

Enter the number of moles of solute (must be ≥ 0)
Enter the number of moles of solvent (must be > 0)
The result is a dimensionless ratio between 0 and 1

5. Frequently Asked Questions (FAQ)

Q1: Why does adding solute lower vapour pressure?
A: Solute particles occupy space at the surface, reducing the number of solvent molecules that can escape into the vapour phase.

Q2: What's considered a "concentrated solution" for this formula?
A: This formula works best for relatively dilute solutions where solute-solute interactions are negligible.

Q3: Does the type of solute matter?
A: The formula assumes the solute is non-volatile. For volatile solutes, additional considerations are needed.

Q4: How accurate is this calculation?
A: Very accurate for ideal solutions. For real solutions, deviations may occur due to intermolecular forces.

Q5: What if I know mass instead of moles?
A: Convert mass to moles using molecular weights before using this calculator.