Babo’s Law

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Babo’s Law states that the vapor pressure of a liquid is lowered when a non-volatile substance is dissolved in it. The decrease in vapor pressure is directly proportional to the concentration of the dissolved non-volatile substance. This phenomenon is a colligative property, meaning it depends on the number of solute particles in the solution rather than their identity.

Details:

• Vapor Pressure: The pressure exerted by a vapor in equilibrium with its liquid or solid phase.
• Non-volatile Substance: A substance with a very low vapor pressure that does not easily evaporate.
• Proportional Relationship: The reduction in vapor pressure \((\Delta P)\)is proportional to the molar concentration (mole fraction) of the solute \((X_{\text{solute}})\) in the solution.

Mathematical Expression:

\[ \Delta P = P_{\text{pure}} – P_{\text{solution}} = k \cdot X_{\text{solute}} \]

where:

• \(\Delta P\) is the decrease in vapor pressure.
• \(P_{\text{pure}}\) is the vapor pressure of the pure solvent.
• \(P_{\text{solution}}\) is the vapor pressure of the solution.
• \(k\) is a proportionality constant.
• \(X_{\text{solute}}\) is the mole fraction of the solute.

Applications:

• Boiling Point Elevation: The boiling point of a solution is higher than that of the pure solvent due to the lowered vapor pressure.
• Freezing Point Depression: The freezing point of a solution is lower than that of the pure solvent for the same reason.
• Osmotic Pressure: Related to the concentration of solutes in a solution, important in biological and chemical systems.

Babo’s Law is an important principle in physical chemistry and helps in understanding the behavior of solutions and their colligative properties.

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