The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour pressure of 1 molal solutio

step 1 One molar solution means one mole of solute, one mole of solute is present in a thousand gram of

The vapour pressure of water is 12.3 kPa at 300 K....

Key Concepts

Molality

Molality is a concentration unit defined as the number of moles of solute per kilogram of solvent. It is particularly useful in studies involving temperature changes because, unlike molarity, molality does not change with temperature. In vapour pressure calculations, molality helps determine how many moles of solvent are present relative to the solute, which is critical for computing mole fraction.

Vapour Pressure Lowering

Vapour pressure lowering is a colligative property that arises when a non-volatile solute is dissolved in a solvent. The introduction of the solute reduces the solvent molecules’ escape tendency into the vapour phase, thereby lowering the overall vapour pressure of the solution compared to the pure solvent.

Raoult's Law

Raoult’s Law states that the vapour pressure of a solvent in an ideal solution is directly proportional to its mole fraction in that solution. This means that when a non-volatile solute is added to a solvent, the vapour pressure of the solvent decreases in proportion to the number of solute particles present, because they reduce the number of solvent molecules at the surface available for evaporation.

Colligative Properties

Colligative properties depend solely on the number of solute particles in the solution rather than their identity. These properties, which include vapour pressure lowering, boiling point elevation, and freezing point depression, are significant because they allow predictions of solution behavior based on concentration alone.

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