When salt is added to water it's ______.

The correct answer is Boiling Point increases.

Key Points

Concept:

• Elevation in the boiling point refers to a condition where the temperature at which a solvent vaporizes is upraised.  
• This phenomenon is a result of the introduction of a non-volatile solute is to the pure solvent.
• The non-volatile solute on adding to the pure solvent disturbs the molecular interaction between the solvent molecule. 
• This reduces the capability of the solvent molecule to transform from the liquid phase to the gaseous phase. The vapour pressure of the solvent is brought down. 
• Thus more energy is required to vaporize the solvent. This energy is provided in the form of an increase in temperature.

Explanation:

• Salt is a non-volatile solute. When it is added to pure water, it interacts with the water molecules and also occupies sites between the top layer of water molecules.
• The intermolecular attraction between salt-water molecules is greater than water-water molecules.
• When water is heated at 100ºC ( Boiling Point of water), the salt molecules makes it difficult for the water molecules to evaporate due to greater attractive forces.
• So, to reach the vaporization stage higher temperature is required. Therefore, when salt is added to water, the boiling point of water increases.

Additional Information

• The boiling point of a solvent is a temperature at which the vapour pressure of the solvent becomes equal to the atmospheric pressure.
• On introducing an agent to the solvent that decreases the vapour pressure of the solvent, the Boiling point is increased.
• On introducing an agent to the solvent that increases the vapour pressure of the solvent, the Boiling point is decreased.