Question

Why nacl solution boil at higher temperature than water but freezes at a lower temperature than water?

Answer 1

Answer:

freezing point depends upon the attraction between the molecules(intermolecular attraction) of the liquid.

Explanation:

when salt (NaCl) is added to water, it decreases the intermolecular attraction as it create attractions between water molecules & Na+ Cl- ions.thus the freezing point decreases after adding salt.

Boiling points depend upon the vapour pressure of the liquid.after adding of the salt, the ions of the liquid surface prevent water molecules from escaping to the atmosphere, thus reducing the vapour pressure.thus the boiling point elevates after adding salt.

Answer 2

Hi mate

here's your answer

When NaCl is added to water the vapor pressure of water over NaCl solution decreases. This vapour pressure in order to become equal with the pressure of the outside atmosphere (for boiling of NaCl solution) thus needs more heating. Hence boiling point elevates and becomes more.

Again, presence of Na+ and Cl- ions in water interferes while freezing the water to make ice. To overcome this interference the solution needs cooling to a temperature lower than the freezing point of water. Remember, it's easier to freeze a pure solvent than to freeze when a solute is dissolved in it because accommodation of Na+ and Cl- in ice cages requires lesser degree of freedom of ions to trap them in ice cages. Therefore the solution needs additional cooling.

This is explained reasonably in Raolt's law of elevation of B.Pt and depression of F. Pt.

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