Answer to Question #131933 in General Chemistry for Meym

Question

How to determine a colorless liquid is a pure water or a solution of salt in water without tasting it?

Answer 1

QUESTION # 131933

How to determine a colourless liquid is a pure water or a solution of salt in water without tasting it?

ANSWER

Boiling point

Boil the colourless liquid and note its boiling point or freeze it and note its freezing point. Pure water boils at 100℃ or 373K and freezes at 0℃ or 273K under 1 atm pressure while the salt solution will have different boiling point and freezing point at 1 atm pressure. Salt raises the boiling point of water and the more salt (or any solute) added, the higher the the boiling point. Salt solution however lower freezing point. Pure water will also convert into vapour on boiling without leaving any residue while the salt solution will leave residue (salt).

Electrical conductivity

The salt solution contains more electrolyte and therefore would show good electrical conductivity while pure water is poor conductor.

Refractive index

Measuring refractive index of the liquid. Rrefractive index of pure water is 1.333 while that of salt solution will be higher. Impurities will change the density of medium and deflect light therefore affecting refractive index. The refractive index increases with increasing concentration of salt solution.