Question

An aqueous solution of hydrochloric acid

• A. obeys Raoult's law
• B. shows negative deviation from Raoult's law
• C. shows positive deviation from Raoult's law
• D. obeys Henry's law at all compositions

Answer 1

The correct option is B shows negative deviation from Raoult's law

Raoult's law states that the vapor pressure of a solvent above a solution is equal to the vapor pressure of the pure solvent at the same temperature scaled by the mole fraction of the solvent present: $[P_{solution}=X_{solvent}{P}_{solvent}^o]$. If the attraction between different molecules, for example between $HCl$ and $H_{2}O$ molecules, is stronger, the escaping tendency from the solution to the vapour phase will be smaller, then the partial vapour pressure will be smaller than predicted by Raoult's law and the system exhibits a negative deviation.