A) Water - hydrochloric acid
B) Benzene - methanol
C) Water - nitric acid
D) Acetone - chloroform
Correct Answer: B
Solution :
Water and hydrochloric acid; and water and nitric acid form miscible solutions. They show no deviation. In case of and\[C{{H}_{3}}OC{{H}_{3}}\]and\[CHC{{l}_{3}}\]there is interaction between them, thus force of attraction between\[C{{H}_{3}}COC{{H}_{3}}....CHC{{l}_{3}}\]is larger than between\[CHC{{l}_{3}}....CHC{{l}_{3}}\]or \[C{{H}_{3}}COC{{H}_{3}}....\text{ }C{{H}_{3}}COC{{H}_{3}}\]and thus vapour pressure is less than expected. It shows a negative deviation. In case of \[C{{H}_{3}}OH,\]there is association by intermolecular H-bonding. When benzene is added to \[C{{H}_{3}}OH,\]H-bonding breaks and thus force of attraction between \[C{{H}_{3}}OH\]and benzene molecules is smaller than between \[C{{H}_{3}}OH\]or benzene molecules (in pure state). Vapour pressure of mixture is greater than expected?a positive deviation. \[\underset{\delta -}{\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{O}}}\,-\overset{\delta +}{\mathop{H}}\,....\underset{\delta -}{\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{O}}}\,-\overset{\delta +}{\mathop{H}}\,....\underset{\delta -}{\overset{\begin{smallmatrix} C{{H}_{3}} \\ | \end{smallmatrix}}{\mathop{O}}}\,-\overset{\delta +}{\mathop{H}}\,....\]
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