Solutions Question 76
Out of the following liquid pair which solution follows the positive deviation from Raoult’s law?
Options:
A) Acetone + Chloroform
B) Water + Nitric acid
C) Water + Hydrochloric acid
D) Benzene + Methanol (no reaction)
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Answer:
Correct Answer: D
Solution:
(1) $ CH_3COCH_3 $ and $ CHCl_3 $ are volatile. On mixing, there is an increase in intermolecular H-bonding due to the formation of chloroform.
Thus, force of attraction between $ (CHCl_3-CH_3COCH_3) $ molecules is larger than between $ (CHCl_3-CHCl_3) $ and $ (CH_3COCH_3-CH_3COOH) $ molecules.
Thus, vaporization decreases, a case of negative deviation. (2) As in [c], negative deviation. (3) When $ HCl $ is mixed with $ H_2O $ , force of attraction between $ HCl $ and $ H_2O $ molecules is increased (due to dissolution), hence vaporization decreases, a case of negative deviation. (4) $ CH_3OH $ molecules are joined by intermolecular H-bonding which contributes to the liquid state.
On adding benzene. H-bonding breaks and the force of attraction between $ CH_3OH $ and benzene molecules is less than between $ CH_3OH-CH_3OH $ and between benzene-benzene. Hence, more is the vaporization of mixture. Thus a case of positive deviation.
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