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  • Try this! Which of the following liquid pairs shows a positive deviation from Raoult's law

Which of the following liquid pairs shows a positive deviation from Raoult's law

  • Option 1)

    Water-nitric acid

  • Option 2)

    Benzene-methanol

  • Option 3)

    Water-hydrochloric acid

  • Option 4)

    Acetone-chloroform

 

Answers (1)

best_answer

As we learned 

 

Condition for positive deviation -

When A - A interactions and B - B  interactions  are  stronger than A - B interactions.

e.g. Ethanol + water

- wherein

\Delta H_{mix}> 0

\Delta V_{mix}> 0

(V_{f}>V_{A}+V_{B} )

\Delta H - Change\: in\: enthalpy

\Delta V - Change\: in\: volume

 

 In solution showing positive type of deviation the partial pressure of each component of solution is greater than the vapour pressure as
expected according to Raoult’s law.
In solution of methanol & benzene methanol molecules are held together due to hydrogen bonding as shown below.

On adding benzene, the benzene molecules get in between the molecule of methanol thus breaking the hydrogen bonds. As the resulting
solution has weak intermolecular attraction, the escaping tendency of alcohol & benzene molecule from the solution increases. Consequently
the vapour pressure of the solution is greater than the vapour pressure as expected from Raoult’s law.

 


Option 1)

Water-nitric acid

Option 2)

Benzene-methanol

Option 3)

Water-hydrochloric acid

Option 4)

Acetone-chloroform

Posted by

Plabita

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