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Question
CBSEENCH12011232

A 0.1  molal aqueous solution  of a weak  acid is 30%  ionised. if Kf for water is 1.86oC/m, the freezing point of the solution will be 

  • -18oC

  • -0.54oC

  • -0.36oC

  • -0.24oC

Solution

D.

-0.24oC

HA space rightwards arrow space space space space space space space space space space straight H to the power of plus space plus space straight A to the power of minus
1 minus straight alpha space space space space space space space space space space space space space space space straight alpha space space space space space space space space straight alpha

1 minus 0.3 space space space space space 0.3 space space space space space space space space 0.3 space

straight i space equals space 1 minus 0.3 space plus 0.3 space plus 0.3
straight i space equals space 1.3
therefore comma
increment straight T subscript straight f space equals space 1.3 space straight x space 1.86 space straight x space 0.1 space equals 0.2418 to the power of straight o straight C
straight T subscript straight f space equals space 0 minus 0.2418 to the power of straight o straight C