A solution containing 62   g ethylene glycol in 250   g water is cooled to - 10 o C . If K f for…

A solution containing 62 g ethylene glycol in 250 g water is cooled to -10oC . If Kf for water is 1.86 K kg mol-1 , the amount of water (in g ) separated as ice is:
  1. 48
  2. 64
  3. 16
  4. 32

Solution

Molecular weight of ethylene glycol

C2H6O2=62

Moles of ethylene glycol =WtM.Wt

=6262=1

 ∆Tf=i×kf×m

∴∆Tf=0--10=10

i=1 for ethylene glycol

∆Tf=1×86×12501000

∆Tf=1.86×4=7.44

As ∆Tf=10 it implies that some amount of water has frozen and this has led to a greater depression of freezing point.

10=1.86×6262Wt of H2O1000

WH2O=186 gm

Hence, the weight of water that has frozen  =( 250−186 )gm

=64 gm

Asked in: JEE Main 2019 (09 Jan Shift 2)

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