5 g of Na 2 SO 4 was dissolved in x   g of H 2 O . The change in freezing point was found to be 3 .82 o…

5g of Na2SO4 was dissolved in x g of H2O . The change in freezing point was found to be 3.82oC . If Na2SO4 is 81.5% ionised, the value of x

( Kf for water =1.86oC kg mol-1 ) is approximately:

(molar mass of S=32 g mol-1 and that of Na=23 g mol-1 )
  1. 25 g
  2. 65 g
  3. 15 g
  4. 45 g

Solution

Na2SO4→2Na++SO42-

i=1+3-1 0.815=2.63

3.82=1.86×2.63×5×1000142×x

∴ x=1.86×2.63×5000142×3.82

=45 gm

Asked in: JEE Main 2017 (08 Apr Online)

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