A) \[0.37{{\,}^{o}}C\]
B) \[0.74{{\,}^{o}}C\]
C) \[0.185{{\,}^{o}}C\]
D) \[0{{\,}^{o}}C\]
Correct Answer: A
Solution :
As we know that, \[\Delta {{t}_{f}}=i\,{{k}_{j}}m\] where, \[\Delta {{t}_{f}}=\]depression in freezing point \[i=\]vant-Hoff factor \[m=\]molality and \[{{k}_{f}}=\] freezing point depression constant. For 0.01 molal NaCI solution \[0.37=2\times {{k}_{f}}\times 0.01\] \[\therefore \] \[{{k}_{f}}=\frac{0.37}{2\times 0.01}\] ?(i) For 0.02 molal urea solution \[\Delta {{t}_{f}}=1\times {{k}_{f}}\times 0.02\] \[\therefore \] \[{{k}_{f}}=\frac{\Delta {{t}_{f}}}{0.02}\] ?(ii) From Eqs (i) and (ii) \[\frac{0.37}{2\times 0.01}=\frac{\Delta {{t}_{f}}}{0.02}\] \[\Delta {{t}_{f}}=\frac{0.37\times 0.02}{2\times 0.01}\] \[\therefore \] \[\Delta {{t}_{f}}=0.37{{\,}^{o}}C\]
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