The freezing point of water is depressed by ` 0.37^@C` in a 0.01 molal NaCI solution. The freezing point of 0.02 molal solution of urea is depressed by

Options

A. `0.37^(@)C`
B. `0.74^(@)C`
C. `0.185^(@)C`
D. `0^(@)C`

Answer

A

Explanation

The depression in freezing point is proportional to molal concentration of the solute i.e.
`DeltaT_(f) prop m`
`DeltaT_(f)=K_(f)mi or K_(f)=(DeltaT_(f))/(ixxm)` = constant
so, `(DeltaT_(f_(NaCl)))/(i_(NaCl)xxm_(NaCl))=(DeltaT_(f_(Urea")))/(m_(Urea)xxi_(Urea))` = constant
`(0.37)/(2xx0.01)=(DeltaT_(f_(Urea)))/(0.02xx1)impliesDeltaT_(f_(Urea))=(0.37xx0.02)/(0.02)=0.37^(@)C`.