Question

The boiling point of an aqueous solution of a non-volatile solute is `100.15^(@)C`. What is the freezing point of an aqueous solution obtained by dilute the above solution with an equal volume of water. The values of `K_(b)` and `K_(f)` for water are `0.512` and `1.86^(@)C mol^(-1)`:
A. `-0.544^(@)C`
B. `-0.512^(@)C`
C. `-0.272 ^(@)C`
D. `-1.86 ^(@)C`

Answer 1

Correct Answer - C
For same solution `(Delta T_(f))/(Delta T_(b))=K_(f)/K_(b) ` or `Delta T_(f) = Delta T_(b) xx K_(f)/K_(b)`
or `Delta T_(f) = (0.15 xx 1.86)/20.512=0.545`
Now on diluting the solution to double
` :. Delta T_(f) = 0.545/2=0.272`
`:. f. pt. = -0.272^(@) C`