Question

A 0.5 molal solution of ethylene glycol in water is used as coolant in a car. If the freezing point constant of water be 1.86°C per mole, the mixture shall freeze at
(a) 0.93°C
(b) –0.93°C
(c) 1.86°C
(d) –1.86°C

Answer 1

Answer: (b) –0.93°C

Explanation:

Depression in freezing point :

$\Delta T_f=k_f\times m$

where,

$T_f$ = change in freezing point = $T_f^0-T_f=0^0C-T_f$

$k_f$ = freezing point constant  = $1.86^0C/mol$

m = molality = 0.5

$0^0C-T_f=1.86^0C/mol\times 0.5$

$T_f=-0.93^0C$

Thus freezing point of solution will be $-0.96^0C$