Question

A motor vehicle radiator was filled with 8 litre of water in which 2 litre of methyl alcohol was added. What is the lowest temperature at which the vehicle can be parked out without a danger of freezing of water? ($K_f$ for water $=1.86Kkgmo{l}^{-1}$ and density of methanol $=0.8g/mL$)

• A. 11.625
• B. -11.625
• C. 14.531
• D. -14.531

Answer 1

Answer: (B)

$\Delta T_f=K_f\frac{W_B\times 1000}{M_B\times W_A}$
Weight of alcohol $\left(W_B\right)=2000\times 0.8$
Weight of water $\left(W_A\right)=8000\times 1$
$\Delta T_f=\frac{1.86\times 2000\times 0.8\times 1000}{32\times 8000}=11.625$
Freezing point of solution $=0-11.625=-11.625^{\circ }C$
So, vehicle cannot be kept out below $-11.625^{\circ }C.$