Question

Coolant used in car radiator is aqueous solution of ethylene glycol. In order to prevent the solution from freezing at $-0.3^{\circ} C$. How much ethylene glycol must be added to $5\, kg$ of water ? $\left( K_f =1 \cdot 86\, Kg\, mol ^{-1}\right)$

• A. 50 g
• B. 55 g
• C. 45 g
• D. 40 g

Answer 1

Answer: (A)

50 g

Answer 2

Let $W g$ of ethylene glycol is added.
The molar mass of ethylene glycol $=62\, g / mol$.
The depression in the freezing point $\Delta T _{ f }= K _{ f } m$
$0.3=1.86 \times \frac{ W }{62\, g / mol \times 5\, kg }$
$W =50\, g$