Question

Coolant used in radiator is aqueous solution of ethylene glycol. In order to prevent the solution from freezing at -0.3C, how much ethylene glycol must be added to 5 kg of water? (Kf = 1.86K kg mol⁻¹)

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

Hint:

Freezing point depression depends on molality, not mass percent.

Answer 1

The Correct Option is A

Step 1: Δ Tf = Kf m m=(0.3)/(1.86)=0.161
Step 2: Moles required: n = 0.161 × 5 = 0.805
Step 3: Mass: m = 0.805 × 62 ≈ 50 g