Question

C2H6O2 is infinitely miscible(soluble) in water. Ethylene glycol is a nonelectrolyte that is used as antifreeze. What is the lowest possible melting point for engine coolant that is 30% ethylene glycol? The Kf for H20 is 1.86 C/m.

Answer 1

Answer:

The lowest possible melting point for engine coolant is -12.8°C

Explanation:

This is about colligative property about freezing point depression.

We think the data 30% as a %m/m. It means that 30 g of ethylene glycol are contained in 100 g of solution. Therefore, we have 70 g of solvent.

Formula for freezing point depression is:

ΔT = Kf . m . i

Where  ΔT = Freezing T° of pure solvent - Freezing T° of solution.

Freezing T° of solvent = 0° (We talk about water)

Let's determine m (molality, moles of solute in 1kg of solvent)

70 g = 0.070 kg

30 g . 1 mol / 62.07 g = 0.483 moles

0.483 mol / 0.070 kg = 6.90 m

We replace data in formula:

0° - Freezing T° of solution = 1.86 °C/m . 6.90m . 1

As ethylene glycol is a nonelectrolyte, i = 1

Freezing T° of solution =  - 12.8°C