Question

How do i solve this

Question #: 9 What mass of ethylene glycol (antifreeze, MW-62.1 gimol) must be added to 10.0 liters of water to produce a solution that freezes at-23.3 ℃? The density of water is 1.00 g/mL and K-1.86 °C/m. A. 7.78 kg B. 26.9 kg C. 0.406 kg D. 12.5 kg

Answer 1

Apply Colligative properties

This is a typical example of colligative properties.

Recall that a solute ( non volatile ) can make a depression/increase in the freezing/boiling point via:

dTf = -Kf*molality * i

dTb = Kb*molality * i

where:

Kf = freezing point constant for the SOLVENT; Kb = boiling point constant for the SOLVENT;

molality = moles of SOLUTE / kg of SOLVENT

i = vant hoff coefficient, typically the total ion/molecular concentration.

At the end:

Tf mix = Tf solvent - dTf

Tb mix = Tb solvent - dTb

then

if Tf = -23.3°C

Tf = 0 - Kf*mol / kg

-23.3 = -1.86 * mol of EG / 10

mol of EG = 23.3/1.86*10 = 125.268

mass = mol*MW = 125.268*62.1 = 7779.14 g = 7.77 kg or 7.78 kg, which is A