Find the expected freezing point of a water solution that contains 287 g of aluminum nitrate (Al(NO3)3) in 8.50 kg of water. Answer in units of ◦C.

Freezing point of solution =  - 2.82°C

Explanation:

Formula to solve this, if we assume complete ionization of salt.

AlNO₃ →  Al³⁺  +  3NO⁻       i = 4

Freezing point of solution = - (Kf. m . i - 0°C)

Freezing point of pure solvent - Freezing point of solution = Kf . m . i

Freezing point of pure solvent = 0°C

Kf for water = 1.86 °C / m

Let's convert the mass of solute to moles → 287 g . 1mol/ 88.98 g = 3.22 moles

m (mol/kg) → 3.22 moles / 8.50 kg = 0.379

Freezing point of solution = - Kf. m . i + 0°C

Freezing point of solution = - 1.86°C /m . 0.379 m . 4 →  - 2.82°C

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