Question

Experimental data for a 1.00 m Mgl₂ aqueous

solution indicate an actual change in the freezing
point of water of -4.78°C. Find the expected
change in the freezing point of water. Suggest a
possible reason for the discrepancy between the
experimental and expected values.

Answer 1

The expected change in freezing point of water can be calculated using the formula:

ΔTf = Kf x molality

Where ΔTf is the change in freezing point, Kf is the freezing point depression constant for water (1.86°C/m), and molality is the molal concentration of the solute (mol of solute/kg of solvent).

Assuming complete dissociation of MgCl2 in water, the molality of the solution can be calculated as:

molality = (1.00 mol MgCl2 / 0.1 kg H2O) = 10.0 mol/kg

Substituting the values into the equation, we get:

ΔTf = (1.86°C/m) x (10.0 mol/kg) = -18.6°C

Therefore, the expected change in the freezing point of water for a 1.00 m MgCl2 solution is -18.6°C.