Understanding the Concepts
* Freezing Point Depression: When a solute (like NiSO₄) is dissolved in a solvent (like water), the freezing point of the solution is lower than the freezing point of the pure solvent. This is called freezing point depression.
* Molality: Molality (m) is a measure of concentration defined as moles of solute per kilogram of solvent.
* Freezing Point Depression Constant: The freezing point depression constant (Kf) is a specific property of the solvent. For water, Kf = 1.86 °C/m.
Steps to Calculate the Freezing Point
1. Calculate the molality of the solution:
* Moles of NiSO₄:
* Molar mass of NiSO₄ = 58.69 g/mol (Ni) + 32.07 g/mol (S) + 4 * 16.00 g/mol (O) = 154.76 g/mol
* Moles of NiSO₄ = 21.6 g / 154.76 g/mol = 0.139 mol
* Kilograms of water:
* 1.00 x 10² g H₂O = 0.100 kg H₂O
* Molality (m):
* m = 0.139 mol / 0.100 kg = 1.39 m
2. Calculate the freezing point depression (ΔTf):
* ΔTf = Kf * m
* ΔTf = 1.86 °C/m * 1.39 m = 2.59 °C
3. Calculate the freezing point of the solution:
* Freezing point of pure water = 0 °C
* Freezing point of solution = 0 °C - 2.59 °C = -2.59 °C
Therefore, the freezing point of this solution is approximately -2.59 °C.
