Colligative Properties
The freezing point of distilled water was determined by recording a thermogram: -0.176. The freezing point of a 0.200 m (molality) solution containing an unknown, ionic compound was determined by recording a second thermogram.
a. Determine the freezing point depression, deltaTf, for the ionic solution.
b. Determine effective molality (m_effective) for the ionic solution.
c. Determine the van't Hoff factor, i, for the ionic compound.
The freezing point of a .200m solution: -.904 degrees Celsius.
To solve these problems, we need to use the concept of colligative properties. Colligative properties are properties of a solution that depend on the number of solute particles, rather than the identity or nature of the solute.
a. To determine the freezing point depression (ΔTf) for the ionic solution, we need to use the formula:
ΔTf = Kf * m
Where:
ΔTf is the freezing point depression,
Kf is the molal freezing point depression constant for the solvent (water in this case),
m is the molality of the solution.
Given that the freezing point of distilled water is -0.176 °C and the molality of the solution is 0.200 m, we can calculate ΔTf as follows:
ΔTf = Kf * m = (-0.176 °C) * (0.200 m) = -0.0352 °C
Therefore, the freezing point depression (ΔTf) for the ionic solution is -0.0352 °C.
b. To determine the effective molality (m_effective) for the ionic solution, we divide the actual molality of the solution by the van't Hoff factor (i):
m_effective = m / i
Given that the molality of the solution is 0.200 m, we need to determine the van't Hoff factor (i) to calculate m_effective.
c. The van't Hoff factor (i) represents the number of particles formed in solution per formula unit of solute. For an ionic compound, it can be determined by considering the dissociation of the compound into its ions.
To find the van't Hoff factor (i), we need to know the nature of the ionic compound. Without that information, we cannot determine the exact value of i.
If you provide the name or formula of the ionic compound, I can help you determine the van't Hoff factor (i).
To determine the freezing point depression (ΔTf) for the ionic solution, you need to know the freezing point of distilled water and the freezing point of the solution. Subtracting the freezing point of the solution from the freezing point of distilled water will give you the freezing point depression.
a. Calculate ΔTf for the ionic solution:
ΔTf = freezing point of distilled water - freezing point of the solution
Given:
Freezing point of distilled water = -0.176 (°C)
Assuming you have the freezing point of the solution, subtract that from the freezing point of distilled water to find ΔTf.
b. To determine the effective molality (m_effective) for the ionic solution, you need to consider the behavior of the ionic compound in the solution. Since it is an ionic compound, it will dissociate into ions when dissolved in water. The number of ions formed by the compound will affect the effective concentration and consequently the effective molality.
c. The van't Hoff factor (i) represents the number of particles formed by an ionic compound when it dissociates in a solution. It is related to the number of ions produced by the compound. You can determine the van't Hoff factor (i) by comparing the observed freezing point depression with the expected freezing point depression for a non-dissociating solute at the same molality. The ratio of the observed to expected freezing point depression is equal to the van't Hoff factor.
To summarize:
a. ΔTf = freezing point of distilled water - freezing point of the solution
b. m_effective = molality of the solution
c. Determine i by comparing the observed freezing point depression to the expected freezing point depression for a non-dissociating solute at the same molality. The ratio of the observed to expected depression is the van't Hoff factor.