What is the freezing point of a solution of 12.0 g of CCl4 dissolved in 750.0 g of benzene? The freezing point of benzene is 5.48°C; Kf is 5.12°C/m.
To find the freezing point of a solution, you need to use the formula for the freezing point depression. The freezing point depression (∆Tf) is calculated as:
∆Tf = Kf * m
Where:
∆Tf = Freezing point depression
Kf = Freezing point depression constant (given as 5.12 °C/m)
m = Molality of the solution in mol solute / kg solvent
To calculate the molality (m), you first need to determine the moles of the solute and the mass of the solvent.
1. Calculate the moles of CCl4 (solute):
To find the moles of CCl4, divide the given mass of CCl4 by its molar mass. The molar mass of CCl4 is 153.82 g/mol.
moles of CCl4 = mass of CCl4 / molar mass of CCl4
moles of CCl4 = 12.0 g / 153.82 g/mol
moles of CCl4 ≈ 0.078 mol
2. Calculate the molality (m):
To find the molality, divide the moles of the solute by the mass of the solvent. The mass of benzene is given as 750.0 g.
molality (m) = moles of solute / mass of solvent in kg
mass of solvent = 750.0 g / 1000 g/kg = 0.750 kg
molality (m) = 0.078 mol / 0.750 kg
molality (m) ≈ 0.104 mol/kg
3. Calculate the freezing point depression (∆Tf):
Using the formula mentioned earlier:
∆Tf = Kf * m
∆Tf = 5.12 °C/m * 0.104 mol/kg
∆Tf ≈ 0.533 °C
4. Calculate the freezing point of the solution:
To find the freezing point of the solution, subtract the freezing point depression from the freezing point of the pure solvent. The freezing point of benzene is given as 5.48 °C.
Freezing point of solution = Freezing point of pure solvent - ∆Tf
Freezing point of solution = 5.48 °C - 0.533 °C
Freezing point of solution ≈ 4.95 °C
Therefore, the freezing point of a solution of 12.0 g of CCl4 dissolved in 750.0 g of benzene is approximately 4.95 °C.
delta T = i*Kb*molality.
molality = moles/kg
mols = grams/molar mass.
Use equation 3 to convert grams CCl4 to moles.
Use equation 2 to convert moles to molality.
Use equation 1 to determine delta T (i = 1).
Then delta T = T(normal)-T(solution). Calcualte T of the solution.
Post your work if you get stuck.