A solution is prepared by combining 3.72 grams of an unknown non-electrolyte with 325.0 grams of chloroform. The freezing point of the mixture is -64.10 oC, while the freezing point of pure chloroform is -63.50oC. The kf of pure chloroform is 4.68 oC/molal.
Based on this information, the molality of the solution is?
The number of moles of non-electrolyte present in the solution is?
Thus, the molar mass of the non-electrolyte is?
delta T = Kf*molality
delta T = 64.10-63.50 = ?
You know delta T and Kf, solve for m.
m = mols/kg solvent
You know m and kg chloroform, solve for mols.
mols = grams/molar mass.
You know mols and grams, solve for molar mass
To determine the molality of the solution, you need to use the freezing point depression equation:
ΔT = Kf * m
Where:
ΔT is the difference in freezing points between the pure solvent and the solution,
Kf is the freezing point depression constant of the solvent, and
m is the molality of the solution.
First, calculate ΔT by subtracting the freezing point of the pure chloroform (-63.50 oC) from the freezing point of the mixture (-64.10 oC):
ΔT = -64.10 oC - (-63.50 oC) = -0.60 oC
Next, substitute the values into the equation and solve for molality (m):
-0.60 oC = (4.68 oC/molal) * m
Divide both sides of the equation by 4.68 oC/molal:
m = -0.60 oC / 4.68 oC/molal
m ≈ -0.128 molal
Therefore, the molality of the solution is approximately -0.128 molal.
To calculate the number of moles of non-electrolyte present in the solution, you need to use the molality definition:
molality (m) = moles of solute / mass of solvent (in kg)
Rearrange the equation to solve for moles of solute:
moles of solute = molality (m) * mass of solvent (in kg)
Convert the mass of chloroform from grams to kilograms:
mass of chloroform = 325.0 g = 325.0 g / 1000 = 0.325 kg
Substitute the values into the equation and solve for moles of solute:
moles of solute = -0.128 molal * 0.325 kg = -0.0416 mol
Therefore, the number of moles of non-electrolyte present in the solution is approximately -0.0416 mol.
To find the molar mass of the non-electrolyte, you can use the formula:
Molar mass (g/mol) = mass of solute (g) / moles of solute
Substitute the values into the equation and solve for the molar mass:
Molar mass = 3.72 g / -0.0416 mol = -89.423 g/mol
Note that the negative sign in the result indicates an error in the calculation because molar mass cannot be negative. Double-check your calculations and ensure that the signs are correct.