1. The organic compound triphenylmethane (C19H16) when pure melts at 171.04 degrees c. When 1.92 grams of hexachlorobenzene (C6CL6) is mixed with 3.74 grams of triphenhlmethane, the melting point of the mixture is 163.19 degrees calcius. Calculate the freezing point depression constant of triphenymethane.
mols solute = grams/molar mass
Solve for mols solute.
m = molality = mols solute/kg solvent
Solve for m
delta T = Kf*m
Solve for Kf
To calculate the freezing point depression constant of triphenylmethane, we need to use the formula:
ΔT = Kf * m
where:
ΔT is the freezing point depression (difference between the pure melting point and the melting point of the mixture),
Kf is the freezing point depression constant, and
m is the molality of the solute.
To find the molality (m) of the solute, we need to calculate the moles of triphenylmethane and the moles of hexachlorobenzene.
Step 1: Calculate the moles of triphenylmethane.
Given:
Mass of triphenylmethane = 3.74 g
Molar mass of triphenylmethane = 19 * 12.01 g/mol + 16 * 1.01 g/mol = 228.36 g/mol
Moles of triphenylmethane = mass / molar mass
Moles of triphenylmethane = 3.74 g / 228.36 g/mol
Step 2: Calculate the moles of hexachlorobenzene.
Given:
Mass of hexachlorobenzene = 1.92 g
Molar mass of hexachlorobenzene = 6 * 12.01 g/mol + 6 * 35.45 g/mol = 284.82 g/mol
Moles of hexachlorobenzene = mass / molar mass
Moles of hexachlorobenzene = 1.92 g / 284.82 g/mol
Step 3: Calculate the molality (m).
Molality (m) = Moles of solute / Mass of solvent (in kg)
In this case, we assume the mass of the solvent is equal to the mass of triphenylmethane since hexachlorobenzene is the solute.
Mass of solvent = mass of triphenylmethane = 3.74 g
Mass of solvent (in kg) = 3.74 g / 1000 g/kg
Now, we have all the values needed to calculate the freezing point depression constant (Kf).
Step 4: Calculate the freezing point depression (ΔT).
Given:
ΔT = 171.04 °C - 163.19 °C = 7.85 °C
Step 5: Calculate the freezing point depression constant (Kf).
Kf = ΔT / m
Now, plug in the values:
Kf = 7.85 °C / (moles of triphenylmethane / mass of solvent (in kg))
Calculate the moles of triphenylmethane from Step 1 and the mass of solvent (in kg).
Finally, substitute these values into the equation to calculate Kf.