The freezing point of benzene is 5.5°C. What is the freezing point of a solution of 8.30 g of naphthalene (C10H8) in 320. g of benzene (Kf of benzene = 4.90°C/m)?
mols naphthalene = grams/molar mass
m naphthalene = mols/kg solvent
Then delta T = Kf*m
Solve for delta T and subtract from the normal freezing point to find new freezing point.
To find the freezing point of the solution, we can use the equation:
ΔT = Kf * m
Where:
ΔT is the change in freezing point
Kf is the freezing point depression constant for the solvent
m is the molality of the solute
To find the molality of the solute (naphthalene), we need to calculate the number of moles of naphthalene and the mass of benzene.
The molar mass of naphthalene (C10H8) is:
(10 x 12.01 g/mol) + (8 x 1.008 g/mol) = 128.18 g/mol
First, we need to convert the mass of naphthalene to moles:
moles of naphthalene = mass / molar mass
moles of naphthalene = 8.30 g / 128.18 g/mol
Next, we need to calculate the molality of the solution:
molality (m) = moles of solute / mass of solvent (in kg)
mass of solvent = 320 g = 320 g / 1000 g/kg
Now we can substitute the values into the equation to find the change in freezing point:
ΔT = Kf * m
Finally, we can calculate the freezing point of the solution:
Freezing point of the solution = freezing point of pure benzene - ΔT
To summarize:
1. Calculate the moles of naphthalene: moles of naphthalene = 8.30 g / 128.18 g/mol
2. Calculate the molality of the solution: molality (m) = moles of solute / mass of solvent (in kg)
mass of solvent = 320 g / 1000 g/kg
3. Calculate the change in freezing point: ΔT = Kf * m
4. Calculate the freezing point of the solution: Freezing point of the solution = freezing point of pure benzene - ΔT.