What is the freezing point of a solution containing 4.134 grams naphthalene (molar mass = 128.2) dissolved in 30.0 grams paradichlorobenzene? The freezing point of pure paradichlorobenzene is 53.0°C and the freezing point depressing constant Kfp is -7.10°C/m.
I'm not sure how to find the freezing point. The only equation I know that might be relevant is the one involving delta T and Kf
That's the one you use.
delta T = Kf*m
m = molality = mols/kg solvent
mols naphthalene = grams/molar mass = 4.134 g/128.2 = ?
kg solvent (that's the paradichlorobenzene) = 30 g = 0.030 kg
Use the mols naphthalene and kg of the paradichlorobenze to solve for molality = m
Plug in m and Kf and solve for delta T
Then knowing freezing point of paradichlorobenzene normally is 53.0 C (given in the problem), subtract delta T to get the new freezing point. Your numvwe should be less than 53.0
Post your work if you get stuck.
Same number I obtained but I didn't use all of those digits. You aren't allowed that many. At the most you aren't allowed more than 3 significant figures.
Nevermind, I got it.
Find deltaT using the Kfp given, and molality with the grams of solute and paradichlorobenzene given (1.07488 m). Multiply the two to get -7.63167, and then subtract that from the freezing point (53°C) to get 45.37°C.
To find the freezing point of the solution, you can use the equation involving delta T and Kf. This equation relates the change in freezing point (delta T) to the freezing point depression constant (Kf), and the molality (moles of solute per kilogram of solvent) of the solution.
The equation can be written as:
delta T = Kf * m
Where:
- delta T is the change in freezing point (in Celsius)
- Kf is the freezing point depression constant (in Celsius per mole)
- m is the molality of the solution (in moles of solute per kilogram of solvent)
To calculate the molality (m) of the solution, you need to determine the moles of naphthalene and the mass of the solvent (paradichlorobenzene).
1. Calculate the moles of naphthalene (solute):
moles of naphthalene = mass of naphthalene / molar mass of naphthalene
moles of naphthalene = 4.134 g / 128.2 g/mol
2. Calculate the mass of the solvent (paradichlorobenzene):
mass of solvent = total mass of solution - mass of solute
mass of solvent = 30.0 g - 4.134 g
3. Calculate the molality of the solution:
molality = moles of solute / mass of solvent (converted to kg)
molality = moles of naphthalene / (mass of solvent / 1000)
4. Finally, calculate the freezing point depression:
delta T = Kf * molality
delta T = -7.10°C/m * molality
This will give you the change in freezing point (delta T) caused by the naphthalene dissolved in paradichlorobenzene.
5. To find the freezing point of the solution, subtract the calculated delta T from the freezing point of pure paradichlorobenzene:
Freezing point of solution = Freezing point of pure paradichlorobenzene - delta T
Freezing point of solution = 53.0°C - delta T
Following these steps, you should be able to find the freezing point of the given solution.