What is the freezing point of a soluton is which 10.0 g of naphthalene [C10H8(s)] is dissolved in 50.0 g of benzene [C6H6(l)]?
Extra info you might need: benzene= 5.12 degrees C m^-1
Answer should be: -2.46
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To find the freezing point of a solution, you can use the formula:
ΔT = Kf * m
Where:
- ΔT is the change in temperature (freezing point depression)
- Kf is the cryoscopic constant (also known as the molal freezing point depression constant) for the solvent
- m is the molality of the solute in the solution.
First, we need to calculate the molality of the solute. Molality (m) is defined as the moles of solute per kilogram of solvent.
1. Calculate the number of moles of naphthalene (C10H8):
- The molar mass of naphthalene is 128 g/mol.
- Use the given mass of naphthalene (10.0 g) to find the moles:
Moles of naphthalene = mass of naphthalene / molar mass of naphthalene
2. Calculate the molality (m) of the solute (naphthalene):
- The mass of the solvent (benzene) is given as 50.0 g.
Mass of the solvent = 50.0 g = 0.050 kg
- Calculate the molality using the formula:
Molality (m) = moles of solute / mass of solvent (in kg)
3. Calculate the freezing point depression (ΔT):
- The cryoscopic constant (Kf) for benzene is given as 5.12 ˚C⋅m⁻¹.
- Use the formula:
ΔT = Kf * m
Finally, find the freezing point of the solution by subtracting the freezing point depression from the freezing point of the pure solvent. The freezing point of pure benzene is 0 ˚C.
Freezing point of solution = Freezing point of pure solvent - ΔT
Now let's calculate the freezing point of the solution using these steps.