b. What is the freezing point depression when 153 g of bromine is added to 100 g of benzene? Kf of benzene is 5.12 C/m
delta T = Kf*molality
Kf = 5.12
mols Br2 = grams/molar mass = 153/160 = 0.956
molality = mols/kg solvent = 0.956/0.100 = ?
Substitute into delta T = Kf*m and solve for delta T.
To determine the freezing point depression, we can use the formula:
ΔTf = Kf * m * i
Where:
ΔTf = freezing point depression
Kf = molal freezing point depression constant of the solvent (benzene in this case)
m = molality of the solute (bromine in this case)
i = van't Hoff factor (the number of particles into which the solute dissociates)
First, let's find the moles of bromine:
Moles of Br2 = mass of Br2 / molar mass of Br2
The molar mass of bromine (Br2) is 79.92 g/mol.
Moles of Br2 = 153 g / 79.92 g/mol
Moles of Br2 ≈ 1.914 mol
Next, let's calculate the molality of the solution:
Molality (m) = moles of solute / mass of solvent (in kg)
The mass of benzene is 100 g. To convert it to kg, we divide by 1000.
Mass of benzene = 100 g / 1000 = 0.1 kg
Molality (m) = 1.914 mol / 0.1 kg
Molality (m) ≈ 19.14 mol/kg
The van't Hoff factor for bromine (Br2) is 1 because it does not dissociate in benzene.
Now, we can calculate the freezing point depression:
ΔTf = Kf * m * i
Given Kf = 5.12 °C/m and i = 1
ΔTf = 5.12 °C/m * 19.14 mol/kg * 1
ΔTf ≈ 97.9856 °C
Therefore, the freezing point depression when 153 g of bromine is added to 100 g of benzene is approximately 97.9856 °C.
To find the freezing point depression, we need to use the equation:
∆T = Kf * m
where ∆T is the freezing point depression, Kf is the freezing point depression constant of benzene, and m is the molality of the solute.
First, let's find the molality of the solute (bromine) by calculating the moles of bromine and the mass of benzene.
1. Calculate the moles of bromine:
Moles = Mass / Molar mass
The molar mass of bromine (Br₂) is 79.90 g/mol. Therefore,
Moles of bromine = 153 g / 79.90 g/mol
2. Calculate the mass of benzene:
Mass of benzene = 100 g
Next, calculate the molality (m) by dividing the moles of solute by the mass of the solvent (benzene) in kg:
Molality (m) = Moles of solute / Mass of solvent (in kg)
Now that we have the molality (m), we can substitute it into the formula to find the freezing point depression (∆T).
∆T = Kf * m
Substituting the values, ∆T = 5.12 C/m * Molality (m)
Calculate the molality (m) and substitute it back into the formula to find the freezing point depression (∆T).