calculate the freezing point of a solution containing 12.2 grams of benzoic acid, dissolved in 250 grams of nitrobenzene. the freezing point of nitrobenzene is 5.7 celsius and its freezing point depression constant is 7.0 celsius/m. please help
What is your question here? Calculate the molality of the benzoic acid, and proceed with the formula. We will be happy to critique your thinking or work.
To calculate the freezing point of a solution, we need to use the concept of freezing point depression.
Freezing point depression is the difference between the freezing point of the pure solvent and the freezing point of the solution. It is directly proportional to the molality of the solute dissolved in the solvent.
The freezing point depression equation is given by:
ΔT = K_f * m
Where:
ΔT is the freezing point depression
K_f is the freezing point depression constant for the solvent
m is the molality of the solute
First, we need to calculate the molality (m) of the benzoic acid:
Molality (m) = moles of solute / mass of solvent (in kg)
To find the moles of solute, we use the molar mass of benzoic acid (C₇H₆O₂) which is 122.12 g/mol:
moles of benzoic acid = mass of benzoic acid / molar mass of benzoic acid
moles of benzoic acid = 12.2 g / 122.12 g/mol
Next, we need to convert the mass of nitrobenzene to kg:
mass of nitrobenzene = 250 g = 0.250 kg
Now, let's calculate the molality (m):
m = moles of solute / mass of solvent (in kg)
m = (12.2 g / 122.12 g/mol) / 0.250 kg
Now we can calculate the freezing point depression (ΔT) using the freezing point depression constant for nitrobenzene, which is 7.0 °C/m:
ΔT = K_f * m
ΔT = 7.0 °C/m * (12.2 g / 122.12 g/mol) / 0.250 kg
Finally, we can find the freezing point of the solution by subtracting the freezing point depression from the freezing point of the pure solvent:
Freezing point of the solution = Freezing point of pure solvent - ΔT
Freezing point of the solution = 5.7 °C - ΔT
Plug in the value of ΔT to find the freezing point of the solution.