Pure lauric acid is melted and the freezing point is determined to be 43 degrees celsius.
A solution is made by dissolving .50 grams of paradicholrobenzene into 3.00 grams of lauric acid.
Determine the molality of this solution. I got 1.1m. which is right.
But then it says the freezing point of the mixture is measured and found to be 39 degrees celsius. Then it says... determine the freezing poitn constant (kf) for lauric acid. how do i do that?
delta T = Kf*m
You know delta T (43-39) and you know m. Calculate Kf.
To determine the freezing point constant (kf) for lauric acid, you can use the freezing point depression equation:
ΔTf = kf * m
where:
ΔTf is the change in freezing point (in Celsius)
kf is the freezing point constant (in Celsius/m)
m is the molality of the solution (in mol/kg)
In this case, you already determined the molality of the solution to be 1.1m, so you need to find the change in freezing point (ΔTf) to calculate kf.
First, calculate the change in freezing point by subtracting the measured freezing point of the mixture (39 degrees Celsius) from the freezing point of pure lauric acid (43 degrees Celsius):
ΔTf = 43°C - 39°C
ΔTf = 4°C
Next, rearrange the freezing point depression equation to solve for kf:
kf = ΔTf / m
Plug in the values:
kf = 4°C / 1.1m
kf ≈ 3.64 °C/m
So, the freezing point constant (kf) for lauric acid is approximately 3.64 °C/m.
To determine the freezing point constant (kf) for lauric acid, you can use the formula:
ΔT = kf * m
Where:
ΔT is the change in freezing point (initial freezing point - final freezing point)
kf is the freezing point depression constant for the solvent (lauric acid)
m is the molality of the solution
In this case, we already know the change in freezing point (ΔT), which is 43°C - 39°C = 4°C.
Using the given molality (m) of the solution, which is 1.1 mol/kg (as you correctly calculated), we can rearrange the formula to solve for kf:
kf = ΔT / m
kf = 4°C / 1.1 mol/kg
Calculating the value, kf is approximately 3.64°C·kg/mol.