An industrial chemist is studying smAll organic compounds for their potential use as an auto antifreeze. When 0.243g of a compound is dissolved in 25.0 ml of water, the freezing point is -0.201 degree celcius.
(A) Calculate the molar mass of compound (dH2O= 1.00g/ml) at temp of solution.
calculate molality first.
-.201=-1.86 m
then, molality= .243/(molmass*.025)
solve for mol mass.
To calculate the molar mass of the compound, we can use the formula:
moles of solute = mass of solute / molar mass of solute
First, we need to find the moles of solute:
moles of solute = mass of solute / molar mass of solute
mass of solute = 0.243 g
moles of solute = 0.243 g / molar mass of solute
Next, we need to find the mass of water in the solution:
mass of water = volume of water x density
density of water = 1.00 g/ml
volume of water = 25.0 ml
mass of water = 25.0 ml x 1.00 g/ml
Now, we can use the freezing point depression formula:
ΔT = Kf x m
Kf = molal freezing point depression constant of water = 1.86 °C/m (given)
ΔT = -0.201 °C (given)
m = molality = moles of solute / mass of water (in kg)
To convert the mass of water to kg:
mass of water (in kg) = mass of water (in g) / 1000
Now, we can plug the values into the formula and solve for m:
-0.201 °C = 1.86 °C/m x (moles of solute / (mass of water (in g) / 1000))
Solving for moles of solute:
moles of solute = -0.201 °C x (mass of water (in g) / 1000) / (1.86 °C/m)
Now, substituting the values:
moles of solute = -0.201 °C x (25.0 g / 1000) / (1.86 °C/m)
Finally, we can substitute the value of moles of solute in the initial equation to find the molar mass of the compound:
0.243 g / molar mass of solute = -0.201 °C x (25.0 g / 1000) / (1.86 °C/m)
Solving for molar mass of solute:
molar mass of solute = 0.243 g / (-0.201 °C x (25.0 g / 1000) / (1.86 °C/m))
Simplifying the calculation will give us the answer.
To calculate the molar mass of the compound, you need to use the colligative property known as the freezing point depression. Freezing point depression occurs when a solute is added to a solvent, lowering the freezing point of the solution compared to the pure solvent.
The formula to calculate freezing point depression is:
ΔTf = Kf * m
Where:
ΔTf is the change in freezing point
Kf is the molal freezing point depression constant specific to the solvent (for water, Kf = 1.86 °C/m)
m is the molality of the solute in the solution
First, we need to calculate the molality (m) of the solution:
Molality (m) = moles of solute / mass of the solvent (in kg)
Given that 0.243 g of the compound is dissolved in 25.0 mL of water, we need to convert mL to kg:
1 mL of water = 1 g
25.0 mL of water = 25.0 g = 0.025 kg
The molality of the solution becomes:
m = moles of solute / 0.025 kg
Next, we need to calculate the change in freezing point (ΔTf):
ΔTf = -0.201 °C (the freezing point depression given in the problem)
Now we can rearrange the freezing point depression formula to solve for the moles of solute:
moles of solute = ΔTf / (Kf * m)
Finally, we can calculate the molar mass of the compound:
Molar mass of the compound = mass of the solute / moles of solute
Using the given information and the calculated values, you can now find the molar mass of the compound.