An ethylene glycol solution contains 20.9 g of ethylene glycol (C2H6O2) in 85.0 mL of water. Compute the freezing point and boiling point of the solution. (Assume a density of 1.00 g/mL for water.)
freezing point
°C
boiling point
°C
How would I set this up?
thanks
moles ethylene clycol = grams/molar mass. Solve for mole.
molality = moles/kg solvent
Solve for molality
delta T = Kf*m and convert to freezing point.
delta T = Kb*m and add to 100 C to convert to boiling point.
Thanks
To calculate the freezing point and boiling point of the ethylene glycol solution, you need to use the molality of the solution and the temperature change constants for the solvent.
First, let's calculate the molality (m) of the solution. Molality is defined as the number of moles of solute (in this case, ethylene glycol) per kilogram of solvent (in this case, water).
1. Calculate the number of moles of ethylene glycol:
moles = mass / molar mass
moles = 20.9 g / 62.07 g/mol
2. Calculate the mass of water in kilograms:
mass_water = volume_water * density_water
mass_water = 85.0 mL * 1.00 g/mL = 85.0 g = 0.0850 kg
3. Calculate the molality:
molality = moles of ethylene glycol / mass of water in kg
molality = (20.9 g / 62.07 g/mol) / 0.0850 kg
Now that we have the molality, we can use temperature change constants to calculate the freezing point depression and boiling point elevation.
4. Calculate the freezing point depression (ΔTf):
ΔTf = -Kf * molality
The freezing point depression constant (Kf) for water is 1.86 °C/molal.
5. Calculate the freezing point:
Freezing point = freezing point of pure water - ΔTf
The freezing point of pure water is 0 °C.
6. Calculate the boiling point elevation (ΔTb):
ΔTb = Kb * molality
The boiling point elevation constant (Kb) for water is 0.512 °C/molal.
7. Calculate the boiling point:
Boiling point = boiling point of pure water + ΔTb
The boiling point of pure water is 100 °C.
Substituting the values into the formulas, we get:
ΔTf = -1.86 °C/molal * molality
Freezing point = 0 °C - ΔTf
ΔTb = 0.512 °C/molal * molality
Boiling point = 100 °C + ΔTb
So, by plugging in the calculated molality value into the formulas, you can determine the freezing point and boiling point of the ethylene glycol solution.