i tried to solve it on my own but im confused about the last part, this i what i have so far..
moles of glycerin= 50.0/92.10=0.54
molality=0.54/0.200=2.7
is that right?
im a little confused about the numbers im supposed to use for step 3...
this was the question:
the freezing point of ethanol (C2H5OH) is -114.6C. the molal freezing point depression constant for ethanol is 2.00C/m. what is the freezing point (C) of a solution prepared by dissolving 50.0 g of glycerin (C3H8O3, A nonelectrolyte) in 200 g of ethanol.
yes,
molal= molessolute/kgsolvent
You have it correct.
im not sure about the last step tho... i know the final answer is -120.0 but im not sure how to get to that...
To find the freezing point of the solution, you need to use the formula for freezing point depression:
ΔT = i * Kf * m
Where:
ΔT is the change in freezing point (in °C)
i is the van't Hoff factor (for non-electrolytes, it is always 1)
Kf is the molal freezing point depression constant of the solvent (given as 2.00 °C/m for ethanol)
m is the molality of the solution
Step 1: Calculate the molality of the solution.
You have correctly calculated the moles of glycerin as 0.54.
Now, you need to calculate the molality, which is moles of solute (glycerin) divided by kilograms of solvent (ethanol).
Mass of solvent (ethanol) = 200 g
Convert mass to kilograms: 200 g ÷ 1000 = 0.200 kg
molality = moles of glycerin / mass of ethanol (in kg)
molality = 0.54 mol / 0.200 kg
molality = 2.7 m (correct)
Step 2: Identify the freezing point depression constant and the change in freezing point.
The molal freezing point depression constant for ethanol is given as 2.00 °C/m (given in the question).
The freezing point of pure ethanol is -114.6 °C (also given in the question).
Step 3: Calculate the change in freezing point (ΔT).
Substitute the given values into the formula:
ΔT = i * Kf * m
ΔT = 1 * 2.00 °C/m * 2.7 m
ΔT = 5.4 °C
Step 4: Calculate the freezing point of the solution.
The freezing point of the solution is the sum of the change in freezing point (ΔT) and the freezing point of the pure solvent.
Freezing point of the solution = -114.6 °C + 5.4 °C
Freezing point of the solution = -109.2 °C
Therefore, the freezing point of the solution prepared by dissolving 50.0 g of glycerin in 200 g of ethanol is -109.2 °C.