Question

1.The freezing point of an aqueous solution prepared by adding 0.0100 mol of acetic acid to 100. g of water is -0.190 C. The freezing point depression of pure water is 0.000 C, and the freezing point depression constant for water is 1.86 C/m. What is the value for the van't Hoff factor for acetic acid in the aqueous solution. You must show work to support your response.

2. Which of the following aqueous solutions should have the lowest freezing point: 0.0500 m C6H12O6, 0.0300 m KBr, or 0.0150m Na2SO4? You must show work to support your answer.

3. Arrange the following solutions in order of increasing freezing point depression: 0.10 m MgCl2 in water , i=2.7, Kf=1.86 C/m; 0.20 m toluene in diethyl ether, i=1.00, Kf=1.79 C/m; and 0.20 m ethylene glycol in ethanol, i=1.00, Kf=1.99 C/m. You must show work to support your answer.

*Sigfigs!!!!!!!*

Answer #1

1)

Tf = 0 - (0.190) = 0.190 oC

molality = moles of solute / mass of solvent (kg)

=0.0100 / 100 x 10^-3

= 0.1 m

Tf = i x Kf x m

0.190 = i x 1.86 x 0.1

van't Hoff factor for acetic acid = i = 1.02

2. )

freezing point inversly proportiaonal to the molality

0.0500 m C6H12O6 = i x m = 1 x 0.05 = 0.05 m

0.03 m KBr = i x m = 2 x 0.03 = 0.06 m

0.015 Na2SO4 = i x m = 3 x 0.015 = 0.045 m

**least freezing point : KBr**

3. )

MgCl2 freezing point depression = i x Kf x m = 2.7 x 1.86 x 0.10 = 0.502 oC

toluene in diethyl ether freezing point depression = 1 x 1.79 x 0.20 = 0.358 oC

ethylene glycol in ethanol = 1 x 1.99 x 0.20 = 0.398 oC

order : **MgCl2 > ethylene glycol in
ethanol > toluene in diethyl ether**

The experimentally measured freezing point of a 1.05 m aqueous
solution of AlCl3 is -6.25°C. The freezing point depression
constant for water is Kf = 1.86°C/m. Assume the freezing point of
pure water is 0.00°C.
Part 1 What is the value of the van't Hoff factor for this
solution?
Part 2 What is the predicted freezing point if there were no ion
clustering in the solution?

What is the normal boiling point of an aqueous solution that has
a freezing point of 1.04 oC. Kf for water 1.86 oC/m (oC-kg/mol).
Hint: Calculate the molality from the freezing point depression and
use it to calculate the normal boiling point.

Calculate the freezing point and boiling point of aqueous 1.9 m
CuCl3 given Kf for water = 1.86 deg.C/m; Kb for water = 0.512 deg
C/m. Assume theoretical value for i. Show work for credit.

1) What is the freezing point of
an aqueous solution made by dissolving 0.139 mole of
MgCl2 in 100.0 g
of water? Kf =
1.86 oC/m

what is the freezing point of an aqueous 200m (NH4)PO4 salt
solution? The Kf of water 1.86 C/m. Assume complete dissociation of
the soluble salt.

The boiling point of an aqueous solution is 101.88 °C. What is
the freezing point? Constants can be found here.
Constants for freezing-point depression and boiling-point
elevation calculations at 1 atm:
Solvent
Formula
Kf value*
(°C/m)
Normal freezing
point (°C)
Kb value
(°C/m)
Normal boiling
point
(°C)
water
H2O
1.86
0.00
0.512
100.00
benzene
C6H6
5.12
5.49
2.53
80.1
cyclohexane
C6H12
20.8
6.59
2.92
80.7
ethanol
C2H6O
1.99
–117.3
1.22
78.4
carbon
tetrachloride
CCl4
29.8
–22.9
5.03
76.8
camphor
C10H16O...

A solution of 5.00 g of sodium chloride in 1.00 kg of water has
a freezing point of –0.299°C. What is the actual (experimental) van
’t Hoff factor for this salt at this concentration?
Kf(water) =
1.86°C/m

An aqueous solution contains the amino acid glycine
(NH2CH2COOH). Assuming that the acid does not
ionize in water, calculate the molality of the solution if it
freezes at −3.75°C.The freezing point depression constant for water
is 1.86°C/m.

5. Determine the molal freezing point depression constant (Kf)
(in °C⋅kg/mol) of water by using the data of three NaCl solutions .
Use Equation 3 in the “Background and Procedure” file, the molality
values of all solutes from Question s 1 – 3 and the freezing point
depression ( ∆T) from Question 4. In your calculation, rewrite the
symbol“m ” (the molality) as “mol/kg” so that the molal freezing
point depression constant will have the correct unit. Make
sure to...

Calculate the freezing point of a solution containing 30 grams of
KCL and 3300.0 grams of water. The molal-freezing-point-depression
constant (Kf) for water is 1.86 degrees Celsius/M

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