Question

To use freezing-point depression or boiling-point elevation to determine the molal concentration of a solution.

The freezing point, *T*f, of a solution is lower than the
freezing point of the pure solvent. The difference in freezing
point is called the freezing-point depression, Δ*T*f:

Δ*T*f=*T*f(solvent)−*T*f(solution)

The boiling point, *T*b, of a solution is higher than the
boiling point of the pure solvent. The difference in boiling point
is called the boiling-point elevation, Δ*T*b:

Δ*T*b=*T*b(solution)−*T*b(solvent)

The molal concentration of the solution, *m*, is directly
proportional to Δ*T*f and Δ*T*b:

*m*=moles of solutekilograms of solvent

B) A solution of water (*K*f=1.86 defreeC/*m*) and
glucose freezes at − 3.75 degree C. What is the molal concentration
of glucose in this solution? Assume that the freezing point of pure
water is 0.00 degree C

C)

A solution of water (*K*b=0.512 ∘C/*m*) and
glucose boils at 101.56 ∘C. What is the molal concentration of
glucose in this solution? Assume that the boiling point of pure
water is 100.00 ∘C.

Answer #1

B) A solution of water (Kf=1.86 defreeC/m) and glucose freezes at − 3.75 degree C.

What is the molal concentration of glucose in this solution? Assume that the freezing point of pure water is 0.00 degree C

dTf = -Kf*m

m = dTf/Kf = (-3.75)/(-1.86) = 2.0161 molal

C)

A solution of water (Kb=0.512 ∘C/m) and glucose boils at 101.56 ∘C. What is the molal concentration of glucose in this solution? Assume that the boiling point of pure water is 100.00 ∘C.

dTb = Kb*m

m = dTb/Kb = (101.56-100)/(0.512) = 3.046875 molal

Assuming 100% dissociation, calculate the freezing point (Tf)
and boiling point (Tb) of 3.26 m Na2SO4(aq).
Tf= ∘C
Tb= ∘C
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...

Since pure water boils at 100.00 ∘C, and since the addition of
solute increases boiling point, the boiling point of an aqueous
solution, Tb, will be Tb=(100.00+ΔTb)∘C Since pure water freezes at
0.00 ∘C, and since the addition of solute decreases freezing point,
the freezing point of an aqueous solution, Tf, will be
Tf=(0.00−ΔTf)∘C
What is the boiling point of a solution made using 735 g of
sucrose, C12H22O11, in 0.225 kg of water, H2O?
What is the freezing point...

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...

The molal boiling point elevation constant for water is 0.512
°C/m. A solution is prepared by dissolving 26.927
g of CaCl2 x H2O in 55.6 g of water. What is the boiling point of
this solution (at 1.000 atm pressure)?
Show all work please. Thank you!

The freezing point depression constant tells how the temperature
changes for a 1 molal concentration of solute. If camphor is
dissolved in cyclohexane so that the concentration is 1.5 molal,
what is the freezing point of the solution? (See Table in lab
procedure for Kf values.)
What are the five major steps in this experiment? a.
b. c. d. e.
An important hazard of cyclohexane is
__________________________________. How will you know if the solute
is completely dissolved?
Howdoyoucleanupthetesttubeattheendoftheexperiment?
4. 5....

1- Express the concentration of a 0.0420 M0.0420 M aqueous
solution of fluoride, F−,F−, in mass percentage and in parts per
million (ppm). Assume the density of the solution is 1.00 g/mL.1.00
g/mL.
mass percentage:
ppm:
2- A solution is made by dissolving 0.618 mol0.618 mol of
nonelectrolyte solute in 795 g795 g of benzene. Calculate the
freezing point, Tf,Tf, and boiling point, Tb,Tb, of the solution.
Constants can be found in the table of colligative constants.
Tf=
Tb=
Solvent...

Calculate the freezing point and boiling point in each solution,
assuming complete dissociation of the solute. Part A Calculate the
freezing point of a solution containing 12.3 g FeCl3 in 180 g
water. Tf = ∘C Request Answer Part B Calculate the boiling point of
a solution above. Tb = ∘C Request Answer Part C Calculate the
freezing point of a solution containing 4.2 % KCl by mass (in
water). Express your answer using two significant figures. Tf = ∘C...

Compare the equations for calculating freezing point depression
and boiling point elevation. Illustrate the difference by
calculating the ΔT for the freezing point and boiling point of 2.0
molality NaCl.

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...

Assuming complete dissociation of the solute, how many grams of
KNO3 must be added to 275 mL of water to produce a solution that
freezes at −14.5 ∘C? The freezing point for pure water is 0.0 ∘C
and Kf is equal to 1.86 ∘C/m ANSWER=109 g PART B NEEDED: If the
3.90 m solution from Part A boils at 103.45 ∘C, what is the actual
value of the van't Hoff factor, i? The boiling point of pure water
is 100.00...

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