Chem 3411 Solution Set 5 - Mindanao State University - Iligan Institute Of Technology - 2010 Page 3

ADVERTISEMENT

CHEM 3411, Fall 2010
Solution Set 5
2
Exercise 5.7b pg 201
Given
The osmotic pressure of an aqueous solution at T = 288 K is Π = 99.0 kPa.
In terms of given variables, this is written:
T = 288 K
Π = 99.0 kPa
Find
Calculate the freezing point T
of the solution.
f
Strategy
In solving this exercise, we’ll use two important equation: the van’t Hoff equation to calculate the concentration
of solute from the solutions osmotic pressure, and the equation for freezing point depression in terms of the solute
concentration.
The van’t Hoff equation (eq 5.38 on pg 173) gives the osmotic pressure Π in terms of solute concentration n
/V
b
n
b
Π =
RT
V
where n
is the moles of solute and V is the solution volume.
b
The solution of volume can be found from the moles of water solution n
.
H
O
2
V = n
V
H
O
m,H
O
2
2
where V
is the molar volume of water which is related to the density of water and its molecular weight
m,H
O
2
M
w,H
O
2
V
=
m,H
O
2
ρ
H
O
2
and this can be substituted into our expression for V .
M
w,H
O
2
V = n
H
O
2
ρ
H
O
2
Substituting this expression for V in the van’t Hoff equation and solving for moles of solute n
gives
b
Πn
M
H
O
w,H
O
2
2
n
=
b
RT ρ
H
O
2
Next, will use the equation for freezing point depression (eq 5.35 on pg 172)
∆T = K
b
f
3

ADVERTISEMENT

00 votes

Related Articles

Related forms

Related Categories

Parent category: Education