Chem m6 colligative properties of solution

(Effective Alternative Secondary Education)
CHEMISTRY
MODULE 6
Colligative Properties of Solution
BUREAU OF SECONDARY EDUCATION
Department of Education
DepEd Complex, Meralco Avenue
Pasig City

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Module 6
Colligative Properties of Solution
What this module is about
When a non-volatile (substances that do not readily form vapors), non-electrolytic
(substances that do not form ions and do not conduct electricity when placed in water)
solute such as sugar is dissolved in a given volume of solvent to form a sugar solution, it
changes the set of properties of the pure solvent entirely. In this regard, the set of
properties such as freezing point, boiling point, vapor pressure, and osmotic pressure of a
solvent are affected by the presence of the solute particles in the solution. This set of
properties will depend only on the number of dissolved particles in the solution and not on
their identity. These properties are collectively known as colligative properties of solution.
This module will focus on four colligative properties of electrolyte and non-electrolyte
solutions namely, vapor pressure lowering, boiling point elevation, freezing point
depression, and osmotic pressure.
To make the discussion easy for you, the module is divided into four lessons:
Lesson 1 – What is the Difference Between Osmotic Pressure and Vapor
Pressure?
Lesson 2 – What is Boiling Point Elevation?
Lesson 3 – What is Freezing Point Lowering?
Lesson 4 – What is the Importance of Colligative Properties in Our Daily
Lives?
What you are expected to learn
After going through this module, you should be able to:
1. differentiate between colligative and non-colligative properties of a solution;
2. differentiate vapor pressure from osmotic pressure;
3. identify boiling point elevation;
4. state and explain freezing point lowering; and
5. apply knowledge of the importance of colligative properties of solutions to daily
living.

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How to learn from this module
Here are some pointers to remember as you go over this module.
1. Read and follow the instructions carefully.
2. Answer the pretest first before reading the content of the module.
3. Take down notes and record points for clarification.
4. Always aim to get at least 70% of the total number of items given.
5. Be sure to answer the posttest at the end of the module.
What to do before (Pretest)
Take the pretest before proceeding to the lessons. Check your answers against the answer
key at the end of the module.
I. Multiple Choice. Choose the letter of the best answer. Write the chosen letter on a
separate sheet of paper.
1. A substance whose water solution conducts an electric current is called a(n)
a. electrolyte c. polar substance
b. nonelectrolyte d. nonpolar substance
2. A substance that vaporizes easily is known as
a. volatile c. electrolyte
b. nonvolatile d. nonelectrolyte
3. Adding a solute such as NaCl to water increases its
a. boiling point c. osmotic pressure
b. melting point d. vapor pressure
4. Which of the following is NOT a colligative property of solution?
a. solubility c. melting point
b. boiling point d. osmotic pressure
5. Which of the following statements is TRUE about vapor pressure?
a. The vapor pressure of the solvent is less than the solution.
b. The vapor pressure of the solution is higher than the pure solvent.
c. The vapor pressure of the pure solvent is higher than the solution.
d. The vapor pressure of the pure solvent and the solution are the same.

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6. The i factor gives the number of particles per formula unit of the solute. What is the i
factor for NaCl?
a. 0 c. 2
b. 1 d. 3
7. What happens during osmosis?
a. Pure solvent diffuses through a membrane but solutes do not.
b. Pure solutes diffuse through a membrane but solvent does not.
c. Gases diffuse through a membrane into a solution and build up pressure.
d. Pure solvent and a solution both diffuse at the same time through a membrane.
8. What is the temperature at which the vapor pressure equals the atmospheric pressure?
a. 100 o
C c. boiling point
b. freezing point d. melting point
9. The freezing point of a solution is always __________ the pure solvent.
a. less than c. greater than
b. same as d. greater than or equal to
10.If a potato is placed in brine (concentrated NaCl solution), the potato cell is expected to:
a. shrink c. become rigid
b. swell d. no considerable change
II. TRUE or FALSE. Write TRUE if the statement is correct. Otherwise, write FALSE.
__________ 1. Colligative properties will only depend on the number of dissolved particles
in the solution and not on their identity.
__________ 2. The addition of a solute will increase the boiling point of the solution.
__________ 3. The van’t Hoff factor is only applicable for non-electrolyte solutions.
__________ 4. The boiling point of the solution is always greater than that of the pure
solvent.
__________ 5. All biological membranes are regulated via osmosis.
Lesson 1. What is the Difference Between Osmotic Pressure and Vapor
Pressure?
Before differentiating these two terminologies, let us first understand the difference
between the two classifications of solutions according to their properties – colligative and
non-colligative properties. Earlier, we have defined that colligative properties will just
Key to answers on page 21.

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depend on the number of dissolved particles in the solution and not on their identity. Non-
colligative properties state otherwise. To clearly understand the difference between these
two properties, let us do Activity 1.1.
What you will do
Activity 1.1 Classifying Colligative and Non-Colligative Properties of Solution
Materials: 1% (w/v) brown sugar solution
0.5 % (w/v) salt solution (NaCl)
thermometer
Procedure:
Prepare the brown sugar and salt solutions of concentration 1% and 0.5%,
respectively. Observe the following properties in the two solutions and identify whether the
property observed is a colligative or non-colligative property based on the definition.
Properties of Solution
0.5 % (w/v) salt
solution
1% (w/v) brown sugar
solution
Solubility (ability of the
solute to be dissolved in
a solvent)
Viscosity of solution
(“viscosity” is a property
of solution to resist flow)
Color of the solution
Taste of solution
Temperature upon
boiling
Temperature upon
freezing
Analysis:
1. Which of the following properties of solution can be considered colligative? Why?
2. Which of the following properties of solution can be considered non-colligative?
Justify your answer.
After finishing the activity, we can clearly distinguish what properties of solution are
colligative and what properties are not. Again, for as long as the number of dissolved
particles in solution is taken into consideration, then that property of solution (e.g. boiling

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point, freezing point, etc.) is a colligative property. On the other hand, if the identity of the
dissolved species and solvent is being analyzed (e.g. color, taste, viscosity, solubility), then
it is a non-colligative property. Having learned their difference, we can now describe vapor
pressure and osmotic pressure of solutions.
Vapor-Pressure Lowering
When a nonvolatile (does not turn to vapor easily) solute is added to a liquid to form
a solution, the vapor pressure above that solution decreases. To understand why that might
occur, let us do a simple experiment in Activity 1.2.
What you will do
Activity 1.2 Vapor-Pressure Lowering
Materials: Water
Aqueous sugar solution
Two glasses
One sealed enclosed container
Procedure:
1. Get two glasses placed side by side in a sealed enclosed
container. One glass contains pure water, the other an equal
volume of an aqueous solution of sugar. Take note of the volume
of water and sugar solution. (See figure 1.1a)
2. Leave the set-up until the next day. Gradually measure the
volume of the sugar solution and that of the pure water. Is there
any change in their original volume? (See figure 1.1b)
Analysis:
1. What can you infer about the change in volume of the sugar solution and that of pure
water?
2. What has caused this change in volume of the sugar solution and that of pure water?
Figure 1.1 Experiment set-up for
vapor-pressure lowering

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After finishing the activity, you should now see why the vapor
pressure of the solvent decreases upon addition of a non-volatile, non-
electrolyte solute (sugar).
The extent to which a nonvolatile solute lowers the vapor pressure is proportional to
its concentration. This was discovered by French chemist Francois Raoult (1830-1907).
Raoult’s law states that for nonelectrolyte solutions, the partial vapor pressure of a solvent
over a solution (P1) is equal to the vapor pressure of the pure solvent (Po
1) multiplied by the
mole fraction of the solvent (X1). This law is mathematically expressed as:
For solutions of electrolytes, the vapor pressure lowering equation can be expressed
as:
where i is the van’t Hoff factor, named after Jacobus Henricus van’ Hoff (1852-1911), who
won the very first Nobel Prize in chemistry in 1901 for his work on colligative properties of
solution. The i factor gives the number of particles per formula unit of the solute. For
example, NaCl solution dissociates to give one Na+
(aq) and one Cl-
(aq), the iNaCl = 2, because
there is one Na+
and one Cl-
ion in solution per formula unit of solute.
On the other hand, if both components of a solution are volatile (readily evaporates),
the vapor pressure of the solution is the sum of the individual partial pressures. The total
pressure is given by Dalton’s law of partial pressure:
Figure 1.2 A nonvolatile solute reduces
the rate of vaporization of the solvent.
P1 = X1 Po
1
P1= iPo
1 X1
PT = PA + PB
or
PT = XA Po
A + XB Po
B

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Sample Problem:
What is the vapor pressure of the solution containing 20 g of sugar (C12H22O11) in 1.5
kg water at 25o
C. Note: Po
water at 25o
C is 24 torr
Explanation:
1 mole of sugar (C12H22O11) is 342 g and 1 mole of water (H2O) is 18 g. The number
of moles of each component is computed as:
For sugar:
OHCmol0.06
OHCg342
OHCmol1
OHCg20 112212
112212
112212
112212 =×
For water:
OHmol83.33
OHCg18
OHC1mol
OHg1500 2
112212
112212
2 =×
And mole fraction of water (solvent) is computed as:
1.00
OHC0.0683.33
OHC83.33
X
112212
112212
OH2
=
+
=
Therefore, the vapor pressure is:
torr24.0P
torr241.00
PXP
OH
OH
o
OHOH
2
222
=
×=
×=
Practice Exercise:
Calculate the vapor pressure of salt solution containing 20 g
salt (NaCl) in 1.5 kg of water at 25o
C? Note: Po
water at 25o
C is
24 torr and molecular weight of NaCl is 58 g/mol.
Note: Remember that NaCl is a strong electrolyte and
dissociates to Na+
and Cl-
ion respectively.
Answer: 48 torr

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Osmotic Pressure
Osmosis is of prime importance to living organisms because it influences the
distribution of nutrients and the release of metabolic waste products. Living cells of both
plants and animals are enclosed by a semipermeable membrane called the cell
membrane, which regulates the flow of liquids and of dissolved solids and gases into and
out of the cell.
The osmotic pressure (Π ) of a solution is the pressure required to stop osmosis.
The osmotic pressure of the solution is given by:
where M is the molarity of solution, R the gas constant (0.0821 L .
atm / K .
mol), and T the
absolute temperature (in Kelvins).
The osmotic pressure is expressed in atm. And since osmotic pressure
measurements are carried out under constant temperature, molarity is preferred over
molality as concentration. Again, for solutions of electrolytes, the osmotic pressure equation
can be expressed as:
where i is the van’t Hoff factor, the number of particles per formula unit of the solute.
Did you know?
Oceans cover over 72% of the earth and a reservoir for
97.2% of the earth’s water. However, out of the 97.2% of
earth’s water, only 2.5% is available as freshwater and less
than 1% is available as groundwater or surface water for
human use. Scientists have found a new, cheaper and more
economical way of making seawater possible for drinking. The
process is known as reverse osmosis. Through this process,
seawater is made to pass through a semi-permeable
membrane and by applying a pressure greater than 30 atm
(Note: 30 atm is the pressure that must be applied to saline
solution of seawater in order to facilitate osmosis), the osmotic
flow would be reversed, and fresh water made to run through
the membrane. Now, that’s chemistry in action!
Π = MRT
Π = iMRT

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Sample Problem:
What is the osmotic pressure of the solution containing 0.2 M sugar (C12H22O11)
solution at 25o
C?
Explanation:
atm4.89
4.89K298
molK
atmL
0.0821
solutionL1
OHCmol0.2
MRT
112212
=Π
=×
⋅
⋅
×=Π
=Π
What you will do
Self-Test 1.1
Now that you are through with the first lesson, try to answer the following questions and see
for yourself how much you learned.
Multiple Choice. Choose the letter of the best answer. Write the chosen letter on a
1. What happens during osmosis?
a. Pure solvent diffuses through a membrane but solutes do not.
b. Pure solutes diffuse through a membrane but solvent does not.
c. Gases diffuse through a membrane into a solution and build up pressure.
d. Pure solvent and a solution both diffuse at the same time through a membrane.
2. What is the van’t hoff factor for CaCl2?
a. 0 c. 2
b. 1 d. 3
3. The osmotic pressure found for a 2.50 g sugar solution at 25o
C is 1.79 atm in a 1.0 L of
water. What is its molar mass (g/mol)?
a. 342 g/mol c. 3.42 g/mol
b. 34.2 g/mol d. 7.32 x 10-2
g/mol
Practice Exercise:
Calculate the osmotic pressure of 0.2 M salt solution (NaCl) at
25 o
C?
Answer: 9.78 atm

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4. Cold-blooded animals and fish thrive in sea water. Which of the following situations is
true about their condition?
a. Their blood has greater osmotic pressure than that of sea water.
b. Their blood has less osmotic pressure than that of sea water.
c. Their blood has the same osmotic pressure as that of sea water.
d. The osmotic pressure of sea water is greater than that of their blood.
5. According to Raoult's law, which statement is FALSE?
a. The vapor pressure of a solvent over a solution decreases as its mole fraction
increases.
b. The solubility of a gas increases as the temperature decreases.
c. The vapor pressure of a solvent over a solution is less than that of pure solvent.
d. The greater the pressure of a gas over a solution the greater its solubility.
Lesson 2. What is Boiling Point Elevation?
Remember that boiling point is the temperature at which the vapor of a liquid is equal
to the atmospheric pressure. In the presence of a non-volatile, non-electrolytic solute such
as sugar, the pressure that will be exerted by the vapor of the solvent is lesser in
comparison with that of the pure solvent at equal volumes. And as a consequence, the
solution will boil at a higher temperature than that of the pure solvent.
To clearly understand what boiling point elevation is all about let us do Activity 2.1.
What you will do
Activity 2.1 Boiling Point Elevation
Materials: three eggs
1 tbsp of salt
1 tbsp of sugar
boiling water
Procedure:
1. Put the first egg in two cups of water and take note of the time until the water
boils.

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2. Again, using two cups of water, put the second egg in the water and add 1 tbsp of
salt. Record the time it will take the water to boil.
3. Repeat step 2, but add 1 tbsp of sugar instead of salt. Again, take note of the
time it will take the water to boil.
4. Compare the time it will take for water to boil and cook the hard-boiled egg in step
1 to step 3. Record your observations.
Analysis:
1. Which set-up took less time to cook hard-boiled eggs? Why?
________________________________________________
2. Did the water take more time to boil when electrolyte (NaCl) solute was added?
Why? ___________________________________________
3. Did the water take more time to boil upon addition of non-electrolyte (sugar)
solute? Justify your answer.
___________________________________________________________
Since we have already established that the boiling point of the solution is greater than
that of the pure solvent, the boiling point elevation (∆Tb) is mathematically expressed as
follows:
where (Kb) is boiling point elevation constant, equivalent to 0.52 o
C/m for aqueous solutions.
This means that, for example, 1 mole of sugar (nonelectrolyte) in 1 kilogram of water will
increase the boiling point from 100o
C to 100.52o
C. And (m) is the molal concentration of
solute. It is also important to note that ∆Tb is a positive quantity and should be added to the
boiling point of pure solvent (water), which is 100o
C.
Remember that molality is used here over molarity because we are dealing with a
solution whose temperature is not constant and concentration cannot be expressed in
molarity because it changes with temperature.
Again, for solutions of electrolytes, the boiling point elevation equation can be
expressed as:
Sample Problem:
At what temperature will the sugar solution boil if 20 g sucrose (C12H22O11) is added
∆Tb = Kbm
∆Tb = iKbm

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to 1.5 kg of water?
Explanation:
Remember that sugar is a nonelectrolyte so there will be no need for the van’t Hoff
factor. A mole of sugar (C12H22O11) is 342 g. Thus, molality of sugar can be
computed as:
m0.04
OHkg
OHCmol0.04
OHCg342
OHCmol1
OHkg1.5
OHCg20
2
112212
112212
112212
2
112212
==×
The boiling point elevation is calculated as:
∆Tb = Kbm
= 0.52 o
C x 0.04 m
m
∆Tb = 0.02o
C
Thus, the boiling point of the solution is:
100o
C + 0.02o
C = 100.02o
C
What you will do
Self-Test 2.1
Again, try to check how much you have learned from the lesson by answering the following
questions.
Multiple Choice. Choose the letter of the best answer. Write the chosen letter on a
Practice Exercise:
At what temperature will salt solution boil if 20 g salt (NaCl) is
added to 1.5 kg of water? (Molecular weight of NaCl is 58
g/mol)
dissociates to Na+
and Cl-
ion, respectively.
Answer: 100.24 o
C

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1. If Solution A contains 5 g NaCl in 100 mL water and Solution B contains 10 g NaCl in
100 mL water, which of the following conditions is true about solution A and B?
a. Solution A has greater boiling point than Solution B.
b. Solution B has greater boiling point than Solution A.
c. Solution A and B have the same boiling point.
d. Solution A has less boiling point than Solution B.
2. What is the boiling point of a 0.20 m NaCl solution in water? For water, Kb is 0.512o
C.
kg/mol.
a. 100.0o
C c. 100.3o
C
b. 100.2o
C d. 100.4o
C
3. What happens to the boiling point of water when 0.5 m sugar (nonelectolyte) is added to
it?
a. 100.0o
C c. greater than 100.0o
C
b. less than 100.0o
C d. none of the above
4. Which of the following statement is TRUE about the boiling point of the solution?
a. The boiling point of the solvent is greater than that of the solution.
b. The boiling point of the solution is less than that of the pure solvent.
c. The boiling point of the solution is the same as that of the pure solvent.
d. The boiling point of the solution is greater than that of the pure solvent.
5. The boiling point of an impure compound is generally __________ that of pure solid.
a. same as c. greater than
b. less than d. greater than or equal to
Lesson 3. What is Freezing Point Depression?
Have you ever tried sprinkling salt over ice? What have you noticed? Salts such as
NaCl and CaCl2 cause ice to melt. This method of thawing depresses the freezing point of
water. To learn more about freezing point depression, it will help to do Activity 3.1.

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What you will do?
Activity 3.1 Freezing Point Depression
Materials: one tsp. salt stirrers
one glass of water spoon
one glass of crushed Ice thermometer
Procedure:
1. Using one glass of water and one glass of crushed ice, stir the mixture; then using
a thermometer, observe and record this temperature.
2. Add one tsp. of salt to the water/ice mixture, then observe and record the
temperature. You should repeat this procedure until the temperature reaches
10o
C. More ice should be added if necessary.
Analysis:
1. What happens to water and ice when salt is added to this mixture?
2. What happens to the temperature when salt is added to the mixture?
3. What variables would cause these differences?
Water freezes at 0o
C and boils at 100o
C. Salt water will not freeze until the
temperature is below 0o
C. The more salt, the lower the freezing point of the solution. In the
above experiment, energy is lost from the water in the form of heat. This heat is used to
melt the ice. Since heat is lost from the water the temperature of the water goes down.
Since there is now salt dissolved in the water it cannot freeze again, hence we observe a
lower temperature.
The freezing point depression (∆Tf) is mathematically expressed as:
where Kf is the freezing point depression constant. equivalent to -1.86 o
C/m for aqueous
solutions. Again, for example, 1 mole of sugar (nonelectrolyte) in 1 kilogram of water will
decrease the freezing point from 0o
C to -1.86o
C. (m) is the molal concentration of solute.
And since we have already established that the freezing point of the solution is less than
that of the pure solvent, then ∆Tf is a negative quantity and should be subtracted from the
freezing point of pure solvent (water), which is 0o
C.
Again, for solutions of electrolytes, the freezing point lowering equation can be
expressed as:
∆Tf = Kf m

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Sample Problem:
At what temperature will the sugar solution freeze if 20 g sucrose (C12H22O11) is
added to 1.5 kg of water?
Explanation:
Since sugar is a nonelectrolyte, there will be no need for the van’t Hoff factor. A mole
of sugar (C12H22O11) is 342 g. Molality (m) of sugar can be computed as:
m0.04
OHkg
OHCmol0.04
OHCg342
OHCmol1
OHkg1.5
OHCg20
2
112212
112212
112212
2
112212
==×
The freezing point depression is calculated as:
∆Tf = Kf m
= -1.86 o
C x 0.04 m
m
∆Tf = -0.07o
C
Thus, the freezing point of the solution is:
0o
C - 0.07o
C = -0.07o
C
∆Tf = iKfm
Practice Exercise:
At what temperature will salt solution freeze if 20 g salt (NaCl)
is added to 1.5 kg of water? (Molecular weight of NaCl is 58
g/mol)
dissociates to Na+
and Cl-
ion, respectively.
Answer: -0.86 o
C

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What you will do
Self-Test 3.1
Let us try to check how much you have learned from this lesson by answering the following
questions.
1. The melting point of an impure compound is generally __________ that of the pure solid.
a. less than c. greater than
b. the same as d. greater than or equal to
2. Adding sodium chloride to water will cause the:
a. boiling point to rise and the freezing point to lower.
b. boiling point to lower and the freezing point to rise.
c. both boiling point and freezing point to rise.
d. both boiling point and freezing point to lower.
3. What is the freezing point of a 0.20 m sucrose (nonelectrolyte)?
Kf = 1.86 o
C /m.
a. 0.00o
C c. 3.7o
C
b. 0.37o
C d. 37o
C
4. What is the freezing point of a 0.50 m NaCl (strong electrolyte)?
Kf = 1.86 o
C /m.
a. 0.0o
C c. 9.3o
C
b. 0.93o
C d. 1.86o
C
5. Which of the following solutions has the HIGHEST freezing point?
a. 0.1 m sugar c. 0.08 m CaCl2
b. 0.1 m NaCl d. 0.04 m Na2SO4
Did you encounter any problem? Well, compare your answers with the answer key
and see for yourself the items you missed. Good luck!
Did you know?
NaCl (salt) is added to ice to make a freezing mixture
that results in a tasty, homemade ice cream. Lowering the
freezing temperature of the ice-water-salt mixture causes the
ice cream ingredients to freeze more quickly.

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Lesson 4. What is the Importance of Colligative Properties in Our Daily
Llife?
We have already established that addition of salt, such as NaCl, lowers the freezing
point of ice. Even some organisms have evolved to survive freezing water temperatures
with natural "antifreeze." Some fishes living in the Arctic ocean have blood containing a
high concentration of a specific protein. This protein behaves like a solute in a solution and
lowers the freezing point in their blood enabling them to survive in very cold temperatures.
Biologists and biochemists often take advantage of osmotic pressure when they
isolate the components of a cell. They further classify solutions depending on the
concentration of the solutes inside the cell as hypertonic, isotonic or hypotonic solutions.
Suppose you cut a potato into cubes and immerse it in brine (concentrated NaCl). What will
happen? The potato will tend to shrink. This method is used for curing meats like country
ham. It is done to eliminate the bacteria since the bacteria cannot survive in high salt
concentration.
Alternatively, hypotonic means the solution has a lower concentration of particles
than the cell. Suppose you cut a potato into cubes, but this time immerse it in water. What
will you notice? There would be more water moving into the potato cell causing it to swell.
When a cell is placed in a solution that has a much smaller ionic strength, water pours into
the cell, and the cell expands until the cell membrane bursts. In the case of red blood cells,
the process is known as hemolysis.
On the other hand, an isotonic solution has the same osmotic strength on both sides
of the semipermeable membrane. Physiological saline (0.9% NaCl) is isotonic with blood.
In this condition, the cell retains its normal shape and function.
Did you know?
Dialysis uses the same principle as osmosis to remove
salt or other ions in the blood. In the dialysis machine, the
blood is circulated through a long tube of cellophane in an
isotonic solution and then returned to the patient’s vein. The
ions can pass out and the large proteins remain. When protein
is found in the urine, that means there is some type of damage
to the kidney. The isotonic solution has 0.6% NaCl, 0.04% KCl,
0.2% NaHCO3, and 0.72% glucose (w/v). Thus no sodium ions
or glucose is lost from the blood. The isotonic solution is
changed every 2 hours and the patient stays on the dialysis
machine for 4 to 7 hours.

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What you will do
Self-Test 4.1
Let us try to check how much you have learned from the lesson by answering the following
questions.
Modified True or False. Write TRUE if the statement is correct otherwise CHANGE the
underlined word to correct the statement.
__________ 1. A hypertonic solution is a solution that has a higher concentration of article
than the cell.
__________ 2. The normal physiological saline concentratrion of the blood is 0.6% NaCl.
__________ 3. Cells shrink if the concentration of solute inside the cell is greater than that
outside the cell.
__________ 4. Hemolysis is the phenomenon that causes the membrane of red blood
cells to burst due to a hypotonic environment inside the cell.
__________ 5. Some fishes living in the Arctic ocean were able to survive in very cold
temperature because their blood contained the same concentration of
solutes as the seawater.
Did you encounter any problem? Well, compare your answers with the answer key
and see for yourself the items you missed. Good luck!
Let’s Summarize
A. Summary of Key Equations
For nonelectrolytes:
Raoult’s Law: P1 = Po
1 X1
Dalton’s Law of Partial Presssure: PT = PA + PB
Osmotic Pressure: Π = MRT
Boiling Point Elevation: ∆Tb = Kbm
Freezing Point Depression: ∆Tf = Kf m
For electrolytes:
Raoult’s Law: P1 = iPo
1 X1
Dalton’s Law of Partial Presssure: PT = iPA + iPB

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Osmotic Pressure: Π = iMRT
Boiling Point Elevation: ∆Tb = iKbm
Freezing Point Depression: ∆Tf = iKf m
B. Summary of Facts and Concepts
1. Colligative properties (or collective properties) are properties that depend only on
the number of solute particles in solution and not on the nature of the solute
particles.
2. The four colligative properties of a solution are vapor pressure, osmotic pressure,
boiling point and freezing point.
3. The change in vapor pressure where the solute is less volatile than the solvent is
regulated by Raoult’s law, which states that the vapor pressure of a solvent over a
solution is equal to the mole fraction of the solvent times the vapor pressure of
pure solvent.
4. The osmotic pressure of a solution is the pressure required to stop osmosis.
5. The freezing point of the solution is always less than the freezing point of the pure
solvent.
6. The boiling point of the solution is always greater than the boiling point of the pure
solvent.
7. In electrolyte solutions, the interaction between ions leads to the formation of ion
pairs. The van’t Hoff factor (i) provides a measure of the extent of dissociation of
electrolytes in solution.
8. Solutions can be classified as hypertonic, hypotonic or isotonic depending on the
concentration of solute inside and outside the cell.
9. A hypertonic solution has a higher concentration of particle than the cell causing
the cell to shrink.
10.A hypotonic solution has a lower concentration of particles than the cell causing
the cell to swell.
11.An isotonic solution has the same osmotic strength on both sides of the
semipermeable membrane.
Posttest
I. Multiple Choice. Choose the letter of the best answer. Write the chosen letter on a
1. According to Raoult's law, which statement is FALSE?
a. The solubility of a gas increases as the temperature decreases.
b. The greater the pressure of a gas over a solution the greater its solubility.
c. The vapor pressure of a solvent over a solution is less than that of pure solvent.
d. The vapor pressure of a solvent over a solution decreases as its mole fraction
increases.

- 22 -
2. Consider a solution made from a nonvolatile solute and a volatile solvent. Which
statement is TRUE?
a. The osmotic pressure is the same as vapor pressure of the solution.
b. The vapor pressure of the solution is always greater than the vapor pressure of
the pure solvent.
c. The boiling point of the solution is always greater than the boiling point of the pure
solvent.
d. The freezing point of the solution is always greater than the freezing point of the
pure solvent.
3. Dissolving a solute such as NaCl in a solvent such as water results in:
a. an increase in the melting point of the liquid
b. a decrease in the boiling point of the liquid
c. a decrease in the vapor pressure of the liquid
d. no change in the boiling point of the liquid
4. What is the freezing point of a solution that contains 10.0 g of glucose (C6H12O6) in 100 g
of H2O? Kf = 1.86 o
C/m?
a. -0.186 o
C c. -0.10 o
C
b. 0.186 o
C d. -1.03 o
C
5. Which of the following solutions has the highest osmotic pressure at 25o
C?
a. 0.2 M KBr c. 0.2 M Na2SO4
b. 0.2 M C2H5OH d. 0.2 M KCl
6. A solution that contains 55.0 g of ascorbic acid (Vitamin C) in 250 g of water freezes at -
2.34 C. Calculate the molar mass (g/mol) of the solute. Kf = 1.86 o
C/m.
a. 1.26 c. 43.6
b. 10.9 d. 175
7. What mass of ethanol, C2H5OH, a nonelectrolyte, must be added to 10.0 L of water to
give a solution that freezes at -10.0o
C? Assume the density of water is 1.0 g/mL?
a. 85.7 kg c. 5.38 kg
b. 24.8 kg d. 2.48 kg
8. If solution A contains 5 grams of NaCl in 100 grams of water and solution B contains 10
grams of NaCl in 100 grams of water, which of the following comparisons is true?
a. A has a higher boiling point and a higher freezing point than B.
b. A has a lower boiling point and a lower freezing point than B.
c. A has a lower boiling point and a higher freezing point than B.
d. A has a higher boiling point and a lower freezing point than B.
9. Which solution has lower concentration of particles than the cell causing the cell to
swell?
a. hypertonic c. isotonic
b. hypotonic d. unsaturated

- 23 -
10.In what temperature does the vapor pressure of the liquid equal the atmospheric
pressure?
a. 100o
C c. melting point
b. boiling point d. freezing point
II. Matching Type. Match the correct equation in Column B with the principles in Column A.
Column A Column B
_____ 1. Raoult’s law a. ∆Tb = Kbm
_____ 2. Dalton’s law of partial pressures b. Π = MRT
_____ 3. Boiling point elevation c. P1= Po
1 X1
_____ 4. Freezing point depression d. PT = PA + PB
_____ 5. Osmotic pressure e. ∆Tf = Kf m
f. ∆P = P2 - P1
Key to Answers
Pretest
I. Multiple Choice II. True or False
1. a 6. c 1. True
2. a 7. a 2. False
3. a 8. c 3. False
4. a 9. a 4. True
5. c 10. a 5. True
Lesson 1 Lesson 2 Lesson 3 Lesson 4
Self-Test 1.1 Self-Test 2.1 Self-Test 3.1 Self-Test 4.1
1. a 1. b 1. a 1. True
2. d 2. b 2. a 2. 0.9 % NaCl
3. b 3. b 3. b 3. True
4. c 4. d 4. d 4. Hypertonic
5. a 5. c 5. c 5. greater

- 24 -
Posttest
I. Multiple Choice II. Matching Type
1. d 6. d 1. c
2. c 7. d 2. d
3. c 8. c 3. a
4. d 9. b 4. e
5. c 10. b 5. b
References
Chang, R.N. (1998). Chemistry. (6th
ed.) USA: McGraw-Hill, Inc.
Green, J. & Damji, S. (2001). Chemistry. (2nd
ed.) Australia: IBID Press, Victoria
Moore, J.W., Stanitski, C.L. & Wood J.L. (1998). The chemical world: Concepts and
applications. (2nd
ed.) USA: Harcourt Brace & Company
Petrucci, R.H. & Harwood, W.S. (1998). General chemistry: Principles and modern
applications. (7th
ed.) New Jersey: Prentice-Hall International
Regalado, E.C. (2000). Chemistry. Philippines: St. Augustine Publications, Inc.

Chem m6 colligative properties of solution

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