Physical Pharmacy-I lab

Laboratory Notebook
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Student ID :
Section registered : 2A

Experiment No. 01.......................................................................................................................... 1
1.1 Name of the experiment ................................................................................................... 1
1.2 Principle ........................................................................................................................... 1
1.3 Required apparatus........................................................................................................... 2
1.4 Required reagents............................................................................................................. 2
1.5 Procedure.......................................................................................................................... 2
1.6 Data and Calculation........................................................................................................ 3
1.7 Result................................................................................................................................ 4
1.8 Precautions ....................................................................................................................... 5
Experiment No. 02.......................................................................................................................... 6
2.1 Name of the experiment ................................................................................................... 6
2.2 Principle ........................................................................................................................... 6
2.3 Required apparatus........................................................................................................... 7
2.4 Required reagents............................................................................................................. 7
2.5 Procedure.......................................................................................................................... 7
2.6 Data and Calculation........................................................................................................ 9
2.7 Result.............................................................................................................................. 11
2.8 Precautions ..................................................................................................................... 12
Experiment No. 03........................................................................................................................ 13
3.1 Name of the experiment ................................................................................................. 13
3.2 Principle ......................................................................................................................... 13
3.3 Required apparatus......................................................................................................... 14
3.4 Required reagents........................................................................................................... 14
3.5 Procedure........................................................................................................................ 14
3.6 Data and Calculation...................................................................................................... 15

3.7 Result.............................................................................................................................. 17
3.8 Precautions ..................................................................................................................... 17
Experiment No. 04........................................................................................................................ 18
4.2 Principle ......................................................................................................................... 18
4.5 Procedure........................................................................................................................ 20
4.7 Result.............................................................................................................................. 24
4.8 Precautions ..................................................................................................................... 24
Experiment No. 05........................................................................................................................ 25
5.2 Principle ......................................................................................................................... 25
5.5 Procedure........................................................................................................................ 26
5.7 Result.............................................................................................................................. 28
5.8 Precautions ..................................................................................................................... 28

1
Experiment No. 01 Date:
1.1 Name of the experiment
Standardization of sodium hydroxide solution using oxalic acid solution.
1.2 Principle
Titration is an analytical technique where the unknown concentration/amount of a substance is
determined with another substance of known concentration/amount by conducting a chemical reaction
between them. In acid-base titration, one of the substance is an acid and the other is base.
Standardization means determination of this unknown concentration. Primary standards are essential
for standardization because these can be used to produce solutions of known concentration. Acidic
primary standards include oxalic acid and potassium hydrogen phthalate. An example of basic primary
standard is sodium carbonate.
In this particular experiment, a solution of sodium hydroxide will be standardized using oxalic acid
solution. Sodium hydroxide is a secondary standard, so the concentration of the solution prepared from
sodium hydroxide is not exact. But the solution prepared from oxalic acid has exact concentration.
oxalic acid reacts with sodium hydroxide as follows:
As we can see, 1 mole of oxalic acid reacts with 2 moles of sodium hydroxide. The relationship
between the concentration of the oxalic acid solution and that of sodium hydroxide solution can be
described as follows:
Here, VNaOH and VOxalic refer to the volumes of sodium hydroxide solution and oxalic acid solution
(respectively) required to reach end-point of titration, SNaOH and SOxalic refer to the concentrations of
sodium hydroxide solution and oxalic acid solution (respectively). Since SOxalic is precisely known and
VNaOH as well as VOxalic can be determined precisely from titration, we can easily determine SNaOH.

2
1.3 Required apparatus
1. Electronic balance
2. Volumetric flask
3. Conical flask
4. Burette
5. Pipette
6. Dropper
1.4 Required reagents
1. Sodium hydroxide
2. Oxalic acid (dihydrate)
3. Phenolphthalein
4. Ethanol
5. Distilled water
1.5 Procedure
Preparation of 100 mL 0.1 M sodium hydroxide solution1.5.1
1. Calculate the amount of sodium hydroxide required to prepare 100 mL of 0.1 M sodium hydroxide
solution.
2. Weigh the calculated amount in an electronic balance and take it in a 100 mL volumetric flask.
3. Add small amount of distilled water to dissolve the solids and then adjust the volume to 100 mL.
Preparation of 100 mL 0.05 M oxalic acid solution1.5.2
1. Calculate the amount of oxalic acid required to prepare 100 mL of 0.05 M oxalic acid solution.
3. Add small amount of distilled water to dissolve the solids and then adjust the volume to 100 mL.
Preparation of phenolphthalein indicator solution1.5.3
1. Calculate the amount of phenolphthalein solid required to prepare 50 mL 0.5% w/v solution of
phenolphthalein.

3
3. Add 25 mL of ethanol and dissolve the solids.
4. Adjust the volume to 50 mL with distilled water.
Standardization of sodium hydroxide solution1.5.4
1. Fill the burette with the sodium hydroxide solution.
2. Take 25 mL of the 0.05 M oxalic acid solution in a 250 mL conical flask.
3. Add 1 drop (0.05 mL) of 0.5% w/v phenolphthalein indicator solution.
4. Titrate the contents of the conical flask against the sodium hydroxide solution in the burette. End
point is indicated by the change of color from colorless to pink. Note down the volume of sodium
hydroxide solution required.
5. Repeat steps 2-4 two more times.
1.6 Data and Calculation
Calculation of the amount of sodium hydroxide required to prepare 100 mL 0.1 M1.6.1
sodium hydroxide solution
The molecular weight of sodium hydroxide is 40 gram/mol. Hence, we can say that:
Calculation of the amount of oxalic acid required to prepare 100 mL 0.05 M oxalic acid1.6.2
solution
The molecular weight of oxalic acid (dihydrate) is 126 gram/mol. Hence, we can say that:

4
Calculation of the amount of phenolphthalein required to prepare 50 mL 0.5% w/v1.6.3
phenolphthalein solution
By definition of % w/v solution, 0.5% w/v solution means that:
Titration data1.6.4
Volume of oxalic acid solution taken = VOxalic = 25 mL
Strength/concentration of oxalic acid solution = SOxalic = 0.05 M
Sl.
No.
Initial Burette reading
(mL)
Final Burette reading
(mL)
Difference
(mL)
Average
(mL)
VNaOH
1
2
3
Now,
1.7 Result
0.1 M Sodium hydroxide solution was prepared and the solution was standardized using standard
oxalic acid solution.
The standardized concentration of the prepared sodium hydroxide solution was ________________ M.

5
1.8 Precautions
1. All weights must be taken carefully. Particularly, the weight of oxalic acid must be precise to
ensure precise concentration.
2. Only 1 drop of the indicator solution should be used.
3. All volumetric reading (e.g. of the volumetric flask and the burette) must be taken considering the
meniscus.
4. Color change must be monitored very carefully.
I verify that the student
performed his lab work following
rules and regulations:
The student performed the
experiment and collected the data:
Sayeda Tahmina Sultana
Sr. Lab Demonstrator
Department of Pharmacy
Northern University Bangladesh
Shadid Uz Zaman
(Course instructor)
Lecturer
Date:__________________ Date:___________________

6
Standardization of hydrochloric acid solution using standardized sodium hydroxide solution.
2.2 Principle
Standardization means to determine the precise concentration of a substance whose precise
concentration is unknown. For secondary standards, even if one weighs the solid accurately to prepare
the solution, the concentration cannot be precisely known due to the nature of secondary standards.
Hence solutions of secondary standards must always be standardized.
Hydrochloric acid is a secondary standard. Hence hydrochloric acid solution must be standardized.
Since it is an acid, common method of standardizing hydrochloric acid solution is to titrate it against a
standardized solution of base. Sodium carbonate (primary standard) solution can be used for this
purpose, but it is more convenient if sodium hydroxide solution could be used.
Unfortunately, sodium hydroxide solution is also a secondary standard. So a solution of sodium
hydroxide must be standardized as well. for standardizing sodium hydroxide solution, oxalic acid
(primary standard) solution is used. The reaction occurs as follows:
As we can see, 1 mole of oxalic acid reacts with 2 moles of sodium hydroxide. The relationship
between the concentration of the oxalic acid solution and that of sodium hydroxide solution can be
described as follows:
Here, VNaOH and VOxalic refer to the volumes of sodium hydroxide solution and oxalic acid solution
(respectively) required to reach end-point of titration, SNaOH and SOxalic refer to the concentrations of
sodium hydroxide solution and oxalic acid solution (respectively).
Once sodium hydroxide solution is standardized, it can be used to standardize hydrochloric acid
solution as per following reaction:

7
As we can see, 1 mole of hydrochloric acid reacts with 1 mole of sodium hydroxide. The relationship
between the concentration of the hydrochloric acid solution and that of sodium hydroxide solution can
be described as follows:
Here, VNaOH and VHCl refer to the volumes of sodium hydroxide solution and hydrochloric acid solution
(respectively) required to reach end-point of titration, SNaOH and SHCl refer to the concentrations of
sodium hydroxide solution and hydrochloric acid solution (respectively).
2. Volumetric flask
3. Conical flask
4. Burette
5. Pipette
6. Dropper
1. Sodium hydroxide
2. Oxalic acid (dihydrate)
3. Hydrochloric acid (reagent grade, 37% w/w)
4. Phenolphthalein
5. Ethanol
6. Distilled water
2.5 Procedure
1.1.1 Preparation of 100 mL 0.1 M sodium hydroxide solution
solution [Remember: sodium hydroxide will be given to you in solid form].
2. Weigh the calculated amount of sodium hydroxide in an electronic balance and take it in a 100 mL
volumetric flask.

8
3. Add small volume of distilled water and dissolve the solid [Remember: Solubilization of sodium
hydroxide is exothermic, so heat will be produced].
1.1.2 Preparation of 100 mL 0.05 M oxalic acid solution
1. Calculate the amount of oxalic acid required to prepare 100 mL of 0.05 M oxalic acid solution
[Note: Oxalic acid will be given to you in solid form].
2. Weigh the calculated amount of oxalic acid in an electronic balance and take it in a 100 mL
volumetric flask.
3. Add small volume of distilled water and dissolve the solid.
1.1.3 Preparation of 100 mL 0.1 M hydrochloric acid solution
1. Calculate the volume of the supplied hydrochloric acid solution you will require to prepare 0.1 M
hydrochloric acid solution [Note: You will be supplied commercial solution of hydrochloric acid
which is highly concentrated and extremely dangerous. Please use caution in handling it. Also note
the product concentration. Usually the commercial product will have a concentration of 37% w/w
which calculates to 12 M].
2. Take a 100 mL volumetric flask and fill it to half by distilled water.
3. Add the calculated volume of hydrochloric acid solution into the volumetric flask using a pipette
[Note: Be very careful. Add slowly].
1.1.4 Standardization of the 0.1 M sodium hydroxide solution
1. Take a 50 mL burette and fill it with the just prepared 0.1 M sodium hydroxide solution.
2. In a 100 mL conical flask, add 10 mL of the just prepared 0.05 M oxalic acid solution.
3. Add 1-2 drops of phenolphthalein indicator [Note: At this point the solution in the conical flask
should be colorless] into the conical flask and titrate with the sodium hydroxide solution just until
the color turns pink.
4. Repeat steps 2 and 3 two more time for a total of three titrations and note down the data.
5. Calculate the actual concentration of the prepared sodium hydroxide solution.

9
1.1.5 Standardization of the 0.1 M hydrochloric acid solution
1. Take a 50 mL burette and fill it with the just prepared 0.1 M sodium hydroxide solution.
2. In a 100 mL conical flask, add 10 mL of the just prepared 0.1 M hydrochloric acid solution.
3. Add 1-2 drops of phenolphthalein indicator [Note: At this point the solution in the conical flask
should be orange in color] into the conical flask and titrate with the sodium hydroxide solution just
until the color turns pink.
6. Calculate the actual concentration of the prepared sodium hydroxide solution.
1.1.6 Calculation of the amount of sodium hydroxide required to prepare 0.1 M 100 mL
solution
1.1.7 Calculation of the amount of oxalic acid required to prepare 0.05 M 100 mL solution
The molecular weight of oxalic acid (dihydrate) is 126 gram/mol. Hence, we can say that:
1.1.8 Calculation of the amount of supplied hydrochloric acid solution required to prepare 0.1
M 100 mL solution
The molecular weight of hydrochloric acid is 36.5 gram/mol. The supplied hydrochloric acid solution
is stated to be 37% w/w and the specific gravity is 1.19.

10
Now, since the supplied solution has a concentration of 37% w/w, we can say:
Since the specific gravity of the supplied hydrochloric acid solution is 1.19, we can say:
1.1.9 Standardization of the prepared sodium hydroxide solution
No. Initial burette reading
(mL)
Final burette reading
(mL)
Volume difference
(mL)
Mean volume
(mL)
VNaOH
1
2
3
Now, the reaction between sodium hydroxide and oxalic acid occurs as shown here:
So, 1 mole of oxalic acid reacts with 2 moles of sodium hydroxide. So the titration equation is written
as:
Here,
VNaOH = The volume of sodium hydroxide solution required = ________ mL
VOxalic = The volume of oxalic acid used = 10 mL
SNaOH = Concentration of sodium hydroxide solution = ?
SOxalic = Concentration of oxalic acid solution = 0.05 M

11
So,
1.1.10 Standardization of the prepared hydrochloric acid solution
(mL)
(mL)
Volume difference
(mL)
Mean volume
(mL)
VNaOH
1
2
3
Now, the reaction between sodium hydroxide and oxalic acid occurs as shown here:
So, 1 mole of hydrochloric acid reacts with 1 moles of sodium hydroxide. So the titration equation is
written as:
Here,
VNaOH = The volume of sodium hydroxide solution required = ________ mL
VHCl = The volume of hydrochloric acid used = 10 mL
SNaOH = Concentration of sodium hydroxide solution = ___________ M
SHCl = Concentration of hydrochloric acid solution = ?
So,
2.7 Result
0.1 M hydrochloric acid solution was prepared and it was standardized using a standardized solution of
sodium hydroxide.
The standardized concentration of the hydrochloric acid solution was found to be ______________ M.

12
2.8 Precautions
1. All weights must be taken carefully. Particularly, the weight of oxalic acid must be precise to
ensure precise concentration.
2. Only 1 drop of the indicator solution should be used.
3. All volumetric reading (e.g. of the volumetric flask and the burette) must be taken considering the
meniscus.
4. Color change must be monitored very carefully.
Shadid Uz Zaman
(Course instructor)
Lecturer
Date:__________________ Date:___________________

13
Determination of the acid dissociation constant (Ka) of a weak acid (acetic acid).
3.2 Principle
Based on the degree of dissociation and release of protons into solution, acids are divided into two
types – strong acids and weak acids. Strong acids completely dissociate in solution and release protons,
but weak acids only partially dissociate. For weak acids, the dissociation of acid to release proton
reaches an equilibrium as shown below:
The acid dissociation constant (Ka) can be defined as:
[ ][ ]
[ ]
Henderson-Hasselbach equation describes the relationship between the pH of a solution made of a
weak acid and its acid dissociation constant as follows:
[ ]
[ ]
Here, [HA] refers to the concentration of the weak acid at equilibrium and [A
] refers to the
concentration of the conjugate base at equilibrium, pH must also be measured at the equilibrium. Now,
when [ ] [ ], equation (2) becomes:
Now, if a titration curve is prepared by plotting pH along y-axis and volume of titrant added along x-
axis, the half-equivalence point is the point where one-half of the end-point volume has been added. At
the half-equivalence point, [ ] [ ], so the pH at the half-equivalence point is the pKa of the weak
acid. From pKa, Ka can be calculated as follows:

14
2. Volumetric flask
3. Beaker
4. Burette
5. Pipette
6. Dropper
7. pH meter
1. Acetic acid
2. Sodium hydroxide
3. Phenolphthalein indicator solution
4. Distilled water
3.5 Procedure
1.1.11 Preparation of 100 mL 0.1 M sodium hydroxide solution
solution [Remember: sodium hydroxide will be given to you in solid form].
2. Weigh the calculated amount of sodium hydroxide in an electronic balance and take it in a 100 mL
volumetric flask.
hydroxide is exothermic, so heat will be produced].
1.1.12 Preparation of 100 mL 0.1 M acetic acid solution
1. Calculate the amount of oxalic acid required to prepare 100 mL of 0.1 M acetic acid solution.
2. Take the appropriate volume of acetic acid and add it to a 100 mL volumetric flask.
3. Add small quantity of distilled water and mix by shaking.

15
1.1.13 Preparation of titration curve
1. Fill the burette with sodium hydroxide solution.
2. Take 25 mL of the acetic acid solution into a beaker (NOTE: conical flask won’t be useful) and add
1-2 drops of phenolphthalein indicator.
3. Place a pH meter and note down the pH of the solution.
4. Begin titration.
5. After addition of each 1 mL of the titrant, measure the pH and note it down.
6. Continue this until the end point is achieved i.e. color changes from colorless to pink.
7. Even after end-point is achieved, take 3-4 more readings.
Calculation of the amount of sodium hydroxide required to prepare 0.1 M 100 mL3.6.1
solution
Calculation of the amount of acetic acid required to prepare 0.1 M 100 mL solution3.6.2
The molecular weight of acetic acid is 60 gram/mol. The supplied acetic acid reagent is stated to have
a specific gravity of 1.05.
Since the specific gravity of the supplied acetic acid reagent is 1.05, we can say:

16
Titration curve data3.6.3
No. Cumulative volume of titrant added (mL) pH
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
Preparation of the titration curve3.6.4
Plot the pH values along the y-axis and the cumulative volume values along x-axis in MS Excel and
connect the points by smooth curve (as opposed to a straight line).

17
Calculation of Ka3.6.5
Find the end-point volume. The end-point volume i.e. titration volume is _____________ mL. So, the
half-equivalence point is ___________ mL. Find the pH that corresponds to the volume of the half-
equivalence point.
The pH of the half-equivalence point = ________
So,
Now,
3.7 Result
The acid dissociation constant (Ka) of acetic acid was found to be _____________________.
3.8 Precautions
1. All weights must be taken carefully.
2. pH must be carefully monitored.
3. Please handle the pH meter with utmost care.
Shadid Uz Zaman
(Course instructor)
Lecturer
Date:__________________ Date:___________________

18
Determination of the solubility product constant (Ksp) of sodium borate (borax) in water.
4.2 Principle
For any salt, in a saturated solution, an equilibrium exists between the salt molecules in the
undissolved solid and the solution. For a salt , the equilibrium can be shown as follows:
In this situation, the solubility product constant (Ksp) at a particular temperature is defined as the
product of equilibrium concentration (at that temperature) of the two ions that make up the salt.
Mathematically Ksp is expressed as:
[ ][ ]
It should be noted that since solubility is temperature-dependent, Ksp is also dependent upon
temperature.
Ksp can be determined for any salt. However, it is mostly applicable for salts which are sparingly
soluble or slightly soluble. For those salts, if the product of the concentrations of the two ion exceeds
the value of Ksp, then the salt will be precipitated.
Now, Borax, also known as sodium borate and sodium tetraborate is a sparingly water-soluble salt.
When dissolved in water, it dissociates and produces an equilibrium at saturated solution as follows:
Note that, for each tetraborate ion ( ) ion, two (2) ions are produced. In another
words, the concentrations of the two ions are related as follows:
[ ] [ ]

19
So, for borax, the Ksp can be determined as:
[ ] [ ]
[ ] [ ]
[ ]
Now, the concentration of ion can be easily determined by titrating the solution with
standardized hydrochloric acid solution. The reaction that occurs is:
Thus, the concentration can be determined using the following equation:
Now, since hydrochloric acid is a secondary standard, it must be standardized prior to titrating with
borax. In this particular experiment, hydrochloric acid solution will be standardized using sodium
carbonate (a primary standard). The reaction between the two is as follows:
The concentration of hydrochloric acid solution can therefore be determined as:
2. Volumetric flask
3. Beaker
4. Burette
5. Pipette
6. Dropper
7. Thermometer

20
1. Borax
2. Hydrochloric acid (37% w/w analytical grade reagent)
3. Methyl orange indicator solution
4. Sodium carbonate
5. Distilled water
4.5 Procedure
Preparation of 100 mL 0.1 M sodium carbonate solution4.5.1
1. Calculate the amount of sodium carbonate required to prepare 100 mL of 0.1 M sodium carbonate
solution [Remember: sodium carbonate will be given to you in solid form].
2. Weigh the calculated amount of sodium carbonate in an electronic balance and take it in a 100 mL
volumetric flask.
carbonate is exothermic, so heat will be produced].
Preparation of 250 mL 0.1 M hydrochloric acid solution4.5.2
1. Calculate the volume of the supplied hydrochloric acid solution you will require to prepare 0.1 M
hydrochloric acid solution [Note: You will be supplied commercial solution of hydrochloric acid
which is highly concentrated and extremely dangerous. Please use caution in handling it. Also
note the product concentration. Usually the commercial product will have a concentration of 37%
w/w which calculates to 12 M].
2. Take a 250 mL volumetric flask and fill it to half by distilled water.
3. Add the calculated volume of hydrochloric acid solution into the volumetric flask using a pipette
[Note: Be very careful. Add slowly].

21
Standardization of the 0.1 M hydrochloric acid solution4.5.3
1. Take a 50 mL burette and fill it with the just prepared 0.1 M hydrochloric acid solution.
2. In a 100 mL conical flask, add 10 mL of the just prepared 0.1 M sodium carbonate solution.
3. Add 1-2 drops of methyl orange indicator [Note: At this point the solution in the conical flask
should be yellow in color] into the conical flask and titrate with the hydrochloric acid solution just
until the color turns red/orange.
8. Calculate the actual concentration of the prepared hydrochloric acid solution.
Determination of solubility product constant4.5.4
1. Take a 250 mL beaker.
2. Add about 100 mL of water.
3. Now slowly add borax to the beaker and stir vigorously to dissolve it.
4. Continue to add borax until borax no longer dissolves and precipitates to the bottom permanently.
5. Place a thermometer in the beaker and note the temperature.
6. Filter the solution of the beaker. During filtration, after the first 25 mL has been filtered, discard
the filtrate. Collect rest of the filtrate.
7. Take 15 mL of the filtrate in a conical flask and add 1-2 drops of methyl orange indicator.
8. Titrate against the standardized hydrochloric acid solution from the burette.
9. Determine the end-point. End point is indicated by the change of color from yellow to red/orange.
Temperature of the borax solution = ______________ °C
Calculation of the amount of sodium carbonate required to prepare 0.1 M 100 mL4.6.1
solution

22
Calculation of the amount of supplied hydrochloric acid solution required to prepare 0.14.6.2
M 250 mL solution
The molecular weight of hydrochloric acid is 36.5 gram/mol. The supplied hydrochloric acid solution
is stated to be 37% w/w and the specific gravity is 1.19.
Now, since the supplied solution has a concentration of 37% w/w, we can say:
Since the specific gravity of the supplied hydrochloric acid solution is 1.19, we can say:
Standardization of the prepared hydrochloric acid solution4.6.3
(mL)
(mL)
Volume difference
(mL)
Mean volume
(mL)
1
2
3
Now,
Here,
VHCl = The volume of hydrochloric acid solution required = ________ mL
= The volume of sodium carbonate solution used = 15 mL
SHCl = Concentration of hydrochloric acid solution = ?
= Concentration of sodium carbonate solution = 0.1

23
So,
Data for the titration between borax and hydrochloric acid4.6.4
(mL)
(mL)
Volume difference
(mL)
Mean volume
(mL)
1
2
3
Now,
Here,
VHCl = The volume of hydrochloric acid solution required = ________ mL
= The volume of borax solution used = 15 mL
SHCl = Concentration of hydrochloric acid solution = ___________ M
= Concentration of borax solution = ?
So,
Calculation of Ksp4.6.5
[ ]
Now,
[ ]

24
4.7 Result
The Ksp of sodium borate/sodium tetraborate/borax in water at _________ °C temperature is
____________________.
4.8 Precautions
2. The borax solution must be completely saturated i.e. there must be some precipitates of borax in
the bottom.
3. The temperature must be kept constant throughout.
4. All color changes must be observed carefully.
Shadid Uz Zaman
(Course instructor)
Lecturer
Date:__________________ Date:___________________

25
Evaluation of freezing point depression of sucrose solution and determination of molecular
weight of sucrose.
5.2 Principle
Colligative properties of a solution are those properties which depend on the number of particles
rather than the type of particles present in the solution. There are mainly four colligative
properties – depression of freezing point, elevation of boiling point, lowering of vapor pressure
and change in osmotic pressure.
Freezing point is the temperature at which a liquid solidifies. The freezing of a liquid is equal to
the melting point of the solid from that liquid. Freezing point depression means that the freezing
point of a solution of a substance will be lower than the that of the pure solvent. Depression of
freezing point is expressed by the following equation:
Here, i is the Van’t Hoff factor which indicates the colligative nature of the substance dissolved,
kf is the freezing point depression constant for a specific solvent, m is the molality of the solution
and is the depression of freezing point. is the freezing point of the pure solvent and
is the freezing point of the solution.
Van’t Hoff factor for most substances is already known. The freezing point depression constant
is also known for many solvents including water. The freezing point depression can be easily
determined for most liquid. So, using the equation above, one can determine the molality of the
solution being studied and from that, can determine its molecular weight with the formula:
Here, M.W. is the molecular weight of the solute, W1 is the weight of the solute dissolved in
grams, W2 is the weight of the solution prepared in grams and m is the molality of the solution.

26
2. Beaker
3. Test tube
4. Thermometer
6. Acetic acid (100%)
5.5 Procedure
Determination of the freezing point of pure acetic acid5.5.1
1. Take about 10 mL of glacial acetic acid in a test tube.
2. Place a thermometer in it and wait till the thermometer stabilizes.
3. Place the test tube in an ice-water bath.
4. Observe the temperature when all of the liquid inside the test tube becomes solid.
5. Record this temperature.
Determination of the freezing point of sucrose solution in acetic acid5.5.2
1. Take the weight of an empty test tube.
2. Take precise 10 mL of acetic acid in that test tube and then add about 0.5 gm of sucrose.
3. Take the weight again.
4. Stir well to dissolve it.
5. Place a thermometer in it and wait till the thermometer stabilizes.
6. Place the test tube in an ice-water bath.
7. Observe the temperature when all of the liquid inside the test tube becomes solid.
8. Record this temperature.

27
Freezing temperature of pure acetic acid = = ___________ °C
Freezing temperature of sucrose solution in acetic acid = = ______________ °C
Depression of freezing temperature =
Van’t Hoff factor of sucrose = i =1
Freezing point depression constant of acetic acid = kf = 3.9 °C/m
Now, since:
We can say,
Now, molecular weight can be calculated as:
Here,
W1 = Weight of solute (sucrose) = 0.5 gm
W2 =
So, we get:

28
5.7 Result
The solution of sucrose in acetic acid showed _______ °C compared pure acetic acid and from
the depression of freezing point data the molecular weight of sucrose was found to be _________
g/mol.
5.8 Precautions
2. Freezing temperatures must be taken very carefully.
performed his lab work
following rules and regulations:
Shadid Uz Zaman
(Course instructor)
Lecturer
Date:__________________ Date:___________________

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