Download Manual Physical Chemistry III

Manual
Physical
Chemistry III
Part 1 (Surface Chemistry)
Part 2 (Catalysis)
Part 3 (Colloids)
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Table of Contents
Experimental 1: Determination of Surface Tension of Liquids by drop weight Method ............................................ 2
Experimental 2: Determination of Surface Tension Liquids by Capillary Rise Method ............................................... 8
Experimental 3: To find out the partition coefficient of iodine between carbon tetrachloride and water. ................ 17
Experimental 4: To find out the equilibrium constant for the tri-iodide formation .................................................. 17
Experimental 5: Determination of the Adsorption Parameters of Oxalic acid on Charcoal ..................................... 22
Experimental 6 Experimental 6: Adsorption of acetic acid on to activated charcoal .............................................. 27
Experimental 7: To find out the partition coefficient of iodine between carbon tetrachloride and water. ................ 31
Experimental 8: To find out the equilibrium constant for the tri-iodide formation .................................................. 37
Experimental 9: Determination of the Adsorption Parameters of Oxalic acid on Charcoal ..................................... 40
Experimental 10: To make a colloid and demonstrate its properties......................................................................... 43
Experimental 11: Stability of the emulsions ............................................................................................................ 51
Experimental 12: To find the critical point for colloidal mixtures composed of different types of starches. ........... 53
Experimental 13: Find out the formula of cupper ammonia complex ...................................................................... 57
Experimental 14: Surface tension of n-butanil solution ........................................................................................... 59
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 1
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 1: Determination of Surface Tension of Liquids by drop weight Method
The surface tension of liquids measured with the stalagmometer
Surface tension of liquids
The molecules of liquids attract each other by cohesive forces resulting into small distances between the
molecules (on the order of 0.1 nm). Thus the compressibility of liquids is lower than that of gas, while the density
is much higher. On the other hand, these cohesive forces are not strong enough to result into the fixed position of
molecules that can be seen in solid matter. Liquids do not keep a fixed shape, but adapt the shape of a container.
Attractive cohesive forces are short range forces which are based on the electronic interactions. They affect
molecules in their close vicinity only (zone of molecular interaction). In the bulk of the liquid, each molecule is
attracted equally in all directions by the neighboring molecules; hence zero net force (Fig. 1). However, the
molecules at the surface do not have other like molecules on all sides around them and they are pulled inwards the
liquid core by non-zero net force (Fig. 1). Consequently, they cohere more strongly to those associated with them
directly on the surface and form a surface "film". Nevertheless, these surface molecules are in the energetically
unfavorable state, which forces liquid to minimize the surface area. The geometrical requirement of smallest
surface area at the fixed volume is satisfied by the sphere. It is the reason why the free drops of water form
spherical droplets.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 2
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
The energetic definition of the surface tension (equation 1) is not the only way to describe it. We can derive
it also from the simple experiment shown in Figure 2. It involves the wire rim with the AB side being able to
move, and a soap film spanning the space inside the rim. We can observe that the movable wire AB is being
pulled towards the soap film, as its area is shrinking down. There is a force in a plane of soap film acting in a
direction perpendicular to the wire. It is called the surface force, and is expressed as
Where l is the length of AB wire and  is the surface tension. According to this, surface
Tension is defined as a ratio of surface force to a length of rim that is pulled by this force
Equation (4) defines the surface tension again in units of N/m.
The measurement of the surface tension of liquids using the stalagmometer.
Stalagmometer is a glass tube, widened in the middle part (Fig. 3). Its volume is calibrated by the scale
shown on the tube, or by the top and bottom lines. The bottom part of stalagmometer is modified such that
the liquid flowing through its smaller diameter forms the drops.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 3
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 4
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental procedure:
1. Mount the clean and dry stalagmometer on the vertical stand.
2. Weigh the mass of the weighing bottle m0.
3. Fill the beaker with distilled water. Mount the tubing with balloon on the top end of stalagmometer. Immerse
the bottom end of stalagmometer into water and fill it up, such that the water level is above the wide part of
stalagmometer.
4. Remove the balloon and collect 20 water drops into the weighing bottle.
5. Weigh the mass of the weighing bottle with water and determine the mass of 20 drops.
6. Empty the weighing bottle and stalagmometer, dry them and prepare for the next measurement.
7. Repeat steps 2-6 for liquids with the unknown surface tension.
8. Knowing the temperature in laboratory, determine the water surface tension using values from the table 1,
and calculate the surface tensions of studied liquids according to the equation (7).
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 5
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental procedure:
1. Fill the stalagmometer up to the top mark with distilled water. Release water to the Weighing bottle and
count how many drops it takes to decrease the water level in stalagmometer down to bottom mark. Write
down the number of drops nH20.
2. Empty and dry the weighing bottle and stalagmometer, and prepare them for the next measurement.
3. Repeat steps 1 and 2 for liquids with the unknown surface tension.
4. Write down the densities of studied liquids according to the notes on bottles, and density of distilled water at
the actual temperature in laboratory from the table 1. Using equation (10), calculate the surface tension for
all the studied liquids.
5. Compare results obtained via the drop-weight method and drop counting method.
Tab. 1: The temperature dependence of the surface tension and distilled water density.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 6
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
The mass of an empty weighing bottle m0:
Tab. 2: The determination of the surface tension by the drop-weight method.
Tab. 3: The determination of the surface tension by the drop counting method
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 7
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 2: Determination of Surface Tension Liquids by Capillary Rise Method
Surface Tension Measurements
In this laboratory exercise we will measure the Surface Tension of Methanol as a function of
S
temperature. This will allow us to determine the Surface Energy (E ) of this liquid. Also, the Surface
Tension of aqueous solutions of Ethanol and n-Butanol will be measured as a function of solute
concentration. Using this data, we will demonstrate that for a sufficiently dilute solution, n-Butanol, a
Surface Active molecule, behaves as a Two Dimensional Ideal Gas. This data will also allow us to
determine the effective cross sectional area of an n-Butanol molecule on the solution’s surface.
The surface tension of a liquid is responsible for such everyday phenomena as the beading of rainwater
and droplet formation and allows for the blowing of soap bubbles. It is responsible for the adhesion of
liquids onto other surfaces and the contraction of surfaces to form spherical drops.
The interface between a liquid and a vapor acts like an elastic balloon surrounding the liquid. In
expanding the surface, molecules in the bulk must move up toward the interface. However, molecules of
the liquid near the surface have a higher energy than those in the bulk because they are held in the liquid
phase by fewer nearest neighbors. So, it requires work to move bulk molecules to the surface. Hence in
requires work to expand the surface area (A) of the liquid.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 8
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Formally, the surface tension () is defined in terms of the Work (W) required to expand the surface area
of the liquid.
Consider a liquid film enclosed by a wire loop (think of a soap film in a toy bubble blower loop) where
one side of the loop is allowed to slide back and forth. A force (f) is applied to counter the contractive
force due to the surface tension of the liquid. Working against the surface tension an incremental
increase in the force will do work Wrev in pulling the slide out a distance dx:
We define the Surface Tension in terms of this force such that:
Where l is the length along the slide and the factor of “2” is required to account for the film’s two sides.
(note the analogy between the intensive parameter , defined as a force per unit length, and the intensive
parameter pressure, defined as a force per area.) Then we relate the surface tension to the change in area
(A) of the film via:
Where dA is the increase in area of the surface of the liquid film.
This work is included in our expression for the Gibbs free energy; since the Free Energy is a measure of
a system’s “useful or available” work, beyond PV expansion work:
Temperature Dependence
As per Adamson (1979,) we define the Surface Gibbs Free Energy per unit area as:
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 9
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
This gives us a Surface Entropy of:
S
S
Measurably, the Surface Energy (E ) and Enthalpy (H ) are usually indistinguishable, so:
It is observed that for most liquids  varies roughly linearly with temperature.
S
The means E remains fairly constant with increasing temperature. That is, until the temperature nears
S
the liquid’s critical temperature (Tc) where upon E drops to zero.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 10
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Concentration Dependence
We define the Excess Surface Concentration of a solute, designated as component “2”, as:
Where is the number of moles of solute in a binary mixture near the solution’s surface. A positive excess
surface concentration suggests the solute is congregating near the surface in levels in excess of its bulk
values. The reverse is true if this quantity is negative.
It is found that certain simple electrolytes give aqueous solutions with 2 < 0. On the other hand, small
polar, organic molecules generate aqueous systems for which 2 > 0. In fact, solutes such as n-Butanol,
which possess a polar head and a non-polar tail aggregate near the surface so as to form a monolayer. In
cases such as these, increases in the bulk concentration will not change the excess surface concentration
of the solute. These solutes are referred to as Surface Active.
It was shown by Gibbs (Adamson 1979) that 2 for dilute binary solutions can be approximated by:
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 11
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Where C is the concentration of the solute. This relation is known as the Gibb’s Isotherm
For sufficiently dilute solutions of surface active molecules, it is found that the surface tension is
proportional to the concentration.
o
Where  is the surface tension of the solvent and b is a proportionality constant.
Capillary Rise Method
Several methods are available for measuring the surface tension of liquids. In this laboratory exercise we
will use the Capillary Rise Method for determining our desired surface tension values.
This methodology employs a small bore capillary which is inserted into the liquid whose surface tension
is to be determined. The height to which the liquid rises in the tube is proportional to the surface tension.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 12
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 13
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimentally, the radius of the capillary’s bore is determined by calibrating the capillary using a fluid
such as Water whose surface tension is known. Once calibrated, a simple height measurement will give
us the surface tension. This derivation requires the meniscus be hemispherical. This can be achieved if
the glass surface is thoroughly clean. Otherwise this will not be true and (Eq. 22) will not hold exactly.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 14
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Procedures
Week 1
1- Prepare solutions of solutes to be measured. These will include:

0.8M aqueous n-Butanol and 7 dilutions of this solution; each a ¾-fold dilution of the previous mix. nButanol is an irritant. Work with it in the Fume Hood. 
 Aq. Ethanol solutions at 20, 40, 60, 80, 100 wt% 

2- Be sure the capillary is soaking in Chromic Acid cleaning solution. (The capillary should be stored in
Distilled Water when not is use.)
Pre-Lab work:
Work out a scheme for preparing about 100 mL of each of the above solutions.
Week 2
1. Rinse the capillary thoroughly with Distilled Water. Also, rinse with the sample to be measured.
o
2. Calibrate each capillary you will be using against Distilled Water in the 25 C Water bath. The surface
o
o
tension of Water over a range of 20 C to 40 C is given by:
With an error of 0.03%. Take at least five readings. Allow the meniscus to approach its equilibrium
position from above and below. Be sure to read the position of the outside Water level.
Place about 100 mL of Distilled Water in the Surface Tension apparatus. Be sure the
capillary, with its measuring ruler, is snuggly fit into the stopper and insert the stopper into
o
the apparatus. Place the entire apparatus into the 25 C water bath. Allow it to stand for at
least 10 minutes before taking any measurements. Be sure to read the correct temperature
of the water bath with an immersion thermometer.
o
3. Measure the surface tension of Methanol over a range of temperatures from about 0 C to
o
about 50 C. Each measurement should be made five times. Allow the meniscus to
approach its equilibrium position from above and below, alternatively.
4. Measure the surface tension of the n-Butanol solutions. Each measurement should be made
five times. Allow the meniscus to approach its equilibrium position from above and below,
alternatively.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 15
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
5. Measure the surface tension of the Aq. Ethanol solutions. Each measurement should be made five times.
Allow the meniscus to approach its equilibrium position from above and below, alternatively.
Be sure to rinse the capillary thoroughly between each measurement and that the samples have come to
o
equilibrium in the Water Baths. Make all the solution measurements at about 25 C.
The meniscus can be difficult to see. If you force the meniscus away from its equilibrium position and
watch it return, you should be able to see it more clearly.
Data Analysis
All results should be accompanied by an appropriate error estimate.
1.
Determine the radius of each capillary used. Use a precise value for the density of Water at your
working temperature. Report both the average result and the std. dev. of the mean for each capillary.
2.
Determine the surface tension for Methanol at each temperature for which it was measured. Plot  vs. T; your
plot should include appropriate error bars. Literature results should be
S
S
Included on your graph. Determine ( / T)P and the Surface Energy E . Include an error estimate for E .
3.
Determine the surface tension for each n-Butanol solution. These solutions are dilute enough that the
density can be taken as that of Water at the measuring temperature. Plot  vs. C; including appropriate
error bars. Identify the “dilute solution” regime. Determine  and  for each solution in this regime.
Verify the solute on the surface is behaving as a
Two Dimensional Ideal Gas by plotting  vs. 1/. Now, plot  vs. lnC. Again, include appropriate error
2
bars. Calculate 2, along with an appropriate error estimate. Express the result in molecules per Å .
2
Obtain the effective cross sectional area of one n-Butanol molecule in Å . Include an appropriate error
estimate. Compare your result with literature values.
4.
Determine the surface tension for each Ethanol solution. (Accurate solution densities will be required.)
Plot  vs. C; including appropriate error bars. Interpret the results.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 16
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 3: To find out the partition coefficient of iodine between carbon tetrachloride and water.
Experimental 4: To find out the equilibrium constant for the tri-iodide formation. I 2  I   I 3
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed

Page 17
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 18
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
IODINE, IODIDE, TRI-IODIDE EQUILIBRIUM
INTRODUCTION
Your assignment is to study the equilibrium between the iodide ion and iodine molecule to form the tri-iodide ion
in aqueous solution (reaction 1), as described by equation 2:
-
where aI3 represents the activity of tri-iodide which is approximately equivalent to the stoichiometric
concentration of the tri-iodide ion, [I3 ] at dilute concentrations. The variables for iodine and iodide are
defined in an analogous manner.
Equation 3 is the Beer's law relationship for absorbance of radiation by the tri-iodide ion and will be
used to determine the tri-iodide molar absorptivity and equilibrium constant for the reaction.
Here A is absorbance, b is the path length of the spectrometer, and ε is the molar absorptivity
coefficient, a value that is dependent on many factors including both wave length and temperature.
Equation 2 can be rearranged to equation 4:
Here the subscript 0 denotes the initial concentrations of the iodine and iodide species after final
dilutions and before equilibrium has been attained.
PRE-LABORATORY EXERCISES
1. Calculate the value for the equilibrium constant for the reaction represented by equation 1 using
thermodynamic data. Use the data given in Table A.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 19
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Table A: Thermodynamic Properties in Aqueous solution at Unit Activity and 25oC.
[Note that ionic properties are based on the assignment of zero value for Hfo, Gfo, and Sfo for H+(aq). Values are for
an effective [1M] , i.e., unit activities can be somewhat different from 1M concentration.] [1]
You will use this theoretical value later to evaluate the accuracy of your experimental value using the
test suggested in your error analyses section.
2. Why is it important to use a constant temperature bath in this exercise?
3. Calculate the concentration of tri-iodide that will give an absorbance of 0.5 where the path length is 1.0
cm and the molar absorptivity is 30,000M-1cm-1.
4. The following data was measured from one iodine/iodide solution. Initially, the iodine concentration
-5
-3
was 4.044 x 10 M and the iodide concentration was 2.371 x 10 M. At equilibrium, the tri-iodide
-5
concentration was 2.53x10 M. What is the experimental equilibrium constant for the reaction?
LABORATORY EXERCISE
1. Before coming to lab, read over the “Spectrometer Operating Instructions” and prepare any questions
about using the Ocean Optic Fiber Optic UV-VIS spectrometer. Since this is the first time you’ve used
the UV-VIS spectrometers in P. Chem. labs, please summarize (in your own words) these instructions in
your pre-laboratory report.
2. Equation (3) is closely obeyed only when the absorbance of tri-iodide is between 0.2 and ~0.8. For this reason,
you will need to find appropriate initial concentrations of
iodine and iodide for this exercise. To this end, you will be using two solutions: a solution of I2 and KI
that will be prepared for you and a 100 mL solution of 0.1 M KI that you must prepare. If you are unsure
how to prepare this solution and calculate its concentration to at least 4 significant figures, please
consult your teaching assistant or the lab supervisor!
4. Since all of the iodine comes from the pre-made stock solution, a suitable baseline level of tri-iodide (with peak
absorbance close to 0.2) can be found by trial and error.
Using volumetric pipets, transfer 2-7 mL of the iodide/iodine stock solution to 100 mL volumetric flasks
1
and dilute to the marks . Place these solutions in a constant temperature bath until thermal equilibrium
has been reached.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 20
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
5. Scan these diluted solutions to determine a spectral region where the tri-iodide absorbs (turn on the light
source in the absorbance mode). Three peaks should be observed, one for the iodide and two for the triiodide (near 300 and 350 nm). Find an amount of stock solution (2-7 mL) where the absorbance of the
largest peak is between 0.18 and 0.25. Note these wavelengths and also this amount of iodide/iodine
stock solution!
6. Place this same amount of the iodide/iodine stock solution into several 100 mL volumetric flasks. To
each flask, add between 1 mL and 10 mL of the 0.1M KI solution and dilute each to the mark with
water. This should increase the absorbance of the weakest peak (why?). At least 7 of these solutions
should be prepared. Leave these samples in the constant temperature bath until thermal equilibrium has
been reached.
7. Scan each sample and save the spectra to a disk (floppy or CD). Re-zero the spectrometer as needed (see the
Spectrometer Operating Instructions).
8. Use both of the peak absorbances (occurring at ~285 and ~350nm) to evaluate your results. Set up a spread sheet
using the absorbance for each sample at each peak and
use a form of iteration to minimize the relative standard deviation of your calculated K eq‘s. Do this by varying the
-1 -1
value of the absorptivity constant (~20, 000M cm < ε
-1 -1)
< ~40,000M cm for each of the peaks. Choose one absorbance spectrum to include it in your report.
Also, prepare a plot of measured absorbance as a function of initial iodide concentration and speculate
on your findings.
TIPS
➦ Discuss assumptions and approximations made in the theory section of your preliminary notebook.
➦ Double-check units and significant figures for ALL reported quantities.
➦ Your experimental procedure section of the preliminary report should contain more than the steps outlined in
this protocol. Each experimental step (numbers 2 through 7) is performed for a reason. Include these reasons
in the experiment section. For instance, consider question 2 in the pre-laboratory exercises.
➦ Ask your teaching assistant or the lab supervisor if you have any questions.
______________________
1
To protect the integrity (i.e., concentration/purity) of the already-prepared KI/I2 stock solution, do not pipet
directly from the bottle containing the stock solution, do not return used solution to the stock, and seal the bottle
with Parafilm when you are finished.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 21
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 5: Determination of the Adsorption Parameters of Oxalic acid on Charcoal
This experiment will demonstrate the adsorption phenomena and teach us to
determine to determine the adsorption parameters.
Introduction:
In general, colloidal dispersions have the property of adsorbing solutes at their
surfaces. Thermodynamically, such adsorption process occurs to reduce the surface free
energy of the dispersion and therefore increases its stability. The degree of adsorption
of a solute (adsorbate) on the adsorbent, depends on 5 factors:
1.
2.
3.
4.
5.
The chemical nature of the adsorbent and the adsorbate.
The specific surface area of the adsorbent.
The temperature of the adsorbate
The concentration of the adsorbate
The pressure of the adsorbate
At a constant temperature, the relation between the amount adsorbed and the
concentration in a limited concentration range may be represented by one of three
adsorption isotherms.
These 3 adsorption’s theories were found by:







Freundlich: Y = X / m =K. Ce 1/n
Langmuir: Y = X / m = {(Ym.b.Ce) / (1 +bCe)}
Bruner, Emmett, Teller => BET:
Y = {(Ym.b’.x) / [(1-x) X [1+(b’-1)x]]}
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 22
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Where:
x : weight of adsorbate in grams, adsorbed by m grams of the adsorbent..
K & n : Freundlich’s Empirical constants
Ce : Equilibrium Constant
Ym: Weight of the adsorbate in grams, adsorbed by one gram of the adsorbent to
form a mono layer.
B: Equilibrium constant of the adsorption process
Adsorbate + Vacant Sites
K1
Occupied Sites
K2
The adsorption parameters of Freundlich
 K & n in Freundlich equation from the linearized equation.
Log Y = Log K + 1 / n X Log Ce
Therefore, a plot of Log Y (on the vertical axis) vs Log Ce should give us a straight line.
The slope of this line is equal to 1 / n, and the intercept is equal to Log K, so we can
evaluate K & n.
The adsorption parameters of Langmuir equations.
 Ym & b in Langmuir equation.
We have seen that Langmuir equation is:
Y = X / m = {(Ym.b.Ce) / (1 +bCe)}
To linearize this equation; we took the reciprocal and multiply it by Ce to get:
Ce / Y = Ce / Ym + 1 / (Ym.b)
Therefore, a plot of Ce / Y (on the vertical axis) vs Ce should give us a straight line.
The slope of this line is equal to 1 / Ym, and the intercept is equal to
1 / (Ym.b), so we can evaluate Ym & b.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 23
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Procedure:
1. In each of the 6 Erlenmeyer flasks provided, introduce 5 g of the adsorbent
(Charcoal).
2. To each of them add 5o ml of a known dilution of a standard solution of
Oxalic Acid provided (e.g. 1N, 0.8N, 0.4N, 0.1N) according to the following
Table:
Flask 1 ml of 1N
Distilled Water Normality
Oxalic Acid
Of Oxalic Acid
1
50
0
1N
2
40
10
0.8N
3
30
20
0.6N
4
20
30
0.4N
5
10
40
0.2N
6
5
45
0.1N
3. Shake occasionally for 15 min and set aside for half an hour to achieve equilibrium
4. Filter and reject the first portion of the filtrate after washing
The receiver with it.
5. Triturate 25ml of the aliquot filtrate in each case with 0.5N
Sodium Hydroxide using Phenolphthalein as an indicator
(2 drops).
6. Calculate the amount adsorbed in each case and list your
Result in the following table.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 24
Chemistry
Department
Equilibrium conc. (Ce)
{(E.P X 0.0225) / volume} X 50
MANUAL PHYSICAL CHEMISTRY III
Oxalic
Acid
Conc.
Ml
from
1N
Oxalic
ml
of H20
to 50ml
Initial
Conc.
(Ci)
1N
0.8N
0.6N
0.4N
0.2N
0.1N
50
40
30
20
10
5
0
10
20
30
40
45
2.25
Amount Adsorbed
X = Ci – Ce
Log Ce
End
Point
1.8
1.35
0.9
0.45
0.225
Y=X/m
Log Y
Ce / Y
After calculations the table will be as follows:
Data Analysis:
Make the following plots.
 Plot 1: Y vs Ce
 Plot 2: Ce/Y vs Ce
 Plot 3: Log Y vs Log Ce
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 25
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
 The first plot (Plot 1) shows that the adsorption phenomena deals with the occupancy at
the surface and as the vacancy increases, the rate of occupancy increases, and at the
end, when no more vacancy is available, the rate of occupancy will be equal to 0.
 The second plot (Plot 2) reflects the linearized form of Langmuir equation. It will help us
finding the Langmuir adsorption parameters: Ym and b.
 The third plot (Plot 3) in fact, reflects the linearized form of Freundlich adsorption
isotherm equation. It is useful to find the Freundlich adsorption parameters: K and n.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 26
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 6: Adsorption of acetic acid on to activated charcoal
STUDY OF ADSORPTION OF ACETIC ACID ON CHARCOAL – VERIFICATION OF
FREUNDLICH'S ADSORPTION ISOTHERM AIM
To study the adsorption of acetic acid on charcoal and to verify the application of freundlich's
adsorption isotherm.
THEORY
Absorption is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some
bulk phase – gas, liquid, or solid material. This is a different process from adsorption, since molecules
undergoing absorption are taken up by the volume, not by the surface (in case of adsorption).
Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a
surface. It is a surface phenomena occurs due to a tendency to lower free energy and entropy. The
surface of any solid or liquid is in a state of strain due to unsaturated force. To lower this strain, they try
to adsorb foreign particles on the surface. Extent of adsorption depends on (a) nature of adsorbent and
adsorbate, (b) nature of surface, (c) temperature and (d) concentration of adsorbate. For a given pair of
adsorbent and adsorbate and at a given temperature relation between extent of adsorption and
concentration is called adsorption isotherm. Freundlich's isotherm is also applicable for absorption of
gases on solid surface. The empirical equation for Freundlich's isotherm is:
(x / m) = K P
n
where 'P' is the pressure of adsorbate (i.e., gas).
(x/m) = K. C
But, here the equation becomes:
n
where 'x' is the amount of adsorbate adsorbed by 'm' gm of the adsorbent; 'C' is the concentration of
adsorbate and 'K' and 'n' are constants. By taking logarithm on both sides, we get
log (x) - log(m) = log K + n log C
log(x) = log (m) + log K + n log C
Hence, a plot of log (x) against log C will be a straight line.
The isotherm is empirical and found to be valid in the low pressure (concentration) range. As
pressure (or concentration) is raised departure from the equation is found. At moderate to high
pressure Langmuir's isotherm is valid and at still high pressure B.E.T. Equation is valid.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 27
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
A different equation is more likely to describe adsorption where the adsorbate exceeds a
monolayer. The Brunauer-Emmett-Teller (BET) equation is:
Where Cs = concentration at which all layers are filled Kb = a coefficient
Its assumptions are:




Adsorbed molecules stay put
Enthalpy of adsorption is the same for any layer
Energy of adsorption is the same for layers other than the first
A new layer can start before another is finished.
The function has an asymptotic maximum as pressure increases without bound. As the temperature
increases, the constants 'k' and 'n' change to reflect the empirical observation that the quantity
adsorbed rises more slowly and higher pressures are required to saturate the surface.
MATERIALS REQUIRED
Standard Oxalic acid solution (0.1 N), NaOH solution, CH3COOH solution, Activated
charcoal, Phenolphthalein indicator, Reagent Bottles (5 each), Burette (50 ml), Pipette
(10 ml), Conical flask (250 ml, 100 ml), filter papers.
PROCEDURE
PART-I: Standardization of NaOH against standard Oxalic acid (0.1N)
1. 10ml of given 0.1N standard Oxalic acid is pipetted out into a 100ml conical flask.
2. This solution is titrated against the given unknown concentration of NaOH using 1-2 drops of
phenolphthalein indicator until the end point is colorless to pale pink.
3. Tabulate the values and repeat the titration for concurrent readings and determine the
concentration of supplied NaOH solution.
Table 1
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 28
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
PART-II: Standardization of Acetic acid using standard NaOH solution.
1. 10ml of given acetic acid solution is pipetted out into a 100ml conical flask.
2. This solution is titrated against the standard NaOH using 1-2 drops of phenolphthalein
indicator until the end point is colorless to pale pink.
3. Tabulate the values and repeat the titration for concurrent readings and determine the
concentration of supplied NaOH solution.
Table 2
PART-III: Verification of Freundlich's Adsorption Isotherm
1. The different concentrations of the solutions are prepared in the reagent bottles of various
proportions are given in the table 3 below .
2. 10 ml of the solution is pipetted out from bottle no. 1 into a conical flask and is titrated against NaOH
solution using phenophthalein indicator and the reading is tabulated as 'V' ml.
3. The above process is repeated for the remaining bottles also.
4. Now, in each of these bottles, 2g of activated charcoal is added.
5. The bottles are shaken by mechanical shaker or by manual shaking using hands for about 3045 minutes and then allowed to rest for 15 minutes.
6. A small filter paper is placed on a funnel and the content of the first bottle is filtered in a 250 ml conical
flask. First 3-4 ml of the filtrate is rejected. This is to saturate the filter paper.
7. 10 ml of the filtrate from bottle no.1 is pipetted out into a 100 ml conical flask and is titrated
against same NaOH solution using phenophthalein indicator.
8. Repeat the titrations for concurrent readings.
9. Similarly, repeat steps 5 & 6 for the remaining bottles also.
10. The readings are tabulated and the volume of NaOH consumed before and after adsorption are to be noted
for each solution and concentration of solution in moles are to be determined.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 29
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Table 3
OBSERVATIONS AND CALCULATIONS
o
Room Temperature = __________________ C.
Amount of Charcoal added, m = _________gm.
Hence, a plot of log (x) vs log C1 gives a straight line,
where 'x' is the extent of adsorption in terms of difference in concentration of solutions
and 'C1' is the concentration of each solution before adsorption.
The slope (n) and intercept (log K) are to be determined from the graph.
COMMENTS AND DISCUSSIONS
The success of the above experiment requires patience on the part of the student,
because attainment of adsorption equilibrium and also subsequent filtration is a very slow
process as impatience may bring error in the experiment.
Care should be taken while preparing the solutions and shaking the bottles also.
Each and every calculation of the tables should be shown clearly with formulas, units, graph
etc.
RESULT
Strength(Concentration)
1.
of NaOH
= __________________
Strength
2.
(Concentration) of AcOH
= __________________
The
3. value of the constant, n
= __________________
The
4. value of the constant, K
= __________________
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 30
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 7: Catalytic Decomposition of Hydrogen Peroxide on Metal Oxide Catalysts
Catalytic Decomposition of Hydrogen peroxide
Theory:
Hydrogen peroxide solution decompose spontaneously liberating
Oxygen in accordance with,
H2O2 →
H2O + ½ O2
The decomposition rate is markedly accelerated by solid such as
Manganese dioxide, potassium dichromate, or colloidal platinum, which act as
a catalyst.
The course of reaction may be followed either by titrating the peroxide
with potassium permanganate in acid medium or by collecting the oxygen gas
evolved.
There are two types of catalysis
1-Homogeneous catalysis
2-Heterogeneous Catalysis
Object:
Determination of the reaction rate of catalytic decomposition of
hydrogen peroxide.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 31
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Materials and Equipments:hydrogen peroxide ( H2O2), H2SO4 , KMnO4 , manganese dioxide ( MnO2,
potassium dichromate , beaker , 2 conical flasks , burette, pipette , Stopwatch.
Part 1:Homogeneous Catalytic decomposition of H2O2 by using K2Cr2O7
solution
Procedure
1- Prepare 250 ml 0.1N KMnO4 .
2- Prepare 250 ml 1.2 % H2O2 solution (10 volumes H2O2 is nearly equal3%).
3- Thermostat the solution of H2O2 at 30ºC for 20 min.
4- Add 3 ml of K2Cr2O7 catalyst and record the time.
5- Pipette out 10 ml of the decomposed mixture into a flask
containing ( 10 ml of 2N H2SO4) and titrate rapidly with 0.1 N KMnO4.
6- Repeat step (5) at increasing time intervals extending for about 90 min.
7- Repeat the experiment from the beginning using 5 ml K2Cr2O7,
8- Tabulate your results as follows:
 (t) : Calculated from start adding manganese dioxide, and in addition to the last minutes.
 (a-x) : is the concentration of H2O2 that not decomposed, expressed in ml of the

permanganate size that consumed in each titration .
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 32
Chemistry
Department
Time
Volume KMnO4 used
Vt = ( a – x)
3 ml catalyst
5 ml catalyst
MANUAL PHYSICAL CHEMISTRY III
Log(Vt) = log (a-x)
3 ml catalyst
5 ml catalyst
3
7
10
20
30
45
60
75
90
 Calculate k and t½, where
 .k = -slope x 2.303

t½ = 0.963 /k
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 33
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Part 2 :Heterogeneous Catalytic decomposition of H2O2 by using MnO2:
Procedure
1- Prepare 250 ml from solution KMnO4 (0.1N).
2- Prepare 250 ml from H2O2 solution.
3- Thermostat the solution of H2O2 at 30ºC for 20 min
4- Mix 100 ml of (1.2%) H2O2 solution and 0.05 gm. from MnO2.
5- Pipette out 10 ml of the decomposed mixture into a flask containing
(10 ml of 2N H2SO4) and titrate rapidly with 0.1 N KMnO4.
6- Repeat step (5) at increasing time intervals extending for about 90 min.
7- Tabulate your results as follows :
Data
Time
Volume KMnO4 used log(Vt) = log (a-x)
Vt = ( a – x)
3
7
10
20
30
45
60
75
90
 Calculate k and t½
where
 k = -slope x 2.303

t½ = 0.963 /k
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 34
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Catalysts for the decomposition of
Hydrogen peroxide
Topic
Reaction rates, catalysis, enzymes.
Timing
About 5 min.
Level
Pre-16.
Description
Several measuring cylinders are set up each containing a little washing up liquid and
a small amount of a catalyst for the decomposition of hydrogen peroxide. Hydrogen
peroxide is poured into the cylinders and a foam rises up the cylinders at a rate that
depends on the effectiveness of the catalyst.
Apparatus
_ Several 250 cm3 measuring cylinders – one for each catalyst to be used.
_ A large tray to catch any foam that spills over the top of the cylinders.
_ Stopwatch or clock with second hand.
Chemicals
The quantities given are for one demonstration.
_ 75 cm3 of 100 volume hydrogen peroxide solution.
_ About 0.5 g of powdered manganese(IV) oxide (manganese dioxide, MnO2).
_ About 0.5 g of lead(IV) oxide (lead dioxide, PbO2).
_ About 0.5 g of iron(III) oxide (red iron oxide, Fe2O3).
_ A small piece (about 1 cm3) of potato.
_ A small piece (about 1 cm3) of liver.
Method
Before the demonstration
Line up five 250 cm 3 measuring cylinders in a tray. Add 75 cm 3 of water to the
75 cm3 of 100 volume hydrogen peroxide solution to make 150 cm 3 of 50 volume
solution.
The demonstration
Place about 1 cm 3 of washing up liquid into each of the measuring cylinders. To each
one add the amount of catalyst specified above. Then add 25 cm 3 of 50 volume
hydrogen peroxide solution to each cylinder. The addition of the catalyst to each
cylinder should be done as nearly simultaneously as possible – using two assistants
will help. Start timing. Foam will rise up the cylinders. The lead dioxide will probably
be fastest, followed by manganese dioxide and liver. Potato will be much slower and
the iron oxide will barely produce any foam. This order could be affected by the
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 35
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
surface areas of the powders. Time how long each foam takes to rise to the top (or
other marked point) of the cylinder. The foam from the first three cylinders will
probably overflow considerably.
Place a glowing spill in the foam; it will re-light confirming that the gas produced
is oxygen.
Teaching tips
Some students may believe that the catalysts – especially the oxides – are reactants
because hydrogen peroxide is not noticeably decomposing at room temperature. The
teacher could point out the venting cap on the peroxide bottle as an indication of
continuous slow decomposition. Alternatively s/he could heat a little hydrogen
peroxide in a conical flask with a bung and delivery tube, collect the gas over water
in a test-tube and test it with a glowing spill to confirm that it is oxygen. This shows
that no other reactant is needed to decompose hydrogen peroxide.
NB: Simply heating 50 volume hydrogen peroxide in a test-tube will not suceed in
demonstrating that oxygen is produced. The steam produced will tend to put out a
glowing spill. Collecting the gas over water has the effect of condensing the steam. It
is also possible to ‘cheat’ by dusting a beaker with a tiny, almost imperceptible,
amount of manganese dioxide prior to the demonstration and pouring hydrogen
peroxide into it. Bubbles of oxygen will be formed in the beaker.
Theory
The reaction is :
2H2O2(aq) 2H2O(l) + O2(g)
This is catalysed by a variety of transition metal compounds and also by peroxidase
enzymes found in many living things.
Extensions
Repeat the experiment but heat the liver and the potato pieces for about five minutes
in boiling water before use. There will be almost no catalytic effect, confirming that
the catalyst in these cases is an enzyme that is denatured by heat.
Investigate the effect of using lumpy or powdered manganese dioxide. The
powdered oxide will be more effective because of its greater surface area.
Try using other metal oxides or iron filings as catalysts.
Animal blood may be used instead of liver if local regulations allow this.
One teacher suggested measuring the height of the foam over suitable time
intervals and plotting a graph.
Further details
The experiment can be done with 20 volume hydrogen peroxide, but is less
spectacular. It is, however, easier to time.
It has been suggested that manganese dioxide is not in fact the catalyst for this
reaction, but that the catalysts are traces of other oxides found on the surface of
manganese dioxide.
Safety
Wear eye protection.
Used liver should be wrapped up in paper and placed in the dustbin.
It is the responsibility of teachers doing this demonstration to carry out an
appropriate risk assessment.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 36
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 8: Catalytic Decomposition of Hydrogen Peroxide on MnO2
Decomposition of Hydrogen
Peroxide by Various Catalysts
Equipment:
3 goblets measuring cylinders spatula
(food grater 200-mL Erlenmeyer flask cheese cloth
or cotton tea filter beaker)
Chemicals:
Hydrogen peroxide solution (6%) iron(III) chloride
solution (0.1 M) manganese dioxide powder catalase
solution (1%) or crude potato extract
(Peeled raw potato deionised water crushed ice)
Safety:
Hydrogen peroxide solution (H2O2): Xn R22-41 S26-39
manganese dioxide (MnO2): Xn R20/22 S25
iron(III) chloride (FeCl3): Xn R22-38-41 S26-39
Xn
It is necessary to wear safety glasses and protective gloves, because every contact with eyes
or skin should be avoided.
Procedure:
Preparation of crude potato extract: Approx. 20 g of peeled raw potato are finely grated by
means of a food grater. The paste is scraped into a 200-mL Erlenmeyer flask and 25 mL icecooled deionized water are added. The flask is swirled in intervals for about 15 min.
Subsequently, the suspension is filtered through a sheet of cheese cloth or a cotton tea filter
into a chilled beaker.
Procedure: 20 mL hydrogen peroxide solutions are filled into each of the three goblets.
Homogeneous catalysis: 2 mL iron(III) chloride solution are added to the first goblet.
Heterogeneous catalysis: A spatula-tip full of powdered manganese dioxide is added to the
second goblet.
Enzymatic catalysis: 1 mL catalase solution or alternatively 2 mL of the filtered clear potato
extract are added to the third goblet.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 37
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Observation:
Homogeneous catalysis: The color of the solution changes from pale yellow to brownish
orange. Additionally, a noticeable formation of gas can be observed after a while. The pale
yellow color returns together with the end of bubbling.
Heterogeneous catalysis: A strong effervescence combined with the formation of fog can be
observed (therefore, the experiment is also known as “genie in a bottle”). The liquid gets dark
because of the finely dispersed black manganese dioxide and the goblet warms up
considerably.
Enzymatic catalysis: In the case of the catalase solution a strong evolution of gas takes places
and the goblet gets warm. The reaction catalyzed by the catalase from potato extract is weaker
and a distinct foam layer is formed.
Explication:
Hydrogen peroxide in aqueous solution exhibits a strong tendency to decompose into water
and oxygen (disproportionation):
The decomposition rate at room temperature is, however, immeasurably small. But the rate
can be appreciably increased by the addition of a catalyst.
3+
Fe ions are an example for a homogeneous catalyst, i.e. the catalyst is in the same phase as
the reaction mixture. The catalytic decomposition of hydrogen peroxide can be essentially
explained by two different mechanisms based on the mutual redox transition
Fe(III)/Fe(V) (KREMER-STEIN mechanism) and Fe(III)/Fe(II) (HABER-WEISS mechanism),
respectively.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 38
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
According to the mechanism proposed by KREMER and STEIN intermediate oxygen complex of
3+
iron with oxidation number +V is primarily formed by the reaction of Fe with
H2O2. This complex reacts with another H2O2 molecule to water and oxygen thereby re-forming
3+
Fe .
3+
According to the mechanism proposed by HABER and W EISS the Fe ions initiate a radical
reaction, after which the chain reactions consume the hydrogen peroxide. This mechanism can
explain the high reaction rates very well.
Chain initiation:Fe
3
Chain propagation: Fe
Fe
3
III
2
 H2 O2 R [Fe OOH]
2
 H2 O2 → Fe
3
 H2 O2  OH· → Fe
 H R Fe
2
 HOO· H
 2 OH
3
 HOO·  H2 O → Fe
2
 H  O 2 H2O
Mangan dioxide is an example for a heterogeneous catalyst, i.e. the phase of the catalyst is
different from that of the reaction mixture. The surface of solid manganese dioxide provides a
particulary favourable environment to catalyze the decomposition, though the mechanism is
not understood very well. For increasing the surface area available for contact with the
hydrogen peroxide solution a finely graded powder is used. The observed fog (the “genie”) is
caused by condensing water vapour mixed with oxygen gas.
Enzymatic catalysis takes an intermediate position, because enzymes are proteins, i.e.
macromolecules with diameters between 10 and 100 nm, that are colloidally dispersed in
solution and mostly much bigger than the substrate molecules. The cytoxin hydrogen peroxide
is one of the by-products of many cellular reactions. Aerobic cells protect themselves against
peroxide by the action of the enzyme catalase. Therefore, catalase is nearly ubiquitous among
animal organisms, especially it is found in liver and red blood cells. But catalase also occurs in
plant tissues, and is especially abundant in plant storage organs such as potato tubers, corms,
and in the fleshy parts of fruits.
The detailed structure of catalase differs from one organism to another, but the general
quaternary structure is analogous to hemoglobin in that catalase is tetrameric and each
polypeptide chain, composed of more than 500 amino acids, contains an iron-centered
porphyrin ring. However, in contrast to hemoglobin, catalase utilizes Fe(III). This iron can
formally be oxidized to Fe(V) in the oxidation-reduction cycle, but the processes at the active
site of the enzyme are not understood very well. But the incorporation of the iron ions in the
porphyrin and in the enzyme protein improves apparently their catalytic activity because the
effect of catalase is much stronger than that of the iron ions in solution.
Disposal:
Hydrogen peroxide solutions can be disposed of down the drain with running water.
Manganese dioxide can be reused after drying.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 39
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 9: Traffic lights
Traffic lights
A catalyst increases the rate of a chemical reaction without itself being permanently changed by the
reaction. The emphasis on permanently changed is important when discussing homogeneous catalysis
because the catalyst does undergo chemical change in providing an alternative reaction pathway of
lower energy. The ability to change oxidation state for transition metals makes them suitable as
homogenous catalysts. A new activated complex is formed with the catalyst because transition metals
can form stable compounds in more than one oxidation state and the transition metal ions can therefore
readily move between oxidation states. During the catalysed reaction the transition metal (TM) ion is
oxidised by one reactant to a higher oxidation state. This is then reduced back to the original form by
reaction with the other reactant. The reactants are therefore converted to the same products as are
formed without the catalyst. The only difference is that the reactants are converted into products more
quickly.
Reactant 1 + TM ion in low oxidation state
Reactant 2 + TM ion in high oxidation state
Product + TM ion in high oxidation state
Product + TM ion in low oxidation state
In this simple demonstration, potassium sodium 2,3-dihydroxybutanedioate or potassium sodium tartrate
(Rochelle salt) is oxidised by hydrogen peroxide in the presence of cobalt(II) ions. You simply mix the
hot reactants and add the catalyst.
C4H4O62- (aq) + 3H2O2(aq)
2CO2(g) + 2HCO2-(aq)+ 4H2O(l)
The interesting feature of this reaction is the colour change which occurs as the reaction proceeds. The initial
colour is pink which changes to dark green and then back to pink again - hence the traffic light reaction. When
you see the coloured intermediate, you can try to stabilise it by cooling the mixture rapidly. The nature of this
intermediate can lead to some stimulating discussion about colour, thermodynamic and kinetic stability.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 40
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Kit
Gloves; spatula;
Beaker, 250cm3; measuring cylinder, 25cm3;
Distilled water; thermometer (0-100°C);
Bunsen burner and mat; tripod and gauze;
Stirring rod; teat pipette; two test tubes and rack;
Potassium sodium 2,3-dihydroxybutanedioate, CO2K(CHOH)2CO2Na.4H2O
(also known as potassium sodium tartrate (Rochelle salt), 1g;
Hydrogen peroxide (20 vol), 20cm3;
Cobalt(II) chloride, CoCl2.6H2O , 0.25g.
Procedure
Dissolve ca 1g of potassium sodium 2,3-dihydroxybutanedioate in ca 50cm3 of water in a beaker. Heat
the solution to about 70°C. Add ca 20cm3 hydrogen peroxide solution and reheat to 70°C. Note any sign
of a reaction. Dissolve ca 0.25g of cobalt(II) chloride in 5cm3 distilled water in a test tube and add to the
hot reaction mixture. There will be an induction period before the reaction proceeds. As soon as the
solution appears dark green, quickly transfer a small portion, using a teat pipette, into a test tube which
is placed in a salted ice-bath.
Safety
Potassium sodium 2,3-dihydroxybutanedioate is an irritant. Hydrogen peroxide is corrosive. Hydrated
cobalt(II) chloride is toxic. The dust may be irritating and, in larger doses, severely damaging to the
respiratory tract. Skin contact, inhalation or ingestion should be avoided.
Special tips
If the reaction gets too hot or the reactants are too concentrated, effervescence from the reaction could
cause the mixture to spill out of the beaker.
Teaching goals
This experiment can lead to a full-scale kinetic investigation by changing the concentration of the
reactants and the catalyst. It can be used to develop a deeper understanding of non-standard electrode
potentials and their use in predicting the feasibility of a reaction:
2HCO2-(aq) + 2CO2(g) + 6H+(aq) + 6eC4H4O62- (aq) + 2H2O(l) E = +0.20V
H2O2(aq) + 2H+(aq) + 2e2H2O(l) E = +1.77V
The reaction is energetically favourable because E is +1.57V, which is large enough for the reaction
to go to completion. However, being thermodynamically feasible does not mean the reaction is
kinetically favourable and the reaction is very slow even when heated because of a high kinetic barrier.
The catalyst will provide an alternative reaction pathway with a lower activation energy.
H2O2(aq) + 2H+(aq) + 2Co2+(aq)
2H2O(l) + 2Co3+(aq)
C4H4O62-(aq) + 2H2O(l) + 6Co3+(aq)
2HCO2-(aq) + 2CO2(g) + 6H+(aq)+ 6Co2+(aq)
For this mechanism to work, the standard electrode potential (SEP) for the Co3+/Co2+ half-cell must lie
within a certain range of values as indicated above (+0.20 V to +1.77V). However, the SEP for the halfcell Co3+ (aq), Co2+ ( aq) | Pt is +1.84V. At first glance, you might think that in non-standard
conditions this value is not that far out of the range required, but concentration or temperature changes
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 41
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
do not alter E values very much. The main reason is cobalt ions can form complexes with the 2,3dihydroxybutanedioate ions - a bidentate ligand. Electrode potentials for half-cells involving complexes
are often substantially different from those involving simple ions. This is another fruitful area for
discussion (crystal and molecular orbital theory).
Unfortunately the value for this half-cell is not quoted in the literature but even if it were shown to be
energetically favourable, there would still be no way of knowing whether the reaction was kinetically
favorable. You would have to do this experiment to find out. Finally, you should note that cobalt(II)
catalysis the decomposition of hydrogen peroxide into water and oxygen and the equations written here
do not take that into account. Clearly, this side reaction will influence any thermodynamic or kinetic
discussion with this reaction.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 42
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 10: To make a colloid and demonstrate its properties
SOLUTIONS AND COLLOIDS
OBJECTIVES
1. To examine the influence of solvent and solute on solution formation
2. To prepare a solution for use in a later experiment
3. To make a colloid and demonstrate its properties
INTRODUCTION
Part I. Influence of solute and solvent on solubility
Solutions are homogeneous mixtures of two or more chemical substances. The components can be
gases, liquids, or solids, and they are uniformly distributed. As a result, the properties of a true solution
are the same throughout the solution. The component of a solution that produces dissolution is called
the solvent and is often present in greater proportion. The component that is dissolved is called the
solute. The components of the solution are of atomic or molecular size. Thus they are too small to
reflect light and solutions will be transparent, though they may be colored or colorless. Often, then, it
becomes necessary to use chemical and physical tests to identify a substance as a solution rather than as
pure solvent. Chemical tests, such as the formation of a precipitate (studied in the experiment on
chemical reactions), are frequently used to identify ions or molecules in a solution.
The solubility of a solute in a particular solvent is a property of that solute. Commonly, the solubility
of a solute in a liquid is reported in grams of solute per 100 mL of solvent. Several factors may
influence the solubility of a solute, including temperature, the nature of the solute, and the nature of the
solvent. To understand how the nature of the solute and solvent affect solubility, the concept of
intermolecular forces must be examined. These are the forces of attraction among particles, and they
exist among solute particles and among solvent particles. In order for a solute particle to dissolve, its
interactions with other solute particles must be overcome and new interactions with the solvent must
form. This happens most readily when intermolecular forces between solute and solvent are similar. If
the interactions between solute particles are stronger than those between solute and solvent, the solute
will not dissolve. Thus polar covalent and soluble ionic compounds are soluble in polar solvents such as
water, and insoluble in nonpolar solvents such as benzene and carbon tetrachloride. Nonpolar covalent
compounds, on the other hand, are much more soluble in nonpolar solvents than in polar solvents. Thus
the general rule-of-thumb is "like dissolves like".
Soluble substances dissolve completely in the solvent and form solutions. Insoluble substances do
not dissolve in the solvent. Two liquids that are completely soluble in each other are called miscible.
When a liquid solute doesn't dissolve in a liquid solvent, but instead forms a separate layer, the liquids
are said to be immiscible.
In Part I of this experiment, you will test the solubility of a series of compounds in two solvents, one
polar and one nonpolar.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 43
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Part II. Preparation of a solution
Since many of the reactions carried out in laboratories and all of those in our bodies take place in
solution, it is necessary to be able to determine the concentration of the solute, or the relationship
between the quantities of solute and solvent found in solutions. Concentrations can be given in many
units, but one of the most commonly used in chemistry is molarity. Concentration expressed as molarity
gives the relationship between the number of moles of solute and the volume of solution. It is defined as:
In order to make a solution of a given molarity, you can weigh out a calculated amount of solute and
dissolve it in enough solvent to make the desired volume of solution. For example, to make 100.0 mL
of a 0.100 M NaCl solution, you need:
This requires you to weigh out:
To prepare the solution, you would weigh out 0.585 g of NaCl, add enough water to dissolve, then
dilute to a total volume of 100.0 mL using a 100 mL volumetric flask.
To calculate the concentration of a solution prepared from a known mass of solute, you must find the
number of moles of that solute, then divide by the total volume of solution. For example, if you weigh
out 0.784 g of NaCl and dissolve it in a total volume of 150.0 mL:
In Part II, you will prepare a solution and determine its concentration for use in a subsequent
experiment.
Part III. Colloids
Part III of this experiment examines colloids. Colloidal suspensions consist of a dispersing medium
and a dispersed material. These can be solids, liquids, or gases. The dispersed material exists as
particles that are much larger than those in a true solution. Though they are small enough to remain
suspended in the dispersing medium, they are large enough to scatter light when an intense beam of light
passes through the suspension. This property of colloids is called the Tyndall effect. Some examples of
colloids include milk (a liquid dispersed in a liquid), smoke (solids in a gas), whipped cream (a gas in a
liquid), and fog (a liquid in air).
In Part III, you will compare a solution and a colloid, using the Tyndall effect to test for the presence
of the colloid.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 44
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
PROCEDURE
Part I. Influence of solute and solvent on solubility
A. Place 8-10 drops of water in each of 9 test tubes. Then add the following solutes and test for
solubility. For solids, add a few crystals. For liquids, add 8-10 drops. Shake to mix and record your
observations.
a. methanol (CH3OH)
b. ethanol (CH3CH2OH)
c. n-propanol (CH3CH2CH2OH)
d. n-butanol (CH3CH2CH2CH2OH)
e. NaCl
f. table sugar (C12H22O11)
g. oil (mixture of compounds containing mostly carbons and hydrogens)
h. MgSO4
i. n-octanol (CH3CH2CH2CH2CH2CH2CH2CH2OH)
B. Repeat the experiment, using 8-10 drops of oil in each test tube instead of water.
Part II. Preparation of a solution
CAUTION: SODIUM HYDROXIDE IS A STRONG BASE. IF IT COMES INTO CONTACT
WITH SKIN, FLUSH IMMEDIATELY WITH LARGE VOLUMES OF WATER.
200 mL of an approximately 0.1 M NaOH solution will be prepared. Weigh out between 0.7
and 1.0 g of NaOH on the laboratory balance, recording the exact weight. Add to a 200 mL
volumetric flask along with enough water to dissolve. Then fill the flask to the mark with water. Mix
thoroughly.
Part III. Preparation and testing of a colloid
Dissolve two small crystals of sodium thiosulfate in 5 mL of deionized water in a large clean test
tube. Check the solution for the Tyndall effect by holding the test tube in the path of the light from one
of the lamps located in the lab. Remember, if you have a true solution it should not exhibit the Tyndall
effect. If you notice the scattering of light, it is probably dust particles and your test tube needs to be
recleaned. Next, add 10 drops of 6 M HCl to the solution of sodium thiosulfate. The reaction which
occurs should generate a colloidal suspension of sulfur in water. The reaction equation is
Now, check the mixture for the Tyndall effect again. Note: sometimes it requires a few minutes for the
Reaction to begin.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 45
Chemistry
Department
SOLUTIONS AND COLLOIDS
LABORATORY REPORT
MANUAL PHYSICAL CHEMISTRY III
NAME __________________________
DATE __________________________
Part I.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 46
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 47
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Part II.
Mass of NaOH + paper: ________
Mass of paper ________
Mass of NaOH ______
Part III. Observations
Thiosulfate solution:
Thiosulfate + HCl:
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 48
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
QUESTIONS
Part I.
1. Methanol, ethanol, propanol, butanol, and octanol are in a class of compounds called alcohols. Given
the following information, prepare a graph of the number of carbon atoms in the compound vs. the
boiling point of the compound. Be sure to use the rules for graphs given in Lab 7. Do you see a
relationship? What is it?
2. Which compounds are soluble in water? In oil?
3. What is the relationship between the number of carbon atoms in an alcohol and its solubility?
4. Predict whether ethanol will be soluble in propanol and justify your prediction.
Part II.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 49
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
5. Calculate the molarity of your solution of NaOH, using the weight obtained in Part II.
Show all your work and be sure to give your answer with the appropriate number of
significant figures. (Volumetric glassware measures volume to 4 significant figures.)
Part III.
6. Was the thiosulfate before addition of HCl colloidal or a true solution? How do you
know? What about after addition of HCl?
7. Explain why you should use your low beam headlights in foggy weather.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 50
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 11: Stability of the emulsions
Stability of Emulsions
Introduction
In this activity we will compare the stability of oil and vinegar emulsions with various
Additives.
Material
6 Test tubes
Test tube rack
Oil
Vinegar
Egg yoke
Milk
Cayenne pepper
Mustard (ground)
Glyceryl Monstearate (GMS)
To Do and Notice
Place 6 test tubes in a test tube rack. Measure out equal volumes of oil and vinegar
into each tube. Label the test tubes 1 through 6 and add the following ingredients:
1. No additions
2. ¼ teaspoon egg yoke
3. ¼ teaspoon milk
4. ¼ teaspoon cayenne pepper
5. ¼ teaspoon ground mustard
6. ¼ teaspoon GMS
Cover and shake each test tube approximately 100 times and place in the test tube rack.
Compare the stability and thickness of each emulsion immediately after shaking and
After letting the solution sit for 10 minutes.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 51
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Which additives formed stable emulsions?
Which additives formed temporary emulsions?
Which additive formed the thickest emulsion?
What’s going on?
Oil and water do not mix. An emulsion is a stable mixture of to liquids that do not
normally mix such as oil and water, or oil and vinegar. Mayonnaise and Hollandaise
sauce are common emulsions, as well as homogenized whole milk (a mixture of butter
fat or cream and milk). In order to form a stable mixture of two repelling liquids, you
need an emulsifying agent, which will prevent the oil droplets or fat from coalescing
and separating from the opposing liquid.
Emulsifying agents perform two duties. They coat the oil droplets with like charges
and reduce the surface tension of the water or vinegar. This reduces the waters ability
to repel oil, and reduces the oils ability to recombine to form larger oil droplets.
Egg yokes contain Lecithin, an emulsifying agent as used in Mayonnaise and
Hollandaise Sauce. Milk contains the protein casein which acts as a natural emulsifier.
Other natural emulsifiers are mustard and cayenne pepper. Commercial sauce
manufacturers use industrial emulsifiers such as monoglycerides and diglycerides that
don’t add flavor, but chemically emulsify the solution.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 52
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 12: To find the critical point for colloidal mixtures composed of different types of starches.
Abstract
What is a colloid? If you have made Oobleck out of corn starch and water, then you know that a colloid is a
mixture that acts like a solid and a liquid at the same time! What is the critical factor to making a colloidal
material? Will different sources of starch change the recipe?
Objective
The purpose of this project is to find the critical point for colloidal mixtures composed of different types of
starches.
Introduction
What do ketchup, Oobleck, and quicksand have in common? They are all made up of tiny, solid particles
suspended in water. Chemists call this type of mixture a colloidal suspension, and the amount of solid and water
to use is called the critical concentration. The critical concentration for each colloidal material is unique and
depends on many different factors.
Colloids have very interesting physical properties. One of the more interesting physical properties of colloidal
materials is that sometimes they seem to be solid and other times they seem to be a liquid. Because of this odd
behavior, colloids are called non-Newtonian fluids, because they break the rules of ideal fluids described by Isaac
Newton in the 1700's.
Colloidal suspensions respond differently to different forces, as seen in this cool Oobleck video by Blake (Kids
Science, 2006). A fast, hard force will cause the colloid to appear solid, but a slow, even force will cause the
colloidal material to flow like a liquid. This can be dangerous if you live in an area with clay soil, because sideways
forces during a flood or earthquake can cause the earth to suddenly become very unstable!
As it turns out, colloidal materials are very common. Even though they have such strange physical properties,
those same properties make them very useful products and materials. Foam, gel, glue, and clay are all examples
of colloidal materials. There are many colloidal materials found in food products, like: marshmallows, mayonnaise,
pudding, milk, butter, and jelly. Building materials like cement, stucco, plaster, and paint are colloidal materials.
Even our bodies and other living organisms are made of colloidal materials! They are everywhere!
In this experiment, you will learn about a very simple colloidal material, starch suspended in water. You will test
starch from different plant sources (corn, potato, rice, tapioca) to see if the colloids share similar physical
properties. You will measure the amount of water needed to make a colloid out of each type of starch. Will these
colloidal suspensions be the same or different?
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 53
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Terms and Concepts
To do this type of experiment you should know what the following terms mean. Have an adult help you search the
internet, or take you to your local library to find out more!





starch
colloid
physical properties
solid
liquid
Questions



How does starch behave as a colloidal material?
What are the physical properties of colloidal materials?
Do different sources of starch change the properties of the colloid?
Bibliography




Exploratorium, 1998. "Science Explorer: Outrageous Ooze — Is This Stuff a Liquid or a Solid?," San Francisco:
Exploratorium. [accessed July 3, 2006]
http://www.exploratorium.edu/science_explorer/ooze.html
Watch this video to see Blake explain how to make Oobleck, show you its physical properties, and talk about
matter:
Kids Science, 2006. "Kids Science Episode 1: Cornstarch Suspension," YouTube.com [accessed July 18, 2006]
http://www.youtube.com/watch?v=fazPiaHvFcg
Watch this video to see how high frequency waves cause very odd behavior in Oobleck, from this paper by
researchers at the Center for Nonlinear Dynamics, University of Texas at Austin:
Merkt, F.; Deegan, R.D.; Goldman, D.; Rericha, E., and Swinney, H.L., 2004. "Persistent holes in a fluid," Phys.
Rev. Letters. 92 184501 [accessed July 3, 2006]
http://chaos.ph.utexas.edu/research/vibrated_cornstarch.htm
Seuss, 1949. Bartholomew and the Oobleck, New York: Random House.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 54
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Materials and Equipment






water
cups
measuring spoons
medicine dropper or small syringe
stir stick
different types of starches:
o corn starch
o potato starch
o tapioca starch
o rice starch
Experimental Procedure
1. You will need to determine the amount of water required to form a colloid from each type of starch, one at a time.
2. Starting with the corn starch, add 1 tbsp of the starch to a small cup or bowl.
3. Add water one drop at a time, stirring frequently and counting the number of drops until the mixture forms a
colloid. You will recognize the colloid when you stir with your stir stick. At first, the mixture will look solid and
separate into clumps, but then the clumps will start to flow together again like a liquid.
4. When you reach the proper consistency for a colloid, stop adding water and record the number of drops in a data
table:
5. Play around with the colloidal material. Poke it with your finger and put some in your hand. What does it look like?
How does it move? What does it feel like? Write down some of the physical properties in your data table.
6. Repeat steps 2–5 with each of the other starches and record your data in the data table.
7. Make a bar graph of your data to compare the different starches. Place the number of drops of water on the left
side (Y-axis) of the graph. Draw a bar for each type of starch up to the matching number of drops. Compare the
bars on the graph representing the different starches. Are they the same or different?
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 55
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Variations



Experiment with the different properties of the colloids. Are they solid or liquid? Do they respond differently to
different kinds of pressure? Push slowly into the colloid with your finger. How does the colloid respond? Poke the
colloid hard with your finger. Does it respond differently? Do all of the colloids respond similarly and have similar
properties? Can you find other ways of testing the physical properties of colloidal materials?
Starches are often used to make gels. What happens if you increase the temperature of your colloidal material?
Try heating up the colloidal starch mixtures. How do they change? Are there new physical properties that you can
observe? Do starches from different plant sources gel at the same temperature and have the same consistency?
For more on gels, try the Science Buddies project Are You Gellin'?
Clay earth behaves like a colloidal material when it has just the right amount of water in it. Can you find the critical
amount of water needed to made a colloidal clay soil? Colloids can appear solid against strong downward forces,
but are very weak against lateral forces that push sideways. Try testing your colloid against these two different
directional forces. Which direction is your colloid the weakest? If your colloid were a clay soil, how would this
contribute to landslides or earthquakes? Can you engineer a way to make colloidal soils resistant to lateral forces
during earthquakes and landslides?
Tell Us About Your Experience
If you completed this project, please help Science Buddies by letting us know how things went! Fill out our I Did
This Project form to submit your comments.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 56
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 13: Find out the formula of cupper ammonia complex
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 57
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 58
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 59
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
Experimental 14: Surface tension of n-butanil solution
Introduction
After being amazed by the apparent “magic” of water’s high surface tension as children, most of us think little of
the consequences of this interesting property of liquids. Surface tension plays a part in many common effects seen
every day: a water stream breaking into droplets and the beading of water on a smooth, non-polar surface are just
two examples.
In this lab, we became closely acquainted with the surface tension of an aqueous solution and what effects it had
on surface concentration. We combined pure n-butanol with water in various concentrations to see how much
effect it would have on the surface tension. Plotting the value of gamma (surface tension) in units of g/s2 for each
of the concentrations presented a linear relationship. The slop of the line gave us what we needed to find the
surface concentration using the Gibbs isotherm equation. Finally, we used this value to find an experimental
molecular crosssectional area which we compared to a theoretical one using computer-built molecular models.
Real-world applications of surface concentration and surface tension might be found in industries requiring
precise control on fluid dynamics or homogenous distribution of solutes in solution. Molecular cross-sectional
area has implications in molecular collisions and the energy found therein.
Experiment and Data
For this experiment, we were charged with measuring the surface tension of aqueous solutions of n-butanol. This
Experiment spanned over the space of two lab periods; during the first period we became acquainted with the
Instrument and made the solutions and during the second we took measurements.
On the first day, we started by cleaning the sensor wire. We carefully removed the wire from its hanger and used a
kim wipe soaked in methanol. After this, we wiped the glass surface tension tray with methanol and let it air dry.
The instrument used was a DeltaPi Single-Channel Microtensioner made by Kibron Inc. In order to calibrate the
sensor,we filled one of the compartments with deionized water and submerged the sensor wire by turning the
knob to lower the sensor arm. Once the tip was submerged, we slowly raised the wire out until it was visibly
pulling the surface of the water up.
We opened the Delta Graph program and clicked on the "Measure" button. We were calibrating with water so the
Tension difference was set at 72.8 mN/m.
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 60
Chemistry
Department
MANUAL PHYSICAL CHEMISTRY III
We clicked on "Calibrate" and the software guided us through the process (sensor in air, take reading,
sensor in water, take reading). The readings were as follows:
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
Page 61
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 62
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 63
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 64
Chemistry
Department
Prepared by Lecturer Sahar Mahmoud
Supervisor Dr. Samah A. Ahmed
MANUAL PHYSICAL CHEMISTRY III
Page 65