General Chemistry Laboratory Workbook
for All B.Tech. Students
Instructors
Dr. Atul Kumar
Dr. Suresh Sarkar
Dr. Kaushambi Mitra
Teaching Assistants
Anitta Regina, Kumari Sheetal, Shivangi Jain, Ashish Kumar Sarangi,
Tamanna Yadav, Somdatta Paul, Suman Kumar Saha, Chanchal Sharma
Course CYP 1010
Indian Institute of Technology Jodhpur
Department Of Chemistry
2025
Laboratory Safety Guidelines
You are required to read, understand and implement the safety precautions indicated in your
laboratory workbook, which are summarized below. Your signature on the attached sheet indicates
your absolute willingness to abide by these precautions while you are in the laboratory.
1. Work in the laboratory only as authorized by your Instructor/Teaching Assistant. Do not perform
unauthorized experiments.
2. You are required to use safety goggles and wear them as directed during all laboratory sessions.
3. Learn emergency procedures and know the locations of the nearest eye wash and
chemicalcleanup materials.
4. If you are injured or if any type of accident or fire occurs, IMMEDIATELY call
yourInstructor/Teaching Assistant for assistance.
5. Carefully read all instructions and thoroughly plan your work.
6. Wear appropriate clothing and shoes, not sandals, in the lab. Confine long hair.
7. Carefully read all labels on chemical bottles and familiarize yourself with the number/color
hazardscodes. Never return excess chemicals to the stock bottles. Do not put a pipette or a
dropper directly into a commercial stock reagent bottle. Instead, pour an aliquot of the reagent
from the stock bottle into a beaker. Use pre-mixed lab reagents as directed in the instructions
for specific laboratory exercises.
8. Do not eat, drink or smoke in the lab. Never taste the chemicals. Smell chemicals cautiously by
wafting the vapors toward you.
9. When mixing or heating chemicals in a test tube, point the test tube away from the people.
10. Do not use any sources of spark or flame in the vicinity of flammable liquids. Note that most
organic solvents are flammable.
11. While mixing acid and water, always add the acid to the water, not vice-versa.
12. Fill a pipette by using a pipette bulb or mechanical pipettor only; never pipette by mouth.
13. If a spill occurs during regular hours, refer it to your teaching assistants or instructor immediately.
If a minor spill occurs when no senior person is available, clean it up immediately by using plenty
ofwater.
14. Dispose of chemicals as directed by your teaching assistant. Organic solvents are never to be
disposed of down the sink. For disposable in-organics, use plenty of water.
15. I have read carefully and understand all of the safety rules contained on this page. I also agree to
read all rules for specific exercises contained in the laboratory workbook required for this course.
Irecognize that it is my responsibility to obey them faithfully.
16. I realize that all chemicals are potentially dangerous; therefore I will exercise care in handling
them. If I am unsure of the potential hazards of any chemical, I will discuss this with my Teaching
Assistant prior to using the chemical in question.
17. I understand that I am required to wear safety goggles at all times when directed to do so in the
laboratory.
18. I also understand that there are dangers involved in wearing all types of contact lenses in
laboratory situations where reactive chemical agents, biological fixatives, or volatile organics are
in use.
19. I am aware that even when safety goggles are worn, the Chemistry Department strongly
discourages wearing of contact lenses in these situations. If I do elect to wear contact lenses in
the laboratory, I will inform my teaching assistant and I will assume all responsibility for damages
caused by wearing them in the lab.
Signature ………………………
Laboratory Workbook
This must be used as a Laboratory Workbook:
1.
Keep the notebook neat and tidy and bring with you at every lab session.
2.
Read the experiment before coming for the class.
3. Try to answer the questions given as “Example Questions” at the end of each experiment.
4. Write the observations and results neatly.
5. Do the calculations on the extra page provided at the end of every experiment.
6.
Write the Results and draw conclusions as indicated.
7.
Sign the Statement at the end of each experiment.
REPORTS CANNOT BE COPIED FROM OTHER STUDENTS AS THEY WILL BE EVALUATED FOR
GRADING. IF ANY PART OF THE REPORT IS COPIED, YOU MAY FACE SEVERE CONSEQUENCES.
Contents
Safety Precautions
Laboratory workbook and grading
Contents
1
2
3
4
5
6
Preparation of Nylon 6,6.
Preparation of double salts
Preparation of salt of Co-ethylenediamine complex.
Preparation of tetraphenyl cyclopentadienone by Aldol Condensation
Determination of Critical Micelle Concentration of a Surfactant by Conductivity Method.
FTIR spectroscopy in combination technique for analysis of caffeine in tea and coffee.
7
The excitation and emission spectrum of Curcumin in solvents ethanol and hexane respectively
and find stokes shift using Fluorescence Spectroscopy.
Surface contact angle, surface tension and surface free energies of different solvents and
substrates respectively.
Study of a reversible redox reaction using Cyclic Voltammetric analysis.
Study of color in complexes using UV visible Spectroscopy
Determination of enantiomeric purity of Naproxen and Ibuprofen.
8
9
10
11
1
Preparation of Nylon6,6
Objective:
Synthesis of Nylon 6,6 polymer using two reactants.
Apparatus: Beakers (50 mL x 2), Volumetric flask (25 mL x 2), Measuring cylinder (10 mL & 25
mL), weight balance, copper wire hook, dropper, watch glass, Glass rod
Chemicals used: 10mL (5% aq.) Hexamethylene diamine, 20% NaOH solution, 10mL Cyclohexane,
0.5 mL Adipoyl chloride.
Theory:
Polymers are macromolecules built from smaller molecular subunits, called monomers.
Synthetic polymers can be classified into two main types according to the mechanism by which
they synthetically grow from monomer to polymer: chain-growth polymers and step-growth
polymers. This classification scheme is an update from historical nomenclature, in which
polymerswere classified by whether there existed a byproduct of the polymerization reaction
(condensation polymerization) or not (addition polymerization). In a step-growth reaction, the
growing polymer chains (of any molecular length) may react with each other to form longer
polymer chains. The monomer or dimer may react in just the same way as a polymer containing
hundreds of monomer units. In chain-growth polymerization, however, only monomers may
react with growing polymer chains. That is, two growing polymer chains cannot join together
as in the case during step-growth polymerization.
Figure 1 Structure of Nylon-6,6 polymer
The first step is the reaction between a molecule of hexamethylenediamine and a
molecule of adipoyl chloride (see Scheme 1 below). The hydrogen atom of the amine group
belonging to hexamethylenediamine forms a hydrochloric acid (HCl) molecule with the chloride
from the acid functional group. The remaining adipoyl chloride molecule and the
hexamethylenediamine molecule will join together to form a larger molecule (polymer). The
molecule formed has an acid group at one end and an amine group at the other (Scheme 1)
andis a nylon 6,6 unit.
In acidic solution, the polymerization reaction will not occur readily. While mixing the
solutions two layers are formed, pH of the mixture should be greater than 7. In the reaction of
adipoyl chloride with hexamethylenediamine, HCl is a co-product which can make the solution
acidic. To avoid this, add 10 drops of 20 % NaOH. It basically neutralizes HCl and keeps the solution
basic. So NaOH is used as a catalyst in this reaction.
Scheme 1: The reaction involved in the synthesis of Nylon 6,6
Step-Growth Polymerization
In this reaction, monomers need not necessarily add sequentially but instead small
polymer chains may couple into larger chains. For example, nylon 6,6 is an aliphatic
polyamide that is synthesized using A-A/B-B step-growth condensation polymerization.The
two monomers involved in this polymerization are hexamethylenediamine and adipoyl acid
each of which is bifuctional (i.e., two ends of each are reactive), and each end contains the
same functionality (i.e., A or B functional groups). The end groups canthen react in a similar
manner with other acid/amine groups present on adipoyl chloride and
hexamethylenediamine as shown below in Scheme 2. After completion of many steps of
this process, the nylon 6,6 polymer will form.
Mechanism:
Scheme 2: Mechanism of Nylon-6,6 synthesis
Procedure:
Method: 1
1) Beaker A: In a 25ml beaker, prepare 10ml of 5% aqueous hexamethylenediamine (1,6hexanediamine, 7 mM) and then add 10 drops of 20% NaOH (Sodium hydroxide).
2) Beaker B: In a 25ml beaker, take 10ml of Cyclohexane and add 1 ml of Adipoyl Chloride.
3) Transfer solution beaker (B) to beaker (A).
4) Use a copper wire with a hook at the end, slowly go around the inside wall of the beaker
to free it of the polymer and in a circular motion, approach the centre of the beaker.
Slowly pull the rope until a few feet of the polymer is out of the solution (if you pull it too
fast the rope will break), and then cut the rope off. Lay this rope on a paper towel to dry.
5) Use paper to get dab excess water out of the fibre and then use a piece of filter paper to
pull more water out of the fibre. Wrap the polyamide in filter paper and place it aside.
6) Collect nylon thread on filter paper and transfer in watch glass.
7) Dry in hot air oven at 110’c for 10mins.
8) Weigh the nylon thread, calculate the % yield and note it down.
9) Dispose of all organic waste in the “organic waste” container. Clean all glassware with
water and put on the rack to dry. Throw away all paper waste. Also clean the balance.
10) Clean your work area. Replace all equipment to the correct storage location.
Figure 4: Formation of nylon-6,6 rope by interfacial polymerization
Precautions:
1) As usual lab safety rules must be followed.
2) Hexamethylenediamine is irritating to the skin, eyes and respiratory system.
3) Adipoyl chloride may be irritating to the skin eyes and muscle membrane.
4) Always work in the hood when working with volatile liquid
chemicals and whenperforming an exothermic reaction.
5) Do not touch the hot plate with bare hands.
Results:
The weight of nylon threads gained finally is..................
The expected weight in the ideal condition is…………..
The percentage yield is.....................
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature :
Example Questions:
1) What is the difference between homopolymer and co-polymer?
Homopolymer: Formed from one type of monomer (e.g., polyethylene).
Copolymer: Formed from two or more types of monomers (e.g., nylon 6,6).
2) What is polymerization and how it can be classified?
Polymerization: A process in which monomers combine to form a polymer.
Addition Polymerization: No by-products (e.g., polyethylene).
Condensation Polymerization: By-products like water are released (e.g., nylon 6,6).
3) What are the steps of polymerization?
Initiation: Formation of active species (radicals, ions).
Propagation: Chain growth through monomer addition.
Termination: End of chain growth (e.g., combination or disproportionation).
4) What is condensation polymerization?
A polymerization process where monomers react, releasing small molecules like
water or HCl as by-products.
Example: Formation of nylon 6,6 from hexamethylenediamine and adipic acid.
5) What do the two numbers correspond to in the name “Nylon-6,6?” What wouldthe
chemical structure of the repeat unit be in “Nylon-2,2”?
First Number (6): Number of carbon atoms in the diamine (hexamethylenediamine).
Second Number (6): Number of carbon atoms in the diacid (adipic acid).
Chemical Structure of Nylon-2,2: Derived from ethylenediamine and oxalic acid with a
repeating unit:
6) Why is a solution of sodium hydroxide added to the solution
ofhexamethylenediamine?
Sodium hydroxide neutralizes the acidic by-products (like HCl) formed during the
polymerization, maintaining a suitable pH for the reaction.
2
Preparation of Double Salts
Objective:
To prepare Ammonium Copper(II)Sulphate Hexahydrate [(NH4)2SO4.CuSO4.6H2O] from the
reaction of Copper Sulphate (CuSO4.5H2O) and Ammonium Sulphate (NH4)2SO4.
Apparatus and Chemicals used:
2 beakers (25 mL), Hotplate with stirrer, filter paper, measuring cylinder (10 mL), glass rod, flask
funnel, 0.01 mol CuSO4.5H2O (2.495 gm CuSO4.5H2O) and 0.01 mol (1.32 gm) ammonium sulphate
(NH4)2SO4, sample vial (10 mL), magnetic bar, spatula.
Theory:
In this experiment, we are preparing double salt which is a salt containing more than one
cation or anion. They form when one salt and more dissolved in a liquid then together
crystallize in a regular pattern. They have their own crystal forms which need not be the same
as that of either of their component salts. This is a solid-state phenomenon where, in
solution, salts are decomposed completely, or nearly so, into their component ions. In this
respect, double salts are distinguished from complex salts, which give complex ions of their
own in solution.
Tetraammine copper (II) sulphate is the inorganic compound with the formula [Cu (NH3)4
(H2O)n] SO4. This dark blue solid is used in the production of cellulose fibres for the production
of rayon.
In the solid-state, the salt contains the [Cu (NH3)4H2O]2+ dictation which has a square pyramidal
molecular geometry. The crystals belong to monoclinic system.
Procedure:
1. Prepare 0.01 mol of CuSO4.5H2O (Solution-A) and 0.01 mol of (NH4)2SO4 (Solution-B) solution in 5
mL water in two different beakers (25 mL capacity).
2. Heat the solutions at 70º C for 5-10 min for complete dissolution.
3. Note: solution should be made clear.
4. Transfer solution-B to solution-A and heat up to 150 - 180 0C to reduce the total volume to ~5 mL
(almost half).
5. Let the beaker cool naturally and take the precaution of not disturbing the beaker after
crystallization has started.
6. The salt will separate in large well-formed crystals if a cold saturated solution is left to evaporate
slowly.
Molar calculations:
Precautions:
1. Wear prescribed glasses or safety glasses at all times in the laboratory.
2. Weigh the salts and mix them in correct proportions.
3. Do not stir or move the beaker once heated because it may cause disturbance at the time when
crystallization starts.
Result:
1. The weight of the double salt formed by this method is …….….……..g.
2. The yield was found to be …………..….
3. The color of the crystal is…………..…………..
SIGNED STATEMENT:
I have only worked with the following persons __________________________________________
______________________________________________________________________________
for this lab experiment. I received no other help and I did not copy another person's work.
Signature :
_______________________________________
Example Questions:
1.
Give five examples of double salts and uses.
2. Define the normal salts, double salts and complex salts with examples.
3. Which types of bond present in following compounds.
i.
KCl
ii.
KAl(SO4)2
iii.
[Co(NH3)6]Cl3
4. If you have given aqueous solution of a) CuSO4 (0.5 M) 10 ml b) (NH4)2SO4 (0.5 M) 10 ml Give answer of the
following questions.
i.
After heating the mixture of the solution a and b as performed experiment double form or not? If form
what is the chemical formula of the product and expected yield.
ii.
How much (mg) CuSO4 and (NH4)2SO4 need to prepare given solution a and b.
5. What is difference between CuSO4 and CuSO4.5H2O salts.
3
Preparation of salt of Co-ethylenediamine complex
Objective:
Preparation of Tris(ethylenediamine)cobalt (III)chloride Co-ordination complex [Co(en)3]Cl3
Apparatus: Beakers (25 mL x 2), Glass rod, measuring cylinder (10 mL), magnetic bar,
spatula, sample vial (10 mL) etc.
Chemicals used: Cobalt chloride, Ethylenediamine, HCl, H2O2 anddistilled water.
Theory:
Tris-(ethylenediamine) cobalt (III) chloride is a coordination complex with the formula
[Co(en)3]Cl3 (where "en" is the abbreviation for ethylenediamine). This complex was
important in the history of coordination chemistry because of its stability and its
stereochemistry. Alfred Werner, who isolated this salt as yellow-gold needle-like crystals and
first described the complex. Ethylenediamine co-ordinates with metallic ions through its
both nitrogen atoms that forms 5-membered rings which are very stable. It has a melting
point of 275 0C and it is soluble in water. The cation [Co (en) 3]3+ is octahedral with Co-N
distances in the range 1.947-1.981 Å. The N-Co-N angles are 85° within the chelate rings and
90° b/w N-atoms on adjacent rings. This compound is diamagnetic in nature.
Figure 1: Isomers of
Tris(ethylenediamine)cobalt(III)chloride.
The synthesis of tris(ethylenediamine)cobalt(III)chloride leads to the formation of two
enantiomers. Enantiomers, or "optical isomers", are mirror images of one another. A mixture
of two enantiomers (known as a racemic mixture) can be very difficult to separate, because
enantiomers typically have the same chemical and physical properties. Indeed, there is only
difference between two optical isomers is, they rotate polarized light in opposite directions.
One of the enantiomers in the pair will rotate the light to the right (dextrorotatory,
designated’d’ or '+') and the other to the left (levorotary, designated 'l' or '-'). The
measurement of the rotation ofpolarized light is a useful analysis for identifying enantiomers
and determining their purity.
[α]λ = is specific rotation at the given wavelength λ
Αobs = is observed rotation of sample measured by “polarimeter” c = is the concentration
(in g/mL)
l = is the path length (in dm)
x = is the optical purity where 0.5 means a racemic mixture of both (+) and (-) enantiomers
is present in equal portions, and 1 means only one pf the enantiomer is present.
Procedure:
A. Synthesis of Tris(ethylene diamine)cobalt(III)chloride.
1. Beaker A: In a 25 mL beaker, prepare solution of CoCl2. 6H2O (240 mg in 10mL) in distilled water.
(Note: clear solution should be formed).
2. Beaker B: In another 25 mL beaker, add 2mL of ethylene diamine followed by 2mL of 6N HCL.
(For neutralization of ethylene diamine).
3. Transfer solution of beaker (A) to beaker (B).
4. 1mL of H2O2 is added to the solution and then heated at 280-300 ℃ with constant stirring until
it becomes 1/3rd in volume.
5. Cool to room temperature.
6. Put it in ice bath for 10 min.
7. Add 5 mL of conc. HCL (12 N) and stir it for 5 min. at room temperature.
8. 5ml of ethanol is to be added if it does not precipitate.
9. Dry and weigh the obtained crystals.
Molar Calculations:
The theoretical yield of [Co (en) 3] Cl3 is 0.01×345.69gm = 3.45gm.
4CoCl2.6H2O + 2C2H4(NH2) (s) + 2HCl + H2O2
4[Co(en)3]Cl3 + 2H2O
Precautions:
1. This experiment involves some very hazardous chemicals such as H2O2 and conc. HCl.
Soavoid direct contact with them and work carefully, thoughtfully and slowly.
2. We should know the appropriate procedure about what to do and in what sequence,
because any disordered steps can cause fire.
3. Waste should be dispose into the lab inorganic waste containers only.
Result:
1. The weight of [Co(en)3]Cl3crystals is…………………mg
2. The yield was found to be………………%
3. The crystals are . ……………in color.
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature:
Example Questions:
1. Why Co3+ complexes are of interest?
2. What are chelates?
3. Give examples of bidenatate , tridentate and hexadentate ligands?
4. What is crystallization? How does it happen?
5. Give example of chiral complexes.
6. What are enantiomers? Draw some examples.
7. What is meant by racemic mixture?
4
Aldol Condensation Reaction
Objective:
To prepare Tetraphenylcyclopentadienone using two reactants.
Apparatus and chemicals required: Dibenzyl Ketone (1,3 diphenyl-2-propanone), Benzil , KOH,
EtOH Beaker, flask, ice bath, condenser, weighing balance, filter paper, spatula, butter paper,
Buchner funnel, water heater etc.
Theory:
In this experiment, we conduct an interesting aldol condensation that involves one ketone that
has α- hydrogen atoms (dibenzyl ketone) and one that does not (benzil). Thus, dibenzyl ketone
will serve as thenucleophile, because it will donate a proton to a base to form an enolate.
Reaction for this can be written as shown in Figure 1:
Figure 1: Aldol reaction
You can work out the mechanism for the reaction by forming an enolate from dibenzyl ketone
in base, allowing it to attack on carbonyl group in benzil, and eliminating water from the
adduct. Repeat the process with the remaining α-hydrogen atoms while closing the fivemembered ring. The final product is a purple solid. Mechanism can be shown in Figure 2 as
shown below:
Figure 2: Mechanism of the aldol condensation reaction
Procedure:
1) Mix 210 mg of benzil and 210 mg of Dibenzyl ketone and 5 ml of ethanol in a small round
bottom flask.
2) Shake the mixture until it becomes uniform.
3) After shaking well, attach a reflux condenser to the flask and heat the mixture on a steam
bath till the solid gets dissolved completely. At the same time take 3 mL of ethanol in another
flask and mix 0.3 g KOH to it.
23 | P a g e
4) When the first flask mixture starts boiling add the mixture of second flask (ethanol + KOH).
5)
Using a Pasteur pipette, add drop-wise ethanolic potassium hydroxide solution
downward through the condenser into the flask. The mixture will immediately turn deeppurple.
6) Raise the temperature of hot water bath to 85ºC and heat the mixture with stirring for
15minutes.
7) At the end of heating period, remove the flask from hot water bath and let it be cooled
toroom temperature.
8) Place the flask in the ice-water bath (for 5 min) and allow the flask to come to the
temperature of the ice-bath and after the complete crystallization of product, collectthedeep
purple crystals on a Büchner funnel. Allow the crystals to dry in air.
9) Weigh the crystals and record the yield directly in your notebook.
10)Clean your work area.
The whole procedure can be shown as:
Precautions:
1) Lab safety rules must be followed
2) Chemicals and apparatus must be handled carefully
3) Foaming may occur while heating the round bottom flask
4) Sudden cooling of round bottom flask may result in breaking, So let it be
cooled down to Room temperature first.
5) Crystals must be washed with ethanol.
Results:
The weight of the crystals gained is......................
Percentage yield is......................
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature :
Example Questions:
1. Give example of compounds that can undergo self-aldol reaction.
2. Draw the structure of compound that gives:
(a)
An aldehyde as product in acidic medium.
(b)
A ketone in basic medium
3. How many α-hydrogens are present in dibenzyl ketone.
4. Complete the following reactions given below:
43
5
Critical Micelle Concentration of a Surfactant
Objective:
Determination of Critical Micelle Concentration of a surfactant by conductivity method.
Apparatus: Conductivity meter, Conductance Cell, Magnetic stirrer with spin bar, volumetric
flask(100 mL), beaker (25 mL, 50mL (2), 100mL(2), 500 mL,), burette (50 mL), pipette (10 mL).
Chemicals required: CetylTrimethyl Ammonium Bromide (CTAB), distilled water.
Introduction:
Figure 1: Example of Surfactant molecules
Surfactants are water-soluble amphiphilic molecules that consist of a non-polar hydrophobic
part(usually a hydrocarbon or fluorocarbon chain) and a polar hydrophilic part (head group) as
shownin Figure 1. The hydrophilic head group can be nonionic, anionic, cationic, or zwitter-ionic.
The balance between hydrophobic and hydrophilic parts gives special properties to surfactants,
e.g. high affinity to adsorb at interfaces and association in solution to form micelles. Soaps and
detergents are common examples of surfactant. The polar head group is soluble in water while
the hydrophobic group is insoluble. When surfactants are dissolved in water they can selfassemble spontaneously beyond a certain concentration. In the assembled structure, the polar
head groups are exposed to water while the hydrophobic tails interact with each other and
exclude water. This is called a micelle (Figure 2) and most commonly these are spherical in shape.
Figure 2: Micelle formation using surfactant molecules.
The concentration at which surfactants start to form micelles is called critical micelle
concentration (CMC). In ionic surfactants, the polar head group is ionic and is associated with a
counter ion. When an ionic surfactant dissolves in water the solvated ions conduct electricity. This
property can be used to determine the CMC of the surfactant using a conductance cell. When a
conductance cell is immersed in de-ionized water, the cell shows very little background
conductance. When an aqueous solution of an ionic surfactant is added to the cell in small aliquots
the conductance increases in a linear manner. Beyond the CMC, there is a change in the rate at
which conductance increases with added surfactant. When the conductance of the solution is
plotted against the concentration of surfactant, a change in the slope of the plot is observed at
CMC. Each surfactant has a characteristic CMC at a given temperature and salt concentration.
43
Several experiments, including light scattering and NMR, show that below the CMC, the surfactant
exists mainly as solvated monomeric species, whereas above the CMC these monomers undergo
self-assembly to form roughly spherical structures (having an overall diameter of ~2-5 nm) known
as micelles. Micelles can be normal or reverse depending on the nature of surfactant (Figure 3).
Micelles are the simplest of all self-assembly structures. The CMC of a surfactant can be obtained
by different techniques, which in general are based on the measurement of a magnitude that
shows an abrupt change at CMC. The surface tension at the air/water interface and the electrical
conductivity of a solution are examples of such magnitudes.
Figure 3: Schematic demonstrating the Normal micelles and reverse micelles.
Conductometry:
The electrical conductivity is a magnitude that describes the ability of a material or solution to
conduct an electric current. The electrical conductivity of a solution depends on the number and
mobility of ions and charged particles present in the solution. In the case of ionic surfactants,
the electrical conductivity increases as the surfactant concentration increases. As when ionic
substances are dissolved in water, the solvated ions make the solution conducting. The electrical
conduction of these solutions obeys Ohm’s law.
However, the formation of micelles can affect the general conductivity trend of the ionic
solution. Below the CMC, the addition of surfactant to an aqueous solution causes an increase
in the number of charge carriers and consequently, an increase in the conductivity. Above the
CMC, further addition of surfactant increases the micelle concentration while the monomer
concentration remains approximately constant (at the CMC level). Since a micelle is much larger
than a surfactant monomer it diffuses more slowly through solution and so is a less efficient
charge carrier. A plot of conductivity against surfactant concentration is, thus expected to
showa break at the CMC. The CMC can be obtained from the inflection point (intersection of
linear fits) in the curve conductivity versus surfactant concentration.
Therefore, in these experiments, the change in conductance of the solution will be used to
determine the critical micelle concentration of surfactant.
A.
1.
2.
3.
Procedure:
In this experiment, a conductivity meter is used to measure the conductivity of a given surfactant.
The concentration of surfactant in the solution is increased by continuous addition of other
concentrated surfactant solution. Please carry out the lab work according to the following
instructions:
Preparation of CTAB standard solution
Prepare a 4 mM aqueous solution of CTAB (Molecular Weight =364.45g/mol) in a 100 mL
standard flask and mark it as sample A.
Note down the exact amount to be weighed in the results and calculation section.
The contents are carefully shaken to ensure uniform concentration and the shaking mustbe
performed carefully to avoid frothing.
B. Conductivity Measurements
1. Firstly, note down the cell constant for the conductivity cell.
2. Measure 25 mL of de-ionized water using a pipette/measuring cylinder and pour into a100
mL beaker containing a magnetic spin bar.
3. Place the beaker on a magnetic stir plate and stir the water.
4. After thoroughly rinsing the conductivity electrode, immerse it into the beaker containingwater
and measure the background conductivity of the solvent water.
5. Fill a burette up to the zero mark with the CTAB solution Sample-A.
6. Run 0.5 mL of the sample-A through burette to the beaker and measure the
conductance.
7. Repeat procedure (6) for 40 more aliquots (each of 0.5 mL added to the solution) andnote
down the conductance.
8. The solution should be gently stirred with a magnetic stirrer throughout the experiment.
9. Repeat the procedure (2)-(8) with 0.3 mL aliquots added 40 times for other CTAB
solutions, in case provided.
10. Clean working table and apparatus after finishing the experiment.
Precautions:
1. The solution must be prepared slowly to avoid frothing.
2. The stirring is controlled not to be too fast during the experiment to avoid the formationof
bubbles as bubbles can affect the conductivity.
3. CTAB solution is added slowly to the water to prevent the formation of bubbles/frothing.
Results and Calculations:
 Amount of CTAB weighed for 4mM 100mL CTAB solution……………..
(a) Conductivity recorded for aqueous CTAB solution (sample A)
43
S.No.
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
Volume of stock
solution of aqueous CTAB
added (mL)
(V1)
Total Volume of
solution in Beaker
(V2)
Conductance
(μS)
Conductivity
(μS/cm)
{CellConstant0.5421}
Concentration of
CTAB in solution
(M2)
1. Fill in the table and Plot the experimental data of conductivity versus surfactant
concentration. Determine the C.M.C. of CTAB from the graphs (intersection of linear
fits).
2. The CMC value for aqueous CTAB has been found to be......................
3.
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature:
43
Example Questions:
1) What electrodes are used in the conductance cell?
2) Write down the units for the following quantities: resistance, conductance, resistivity, and
conductivity.
3) How the conductance for strong electrolyte and for weak electrolyte varies with
concentration?
4) What does the slope of conductivity versus concentration plot for a strong electrolyte
measure?
5) When a voltage is applied across a conductance, electrolysis of the electrolyte is a potential
problem. How is this overcome when measuring conductance in a conductance cell?
6) Draw a cartoon structure of a surfactant molecule and a spherical micelle. What is the typical
size of a micelle?
7) In the conductance versus concentration plot mentioned above, there is a change in the slopeat
CMC. Why?
43
6
Qualitative estimation of caffeine by FTIR spectroscopy
Objective:
Qualitative estimation of caffeine content using FTIR with ATR technique.
Equipment: Bruker ALPHA II FT-IR, ATR accessories, standard flask, dropper, Kimberly-Clark
wipes/tissue papers, 25 mL volumetric flask
Chemicals: Sample: caffeine solutions (0.1M, 0.5M, 1M, 1.5M in 25 mL CHCl3; used 25 mL
volumetric flask).
Solvents: Chloroform (for sample preparation), isopropanol (for cleaning ATR crystal).
Theory:
Mid-Infrared (IR) spectroscopy is an extremely reliable and well recognized fingerprinting
method. Simply, it is the absorption measurement of different IR frequencies by a sample
positioned in the path of an IR beam. The main goal of IR spectroscopic analysis is to determine
the chemical functional groups in the sample. Different functional groups absorb characteristic
frequencies of IR radiation. Using various sampling accessories, IR spectrometers can accept a
wide range of sample types such as gases, liquids, and solids. Thus, IR spectroscopy is an
important and populartool for structural elucidation and compound identification. Traditionally
IR spectrometers have been used to analyze solids, liquids and gases by means of transmitting
the infrared radiation directly through the sample with a sample thickness not more than a few
tens of microns. This needs careful preparation of solid sample i.e.,
a) Grinding the solid sample to fine powder, and
b) Evenly dispersing it in a matrix.
KBr is probably the most widely used matrix material. Liquids are measured in form of a thin film.
Fourier-transform infrared (FTIR) spectroscopy is based on the idea of the interference of
radiation between two beams to yield an interferogram. The latter is a signal produced as a
function of the change of path length between the two beams. The two domains of distance
andfrequency are interconvertible by the mathematical method of Fourier-transformation.
The basic components of an FTIR spectrometer are shown schematically in Figure 1. The
radiationemerging from the source is passed through an interferometer to the sample before
reaching a detector. Upon amplification of the signal, in which high-frequency contributions
have been eliminated by a filter, the data are converted to digital form by an analog-to-digital
converter and transferred to the computer for Fourier-transformation.
Figure 1: Basic components of FTIR spectrometer.
For a molecule to show infrared absorptions it must possess a specific feature, i.e. an electric
dipole moment of the molecule must change during the vibration. This is the selection rule for
infrared spectroscopy. Figure 2 illustrates an example of an ‘infrared-active’ molecule, a
heteronuclear diatomic molecule. The dipole moment of such a molecule changes as the bond
43
expands and contracts. By comparison, an example of an ‘infrared-inactive’ molecule is a
homonuclear diatomic molecule because its dipole moment remains zero no matter how long
the bond.
Figure 2: Change in the dipole moment of a heteronuclear diatomic molecule.
Modes of Vibration
The interactions of infrared radiation with matter may be understood in terms of changes in
molecular dipoles associated with vibrations and rotations. For a diatomic molecule, only one
vibration that corresponds to the stretching and compression of the bond is possible. This
accounts for one degree of vibrational freedom.
Polyatomic molecules containing many (N) atoms will have 3N degrees of freedom. Looking
first at the case of molecules containing three atoms, two groups of triatomic molecules may
be distinguished, i.e. linear and non-linear. A non-linear B–A–B type triatomic molecule has
three modes, two of which correspond to stretching motions, with the remainder
corresponding to a bending motion. A linear type triatomic has four modes, two of which have
the same frequency, and are said to be degenerate. Two other concepts are also used to explain
the frequency of vibrational modes. These are the stiffness of the bond and the masses of the
atoms at each end of the bond. The stiffness of the bond can be characterized by a
proportionality constant termedtheforce constant, k (derived from Hooke’s law). The reduced
mass, μ, provides a useful way of simplifying our calculations by combining the individual
atomic masses, and may be expressed as follows:
The equation relating the force constant, the reduced mass and the frequency of IR absorption is:
Recently the technique of attenuated total reflectance (ATR) revolutionized solid and liquid
sample analysis because it combats the most challenging aspects namely sample preparation
andspectral reproducibility. An attenuated total reflection accessory operates by measuring
the changes that occur in a totally internally reflected infrared beam when the beam comes
into contact with a sample (indicated in Figure 3). An infrared beam is directed onto an optically
densecrystal with a high refractive index at a certain angle. This internal reflectance creates an
evanescent wave that extends beyond the surface of the crystal into the sample held in contact
with the crystal. It can be easier to think of this evanescent wave as a bubble of infrared that
sits on the surface of the crystal. This evanescent wave protrudes only a few microns (0.5 μ - 5
μ) beyond the crystal surface and into the sample. Consequently, there must be good contact
between the sample and the crystal surface. In regions of the infrared spectrum where
the
sample absorbs energy, the evanescent wave will be attenuated or altered. The attenuated energy
from each evanescent wave is passed back to the IR beam, which then exits the opposite end of
the crystal and is passed to the detector in the IR spectrometer. The system then generates an
infrared spectrum.
There are a number of crystal materials available for ATR. Zinc Selenide (ZnSe) and Germanium are
by far the most commonly used for HATR sampling while diamond is the best crystal choice due
to its robustness and durability. As with all FT-IR measurements, an infrared background is
collected, in this case, from the clean ATR crystal. The crystals are usually cleaned by using a
solvent soaked piece of tissue. Typically water, methanol or isopropanol are used to clean ATR
crystals. The ATR crystal must be checked for contamination and carry over before sample
presentation, this is true for all liquids and solids.
Figure 3: Attenuated Total Reflection Cell
Methods for sample preparation
1.
IR spectroscopy is used for the characterization of solid, liquid or gas samples. Material
containingsample must be transparent to the IR radiation. So, the salts like NaCl, KBr are only
used.
Sampling of solids
Various techniques used for preparing solid samples are as follows
43
a)
Mull technique: In this technique, the finely crushed sample is mixed with Nujol (mulling agent)
in n a marble or agate mortar, with a pestle to make a thick paste. A thin film is applied onto the
salt plates. This is then mounted in a path of IR beam and the spectrumis recorded.
b)
Solid run in Solution – In this technique, solid sample may be dissolved in a non- aqueoussolvent
provided that there is no chemical interaction with the solvent and the solvent is not absorbed in
the range to be studied. A drop of solution is placed on the surface of alkali metal disc and solvent
is evaporated to dryness leaving a thin film of the solute.
c)
Case film technique – If the solid is amorphous in nature then the sample is deposited onthe
surface of a KBr or NaCl cell by evaporation of a solution of the solid and ensured that the film is
not too thick to pass the radiation.
d)
Pressed pellet technique – In this technique, a small amount of finely ground solid sampleis mixed
with 100 times its weight of potassium bromide and compressed into a thin transparent pellet
using a hydraulic press. These pellets are transparent to IR radiation and it is used for analysis.
2.
Sampling of liquids
Liquid sample cells can be sandwiched using liquid sample cells of highly purified alkali
halides, normally NaCl. Other salts such as KBr and CaF2 can also are used. Aqueous solvents
cannot be used because they cannot dissolve alkali halides. Organic solvents like chloroform
can be used. The sample thickness should be selected so that the transmittance lies between
15-20%. For most liquids, the sample cell thickness is 0.01-0.05 mm. Some salt plates are
highlysoluble in water, so the sample and washing reagents must be anhydrous.
3.
Sampling of gases
The sample cell is made up of NaCl, KBr etc. and it is similar to the liquid sample cell. A sample
cell with a long path length (5 – 10 cm) is needed because the gases show relatively weak
absorbance.
Figure 4: IR absorptions of common functional groups
Procedure:
(a) Sample preparation (caffeine) for FTIR
1. 0.1M, 0.5M, 1M and 1.5M of caffeine samples dissolved in 25 mL of CHCl3 separately
(Volumetric flask, 25 ml) and shaken properly so that maximum amount of caffeine gets
dissolved in CHCl3.
2. Chloroform layer might contain impurities; therefore, it is recommended to filter it again
with the help of silica gel.
3. A transparent clear solution of caffeine dissolved in chloroform was obtained.
4. This caffeine samples are used for FTIR measurements.
(b) Recording FTIR spectrum of caffeine in chloroform
1. 5 mL of each of caffeine in chloroform will be used for Recording FTIR spectrum.
2. Record an open beam background spectrum through the clean diamond crystal after
rinsing it with chloroform.
3. Prepare a layer of 0.5 mL of caffeine solution in chloroform on to the crystal.
4. Allow the solvent to dry.
5. Collect the interferograms of the caffeine film formed on ATR crystal.
6. The transmission spectrum can be transformed into an absorption spectrum to
getabsorbance value.
7. Clean the caffeine film from the diamond crystal using chloroform before placing
thenext sample for measurement.
8. Repeat steps 1-6 for caffeine in chloroform extracted from coffee.
9. Identify two characteristic bands of caffeine in both samples.
Precautions:
1. Be careful while using the equipment as it is expensive.
2.Prepare the solutions carefully.
Result:
1. Label the bonds present in the IR spectra of caffeine.
2. The characteristic IR band for caffeine appeared at
……………………………………………………………………………………….…
……………….
3. Measure and compare the absorbance value at 1655cm-1 band for both samples to
qualitatively comment on the relative caffeine content for extracted sample A and sample B.
4. Prepare a Plot of absorbance at 1655 cm-1 vs. increasing caffeine concentration as shown in
figure 4) and explain its significance.
Figure 4. Standard curve for caffeine solution as determined by absorption at 1655 cm-1
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature:
43
Example Questions:
1) In which region of the electromagnetic spectrum does infrared radiation occur?
And whathappens to molecule when it absorbs infrared radiation?
2) How is the wavelength controlled in an FTIR spectrometer? What is the
relationshipbetween wavelength and wavenumber?
3) What are the selection rules for FTIR absorption?
4) How does the IR spectrum of molecule N2 look like?
5) Why KBr pellets are used to prepare solid samples in FTIR?
6)
Why diamond crystal is best choice for ATR?
7) Draw the structure of Caffeine and try to assign peaks for all the functional groups present in the
molecule. How Caffeine can affect the human health?
43
43
7
Stokes shift by Fluorescence Spectroscopy
Objective:
To understand the principle of Fluorescence Spectroscopy, to plot the excitation and emission
spectrum of curcumin in solvents respectively ethanol and hexane and find stokes shift by using
fluorescence spectroscopy.
Apparatus: Fluorescence Spectrometer, Quartz cuvettes, standard flask, dropper, tissue paper.
Chemicals used: Curcumin dye (sample), Ethanol, Hexane.
Theory:
Fluorescence is a spectrochemical method of analysis where the molecules of the analyte are
excited by irradiation at a certain wavelength and emit radiation of a different wavelength. The
emission spectrum provides information for both qualitative and quantitative analysis. As shown in
Figure 1 when light of an appropriate wavelength is absorbed by a molecule (i.e., excitation), the
electronic state of the molecule changes from the ground state to one of many vibrational levels in
one of the excited electronic states. The excited electronic state is usually the first excited singlet
state, S1 (Figure 1). Once the molecule is in this excited state, relaxation can occur via several
processes. Fluorescence is one of these processes and results in the emission of light
(Refer to Figure 1 during the following discussion).
Figure 1: Electronic transition energy level diagram
1.
Following absorption, a number of vibrational levels of the excited state are populated. Molecules in
these higher vibrational levels then relax to the lowest vibrational level of the excited state
(vibrational relaxation). From the lowest vibrational level, several processes can cause the molecule
to relax to its ground state. The most important pathways are:
Collisional deactivation (external conversion) leading to nonradioactive relaxation shown inJablonski
diagram (Figure 2).
2. Intersystem Crossing (10-9s): In this process, if the energy states of the singlet state overlaps those
of the triplet state, as illustrated in Figure 1, vibrational coupling can occur between thetwo states.
Molecules in the single excited state can cross over to the triplet excited state.
3. Phosphorescence: This is the relaxation of the molecule from the triplet excited state to thesinglet
ground state with emission of light. Because this is a classically forbidden transition, the triplet
state has a long lifetime and the rate of phosphorescence is slow (10-2 to 100 sec).
4. Fluorescence: Corresponds to the relaxation of the molecule from the singlet excited state to
the singlet ground state with emission of light. Fluorescence has short lifetime (~10-8 sec) so
that in many molecules it can compete favorably with collisional deactivation, intersystem
crossing and phosphorescence. The wavelength (and thus the energy) of the light emitted is
dependent on the energy gap between the ground state and the singlet excited state. An
overall energy balance for the fluorescence process could be written as:
E fluor= Eabs− Evib − Esolv.relax. (1)
Where Efluor is the energy of the emitted light, Eabs is the energy of the light absorbed by the
molecule during excitation, and Evib is the energy lost by the molecule from vibrational relaxation.
The Esolv.relax term arises from the need for the solvent cage of the molecule to reorient itself in the
excited state and then again when the molecule relaxes to the ground state.As can be seen from
Equation (1), fluorescence energy is always less than the absorption energy for a given molecule.
Thus the emitted light is observed at longer wavelengths than the excitation. The corresponding
shift in wavelength is called the Stoke’s shift.
5. Internal Conversion: Direct vibrational coupling between the ground and excited electronic states
(vibronic level overlap) and quantum mechanical tunneling (no direct vibronic overlapbut small
energy gap) are internal conversion processes. This is a rapid process (10-12 sec) relative to the
average lifetime of the lowest excited singlet state (10-8 sec) and therefore competes effectively
with fluorescence in most molecules.
Other processes, which may compete with fluorescence, are excited state isomerization,
photoionization, photo dissociation and acid-base equilibria. Fluorescence intensity may also be
reduced or eliminated if the luminescing molecule forms ground or excited state complexes
(quenching). The quantum yield or quantum efficiency for fluorescence is therefore the ratio of
the number of molecules that luminesce to the total number of excited molecules.
Figure 2: Showing Jablonski Diagram
Procedure:
A. Excitation spectrum of Curcumin in ethanol
In this part of the experiment, we will investigate the variation of fluorescent intensity
when thewavelength of excitation is varied with fixed emission monochromatic
wavelength.
1) Using a glass dropper fill the optical cell with ethanol solution and record the excitation
spectrum and find out the excitation wavelength corresponding to absorption maxima.
2) Set excitation range from 300nm to 500nm.
3) Keep the excitation and emission slit width as 5nm.
4) Set emission wavelength as 520nm.
5) Note the wavelength at excitation maxima.
43
B. Emission spectrum of Curcumin in ethanol
In this part, we will determine the variation of fluorescent intensity with variation in
wavelength of emission. This study is carried out by leaving the excitation monochromator fixed
while varying the wavelength of the emission monochromator.
Use the same sample from part A.
1) Set the excitation wavelength to the wavelength of maximum response determined in Part A.
2) Set emission wavelength range to 400-700 nm.
3) Note the emission wavelength corresponding to maximum fluorescence intensity.
4) Repeat the whole procedure for the second sample with hexane. Lab instructor will help in
recording the spectra.
Precautions:
1. Be careful while using the equipment.
2. Handle and wash the cuvettes carefully.
3. Please shut down the main power of the equipment after use.
Result:
The emission spectrum peak of curcumin in
a) Ethanol was found at .................................. nm
b) Hexane was found at ................................... nm
The stokes shift of curcumin in
a) Ethanol is .................................. nm
b) Hexane is ................................... nm
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature:
Example Questions:
1. Give the structure of curcumin.
2. Qualitatively comment on the effect of solvent polarity on the spectra.
3. What is the difference between Fluorescence and Phosphorescence?
4. Explain Radiative and Non-Radiative Deacay.
43
8
Contact Angle
Objective:
Determination of Surface contact angle, surface tension and surface free energies of different
solvents and substrates respectively.
Apparatus: Contact angle meter, Surface or substrate, tissue paper.
Chemicals used: n-Heptane, n-Octane, n-Undecane, n-Tetradecane, n-hexadecane, Cycloocatne,
Bicyclohexyl, Acetone, Hexane, Ethanol.
Theory:
The interaction between a liquid and a solid involves three interfaces; the solid-liquid interface,
the liquid-vapor interface and the solid-vapor interface. Each of these interfaces has an
associatedsurface tension, γ, which represents the energy required to create a unit area of that
particular interface.
Figure 1: Diagram of the contact angle
The angle between a liquid drop and a solid surface, Young’s contact angle, is related to the
surface tensions of the three interfaces according to the relationship:
cos θY = (γSolid-Vapor - γSolid-Liquid) / γLiquid-Vapor
(1)
The magnitude of Young’s contact angle is a result of energy minimization. If the liquid-vapor
surface tension is smaller than the solid-vapor surface tension (γLV < γSV), the liquid-solid
interface will increase to minimize energy. As the drop wets the surface, the contact angle
approaches zero.
Measurement methods for contact angle
1. Half angle method (θ/2): A droplet rest on a solid surface shapes a part of sphere. The
cross sectional view of this droplet is captured through CCD camera. Then, both the left
and rightends and the apex of the droplet are detected with image processing, and the
radius of the droplet base (r) and height (h) is obtained.
The contact angle θ can be obtained with the substitution of the r and h in the equation
below:
tanθ = h/r
2. Tangent method: This method regards the droplet’s shape near the end points
(three-end-points) as a part of circle. From the three points a virtual circle can be
drawn. The centre of the circle is defined and a tangent line at the point can be
drawn.
The angle between the tangent line and the droplet’s base line is the contact angle of
one end. Similarly the contact angle of other end can also be measured.
43
Tangent method can obtain both contact angles on the left and right side of the
droplet respectively. If there is a difference between the right and the left value, tangent
method is used.
3.
Curve fitting methods: Curve fitting method suppose that the droplet fits the
part of circle or ellipse. A curve is determined by fitting to all the observation points
on the droplet profile in specified area (fit section) with the least square method. This
calculation determines the parameter of either circle or ellipse and the contact angle
isfigured out by the differential coefficient at the droplet end.
The critical surface tension of a material, γc, is a measure of the surface’s wettability and
it is proportional to the surface free energy of the material. A liquid with a surface tension
less than or equal to the critical surface tension of a particular material will “wet” that
surface, i.e. the contactangle will be less than or equal to 90o. A material’s critical surface
tension can be determined from a Zisman Plot, which measures variation in Young’s
contact angle as a function of the surface tension of a series of liquids. Zisman noticed
empirically that a plot of cos(θ) versus γLV is often linear. The value for which cos(θ)
extrapolates to 1 is termed the critical surface tension. . A typicalZisman Plot is shown in
Figure 2.
Figure 2: A typical Zisman Plot
Procedure:
1.
Clean the given substrate with ethanol and place it on the sample stage.
2.
Clean the syringe with acetone and pre-rinse turning the syringe upside down
and thenfill the syringe with the test liquid and secure in the syringe holder above the
sample stage.
3.
Operating the instrument:
I.
a)
b)
c)
d)
e)
f)
g)
Contact Angle Measurement
Click on FAMAS (software on the desktop).
Click Setup ---> Image Monitor.
Focus the needle manually first and then click on Needle Point Detection button.
Click on C.A measurement (sessile drop).
Click on Measure button in the image monitor and then make a droplet.
Wait till the droplet is deposited on the surface. After the droplet is
deposited immediately contact angle is displayed on the screen.
Double click the result obtained and a window will open.
h) In the Method box there will get four different methods (A Half Angle, Circle
Fitting, Ellipse Fitting and Tangent method) by clicking on which we can obtain
the desiredcontact angle.
i) Click on File ---> Save Data.
j) Repeat the same procedure for all other substrates.
II.
Interfacial Tension measurement
a) Click Setup ---> Image Monitor.
b) Focus the needle manually first and then click on Needle Point
Detectionbutton.
c) Click on I.T measurement (Pendant drop).
d) Click on Measure button in the image monitor and then make a droplet.
e) Check that the droplet remains in the air and the interfacial
tension isdisplayed on the screen.
f) Click on File ---> Save Data.
g) Repeat the same procedure for all the liquid samples.
III.
Surface Free Energy
measurement a)
4. Zisman plot:
Plot the mean cosine value for each liquid against its surface tension. Find the best linear
fit and extrapolate this line to find the surface tension value that gives a cosine value of 1.
Precautions:
1. Handle and wash the syringe carefully.
2. Be careful while using the equipment.
43
1.
Result:
Contact angle of Water with different surfaces:
Surface
Mean θ for surface
Half Angle
Circle Fitting
Ellipse Fitting
Tangent
Teflon plate
Acrylic sheet
Stainless steel
Glass slide
Aluminum sheet
2. Free energies of different solvents on Teflon plate as substrate:
Solvent
Free energy value
Water
Glycerol
Benzyl alcohol
Hexadecane
Heptadecane
3. Plot the mean cosine value for each liquid against its surface tension. Find the best linear fit
and extrapolate this line to find the surface tension value that gives a cosine value of 1.
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature:
43
Example Questions:
1. What is the contact angle a measurement of and where can it be found?
2. What do you expect to see if the liquid surface tension is less than or equal to
thecritical surface tension of a surface?
3. Why is it difficult to measure the surface free energy of a solid? How can the
Zismanplot be used to estimate this value?
4. What is hydrophobicity and hydrophilicity? Give an example of a hydrophobic
andhydrophilic surface encountered in day-to-day life.
43
9
Study of Redox Reactions using Cyclic Voltammetry
Objective:
(a) To understand the theory and working principle of Cyclic Voltammetry (CV)
(b) To perform CV on ferricyanide solution and understand its electrochemical properties for
example Ep, Diffusion rate, Ip
Apparatus: CH Instrument Electrochemical Workstation, electrodes: Pt electrode working
electrode (3-4 mm diameter, planar), Pt wire counter electrode and Ag/AgCl reference electrode,
electrochemical cell (small volume), Polishing kit], Volumetric flasks (100 mL) with ground glass
stoppers and pipettes.
Chemical used: Potassium ferricyanide [K3Fe(CN)6], Potassium nitrate [KNO3], distilled water.
Theory:
Cyclic Voltammetry (CV) is popular for its relative simplicity and its high information content. It is
used most often as a diagnostic tool for elucidating electrode mechanisms.
Figure 1: A typical waveform used and the corresponding Cyclic Voltmmogram (CV) .
The traces in Figure 1 are called cyclic voltammograms. The x-axis represents a parameter that is
imposed on the system, here the applied potential (E), while the y-axis is the response, here the
resulting current (i) passed. Each trace contains an arrow indicating the direction in which the
potential was scanned to record the data. The arrow indicates the beginning and sweep direction
of the first segment (or “forward scan”), and the caption indicates the conditions of the
experiment.
A crucial parameter can be found in the caption of Figure 1: “υ = 100 mV/s”. This value is called the
scan rate (υ).
It indicates that during the experiment the potential was varied linearly at the speed (scan
rate) of 100 mV per second. The waveform of the voltage applied to a working electrode in CV is
triangular shaped (i.e., the forward and reverse scan).
Since this voltage varies linearly with time, the scan rate is the slope (V/s).
Figure 2 CV for the reduction of 4.8 mM ferricyanide in 0.1 M KCl at a 1.0 mm glassy carbon
electrode at a scan rate of 100 mV/s.
An example of a CV for the reduction of ferricyanide to ferrocyanide is shown in Figure 2. In
this experiment, the basics of CV will be illustrated by looking at the one electron reduction of
ferricyanide to ferrocyanide. This redox couple exhibits nearly a reversible electrode reaction
without any complications of proceeding or post chemical reactions. Thus,
ferricyanide/ferrocyanide couple has been a popular choice through the years to use as a standard
to demonstrate CV experiment.
This equilibrium is described by the Nernst equation (eq 1). The Nernst equation relates the
potential of an electrochemical reaction. The peak shape of the reductive and reverse oxidative
current versus electrode potential curve (I-E) in Figure 2 is typical of an electrode reaction in which
the rate is governed by diffusion of the electroactive species to a planar electrode surface. That
is, the rate of the electron transfer step is fast compared to the rate at which ferricyanide is
transported (diffuses) from the bulk solution to the electrode surface due to a concentration
gradient, as ferricyanide is reduced to ferrocyanide. In such a case, thepeak current, Ip, is governed
by the Randle-Sevcik relationship:
Ip = k n3/2 A D1/2Cb υ½ ............................................ (1)
where the constant k = 2.72 x 105 ; n is the number of moles of electrons transferred per mole
of electroactive species (e.g., ferricyanide); A is the area of the electrode in cm2 ; D is the diffusion
coefficient in cm2/s; Cb is the solution concentration in mole/L; and υ is the scan rateof the potential
in volt/s.
The Ip is linearly proportional to the bulk concentration, Cb, of the electroactive species, and
the square root of the scan rate, υ1/2. Thus, an important diagnostic is a plot of the Ip vs. υ 1/2. If the
plot is linear, it is reasonably safe to say that the electrode reaction is controlled by diffusion,
which is the mass transport rate of the electroactive species to the surface of the electrode across
a concentration gradient.
The thickness, δ, of the diffusion layer can be approximated by δ ~ [D t]1/2, where D is the
diffusion coefficient and t is time in seconds. A quiet (i.e. unstirred solution) is required. Another
important diagnostic for characterizing the electrode reaction is the value of the peak potential,
Ep.
When the rate of electron transfer is fast, the Ep value will be independent of the scan rate;
indicating a reversible electrode reaction. Then the difference between the anodic peak potential,
Epa, and the cathodic, Epc value will be equal to 57 mV/n.
The electrode reaction during the scan from +600 mV to 0.0 mV is
FeIII(CN)63- + eFeII(CN)6 4Eo = 0.361V versus NHE at 25ºC
(2)
The electrode potential, E, is thermodynamically determined by the Nernst relationship:
E = Eo + (0.0591/n) log (aox/aR)
(3)
where aox is the activity of the oxidized species, ferricyanide in the present case, and aR is the
activity of the reduced species, ferrocyanide. Experimentally, the activity is affected by the
presence of other ions. For practicality, formal potential (Eo’) is defined that make use of
concentration in mole/L rather than activity (which we do not know). Thus, the Nernst becomes :
E = Eo’ + (0.0591/n) log [Cox/CR]
... (4)
The Formal Potential, Eo’, depends on the nature of electrolytes in the solution. Table 1 is thelist of
Formal Potentials for ferri/ferrocyanide in aqueous solutions at 25ºC versus NHE:
Fe(CN)63- + e- = Fe(CN) 4Table 1: Formal Potentials for ferri/ferrocyanide in aqueous solutions at 25ºC vs. NHE
S. No.
1.
2.
3.
Ferri/ferrocyanide
(in different solvents)
0.1 M HCl
1.0 M HCl
1.0 M HCLO4
Eovalue
0.56 V
0.71 V
0.72 V
The potential, E, at any point along the I-E wave should reflect the concentration of the
ferricyanide and ferrocyanide at the electrode surface independent of background electrolyte.
Irreversibility is when the rate of electron transfer is sufficiently slow so that the potential no
longer reflects the equilibrium activity of the redox couple at the electrode surface. In such a case,
the Ep values will change as a function of the scan rate. A unique feature of an electrochemical
reaction is that a ‘reversible’ electrode reaction at low scan rates can become ‘irreversible’ at high
scan rates.
Figure 3: Schematic representation of electrochemical cell for CV experiment.
The working electrode is Pt electrode; it carries out the electrochemical event of interest. The
type of working electrode can be varied from experiment to experiment to provide different
potentialwindows or to reduce/promote surface adsorption of the species of interest.
The reference electrode is Ag/AgCl electrode, it has a well defined and stable equilibrium
potential. It is used as a reference point against which the potential of other electrodes can be
measured in an electrochemical cell.
The counter electrode is Pt wire. The purpose of the counter electrode is to complete the
electrical circuit. Current is recorded as electrons flow between the WE and CE.
Procedure:
1. Polishing: Prepare the working glassy carbon electrode by first lightly polishing the
electrode surface with 1 μm or smaller particles of alumina (wet) on a flat polishing plate.
Wash the electrode carefully with pure water to remove any alumina. If a sonicator is
available, fill a small beaker with de-ionized water, place the electrode (tip down) and
sonicate for 1 minute. Remove, rinse with pure water and touch the edges of the tip with
clean soft lint-free tissue paper but do not touch the electrode surface.
2. Prepare 2, 6 and 10 mM ferricyanide in 1M KNO3 in 100 mL volumetric flasks.
3. Switch on the electrochemical workstation. Make the connections for three
electrodeassembly by connecting appropriate crocodile clips to the respective
electrode.
4. Turn on the computer and click on the CH1660E Electrochemical Workstation(Software).
5. Click on Setup ---> Technique ---> CV- Cyclic Voltammetry.
6. A window will open in that window fill the following parameters and click on Ok.
a) Initial E (V) = 0
b) High E (V) = 0.6
c) Low E (V) = 0
d) Final E (V) = 1
e) Scan rate (V/s) = 0.01/0.05/0.1
f) Sweep Segments = 2
g) Sample Interval (V) = 0.001
h) Sensitivity (A/V) = 1.e-006/ 1.e-005
i) Quiet time (s) = 2
7. Run a CV scan from an initial potential (Ei) of 05.0 V to 0.6 V and then back to 0.0V at
ascan rate of 50 mV/s for 4 cycles.
8. Run duplicate CVs on each ferricyanide solution (2, 6 and 10 mM) at the scan rate
of100mV/s.
9. Run duplicate CVs on the 2 mM ferricyanide solution at scan rates of 20, 50 and 100 mV/s.
10. Label and save each CV with the “save function” if using electrochemical workstation
orprint out a hardcopy of what you want to save from the potentiostat.
Precautions
1. Note: With computerized potentiostats you may be able to use Math function to
determine Ep and Ip values. Similarly, the Ip values can often be corrected for the
background charging current.
2. Write a short summary of what you did in this experiment, noting any deviations or
substitutions in the procedure. Show example cyclic voltammograms.
Results:
1. Plot Ip versus concentration of ferricyanide. Fit it linearly. Determine the concentration of the
unknown sample of ferricyanide from this calibration plot.
2. Determine the Eo’ value from the voltammograms. If the values vary with the scan rate, plot them
versus the scan rate and extrapolate to obtain the Eo ’ at zero scan rate. Compare this value with
the tabulated formal potential of ferri/ferrocyanide in 0.1 M HCl.
3.
Tabulate the difference between Epc and Epa values – are they close to the theoretical valuefor a
reversible electrode reaction? If not, can you account for the deviation?
4. Plot Ipa and Ipc vs. ν1/2, and from the slope, determine the value of the diffusion coefficient (must
measure the electrode area). How does your value compare to the literature one of
0.62 x 10-5 cm2/s? Should there be a difference in the diffusion coefficient between ferricyanide
and ferrocyanide? If so, why?
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature :………………………………………………..
Example Questions:
1. What type of waveform is used for Cyclic Voltametry experiments?
2. What is diffusion controlled reaction?
3. What is the difference between a Faradic and non-Faradic reaction?
4. How do you know if a reaction is reversible from CV measurements.
5. How can one calculate electrochemically active surface area of the electrode from the
CVmeasurements?
6. How the current varies with scan rate? Explain.
7. What information can be obtained from CV measurements.
10
Color of Complexes by UV-visible Spectroscopy
Objective:
To Experimentally Identify the Color of Complexes with Help of UV-visible
SpectrophotometryApparatus: UV-visible spectrometer, cuvettes, standard flask, glass
rods.
Chemicals required: CoCl2.6H2O.HCl, [Co(en)3]Cl3, [CuCl4]2-, [Cu(NH3)6]2+, [Co(en)2Cl2]+,
distilled water.
Theory:
Most transition metal complexes are colored as shown in Figure 1. This implies that as white light
is passed through a sample of the complex, some of the wavelengths of the visible spectrum
are absorbed by the sample and the rest transmitted, so the complementary color is imparted
to the complex (see Table 1).
Figure 1: Colored Transition Metal Complexes
Table 1: Color absorbed and color transmitted (complementary color).
Approximate λ range
Color Of Light
(In nm)
Absorbed
Red
700-620
Orange
620-580
Yellow
580-560
Green
560-490
Blue
490-430
Violet
430-380
Color Of Light
Transmitted
Green
Blue
Violet
Red
Orange
Yellow
A preliminary idea of color can be gained by synthesizing different complexes of the same
metal using different ligands and visually observing their color. Spectroscopically, using UVvisible spectrophotometers, the ligands can be quantitatively ranked by the lowest energy
wavelengthsof maximum absorption (λmax). Being a direct function of Δo, the λmax of lowest
energy can be used to accurately generate the spectrochemical series. In general, the lowest
energy (i.e. highest wavelength) absorption maximum corresponds to the Δo transition. The
stronger the ligand, more is its interaction with the metal ion and greater is the corresponding
crystal field splitting; hence, smaller will be the value of λmax. Variation in Δo values with
varying ligands for the same central metal ion gives rise to different colours (absorption
spectra) of metal complexes; based on this variation, a series called the spectrochemical series
has been develop
It arranges the ligands in the increasing order of the crystal field splitting exerted by them.
I-<Br-<S2-<SCN-<Cl-<N3-<F-<OH-<C2O 2-<O2-<H2O<NCS-<py<NH3<en<bipy<phen<NO -<PPh3<CN4
2
<CO
Absorption Band Intensity
There are two selection rules governing the intensity of the bands observed:
1. Laporte Selection Rule: This rule is particularly applicable to centrosymmetric molecules i.e
molecules with an inversion centre. Orbitals and states in such molecules can be described with the
symmetry labels g (gerade) and u (ungerade). Laporte-allowed transitions are those that involve
a change in parity: g-u or u-g. Laporte-forbidden transitions are those involving states having the
same parity: g-g or u-u. d-d transitions are therefore Laporte forbidden as all d-orbitalshave the ‘g’
symmetry.
2. Spin Multiplicity Rule: Transitions between states with different spin multiplicities are
forbidden. Thus, a lower-energy absorption band can be less intense than a higher-energy one if it
violates any of the above selection rules. Sometimes a forbidden transition can get mixed with some
allowed transition nearby and thus become partially allowed itself and thus borrow intensity from
the allowed transition.
Table 2: Intensities of Spectral Bands in 3d Complexes.
Band Type
Spin-forbidden
Laporte-forbidden d-d
Laporte-allowed d-d
Symmetry-allowed (e.g CT)
εmax/M-1 cm-1
<1
20-100
500
1000-50000
Transitions that are not governed by symmetry restrictions like charge-transfer bands have much
higher intensities.
Basic Theory of Absorption Spectroscopy
Absorption spectroscopic methods of analysis rank among the most widespread and powerful
tools for quantitative analysis. The use of a spectrophotometer to determine the extent of
absorption of various wavelengths of visible light by a given solution is commonly is governed by
the Beer-Lambert law as follows:
A  log10(I0/I)
A = εcl
where A is the absorbance of the solution which is measured using the spectrophotometer andis
dimensionless, c is the concentration (M; molar), l is the path length traveled by the light beam
through the sample in cm and ε is the molar absorptivity or extinction coefficient (M-1cm-1). If one
knows the concentration and the path length, then from the observed absorbance (A) the ε value
can be calculated. The ε value is a fundamental characteristic of the species under investigation
and determines the intensity of the spectroscopic transition.
Procedure:
1. Preparation of CoCl2.6H2O.HCl,[Co(en)3]Cl3, [CuCl4]2, [Cu(NH3)6]2+, [Co(en)2Cl2]+.
2. Operating The Visible Spectrophotometer
a. Switch on the power supply from power board.
b. Start the computer system and UV machine.
c. Click on M Wave Professional (software on desktop).
d. Put reference solvent in cuvette and place the cuvette in Cell 1 in UV machine.
e. Click File ---> New ---> Spectrum Scan.
f. Operation ---> Setup ---> Set all the desired parameters ---> ok.
g. Click on Operation ---> Blank (for reference measurement).
h. Put the sample in the cuvette and place the cuvette in the same cell.
i. Click on Operation ---> Start (for sample measurement).
j. The graph will be displayed on the screen.
k. Now click on File ---> Export to Microsoft Excel.
l. For shutting down the computer --->click on close button in software ---> After
shuttingdown computer --> close back switch of machine.
m. Switch off the power supply from power board.
n. Record the UV-Vis spectra of each of the prepared complexes between wavelengths
340-800 nm after proper mixing.
3. Record the UV-visible spectra of each of the prepared complexes between
wavelengths340-800 nm after proper mixing.
Precautions:
1. Handle and Wash the cuvette carefully.
2. Please shut down the main power of the equipment after use.
Results:
For data analysis, fill in the table given below and plot your data graphically for each of the
complexes.
For a comparative study, plot the data for all the complexes of a particular metal in a
singlegraph.
Table 1: Absorbance peaks corresponding to Δo and ε values for the Δo peak.
Complex
λ at Δo Transition
(nm)
Changing ligand
[Co(en)3]3+
CoCl2. 6H2O
[Cu(NH3)6]3+
Changing coordination number
[CuCl4]2[Co(en)3]3+
Changing oxidation state
[Co(en)3]3+
[Co(en)2Cl2]+
Corresponding
Absorbance
ε (M-1cm-1)
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature:
Example Questions:
1. Explain the working principle of UV-Visible Spectroscopy.
UV-Visible spectroscopy is based on the absorption of ultraviolet or visible light by molecules.
When light passes through a sample, specific wavelengths corresponding to electronic
transitions are absorbed, promoting electrons from lower energy states (ground state) to
higher energy states (excited state). The resulting absorption spectrum provides information
about the sample's electronic structure
2. Are there any limitations on Lambert beer law.
Yes, the Lambert-Beer law has limitations. It assumes linearity between absorbance and
concentration, which can deviate at high concentrations due to molecular interactions,
scattering, or chemical changes in the sample. Non-monochromatic light or instrumental
inaccuracies can also lead to deviations.
3. Why the CFSE values vary with the nature of ligand.
The Crystal Field Stabilization Energy (CFSE) depends on the ligand's ability to split the dorbital energies in a coordination complex. Strong field ligands, according to the
spectrochemical series, cause greater splitting, leading to higher CFSE values, while weak
field ligands result in smaller splittings.
4. How CFSE values are related with the absorption of the complex.
CFSE values are directly linked to the energy gap between d-orbitals in a complex. This
energy gap corresponds to the wavelength of light absorbed during d-d transitions. A
larger CFSE leads to absorption at shorter wavelengths (higher energy), while smaller
CFSE shifts absorption to longer wavelengths.
5. Can you see a charge transfer band in the UV-Visible Spectroscopy.
Yes, charge transfer bands are observable in UV-Visible spectroscopy. These arise from
electronic transitions where an electron is transferred between a ligand and the central
metal ion (ligand-to-metal or metal-to-ligand charge transfer). They are typically intense
and occur at distinct wavelengths.
6. Explain with examples the selection rules for electronic spectroscopy.
6
Determination of enantiomeric purity of Naproxen and
Ibuprofen.
Objective:
Determination of Enantiomeric Purity of Naproxen and Ibuprofen.
Apparatus: Polari meter, Beaker (50 mL), Glass rod
Chemicals used: Naproxen tablets, Ibuprofen tablets, methanol.
Theory:
Polarimetry is a sensitive, nondestructive technique for measuring the optical activity
exhibited by inorganic and organic compounds. A compound is considered to be optically active
if linearly polarized light is rotated when passing through it. The amount of optical rotation is
determined by the molecular structure and concentration of chiral molecules in the substance.
Each optically active substance has its own specific rotation.
Enantiomeric excess is the ratio of the observed optical rotation of a sample consisting of
a mixture of enantiomers to the optical rotation of one pure enantiomer. It can be calculated by
the formula:
Figure 1: R and S enantiomers of Naproxen
Naproxen is used to relieve pain from various conditions such as headache, muscle aches,
tendonitis, dental pain, and menstrual cramps. It also reduces pain, swelling, and joint stiffness.
This medication is known as a nonsteroidal anti-inflammatory drug (NSAID). It works by
blocking your body's production of certain natural substances that cause inflammation.
The (S) is safe to use. The (R) isomer is reported to be liver toxin.
Figure 2: R and S enantiomers of Ibuprofen.
Ibuprofen is used to relieve pain from various conditions such as headache, dental pain,
menstrual cramps, muscle aches, or arthritis. It is also used to reduce fever and to relieve minor
aches and pain due to the common cold or flu. Ibuprofen is a nonsteroidal anti-inflammatorydrug
(NSAID). It works by blocking your body's production of certain natural substances that cause
inflammation. This effect helps to decrease swelling, pain, or fever. It is the S form which isthe
pharmacologically active component that inhibits prostaglandin synthesis while the R formhas
no anti‐ inflammatory effect.
Procedure:
1. Dissolve 5 tablets of Naproxen in 15mL of methanol in a beaker
2. Keep the tablets in methanol until the outer layer begin to peel away from the inner
tablet. As soon as this happens, carefully remove the inner tablets from the liquid.
3. Place the 5 inner tablets in 20mL of fresh methanol in a 50 mL flask.
4. Swirl and dissolve the tablets.
5. It will take 20 min to dissolve the tablet at room temperature.
6. Filter the solution to remove the residual material.
7. Evaporate the resulting solution to a volume suitable to use in an available
Polarimetertube (8-9 mL).
8. Transfer all the solution to the Polarimeter tube and measure the optical rotation.
9. Repeat steps 1-8 for Ibuprofen tablets.
Precautions:
1. Be careful while using the equipment as it is expensive.
2. Prepare the solutions carefully.
Result:
The enantiomeric purity of
a) Naproxen is ………………………………
b) Ibuprofen is ………………………………
SIGNED STATEMENT:
I have only worked with the following persons
for this lab experiment. I received no other help and I did not copy another person's work.
Signature:
Example Questions:
1. Define enantiomeric excess.
2. How will you differentiate between R and S configuration in a molecule?
3. Define specific rotation and give its formula.