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Experiment No.1

Measurement of porosity, average pore size and pore size distribution by

using Mercury Porosimeter for porous powder and solid samples

Objective:

To measure the porosity, average pore diameter and pore size distribution of porous solid

samples.

Introduction:

The frication of void space or empty space in a porous solid material is represented by porosity

of that material. The fraction of the volume of voids over the total volume gives the value of

Porosity. The term porosity is used in multiple fields

including pharmaceutics, ceramics, metallurgy, materials, manufacturing, earth sciences, soil

mechanics and engineering. For any porous solid or powdered sample porosity is considered as

one of the very important property.

Mercury is ideal as an intrusion liquid in the porosimetry method because it does not wet nor

react with most materials. By measuring the amount of mercury intruded into the pores of a

powdered or solid sample, the porosimeter give valuable data from which pore size, volume and

distribution can be determined. Normally in porous solid samples different pores are present e.g.

through pores, cross linked pores, blind pores and closed pores (as shown in the figure below).

Closed pores are not accessible to mercury. Hence, pororsimetry does not account for closed

pores.

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Figure 1Schematic representation of different pores(Giesche et al.).

Theory:

Mercury porosimetry is based on the capillary law governing liquid penetration into small pores.This law, in the case of a non-wetting liquid like mercury and cylindrical pores, is expressed by

the Washburn equation:

1( )4 cosDP

..(i)

Where,

D is the pore diameter,

P is the applied pressure,

is the surface tension,

and is the contact angle, all in consistent units. The volume of mercury V penetrating the

pores is measured directly as a function of applied pressure. This P-V information serves as a

unique characterization of pore structure.

Pores are rarely cylindrical; hence the above equation constitutes a special model. Such a

model may not best represent pores in actual materials, but its use is generally accepted as thepractical means for treating what, otherwise, would be a most complex problem. The surface

tension of mercury varies with purity; it is usually accepted value and the value recommended

here is 485 dynes/cm. The contact angle between mercury and the solid containing the pores

varies somewhat with solid composition. A value of 130 is recommended in the absence of

specific information to the contrary.

Mercury extruding from pores upon reduction of pressure is in general accord with the above

equation, but indicated pore diameters are always offset toward larger diameters. This results

from equivalent volumes of mercury extruding at pressures lower than those at which the pores

were intruded. It is also commonly observed that actual pores always trap mercury. The first

phenomenon is usually attributed to receding contact angles being less than advancing ones. The

second is likely due to pore irregularities giving rise to enlarged chambers and inkwell

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iv. Porosimeter

Chemicals required:

i.

Mercuryii. 2-Propanol-for cleaning the sample holder

Results: (for granular activated carbon samples)

1.Pycnometer data:

Skeleton density of GAC= 1.54 g/cc

Skeleton volume of the sample= 4.72 cc

Total volume of the sample= 13.6cc

Considering 60% inter particular gap sample volume will be= 5.44 cc

Porosity of the sample = 13.23%

2. Pycnometer and BET data:

True density of GAC= 1.54 g/cc

True volume of the sample= 0.65 cc/g

Pore volume calculated from BET data= 0.19 cc/g

Porosity of the sample = 22.06%

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3. Porosimeter data:

Pore size distribution

1000 10000 100000

1E-6

1E-5

Differentialintrusion(ml/g/A)

Pore size(A)

Porosity = 8.4182 %

Average Pore Diameter = 6299 A

Comparison:

Samplename

Average Porediameter ()

Porosity(%)

(Pyncometer)

Porosity(%)

(Pyncometer& BET)

Porosity(%)

(Porsimeter)

GAC 6299 13.23 22.6 8.4

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CL 610 (Experimental Methods)

Experiment 2

Karl Fischer volumetric titration

Instructors

Prof. RajdipBandyopadhyaya

Prof. Y S Mayya

T.A. Incharge

Pushkar Ballal

Group: M1

Member 1(133010001)

Member 2 (133010002)

Experiment Date:

Submission Date:

Department of Chemical Engineering

I.I.T. Bombay

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Measurement of moisture content using Karl Fischer volumetric

titration in a sample

Aim:

To determine the moisture content of given samples by Karl Fischer volumetric

titrationtechnique.

Introduction and Principle:

Karl Fischer titration is a widely used analytical method for quantifying water content in a

variety of products. The fundamental principle behind it is based on the Bunsen Reaction

between iodine and sulphur dioxide in an aqueous medium.

I2+ SO2+ 2H2O 2HI + H2SO4

Karl Fischer discovered that this reaction could be modified to be used for the determination of

water in a non-aqueous system containing an excess of sulfur dioxide. He used a primary

alcohol (methanol) as the solvent, and a base (pyridine) as the buffering agent. The reagents

most frequently used today are pyridine-free and contain imidazole or primary amines instead.

Apparatus and Instrument:

Glassware Beakers, Titration flask with magnetic stirrer

Karl Fischer Titrator, Weighing balance

Chemicals:

Karl Fischer reagent,

Karl Fischer grade dry methanol

Di-sodium tartrate dihydrate (purified)

Samples (KCl and Glycerol)

Theory:

Volumetric Karl Fischer titration requires the determination of the titer of the Karl Fischer

reagent. It is usually quoted in mg of water per ml (mgH2O/ml of KF reagent) of Karl Fischer

reagent. In volumetric Karl Fischer, iodine is added mechanically (directly as a component of KF

reagent) to a solvent containing the sample by means of a burette during the titration. Water is

quantified on the basis of the volume of Karl Fischer reagent consumed.

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Volumetric titration is best suited for determination of water content in the range of 0.1% to

100%.

Volumetric Karl-Fisher titration:The volumetric Karl-Fisher titration takes advantage of the fact

that iodine contained in the Karl-Fisher reagents reacts quantitatively and selectively with

water as shown below,

I2+ SO2+ H2O + 3Base + CH3OH 2Base HI + Base HSO4CH3

The quantification is based on the stoichiometric principle that 1 mole of iodine (254g) reacts

with 1 mole of water (18g). Water and iodine are consumed in 1:1 ratio in the above reaction.

Once all of the water present is consumed, the presence of excess iodine is detected

Volta metrically by the titrator indicator electrode. The titration systems employ controlled

current-voltage detection (constant-current polarization voltage detection). A constant current

of 1-30A is applied to two platinum electrodes. If the titration solution has a relatively high

water content, a polarization voltage of 300-500mV will be produced. As the Karl Fischer

titration continues and the end-point approaches, the voltage suddenly drops to 10-50 mV.

With volumetric analysis, the endpoint is deemed to have been reached after the voltage has

remained at this level for a specific period of time. In commercially available titration systems,

the period is 30-60 seconds.

The amount of water present in the sample is then calculated based on the concentration of

iodine in the Karl Fisher titrating reagent (i.e., titer) and the amount of Karl Fisher Reagent

consumed in the titration.

Procedure:

Step 1: Place approximately 40-50ml of KF-grade dry methanol into the titration flask which

hasbeen well dried in a hot-air oven overnight.

Step 2:Fill the desiccant tubes with appropriate desiccants e.g. silica gel and molecular sieves

and place them at appropriate positions on the titration flask. Also, attach the KF dispenser

onthe flask.

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Step 3:Carry out a pre-titration/Neutralization so as to eliminate all the traces of water that

may have been added along with the solvent. It is however, not necessary to read the amount

of KF reagenttitrated at this time.

Step 4:Add a fixed quantity of Di-sodium tartrate dihydrate into the flask (note the amount

taken) and carry out the titration so determine the titer of the KF reagent being used for

theexperiment.

Step 5: Add the sample containing unknown amount of moisture to the flask and run the

titration.Repeat the titrations for each sample thrice. Note the amount of sample taken in each

run.The Karl Fischer reagent, the titer of which (mgH2O/ml) has now been determined,

istitrated until the end-point is reached. The end-point is detected electrically by means of

adetection circuit built into the titration system.

Step 6:Note the readings and calculate the moisture content of the given samples.

Calculation:

Concentration factor= 5.4102 (mg of H2O/ml of KF)

Leak rate = 10 L/min = 10 10-3

ml/min

Weight of Disodium tartrate dihydrate used in standardization = 107.86 mg

Blank volume = 0 ml

The percentage of moisture can also be calculated from the given formulae

%

=100 ( )

%= ( )/

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where S = Strength of KF reagent(mg/ml)

W = Weight of Sample (mg)

KF = Volume of KF consumed during titration (ml)

B = Blank volume entered(ml)

L = Leak Rate (l/min)

Sample calculation by formulae:

1st

reading KCl %= .(. ).

=1.06402

Similarly find out % moisture for other reading and Glycerol sample also. Calculated data are

shown in Table 1 (KCl) & Table 2 (Glycerol)

Table 1:Potassium chloride(KCl) Data:

Sr.

No

Weight, W

(mg)

Volume of Karl

Fischer Reagent

Dispensed, KF

(ml)

% moisture

(from

experiment)

% moisture

(from

calculation)

% error in

calculation

Coefficient

of

Variation

1 112.87 0.222 1.064 1.064 -0.002

0.2392 90.00 0.287 1.731 1.725 0.339

3 95.25 0.246 1.400 1.397 0.202

Table 2: Glycerol Data:

Sr.

No

Weight, W

(mg)

Volume of Karl

Fischer Reagent

Dispensed, KF

(ml)

% moisture

(from

experiment)

% moisture

(from

calculation)

% error in

calculation

Coefficient

of

Variation

1 221 4.379 10.720 10.720 0.004

0.0952 96 1.605 9.045 9.045 0.0023 142 2.810 10.706 10.706 0.003

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Conclusion:

The average % moisture in Sample1 (KCl) : (1.064 + 1.731 + 1.4 )/3 = 1.398

The average % moisture in Sample2 (Glycerol) : (10.720 + 9.045 + 10.706 )/3 = 10.157

The coefficient of variation is little high in case of solid sample but significantly low in liquid

sample. The reason behind this may be due improper mixing of solid sample granular particle in

solution.

Karl Fischer method widely used because of high accuracy and precision. The advantages

include small sample quantities required, easy sample preparation, short analysis duration,

independent of presence of other volatiles and suitability for automation.

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Thin film formation by spin coating and thickness measurement by Ellipsometry

Objective

The objective of this experiment is to make a thin-film of polymer by spin coating and measurethickness of the polymer thin film by ellipsometry.

Introduction

Optical measurement techniques are normally non-invasive. These techniques do not involve any

physical contact with the surface and do not destruct the surface. This is a lucrative property of a

measurement technique on nanoscale. Several optical measurement techniques based on the

reflection or transmissions of light from a surface are interferometry, reflectometry and

ellipsometry. There are three different types of ellipsometry, namely scattering, transmission and

reflection ellipsometry. This experiment deals with the reflection ellipsometry only. One of the

applications is in the semiconductor industry, which deals with a thin layer of SiO2on a silicon

wafer. To ensure the thickness of this film, process engineers use ellipsometry to measure the

film thickness of sample wafers. Ellipsometry is known for the high accuracy when measuring

very thin film, with a thickness in the Angstrm scale or below. Other applications of

ellipsometry involve determination of the refractive index, the surface roughness or the

uniformity of a sample and more.

Instruments required

i. Ultra-Sonicator

ii. Spin coater with vacuum pump

iii. Ellipsometer

Chemicals required

i. Polystyrene

ii. Toluene

iii. Silicon wafer (as substrate)

Theory

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a) Spin coating

Spin coating is one of the standard methods for obtaining uniformly thick dielectric films.

The substrate on which the desired material is to be coated is mounted on the spin coater and

held by vacuum. The polymer dissolved in a suitable volatile solvent or synthesized in solution is

poured on the substrate and it is spun a t high speeds o f the order of few thousand rpm. Clearly

the film thickness will increase with the increase in concentration in solution and will reduce

with the increase in spin speed. But other factors like viscosity, volatility of the solvent used,

humidity of the environment, etc. also matter.

The mechanism of film formation can be split into 2 stages. The first stage involves the

interplay between the centrifugal and viscous forces followed by evaporation. Meyerhofer (1978)

predicted the final thickness, hf in terms several solution parameters as given by the following

equation:

13

2(1 )

f

eh x

x K

Where eand Kare the evaporation and flow constants defined below and xis the effective solid

constant of the solution.

2

3

e C

K

Where is the rotation rate, is the density of the solution, is its viscosity and C is

a proportionality constant that depends on whether airflow above the surface is laminar or

turbulent and on the diffusivity of the solvent molecules in air.

Substituting e and K in the equation for hf we can see that the thickness varies linearly as the

inverse square root of spinning speed, when other parameters remain the same.

tconshf

tan

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This is the relationship which we will verify experimentally.

b) Ellipsometry

Ellipsometry is primarily used to determine film thickness and optical constants. However, it is

also applied to characterize composition, crystallinity, roughness, doping concentration, and

other material properties associated with a change in optical response.

The polarization change is represented as an amplitude ratio, , and the phase difference, . The

measured response depends on optical properties and thickness of individual materials.

Ellipsometry measures the interaction between light and material.

When light enters a different medium the dielectric constant of the medium changes the electrical

field strength. As light is electromagnetic wave, in a different dielectric medium, it changes its

velocity for which it changes its trajectory and wavelength. When a polarized light beam falls at

the interface of two dielectric media, its electric vector can be separated into two orthogonal

components parallel and perpendicular to the plane of incidence (p and s components

respectively). When these components traverse through the medium and undergo reflection and

refraction, there is a change in the polarization of the light which is a function of amplitude ratio

and phase difference of these components. The change in polarization is the ellipsometry

measurement, commonly written as:

tan exp(i ) p

s

R

R

Where tan p

s

R

R

which again can be derived from Maxwells theory as a function of total

reflectance R, refractive index, incident angle, wavelength of the incident light and thickness of

the film. Out of these parameters except the thickness other parameters are constant for a given

system, thus calculable (or can be found in literature).

For a transparent film the Cauchy relationship is typically given as:

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2 4( )

B Cn A

Where, the three terms are adjusted to match the refractive index for the material.

So in the model the only unknown variable remains, is thickness for the film, as the total

reflectance is also a function of refractive index and incident angle.

The ellipsometer experimentally measures the amplitude ratio vs. wavelength of light and phase

difference vs. wavelength of light which is the fitted with the theoretically obtained amplitude

ratio vs. wavelength of light and phase difference vs. wavelength of light, having the fitting

parameters A, B, C (Cauchy parameters) and hf. These parameters are fitted to obtain the film

thickness.A known polarization is reflected or transmitted from the sample and the output polarization is

measured. A sample ellipsometry measurement is shown in Figure 1. The incident light is linear

with both p- and s- components. The reflected light has undergone amplitude and phase changes

for both p- and s- polarized light, and ellipsometry measures their changes.

Figure 1 Typical ellipsometry configuration, where linearly polarized light is reflected from the

sam le surface and the olarization chan e is measured to determine the sam le res onse

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Experimental Data: (for PS film over silicon wafer)

ROTSPEED(rpm)

MSEVALUE

THICKNESS(nm)

Meanthickness

Deviationfrommean

Square ofdeviation

Standarddeviation

2000 3.761 58.113 0.047 0.002209

3.564 58.004 58.066 -0.062 0.003844 0.056

4.32 58.081 0.015 0.000225

4000 3.769 43.0886 0.0385 0.0014822

3.717 43.055 43.0501 0.0049 0.000024 0.04115

3.76 43.0067 -0.0434 0.0018835

6000 4.029 36.128 0.00067 4.489*10-

4.028 36.127 36.12733 -0.00033 1.089*10- 5.773*10-

4.027 36.127 -0.00033 1.089*10-

Discussion:

1. Rotational speed of the substrate during film preparation is most vital parameter whichaffects the thickness of film. It is observed from the results that film thickness increaseswith decease in rotational speed.

2. Viscosity of the liquid also affects the film thickness. With increase in solutionviscosity, viscous resistance to the flow of liquid outwards due to centrifugal force

decreases, which leads to increase in film thickness.

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3. Lager is standard deviation; more is the non uniformity in the film thickness. In ourexperimental results, standard deviation is more in case of low rpm film.

4. Solution surface tension also plays a role. As the surface tension of solvent decreases,evaporation rate increases leaving behind the concentrated solution which gives higher

thickness.

5.

Room temperature and relative humidity of surrounding air also affect the finalthickness of film. The larger is difference in partial pressure of solvent between the free

surface of the liquid layer and the bulk of the air, solution will be concentrated more tomake the viscosity high which causes the higher thickness. Temperature also acts in the

same way.6. Film thickness decreases from centre to the edges on the substrate due to increased shear

rate with radius. Non Newtonian shear thinning behaviour is observed towards the edge

of substrate.7. Higher is the initial concentration of solution higher is the viscosity and hence higher

thickness of film.

Souces of error:

1. During the coating different amount of solution may be put on the substrate, whichcauses thickness difference

2. Substrate centre may not be kept at the centre of chuck which always cause the

thickness non uniformity3. Air bubbles, particles in solution and also particles on the substrate can also cause

the non uniformity in film thickness.4. Temperature and humidity variation during coating can affect the drying rate of

film resulting in thickness variation.

5. Surface roughness of substrates may be different.6.

Thickness may be measured at different positions for different samples which can

give different film thickness7. Lager spinning time may lead to low thickness.8. There may be a mistake in setting the speed.

Conclusion:

The thickness widely varies with each experiment, showing significant error in experiment

condition. The main reason for this is the substrate was not smooth enough (there were residue

left of the previous experiment. As the silicon wafers were cleaned by the solvent, which in this

case is toluene, is volatile and dries off quickly. There are chances of dust particle attachment on

the surface. These particles are hard to remove by air blowing).

Another reason for error can be because of the different position of the film is measured in

different experiment. As the thickness is a function of the radial position of the film. The only

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solution of this problem can be achieved by measuring more number of points, which is difficult

to achieve within given time.

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Experiment Report

CL 610 EXPERIMENTAL METHODS

Experiment No. 4

Nanoparticle Formation Using Microemulsion Template and Particle Size Estimation

Using UV-Vis Spectrophotometer

Submitted By: Group No. Submitted To:

Prof. Rajdip Bandyopadhyaya

Prof. Y S Mayya

Date of Experiment:

Date of submission:

Department of Chemical Engineering

Indian Institute of Technology Bombay

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Objective:

To prepare cadmium sulfide (CdS) nanoparticles in water in oil (w/o) microemulsions and

estimate their size with the help of UV-Visible spectrophotometer.

Introduction:

Nanoparticles are collections of atoms or molecules that form clusters with diameters less

than 100 nm. The chemical and physical properties of nanometer-sized materials can differ from

the bulk material. Changes in color and chemical reactivity are readily apparent with many

nanomaterials. Nanoparticles tend to combine to form larger, bulk particles, so special methods

are used, like w/o microemulsion drops as template, to limit their growth.

The potential applications of nanoparticles of metal sulphides are in optoelectronic devices,

photocatalysis for solar energy conversion and photo degradation of water pollutants. Since the

electronic properties of semiconductor nanoparticles are size dependent, in order to modulate

their chemical, optical and electrical properties, a fine size control is required. Among the

various method employed to produce size controlled nanoparticles, a promising one is based on

the use of water in oil (w/o) microemulsions.

Principle and theory:

Microemulsions are a thermodynamically stable dispersion of nanometer-sized water drops in a

continuous oil medium. The stability of these drops is attributed to the presence of adsorbed

surfactant molecules at the oil-water interface of the drop. The drops undergo Brownian motion,

thus colliding with each other and occasionally coalescing. Due to coalescence exchange their

contents thus brings the two reactants together inside a single drop for reaction. So, the insoluble

reaction product nucleates to form a nanoparticle inside the drop.

Coagulation of two nanoparticles during coalescence of the two nucleated drops is responsible

for size enlargement of nanoparticles. However, coagulation is constrained by the fact that the

coagulated nanoparticle size cannot exceed the size of an individual drop. This is based on the

fact that, when a growing nanoparticle approaches the diameter of a microemulsion drop, the

head groups of surfactant molecules surrounding the drop can physically adsorb on the

nanoparticle surface. Thus, the nanoparticle can become strongly encapsulated in the drop, in

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comparison to when the particle diameter is much less than the drop diameter. Therefore, it is

hypothesized that particles of diameter equal to the drop diameter cannot coagulate further with

any other nanoparticle.

In this experiment, we will use a uv-spectrophotometer to precisely measure which wavelengths

of light are absorbed by the cadmium sulfide nanoparticles.

Chemicals: Sodium dioctylsulfosuccinate(AOT), Cadmium Nitrate, Sodium Sulfide, iso-Octane, Millipore water.

Apparatus: UV-Visible spectrophotometer with a pair of quartz cuvettes, sonicator, analytical

balance, micropipettes of 100, 1000 and 5000 l capacity.

Procedure:

1. Prepare the following three stock solutions:

a. Stock solution 1: 100 ml 0.1 M AOT/Iso-octane solution.

b. Stock solution 2: 10 ml of 0.037M Cd(NO3)2aqueous solution.

c. Stock solution 3: 10 ml of 0.037 M Na2S solution.

2. Prepare microemulsions A and B for R = 5 (where R is mole ratio of water to surfactant

AOT) and record absorbance spectra:

a. Microemulsion A: for R = 5, take 10 ml of stock solution 1, calculate the amount

of water needed and the total volume (volume of AOT/Iso-octane and water).

Now mix stock solutions 1 and 2 such that Cd2+

concentration is 0.0003315 M

with respect to total volume.

b. Microemulsion B: for R = 5, take 10 ml of stock solution 1, calculate the amount

of water needed and the total volume (volume of AOT/Iso-octane and water).

Now mix stock solutions 1 and 3 such that S2- concentration is 0.0003315 M

respect to total volume.

c. Sonicate the microemulsions A and B for 10 minutes in a sonicator .

d. To measure the absorption spectrum of the microemulsion , 1.5 ml microemulsion

A was added to the cuvette and placed in the UV-Vis spectrophotometer, after

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that 1.5 ml of microemulsion B was added to it and after waiting for 1 minute

absorption spectrum was measured.

e. . Repeat steps c and d two more times do make total four readings for same R.

3. Repeat step 2 for R = 10 and 15.

Observations:

1. Plot absorbance data as a function of wavelength.

Graph1:

Graph 2:

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2. Note the region in the spectrum where the absorbance increases linearly. Calculate the X

intercept and slope. Find cutoff wavelength of spectrum cutoffby formula cutoff =-

(slope/intercept).

Graph 3:

Convert the cut-off wavelength into units of Joules usingnano

gE = hc/ where h is Plancks

constant and c is velocity of light.

3. Below is the equation for determining band gap of the nanometer-sized CdS particle.

Rearrange that equation to solve for particle radius. Report the size of particles with mean

and standard deviation.

r

e

mmr

hEE

ohe

bulk

g

nano

g4

8.111

8

2

**2

2

Use the values of physical constants listed below to calculate the radius of particles.

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nano

gE = band gap of nanoparticle CdS as determined from the samples UV/visible absorbance

spectrum, J

bulk

gE = band gap of bulk CdS at room temperature, 3.88 10-19J (2.42 eV)

h = Plancks constant, 6.626 10-34

J s

r = particle radius, m

*

em = effective mass of a conduction band electron in CdS, 1.73 10-31kg

*

hm = effective mass of a valence band hole in CdS, 7.29 10-31kg

e = elementary charge of an electron, 1.602 10-19C

= pi, 3.14159

= relative permittivity of CdS, 5.7

o= permittivity of a vacuum, 8.854 10-12C2(J m)-1

Analysis and Discussion:

Table 1:

S.No. Time cutoff (nm) Egnano

in 10-19

J Dia (nm)

1 1 min 363.409 5.46491 6.66

2 4 min 363.9852 5.4562 6.702

3 7 min 365.48494 5.4338 6.7239

4 10 min 365.6526 5.43138 6.7258

Graph 4:

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The data obtained shows the similar behaviour of variation of CdS nanoparticle formation as per

literature i.e. size of nanoparticle increases with time but after certain period of time variation in

size become negaligible as shown in graph 4.

Precautions:

1. Make sure the cuvettes are clean and scratch free. Use them gently

2. Wipe the cuvettes using a soft tissue.

3. Keep the sample compartment clean and do not spill any samples into the sample

compartment.

References:

Caponetti E, Pedone L, Chillura Martino D, Panto V and Turco Liveri V, Synthesis, size

control, and passivation of CdS nanoparticles in water/AOT/n-heptane microemulsions,

Materials Science and Engineering C, 2003, 23, 531539.

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HPTLC

Experiment No. 5

Objective: To measure the unknown concentration of Benzophenone and Benzhydrol in a

mixture.

Apparatus used: TLC Plate, Applicator, Glass developing chamber, TLC UV Scanner, Syringe,

Beakers, Measuring cylinder, Sample bottles.

Chemicals used: Benzophenone, Benzhydrol, Methanol, Hexane, Toluene.

Introduction

Thin Layer Chromatography (TLC) is an extremely useful technique for monitoring reactions,identify compounds given in a mixture and determine the purity of a substance. TLC uses a

stationary phase, usually alumina or silica and the mobile phase is a solvent whose polarity is

chosen according to the requirements. The reaction mixture in the form of a solution is applied to

the plate and then the experiment is run by allowing a solvent (or combination of solvents) to

move up the plate by capillary action.

High Performance Thin Layer Chromatography (HPTLC) is an enhanced form of thin layer

chromatography (TLC). A number of enhancements can be made to the basic method of thin

layer chromatography to automate different steps, to increase the resolution achieved and to

allow more accurate quantitative measurements. Automation allows overcoming the uncertainty

in droplet size and position when the sample is applied to the TLC plate by hand.

Principle

Depending on the polarity of the components of the mixture, different compounds ill travel

different distances up the plate. More polar compounds will be retained in the polar silica

stationary phase and travel a shorter distance on the plate. Non-polar substances will have a

higher affinity for the mobile phase and thus travel a larger distance on the plate. The measure of

the distance a compound travels is called the Rf value or the Retention factor. The Rf is defined

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as the ratio of distance the compound migrated from where it was originally spotted to the

distance covered by the solvent.

Procedure:

1.

Two standard solutions of 150 ppm Benzophenone and 2500 ppm Benzhydrol each was

prepared in 5ml of methanol.

2. Mixtures of Benzophenone and Benzhydrol in unknown proportions were also prepared.

3. 30ml of developing solvent containing Hexane-Toluene in a ratio of 30:70 was prepared

and poured in the developing chamber.

4.

The HPTLC instrument (applicator) was started and various parameters like Plate width,

Band width, Band pitch and start position were set. Based on these parameters the

number of tracks available on the TLC plate was calculated to be 13.

5. In the first five tracks, bands of pure Benzophenone solution, in the middle five tracks,

bands of pure Benzhydrol solution and in the last three tracks, bands of unknown samples

were loaded by entering different volumes of the samples in each track.

6. After applying the samples, the TLC plate was kept in the developing chamber containing

the solvent. The plate was removed when the solvent had covered 75% of the plate and

was dried with the help of a dryer.

7. The TLC plate was placed under a UV lamp for identification of the bands after they had

migrated.

8. The plate was then analyzed by using the TLC scanner in order to obtain the

chromatograms using the CAMAG software at 254nm wavelength. Each track was

separately analyzed and depending on the number of components present they showed

one or two peaks. By using the integration option the areas under the peaks were

obtained.

Preparation of standard solutions of Benzophenone and Benzhydrol:

5.94 mg of Benzophenone was dissolved in 50 ml of Methanol (density: 0.791 g/cc) to give a

solution of 150 ppm. 98.99 mg of Benzhydrol was dissolved in 50 ml of Methanol (density:

0.791 g/cc) to give a solution on 2500 ppm.

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Parameters entered:

Plate width = 200 mm

Space between bands = 10 mm

Band width = 4 mm

Start position = 10 mm

Observations:Table 1:

Calibration data for Benzophenone standard

y = 5526.8x + 3233.4

R = 0.9938

0

2000

4000

6000

8000

10000

12000

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Area

Amount of Benzophenone (g)

Peak Area vs Amount of Benzophenone

Track no Volume (l) Peak AreaAmount of

Benzophenone (g)

1 4 5740.7 0.47

2 6 7178.1 0.71

3 8 8628.4 0.95

4 10 9974.9 1.19

5 12 10908.1 1.43

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Table 2: Calibration data for Benzhydrol standard

Table 3: Unknown

Therefore:

For BP, y = 5526x + 3233

y = 225.14x + 803.46R = 0.9844

0

1000

2000

3000

4000

5000

6000

7000

0 5 10 15 20 25

Area

Amount of Benzhydrol (g)

Peak Area vs Amount of Benzhydrol

Track no Volume (l) Peak AreaAmount of

Benzhydrol (g)

6 4 2367 7.92

7 6 3725.3 11.88

8 8 4419.5 15.84

9 10 5296.1 19.80

10 12 6039 23.75

Track no Volume (l)Peak Area

corresponding to BP

Peak Area

corresponding to BH

11 12 7391 3532.8

12 14 8035.2 3903.3

13 16 8810.7 4399.1

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For BH, y = 225.18x + 803.4

For concentration in ppm:((amount in g)/ (vol in l x 791)) x 106

For volume ratio: V1/V2 = (ppm of BP x 2500) / (ppm of BH x 150)

Table 4: Amount and concentration of unknown

Track noVolume of

sample (l)

Amount of

BP (g)

Amount of

BH (g)

ppm of

BP

ppm of

BH

Volume ratio of

original solutions

11 12 0.75 12.13 79.27 1277.42 1.03

12 14 0.87 13.77 78.47 1243.56 1.05

13 16 1.00 15.97 79.75 1262.15 1.05

Results:

For the unknown sample:

Average concentration of Benzophenone = 79.16 ppm

Percentage error = 5.55 % (Actual concentration = 75 ppm)

Average concentration of Benzhydrol = 1261.04 ppm

Percentage error = 0.88 % (Actual concentration = 1250 ppm)

Average volume ratio of standard solutions of Benzophenone to Benzhydrol added to make

the unknown solution = 1.04

0

10

2030

40

50

60

70

80

0 20 40 60 80

Height(AU)

Distance (mm)

Benzophenone

Benzhydrol

A representative chromatogram

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Conclusions:

1) HPTLC was used to measure the unknown concentrations of Benzophenone and

Benzhydrol in the given mixture.2) There exists a linear relationship between peak area and amount of component in a

solution.

3) Benzhydrol being more polar experiences more interaction with the stationary phase

(silica) compared to Benzophenone. Benzophenone thus has a higher value of Retention

factor (Rf) which explains Benzophenone travelling a greater distance in the TLC plate.

Comments on errors:

1. If the compound runs as a streak, the sample may have been overloaded or it may contain

many components which appear as a streak. In this case, dilute the sample and run again.

2. While scanning the TLC plate, take care to place the UV light bean exactly on top of the

spot failing which one may get an erroneous intensity value.

3. While preparing the sample try to keep the samples covered as methanol is a volatile

compound and it evaporates even at room temperature thus drastically changing the ppm

concentration of the sample.

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EXPERIMENT NO. 6

TA ARSHNOOR KHAN

EXPERIMENTAL METHODS

CL 610

ATOMIC

ABSORBTION SPECTROSCOPY

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OBJECTIVE OF THE EXPERIMENT:

To determine the concentration of metal ion using Atomic Absorption

Spectroscopy (AAS) and study its extraction using suitable extractant.

THEORY:

PRINCIPLE OF WORKING:

The technique makes use of absorption spectrometry to assess the concentration ofan analyte in a sample. It requires standards with known analyte content to

establish the relation between the measured absorbance and the analyte

concentration and relies therefore on the Beer-Lambert Law. In short, the electrons

of the atoms in the atomizer can be promoted to higher orbitals (excited state) for a

short period of time (nanoseconds) by absorbing a defined quantity of energy

(radiation of a given wavelength). This amount of energy, i.e., wavelength, is

specific to a particular electron transition in a particular element. In general, each

wavelength corresponds to only one element, and the width of an absorption line is

only of the order of a few picometers (pm), which gives the technique its elemental

selectivity. The radiation flux without a sample and with a sample in the atomizer

is measured using a detector, and the ratio between the two values (the absorbance)

is converted to analyte concentration or mass using the Beer-Lambert Law.

Atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the

quantitative determination of chemical elements employing the absorption of

optical radiation (light) by free atoms in the gaseous state.

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In analytical chemistry the technique is used for determining the concentration of a

particular element (the analyte) in a sample to be analyzed. AAS can be used to

determine over 70 different elements in solution or directly in solid samples

employed in pharmacology, biophysics and toxicology research.

Atomic absorption spectrometry was first used as an analytical technique, and the

underlying principles were established in the second half of the 19th century by

Robert Wilhelm Bunsen and Gustav Robert Kirchhoff, both professors at the

University of Heidelberg, Germany.

APPARATUS AND INSTRUMENTS:

Syringe

Sampling bottles

Glass wares

Atomic Absorption Spectrometer (Model: GBC-902)

CHEMICALS USED:

1000 ppm stock of metal ion Tetrabutyl phosphate(TBP)

8N HNO3

0.1N HCl

Paraffin oil

Distilled water

EXPERIMENTAL PROCEDURE:

1. First we have to prepare the sample.

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2. A stock solution of 1000 ppm is given which is diluted with distilled water to

form samples of different concentrations.

3. An emulsion is prepared

4. Quantity of emulsion prepared: 20 ml

97% v/v of Paraffin=19.4 ml

3% v/v of TBP= 0.6 ml

5. The aques /feed phase is of the sample provided of unknown conc of same metal

ion (50 ml).

6. To this sample emulsion is dispersed

7. This emulsion will be provided.

Step1:

An amount of emulsion and aqueous phase is stirred with the help of stirrer at

some fixed rpm.

Step2:

With the help of syringe, sample is collected from aqueous phase in sampling

bottles, with the help of syringe

Setting up of instrument:

The exhaust and hood is put on.

The corresponding slit width (0.2mm) and wavelength(386 nm) is fixed.

The lamp is selected and fitted corresponding for the given metal ion.

The power is switched on .

The current for the lamp is setted up.

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Plot of absorbance vs. Concentration for Cu:

CALIBRATION TABLE for Fe

Sample

no.

Concentration

(ppm)

Absorbance

Observation

1

Observation

2

Observation

3

average Std

deviation

1 50 0.065 0.066 0.067 0.066 0.0030

2 80 0.121 0.121 0.122 0.121 0.001

3 120 0.176 0.179 0.182 0.179 0.000577

4 140 0.233 0.234 0.232 0.233 0.000577

y = 0.0008x + 0.082

R = 0.977

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 100 200 300 400 500 600

Absorbence

conc in ppm

Cu

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Plot of absorbance vs Concentration for Fe:

UNKNOWN SAMPLE:

Sample Absorbance for

Cu

Absorbence for fe Conc of

Cu in

ppm

Conc of fe

in ppm

1 0.243 0.130 201 153

Concentration Quantity of

extract ant

Quantity of

aques phase

Absorbence

after

extraction

Conc in aq

phase

Distribution

coeffecient

y = 0.0018x - 0.0238

R = 0.9884

0

0.05

0.1

0.15

0.2

0.25

0 20 40 60 80 100 120 140 160

absorben

ce

conc in ppm

Fe

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1000 ppm of

Cu

2 ml 20 ml 0.203 180 ppm 4.5

Seperation Factor = ( Distribution coefficient of Cu) / ( Distribution coefficient

of Fe)

UNKNOWN SAMPLE:

Sample time(min)

absorbance

Readings

from

caliberation

ln(CA0/CA)

1 0 0.78 1000 0

2 1 0.167 122.4 2.1

3 1.5 0.127 63 2.76

4 2 0.107 35.2 3.34

RESULTS:

In caliberation ,concentration v/s absorbance fits the linear data.

ln CA0/CA v/s time also fits a straight line with slope= 1.7821

y = 1.7821x

R = 0.9751

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5

ln

CA0

/CA

Time (min)

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Here slope= k,

So rate constant (k) = 1.7821

The unknown sample had 153 ppm of Fe and 201 ppm of Cu

D for Cu is 4.5

DISCUSSIONS:

Last two readings of absorbance were neglected, as they were corresponding

to negative concentration, which is not possible. One reason for this error

may be due to presence of dust particle in environment.

Calibration curves are straight lines with a good fit of trend line.

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CL 610

EXPERIMENTAL METHODS IN CHEMICAL

ENGINEERING

Particle size analysis and zeta potential

Submitted by:

Prerna Chandna

Roll No:114020012

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Aim:

The aim is to compare the size of aqueous C-Tab micelle with &without decane and also compare size

of silica particle with and without decane solution.

Introduction and Principle:

Interaction of light with the electric field of a small particle or molecule.

When photon collide with particle it induces oscillating dipole in the electron cloud .As dipole energy

changes ,it is radiated in all directions called Scattered light. Dynamic Light scattering is the

characterization technique to find the size of particles, emulsions or molecules, which is dispersed /

dissolved in a liquid.

Stoke Einstein Theory: Intensity fluctuations yields the velocity of the Brownian motion and hence

the particle size .Brownian motion of particles / molecules in suspension causes light to be scattered at

different intensities.

Mie Theory: It describe how spherical particles of all sizes and optical properties scatter light .When

particles size become larger than 1 /10 of laser wavelength(), then scattering is not isotropic (same in all

direction) but it gives maxima and minima with respect to angle.

The Zetasizer Nano uses Mie theory to convert the intensity size distributions into volume and number

for all sizes of particles.

Chemicals: C-tab, Silica nano-particles with and without decane ,NaOH pellets.

Stock Solutions Required:

C-Tab in NaOH(12mg)-Water(24ml) solution=12mg

C-Tab in NaOH(12mg)-decane(1.2ml)-Water(24ml) solution=12mg

Silica particles in water(10ml)=10mg

Silica particles with decane in water(10ml) =10mg

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Apparatus Used:

DLS

Stirrer

Weighing machine

Sonicator

Theory: Dynamic light scattering probes the diffusion of particulate materials either in

solution or in suspension. By determining the rate of diffusion (the diffusion coefficient),

information regarding the size of particles can be obtained. The common property of these

particles that is probed is their movement.

The relative positions of the particles in the scattering volume at any instant determine

the magnitude of constructive or destructive interference of the scattered light. Since the

diffusion rate of particles is determined by their sizes in a given environment, information

about their size is contained in the rate of fluctuation of the scattered light. The scattered

light and its changes in intensity are detected as the following signals:

Intensity vs time signal

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Procedure:

1)Sampling bottles are washed and oven-dried to remove any impurities present.

2)Stock solution of C-tab- water solution is prepared and slowly stirred at300rpm for 45minutes.Then

filtration is done with syringe filter.

3)Stock solution of C-tab, water-decane is prepared and slowly stirred it for 300rpmfor 45 minutes. Then

filtration is done with 0.22m syringe filter.

4)Solution of silica particles with water is prepared, then filter it with syringe filter and sonicates it for

20 minutes.

5)Solution of silica-decane particle is prepared ,then filter it with syringe filter and sonicate it for

20minutes,

6)The size distribution is measured for all prepared samples using DLS apparatus, using the known

values of viscosities and refractive indices of the solutions.

Observations:

Micelle of C-tab water solution

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Micelle formation of C-tab-water-decane solution:

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Silica particles with water:

Silica particles water-decane solution

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Results:

Solution Number mean diameter (nm)

Run 1 Run 2 Run 3 Mean diameter (nm)

CTAB without decane 4.8286 4.9786 4.7711 4.8594

CTAB with decane 5.7310 6.2326 6.2996 6.0877

Silica particles without decane 38.710 70.660 117.39 75.590

Silica particles with decane 162.19 160.60 186.20 169.66

Conclusion:

Size of C-tab decane micelle is greater than C-tab micelle.

Size of Silica nano-particles with decane is greater than Silica nano-particle without decane.

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Objective:

To get aquainted with Graphic Uer Interface(GUI) of Comsol Multliphysics 4.2.

To solve and analyse problem related to Chemical Engineering using this software.

Introduction and Theory

Comsol Multiphysics 4.2 provides a powerful interactive environment for modeling and solv-

ing all kinds of scientific and engineering problems based on partial differential equations

(PDEs). With this software one can easily extend conventional models for one type of

physics into multiphysics models that solve coupled physics phenomena and do so simul-

taneously. With the built-in physics modes it is possible to build models by defining the rel-

evant physical quantities such as material properties, loads, constraints, sources, and fluxes

rather than by defining the underlying equations. One can always apply these variables, ex-

pressions, or numbers directly to solid domains, boundaries, edges, and points independently

of the computational mesh. COMSOL Multiphysics then internally compiles a set of PDEs

representing the entire model.

When solving the models, COMSOL Multiphysics uses the proven finite element method

(FEM). The software runs the finite element analysis together with adaptive meshing and er-

ror control using a variety of numerical solvers. PDEs form the basis for the laws of science

and provide the foundation for modeling a wide range of scientific and engineering phenom-

ena. Therefore one can use COMSOL Multiphysics in many application areas.

A priori requirements

Problem Statement : In this section, a problem that involves certain physical phe-

nomenon will be described. Also, material properties, geometric dimensions, temper-

ature conditions and other relevant specifications to be listed here.

Observations:Typically, this section lists certain noticeable facts or assumptions about

the problem statement.Analyzing the results obtained with change in certain parame-

ters of the physics involved.

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Basic steps of modelling and simulation

1. Select Dimensionality suitable to the problem(2D or 3D).

2. Choose the physics or multiple physics that is or are required to describe the problem

at hand.Also choose the stationary or transient study as per problem requirement.

3. Using geometry build tool build the geometry required for the problem.

4. Choose material or specify necessary properties manually.

5. Specify all the relevant boundary conditions.

6. Choose the complexity of mesh as needed by the problem.

7. Set the solver parameters.

Problem Statement

One end of cylindrical fin is maintained at temperature T0 .Simulate following scenarios in

2D axisymmetric

Uninsulated Fin

Fin with insulated Tip

Fin with insulated cylindrical surface.

Assume that uninsulated surfaces are losing heat to the surroundings by convection. Assum-

ing constant h, k, and T1, compute total heat transfer, Qf, for all the cases. Compare the

results of these cases with each other to make a judgment and comment on what the effect

of insulating an tip & surface on heat transfer rate is. Thermal and geometric parameters for

the model are listed below.

T0= 100C, T1= 20C

k=160 W/m/C

h= 10 W/m2/C

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Length of fin=30cm,Radius of fin=0.5cm

Task:

Using COMSOL, show the axial temperature distribution for all cases (to be plotted

on single axis).

Using COMSOL, show change the heat transfer flux for all cases.

Case 1: Uninsulated Fin

Figure 1: Uninsultated fin

Figure 2: Uninsulated Tip:Axial Temperature profile

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Figure 3: Uninsulated :Axial heat flux profile

Case 2: Insulated Tip

Figure 4: Insulated Tip

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Figure 5: Insulated Tip:Axial Temperature Profile

Figure 6: Insulated Tip:Axial heat flux profile

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Case 3: Insulated Surface

Figure 7: Insulated surface

Figure 8: Insulated Surface: Axial Temperature Profile

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Figure 9: Insulated Surface:Axial Heat flux profile

Conclusion and Discussion

The heat flux is less and is constant for Case3:insulation on cylindrical surface, as compared

to other cases.Moreover, from the temperature profiles2,5and8it is clear that insulating tip

has a large temperature gradient axially but insulating the surface has very small temperature

gradient.The uninsulated and insulated tip show almost similar temperature and heat flux

profile.

The reason for the above observations lies in the fact that the tip surface area is small as com-

pared to the cylindrical surface area of the fin, therefore insulating curved surface decrease

the heat transfer by a huge margin than insulating a tip of fin.

Considering the fact that fin is mostly used for cooling purpose it is better to use insulted tip

than insulated surface.

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Thermo Gravimetric-Differential Thermal Analysis

(TG-DTA)

Objective:To get acquainted with Thermal Analysis(TA) techniques and to analyse given sample usingcoupled TGA and DSC for chemical and physical changes like dehydration, decomposition,

melting temperature, phase change, heat absorption, etc..

Introduction:

On heating, material undergo changes in its structural and chemical composition like fusion,

melting, crystallization, oxidation, decomposition, transition, expansion, sintering, etc.. In

addition to that when subjected to a temperature change, various properties such as heat flow,

mass, pressure, electrical properties, magnetic properties, optical properties may change

depending on sample characteristics. Using Thermal Analysis (TGA and DTA are methods of

thermal analysis), such changes can be monitored in at controlled atmosphere.

Principle:Table 1. shows different TA techniques and their applications.

Technique Property Measured Applications

Thermogravimetric Analysis(TGA)

Mass difference Sample purity,decomposition, dehydration,

oxidation

Differential ThermalAnalysis

(DTA)

Temperature difference Phase change, dehydration,

decomposition, reactions

Thermo Gravimetric Analysis (TGA):

The thermo gravimetric analysis is a technique in which the mass of a substance is measured

as a function of temperature or time while the substance is subjected to a controlled

temperature programme in a specified atmosphere. In case of temperature dependant

measurements:

m = m(T) or m = m(T)- m(T0) ...........................(1)In case of time dependent measurements:

m = m(t) or m = m(t)- m(t0) ...........................(2)

Where, m is mass of sample at temperature T in case of non-isothermal measurements or time

t in case of isothermal measurements. The m(T0) or m(t0) is the initial mass.

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Figure1: TG-DTA curve for CuSO4.5H2O

Factors affecting the TGA curve:The nature, precision and accuracy of the TGA experiment depend on various factors. They

are,

Furnace heating rate

Furnace atmosphere

Particle size of sample

Sample packing

Differential Thermal Analysis (DTA):

In Differential Thermal Analysis technique, the sample and reference material are

simultaneously heated. The temperature of sample and reference material is sensed and

recorded individually. The temperature change while heating is plotted to analyse chemical

and physical transformations like melting, sublimation, crystal transitions and crystallisation.

Apparatus:

It contains the following components The electrobalance and its controller: Null point weighing mechanism.

The furnace and temperature sensors: MoSi 2based furnace with aluminarefractories and a thermocouple Pt-30%Rh(+) Vs Pt-6%Rh (-) for operation to 1500 to

1700oC

Purge gas flow controller

Programmer or computer

Data acquisition device

0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0Time /min

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

DTA /(mW/mg)

30

40

50

60

70

80

90

100

TG /%

200

400

600

800

1000

Temperature /C

Residual Mass: 29.21 % (97.

Mass Change: -29.13 %

Mass Change: -7.04 %

Mass Change: -31.5

[1]

[1]

[1] e

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Instrument in lab:

Company: M/s. NETZCSH Gerabau GmbH.

Model: Simultaneous TGA-DSC Apparatus STA 409PC/4/H LUXX is hyphenated TGA and

DSC.

Temperature range: 25 to 1550oC

Experimental Procedure:

Starting Procedure

Switch ON the power supply for furnace unit, power unit, adapter unit, and the computer

(in all 5 switched to be ON)

Switch ON the equipments in following order,

a.

Power unit (switch in front)

b. Furnace unit (switch at back)

c.

Gas control unit (switch in front)

d.

Water circulation unit (kept near cylinders)

Ensure the connected gases (N2/O2/Zero Air) are ON. Pressure of 2kg/cm2 is to be

maintained.

Analysis Procedure:

Analysis works in two steps,

BASELINE CORRECTION, for removing the impurities and standardizing the

apparatus.

TG-DTA ANALYSIS, to analyze the % weight loss with temperature and time for the

sample under consideration.

Baseline Correction

Weigh the cleaned reference and the analysis pan manually and note down the weight

Furnace unit consist of three switches for operation UP/DOWN (front panel) SAFETY

(side panel). To OPEN the unit PUSH UP+SAFETY switch together till the unit is ready

for further usage.

Carefully place the weighed pan on the sensors using small forks. DO NOT insert the pan

forcefully to the sensors. CLOSE the unit using DOWN+SAFETY switch together.

Kindly note the weight (in mg) of both the pans for further usage.

Baseline correction has to be performed on the same program (heating rate, temp range,

holding time etc.) as going to be used for analysis.

Open the software STA409PC from the desktop icon.

Goto - TOOLS - Weighing Option Manual

File - New - gives anew window with multiple tabs.

o

Under MEASUREMENT mark CORRECTION

o Enter SAMPLE ID, and CRUSIBLE MASS

o

Under REFERENCE enter CRUSIBLE MASS,

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1. Sample: CaC2O4.H2O

Observations:

Initial Sample Mass =21.192 mgTemperature range = 25-900OC

Heating Rate = 15 K/min

Calculations:

In TGA, three stages are there.

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Sample: CaC2O4.H2O

Step

Reaction Theoretical

Mass

Loss

Measured

Mass

Loss

% Error

1 CaC2O4.H2O CaC2O4+H2O 12.32% 12.41% 0.73%

2 CaC2O4 CaCO3+ CO 19.17% 19.04% -0.67%

3 CaCO3 CaO + CO2 30.13% 29.93% -0.66%

Sample contains monohydrate. Hence, in first stage dehydration takes place. Decomposition startsat the temperature of 520

oC and continues subsequently in the third stage. Products of

decomposition can be analysed using above data. The area under the exothermic/endothermic peaks

gives the enthalpy of the thermal event.

2. Heat change observed:

Step H (KJ/mole)

1 -26.42

2 -7.6

3 -31.38

Result:The number of water molecules associated with the sample crystal structure was found as one.Decomposition starts at the temperature of 520oC.

-1.00E+01

-5.00E+00

0.00E+00

5.00E+00

1.00E+01

1.50E+01

2.00E+01

2.50E+01

3.00E+01

3.50E+01

0 100 200 300 400 500 600 700 800 900 1000

DTA(mW)

Temperature(C)

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2. Sample: CuSO4.5H2O

Observations:

Initial Sample Mass = 37.732 mgTemperature range = 25-1000OC

Heating Rate = 10 K/min

Calculations:

In TGA, three stages are there.

Sample: CuSO4.5H2O

Step 1: CuSO4.5H2O CuSO4.H2O + 4H2O

Theoretical Mass Loss : 28.86%

Measured Mass Loss : 29.13%

Step 2: CuSO4.H2O CuSO4+ H2O

Theoretical Mass Loss : 10.13%

0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0Time /min

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

DTA /(mW/mg)

30

40

50

60

70

80

90

100

TG /%

200

400

600

800

1000

Temperature /C

Residual Mass: 29.21 % (97.

Mass Change: -29.13 %

Mass Change: -7.04 %

Mass Change: -31.5

[1]

[1]

[1] e

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Measured Mass Loss : 07.04%

Step 3: Decomposition to CuO

CuSO4 CuO + SO3

Theoretical Mass Loss : 31.85%

Residual mass : 29.21% (Measured)

2. Heat change observed:

step H (J)

1 -16

2 -1.6

3 -10

4 -0.035

5 -7.3

Result:The number of water molecules associated with the sample crystal structure was found as five.

Dehydration takes place in two steps.

Conclusions:The Simultaneous thermal analysis procedure was used to observe the behaviour of CaC2O4 .H2O

crystals and CuSO4 .5H2O crystals on heating in a temperature range of 25-1000OC. As, sample isheated dehydration takes place. Enthalpy changes in corresponding to dehydration stages werecalculated. When all the water molecules are removed, and temperature is increased beyond that, then

decomposition of crystals takes place. Enthalpy associated with the thermal events can be known by

calculating the area under the curves of DTA vs time plots.

References:

Brown, M. E. (Ed.), 2007, Introduction to Thermal Analysis: techniques andApplications, 2nd Edition, Springer, New Delhi, 1-90.

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Preparation of langmuir films

EXPERIMENT NO. 10

TA- DEEPTI PATIL

Aim: To prepare Langmuir films and plot (-A) isotherms.

Theory

Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid or

dissolved solids. It is a random distribution of molecules on the material surface. For eg:

Capturing and using waste heat to provide cold water for air conditioning.

The most common technique for studying Langmuir monolayers of amphiphilic substances has

been to measure the surface pressure as a function of the surface area. An amphiphile is a

molecule that consists of two parts, each of which has an affinity for a different phase.When a long chain amphiphilic molecule (e.g. fatty acid) is spread with the aid of a volatile

solvent onto water surface, the solvent evaporates until only a monolayer remains. The polar

head attaches itself to the water surface while the nonpolar tail protrudes into the air.If the

surface tension of the water is lowered by the addition of thesolute (e.g. fatty acid like stearic or

oleic acid) the monomolecular layer of the solute onthe surface may be considered to exert a film

pressure () suchthat

= 0 (1)

where 0is the surface tension of pure water and is the surface tension of the monolayer

covered water.

The plot of surface pressure as a function of the area of water surface available to the molecules

at constant temperature is known as surface pressure-area isotherm.

Application of Langmuir monolayers

1. Langmuir monolayers of oils on ponds are known to have a damping effect on surface

turbulance and retardation of evaporation.

2. Langmuir monolayers at the oil-water interface act as emulsifying agents.

3. Langmuir layers can be transferred to a soild substrate. The resulting Langmuir- Blodgett film

have many potential applications such as molecular electronics, piezoelectronic organic films,

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waveguides, nonlinear optics etc. is that monolayers can be deposited on almost any kind of solid

substrate.

Interpretation of Surface Pressure

There is an analogy between and A with p and V of an ideal gas for very large areas.

The and A show a simple inverse proportionality such as pressure and volume for an ideal gas.

Identification of area as the two-dimensional equivalent of volume is a straight forward

geometrical concept. As the area is decreased, a more complex relationship is needed to connect

these variables, just as the equation of state becomes more complex for non ideal gases and

condensed phases. It can be shown that a typical value of 10mNm -1corresponds to about

100atm of three-dimensional pressure. In view of this, it is not too surprising that insoluble

monolayers do not usually display a simple inverse proportionality between and A. At

pressures this high, three-dimensional matter is not likely to obey the ideal gas law either.For the

gaseous state, the two-dimensional equivalent of Amagat's law for gases can be employed:

(A-A0)=qRT (2)

Where A0has the aspect of an excluded area per mole and q gives a measure of the number of

moles in the system. Rearrangement yields the linear form:

A =A0+qRT/ (3)

This form is obeyed fairly well around a value of 5-10 mN-m-l. The value of A

0depends on the

chain length of amphiphile used and is larger for longer chain surfactants such ssodium dodecyl

sulphate.

Apparatus: Langmuir balance, volumetric flasks, beakers, microsyringe.

Chemicals: Acetone, Millipore water, Acetone, Millipore water, 1mg/ml Stearic acid/hexane

solution

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Procedure:

Step 1: First clean the trough using distilled water and then with acetone. Further wash away the

acetone using distilled water.

Step2. Pour distilled water in the trough and avoid any air bubbles present in the trough.

Step 3. Click on sgserver icon

Go to control panel

A screen will be shown on which manual control unit will be displayed showing surface

pressure, barrier position & barrier speed.

From the manual control unit set the barrier position & balance as zero because of which the

barriers are at extreme position.

Step 4. Heat the Wilhelmy plate to avoid contamination. Hang the plate on its hook using

tweezers

Step 5.Remove the dirt from water-air interface till surface pressure is close to zero mN/m.Close

in the barriers by means of switch. A positive value of surface pressure is displayed.

Step 6. Bring the barriers to extreme position and set balance and barrier position to zero (use

the switch/manual control unit).

Step 7Using micro syringe the solution is gently placed on thesubphase.

Step 8. Wait 20 minutes for the solvent to evaporate.

Step 9 Press the icon for KSV LB control software and then go to Experiments.

Go File. New Isotherm

Fill up the screen and set values as

Step 10. Fill up the next screen: Constant rate compression which also includes recording

options and target options.

From go to target (target= mN/m).

Rate is 10 mm/min and then click Go

Step 11Plot the graph between surface pressure vs. mean molecular area.

Step 12Stop and save the data.

Step 13 Repeat this procedure for three runs.

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Experimental Data Input /Observations:

1) Stearic acid concentration = C = 1 mg/ml,

2) volume of stearic acid poured =V = 20 l

3) Temparature = 240C = 297K

4) pH = 6.9 (water)

5) Wihelmy plate perimeter = 39.240 mm

6) Trough width = 75.0 mm

7) Water surface tension = 72.86 mN/m, Least Count = 0.01

8) Compression Method = Constant rate compression

9) Compression rate = 10 mm/min

10)Target (Surface pressure) = 55 mN/m

11)Stearic acid molecular weight = M =284 gm/mole

Graphs:

a) Plot vs a, and identify the gas, liquid and solid regions, where a is area per molecule in

angstrom square

b) Plot A vs 1/, restricting values in the range 5 10 mN/m. A must be in m2and in

N/m. Get slope and intercept to calculate excluded area A0 for all the molecules and q,

the measure of number of moles taken

Calculation:

Step 1: After taking three runs, -A isotherm is plotted for stearic acid on pure water which is

shown in fig 1.

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Fig 1: Mean Molecular Area (m2) vs Surface Pressure(mN/m)

Step 2:Plot Avs1/to find out the values of A0and q for stearic acid system on water interface.

The significance of find out the value of slope gives the q value & intercept value is used to

measure the gives the measure of an excluded area per mole.

Fig 2: 1/Surface Pressure (N/m) vs Area (m2)

Calculations

Run1 y = 2.71E-05x + 1.46E-02R = 0.976

Slope = 2.71E-05

C = 1.46E-02

0

0.005

0.01

0.015

0.02

0.025

80 130 180 230

Area(m2)

1/

Run1

run2

run3

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Run2

y = 1.04E-05x + 1.27E-02R = 0.976

Slope = 1.04E-05

C = 1.27E-02

Run3y = 8.2E-06x + 1.15E-02

R = 0.976

Slope = 8.2E-06

C = 1.15E-02

For Run 1

From the plot, using equation no (i),

we obtain values of A0and q

= + ----------------------(i) compare with y = mx+c

=

8.314 297

= 2.71 10

8.314 297

q = 3.0975* 10-09

mol

A0= 1.46* 10

-2

For Run 2

= 1.04 10

8.314 297

q = 4.21179* 10

-09

mol

A0= 1.27*10

-2

For Run 3

= 8.2 10

8.314 297

q = 3.32084* 10-09

mol,

A0= 1.44*10

-2

Results table

Run q (moles) A (m )

1 3.0975 * 10-

0.0146

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2 4.21179* 10-09

0.0127

3 3.32084* 10-09

0.0144

Standard Deviation2.64727* 10

- 6.60E-04

Overall Observation

Surface pressure is basically a change in surface tension. It is the function of area of

water surface available for each molecule in the solution.

The most common technique for studying Langmuir monolayers of amphiphilic

substances has been to measure the surface pressure as a function of the surface area.

In Langmuir films, the area decreases the surface concentration increases and surface

pressure increases.

The spreading time for the amphiphilic substance should be sufficient for the proper

distribution on the water surface.

The sample which consists of the solvent should be volatile enough to evaporate so as to

find the surface pressure of the fatty acid easily.

Characteristics of Solvent:

Immiscible in water

Non reactive

High vapour pressure

High volatility

Conclusions:

The Langmuir mono layers are formed and the -A isotherm plotted.

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In case of Langmuir film formation, as the area decreases the surface concentration increases and

surface pressure increases.

During the monolayer formation, which is the length of time required for a surface to be covered

by an adsorbate, the molecules are almost flat on the water surface. Then after decreasing the

surface area, the molecules come closer similar to a phase change from gas phase to liquid phase

with the hydrophilic chains beginning to interact with each other.

As in normal phase change, volume changes with pressure similarly for Langmuir film, surface

pressure is dependent on surface area.When the barriers come closer, i.e. the surface area

decreases, beyond the close packed region, similarly to a phase change from liquid to solid

phase, the molecules are forced out of the monolayer.The film breaks and collapses resulting in

the decrease of surface pressure.

Reproducibility could not be achieved may be due to the spreading of surfactant-solvent mixture

on the water surface.

Shut Down procedure:

Clean the trough and the barriers with distilled water and Wilhelmy plate with acetone.

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1

CL 610: Experimental Methods

EXPERIMENT NO. 11

Determination of Dynamic Surface Tension of a SurfactantUsing a Bubble Pressure Tensiometer

TA: Shital D. Bachchhav

AIM:

(1) To determine the dynamic surface tension of a given surfactant solution using the maximumbubble pressure technique

(2) To calculate the rate constant for demicellization of the given surfactant solution

INTRODUTION: Bubble pressure tensiometry is used to study various dynamic surface

phenomena including industrial and biological applications. Many industrial processes, such as

coating, printing and flotation, operate under dynamic conditions and therefore surface tension

determined within short life spans provides often more relevant information than equilibrium

state values.

THEORY: The method is based on the measurement of the maximum pressure in a bubble

growing at the tip of a capillary immersed into the liquid under study. When a bubble grows at

the tip of a capillary, the pressure inside the capillary is measured. Maximum pressure is reached

when the bubble is hemispherical, after which it grows quickly, separates from the capillary and

a new bubble is formed. The surface tension is calculated by the Laplace equation taking the

capillary radius as radius of curvature

..(1)

The maximum internal pressure in a gas bubble forming at an orifice in a test liquid is the sum of

two components, one hydrostatic and the other due to surface tension. Pressure Pis indicated by

the transducer output and is recorded as voltage in the drive of the recorder. Linear relationship

has been taken between maximum pressure and voltage

maxkPV (2)

max

2P

r

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3

RESULTS AND OBSERVATIONS:

Table1: Calibration for pure water and ethanol

Sample Temp

(oC)

Voltage(Volts)

Surface Tension(mN/m)

DI water 24.1 4.10 72.00

15% Ethanol+DI water 24.1 2.10 42.72

40% Ethanol+DI water 24.1 1.48 30.69

Ethanol 24.1 1.00 22.39

Figure1: Voltage vs. Surface tension calibration curve

Table2:Dynamic surface tension at different bubbling flow rates of 5 mM SDS solution.

S. No Bubble frequency

(bubbles/s)

Voltage

(volts)

Surface tension (mN/m)

1 0.156 1.7 27.41

2 0.625 1.8 29.03

3 0.833 2.0 32.25

4 1.667 2.3 37.095 2.000 2.4 38.70

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4

Table3:Dynamic surface tension at different bubbling flow rates of 12 mM SDS solution.

S. No Bubble frequency

(bubbles/s)

Voltage

(volts)

Surface tension (mN/m)

1 0.250 1.78 28.70

2 0.714 1.79 28.87

3 1.000 1.80 29.03

4 1.666 1.91 30.80

5 2.500 2.0 32.25

Figure 2: Surface tension change with respect bubble frequency for () 5 mM SDS and () 12mM SDS solution.

DETERMINATION OF RATE CONSTANT FOR DEMICELLIZATION:

Critical micelle concentration (CMC) of SDS = 8 mM

We take one above CMC (12 mM) and one below CMC (5 mM) to analyse the characteristic.

Ward and Tordai suggested a model equation for determination of surface tension under such

conditions which are given below for two solutions mentioned above.

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5

For concentration below CMC and for diffusion controlled adsorption the reduction of (t)

follows square root decay

0 0( ) 2 H B F

t

D tt R T C

(4)

For concentration above CMC and for diffusion controlled adsorption the reduction of (t)

follows square root decay

2

0

1( )

2

e q

t e q

L B F

R Tt

c t D k

.. (5)

Where,

HBF and LBF are higher and lower bubble frequency respectively

t0 - Surface tension of the solution at highest bubble frequency = 38.70 mN/m

0- Surface tension of pure water in mN/n = 72.29 mN/m

R- Universal gas constant = 8.314 J/K

T- Temperature of the solution = 296 K

C- Bulk surfactant concentration in mM = 5 mM

Substituting these values in eq(4)

D- Diffusion coefficient in m2/s = 1.67*10

-11m

2/s

Substituting the value in equation (5) with the below datas the rate constant for demicellization

t HBF - Surface age corresponding to highest bubble frequency in sec = 6.9 s

t - Surface tension of the solution at lowest bubble frequency in mN/m = 28.70mN/m

eq - Equilibrium surface tension = 33.997 mN/m

C0 - Critical micelle concentration in mM = 8 mM

eq= -1/RT (d eq/dlnc) = equilibrium surface adsorption in mol/m

2= 3.56*10

-6mol/m

2

The rate constant for demicellization k = 1.71*10-4sec-1

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6

Conclusion:

The increase in bubble frequency causes increase in surface tension, as more bubbles are formedmore is the decrease in surfactant concentration in the bulk because surfactant molecules

preferably attaches on new surfaces(i.e. bubbles) this increases the surface tension.With the

increase in concentration again the surface tension decreases.The rate of demicellization is1.71*10-4s-1

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CL-610 Experimental Methods

EXP NO.-12 STOPPED FLOW REACTOR

Lab Report

By

Shashikant

(10402003)

Teaching Assistant

Department of Chemical Engineering

Indian Institute of Technology Bombay, Mumbai-400 076

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TITLE: - STOPPED FLOW REACTOR

AIM:

To study the reaction kinetics of the reduction of 2, 6-dichlorophenolindophenol(DCPIP) by

Ascorbic acid (AA) in absorbance mode and find the dead time (theoretically) using MOS-200/M, a stopped-flow module and Bio-Kine 32 V4.51

INTRODUCTION

A stopped flow instrument is a rapid mixing device used to study the chemical kinetics of a

reaction in solution. After two or more solutions containing the reagents are mixed, they are

studied by whatever experimental methods are deemed suitable. Different forms

of spectroscopy and scattering of radiation are common methods used. A stopped flow

instrument coupled to either a circular dichroism spectrometer or a fluorescence spectrometer is

often used in the field of protein folding, to observe rapid unfolding and/or refolding of proteins.

THEORY

The stopped flow technique is a flow injection technique in which reactants are rapidly injected

in a cuvette mixing chamber by forcing the reagents from syringes through jets and flow is

stopped suddenly in detector cell. This method is used for the study of reaction kinetics of very

fast reaction in solution viz. enzymatic reactions.

Dead time:- It is a critical performance parameter in Stopped flow technique, which is

difference in time between the end of mixing point and the start of observation point. In otherwords, It is the ratio of volume of cuvette (V) to the volumetric flow rate in the chamber (q).

REACTION

DCPIP L Ascorbic Acid L-Dehydo Ascorbic Acid

APPARATUS

MOS-200/M ( with 150W Xenon mercury lamp)

FC-15 cuvette

SFM-20 equipped with 10 ml syringes

Bio-Kine software

Beakers, Volumetric flask

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CHEMICALS

De-ionized (DI) water

100 ml of 10 mM Ascorbic acid (pH=9)

100 ml of 0.5mM DCPIP

APPLICATION

1. SFM finds application in analysis of very small quantities of material of order of less than 0.7

to 500 L and handling of corrosive materials(e.g H2SO4).

2. It is widely used for the study of mechanism of Ozone- Alkene reaction in gas phase for the

purpose of atmospheric modeling.

Fig. 1: Classical Stopped-flow design

PROCEDURE

A. Prepare stock solutions of concentration 0.5 mM of DCPIP and AA of 10 mM from the

respective salts.

B. Switch on the ALX 250 and ensure that power reaches 150 W. Meanwhile, switch on the

PMS 250 and MPS 70/2.

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C. Start Bio-Kine interface software ion on desktop which will control SFM.

D. Set wavelength 524 nm and ensure AUTO MODE in spectrometer settings.

E. After the settings are done, purge the cuvette manually by injecting DI water through

syringes to ensure no previous contamination.

F.

Water referencing:-

1. Fill both the syringes with DI water and fix on SFM

2. Click on Mixing sequence in interface, set appropriate values of mixing ratio,

total volume/shot and total flow rate, ensuring a safe mode(green color)of

operation and click on Ready.

3. Click on device form toolbar, select transient recorder kinetics and on the

acquisition setup start giving shots under shot control with periodic view on y-

auto-scale and observe absorbance-time plot.

4. Ensure absorbance reading of water reference zero or close to zero, otherwise

reset reference voltage or increase number of shots to make base line zero or closeto zero.

G. After water referencing, a calibration for pure DCPIP (0.5mM) and DCPIP-H2O system

for varying mixing ratio (2:1, 1:1, 1:2, 1:3, 1:4, 1:5) is recorded.

H. Replace the syringe containing DI water with AA of 10mM concentration and 0.5 mM

concentration of DCPIP. Repeat the steps (G)for the reaction mixture of DCPIP-AA

(pH=9) for different mixing ratio (4:1, 3:1, 2:1) kinetics of which is to be determined

through SFM 20.

I. Record absorbance value from absorbance time plot on software interface.

J.

Rinse the system with DI water and switch off all the devices.

Let A and B are two reactants such that

A A Br KC C

If B in excess, then KCBwill be constant and reaction will be pseudo first order. In such case:

-rA=K1CA

Here K1=KCB

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RESULTS

Table 1: Calibration for DCPIP-Water System

C1 (mM) C2 (mM)

Mixing ratio

DCPIP : Water V (mL/sec) C (mM) Absorbance (AU)0.5 0 2:1 4 0.3333 0.394

0.5 0 1:1 5.5 0.25 0.268

0.5 0 1:2 5.5 0.1667 0.199

0.5 0 1:3 4 0.125 0.160

0.5 0 1:4 4 0.1 0.132

0.5 0 1:5 4 0.0833 0.112

0.5 0 0:1 5.5 0 0.0001

C1: Concentration of pure DCPIP in solution (mM)

C2: Concentration of DCPIP in pure water (mM)V: Total volumetric flow rate (mL/sec)

C: Concentration of DCPIP in mixture (mM)

Fig.1: Calibration curve for DCPIP + H2O system.

y = 1.1192x + 0.0115R = 0.9897

0

0.1

0.2

0.3

0.4

0.5

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Absorbanc

e(AU)

Conc. of DCPIP (mM)

Calibration Curve (DCPIP + H2O)

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DCPIP + Ascorbic Acid (4:1)

Fig.2: DCPIP + Ascorbic acid with mixing ratio:-4:1

Fig.3: Evaluating rate Constant (k) for DCPIP + AA, Flow Rate:-4:1

0

0.1

0.2

0.3

0.4

0.5

0.00E+00 1.00E+00 2.00E+00 3.00E+00 4.00E+00

Conc.

(mM)

Time (s)

Conc. Vs Time

y = 0.3395x + 0.045R = 0.999

0

0.2

0.4

0.6

0.8

1

1.2

0 0.5 1 1.5 2 2.5 3 3.5

ln(C0/C)

Time (s)

ln(C0/C) vs Time

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DCPIP + Ascorbic Acid (3:1)

Fig.4: DCPIP + Ascorbic acid with mixing ratio:-3:1

Fig.5: Evaluating rate Constant (k) for DCPIP + AA, Flow Rate:-3:1

0

0.05

0.1

0.15

0.2

0.25

0.30.35

0.4

0.00E+00 1.00E+00 2.00E+00 3.00E+00 4.00E+00

Conc.

(mM)

Time (s)

Conc. Vs Time

y = 0.3796x + 0.0364R = 0.9983

0

0.2

0.4

0.6

0.81

1.2

1.4

0 0.5 1 1.5 2 2.5 3 3.5

ln(C0/C)

Time (s)

ln(C0/C) vs Time

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DCPIP + Ascorbic Acid (2:1)

Fig.6: DCPIP + Ascorbic acid with mixing ratio:-2:1

Fig.7: Evaluating rate Constant (k) for DCPIP + AA, Flow Rate:-2:1

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.00E+00 1.00E+00 2.00E+00 3.00E+00 4.00E+00

Conc.

(mM)

Time (s)

Conc. Vs Time

y = 0.4795x + 0.1121R = 0.9935

0

0.5

1

1.5

2

0 0.5 1 1.5 2 2.5 3 3.5

ln(C0/C)

Time (s)

ln(C0/C) vs Time

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Calculating Dead Time:

ln(Cf/C0) = k *td

Cf= Feed Concentration of DCPIP

C0=Concentration of DCPIP at the beginning of observation

Table 2: Rate constant (k) for DCPIP + AA system

Sl.No. Mixing ratioDCPIP : AA

Molar ratioDCPIP : AA

Totalflow rate

(mL/s)

InitialConc. (C0),

(mM/lt)

Feed Conc.(Cf),

(mM/lt)

Rateconstant

(k), (1/s)

DeadTime

(td), (s)

1 4:1 1:5 4 0.392 0.4 0.340 0.060

2 3:1 1:667 4 0.375 0.375 0.380 0.002

3 2:1 1:10 4 0.321 0.333 0.480 0.078

DISCUSSIONS

1. Conc