The document describes procedures for determining the available chlorine content in a bleaching powder sample using iodometric titration. Key steps include:
1. Standardizing a sodium thiosulfate solution by titrating it against a primary standard potassium dichromate solution in the presence of excess potassium iodide.
2. Dissolving a bleaching powder sample in water and liberating chlorine by adding acetic acid.
3. Reacting the liberated chlorine with excess potassium iodide to generate iodine, then titrating the iodine with the standardized sodium thiosulfate solution.
4. Calculating the available chlorine content based on the titration
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Physical Chemistry
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Physical Chemistry
Karl fischer titration is an analytic system to determine the trace amount of water in solid, gases and liquids. It is a very efficient and accurate technique. In this presentation we go deeper about this titration system.
content- Principle
Ilkovic equation
Construction and working of dropping mercury electrode and rotating platinum electrode
Applications
Polarography is a voltammetric technique in which chemical species (ions or molecules) undergo oxidation (lose electrons) or reduction (gain electrons) at the surface of a dropping mercury electrode (DME) at an applied potential. Polarography only applies to the DME.
Objective of polarography
Polarography is an electroanalytical technique that measures the current flowing between two electrodes in the solution (in the presence of gradually increasing applied voltage) to determine the concentration of solute and its nature respectively
Polarography is based upon the principle that gradually increasing voltage is applied between two electrodes, one of which is polarisable (dropping mercury electrode) and other is non-polarisable and current flowing between the two electrodes is recorded.
A sigmoid shape current-voltage curve is obtained from which half wave potential as well as diffusion current is calculated.
Diffusion current is used for determination of concentration of substance.
Half wave potential is characteristic of every element.
Ilkovic equation is a relation used in polarography relating the diffusion current (id) and the concentration of the non-polarisable electrode, i.e., the substance reduced or oxidised at the dropping mercury electrode (polarisable electrode).
Definitions of types of currents
1. Residual current (ir), 2. Migration current (im): , 3. Diffusion current (id) 4.Half wave potential 5. Limiting current (il)
Dropping mercury electrode- Dropping mercury electrode (DME) is a polarisable electrode and can act as both anode and cathode.
The pool of mercury acts as counter electrode,
i.e., anode if DME is cathode or
cathode if DME is anode.
The counter electrode is a non-polarisable electrode.
To the analyte solution, electrolyte like KCl is added i.e., 50-100 times of sample concentration.
Pure nitrogen or hydrogen gas is bubbled through the solution, to expel (remove) out oxygen.
Eg: If the analyte solution contains cadmium ions, then cadmium ions are discharged at cathode (-)
Cd2+ + 2e- → Cd
Then, gradually increasing voltage is applied to the polarographic cell and current is recorded.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound and this is used in qualitative analysis.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound
RAOULT'S LAW ( Physical & Analytical Chemistry)Hasnaın Sheıkh
Name; Hasnain Nawaz
Surname : Shaikh
ROLL NO: 16 CH 42
B.E: Chemical Engineering (In Progress).
Mehran University of Engineering and Technology
Jamshore, ISO 9001 Certified.
Potentiometry, Electrochemical cell, construction and working of indicator an...Vandana Devesh Sharma
Potentiometry - Electrochemical cell -Construction and working of reference (Standard hydrogen, silver chloride electrode and calomel electrode)
Indicator electrodes (metal electrodes and glass electrode)
Methods to determine end point of potentiometric titration
and applications
Potentiometry is the method to find the concentration of solute in
A given solution by measuring the potential between two Electrodes
(reference and Indicator electrode) . Potentiometric titration involves
the measurement of the potential of the indicator electrode and
reference electrode.
In potentiometric titration reference and indicator electrodes are
immersed in the solution of particular analyte (titrand) and
potential of indicator electrode is measured with relation to
reference electrode.
Titrant is added in analyte (Titrand) and change in potential is noted
down.
At the end point there is sharp change in potential on indicator
electrode.
Graph is plotted between the indicator electrode potential and
volume of titrant added.
This method is used for determination of sharp end point.
Types of Potentiometric Titration
1. Acid-base titration 2. Redox Titration 3.Complexometric titration 4. Precipitation Titration
Karl fischer titration is an analytic system to determine the trace amount of water in solid, gases and liquids. It is a very efficient and accurate technique. In this presentation we go deeper about this titration system.
content- Principle
Ilkovic equation
Construction and working of dropping mercury electrode and rotating platinum electrode
Applications
Polarography is a voltammetric technique in which chemical species (ions or molecules) undergo oxidation (lose electrons) or reduction (gain electrons) at the surface of a dropping mercury electrode (DME) at an applied potential. Polarography only applies to the DME.
Objective of polarography
Polarography is an electroanalytical technique that measures the current flowing between two electrodes in the solution (in the presence of gradually increasing applied voltage) to determine the concentration of solute and its nature respectively
Polarography is based upon the principle that gradually increasing voltage is applied between two electrodes, one of which is polarisable (dropping mercury electrode) and other is non-polarisable and current flowing between the two electrodes is recorded.
A sigmoid shape current-voltage curve is obtained from which half wave potential as well as diffusion current is calculated.
Diffusion current is used for determination of concentration of substance.
Half wave potential is characteristic of every element.
Ilkovic equation is a relation used in polarography relating the diffusion current (id) and the concentration of the non-polarisable electrode, i.e., the substance reduced or oxidised at the dropping mercury electrode (polarisable electrode).
Definitions of types of currents
1. Residual current (ir), 2. Migration current (im): , 3. Diffusion current (id) 4.Half wave potential 5. Limiting current (il)
Dropping mercury electrode- Dropping mercury electrode (DME) is a polarisable electrode and can act as both anode and cathode.
The pool of mercury acts as counter electrode,
i.e., anode if DME is cathode or
cathode if DME is anode.
The counter electrode is a non-polarisable electrode.
To the analyte solution, electrolyte like KCl is added i.e., 50-100 times of sample concentration.
Pure nitrogen or hydrogen gas is bubbled through the solution, to expel (remove) out oxygen.
Eg: If the analyte solution contains cadmium ions, then cadmium ions are discharged at cathode (-)
Cd2+ + 2e- → Cd
Then, gradually increasing voltage is applied to the polarographic cell and current is recorded.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound and this is used in qualitative analysis.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound
RAOULT'S LAW ( Physical & Analytical Chemistry)Hasnaın Sheıkh
Name; Hasnain Nawaz
Surname : Shaikh
ROLL NO: 16 CH 42
B.E: Chemical Engineering (In Progress).
Mehran University of Engineering and Technology
Jamshore, ISO 9001 Certified.
Potentiometry, Electrochemical cell, construction and working of indicator an...Vandana Devesh Sharma
Potentiometry - Electrochemical cell -Construction and working of reference (Standard hydrogen, silver chloride electrode and calomel electrode)
Indicator electrodes (metal electrodes and glass electrode)
Methods to determine end point of potentiometric titration
and applications
Potentiometry is the method to find the concentration of solute in
A given solution by measuring the potential between two Electrodes
(reference and Indicator electrode) . Potentiometric titration involves
the measurement of the potential of the indicator electrode and
reference electrode.
In potentiometric titration reference and indicator electrodes are
immersed in the solution of particular analyte (titrand) and
potential of indicator electrode is measured with relation to
reference electrode.
Titrant is added in analyte (Titrand) and change in potential is noted
down.
At the end point there is sharp change in potential on indicator
electrode.
Graph is plotted between the indicator electrode potential and
volume of titrant added.
This method is used for determination of sharp end point.
Types of Potentiometric Titration
1. Acid-base titration 2. Redox Titration 3.Complexometric titration 4. Precipitation Titration
Synthesis of tris (thiourea) copper (i) sulphate by kwezi mwaka juliusMakerere University
its a well described report on SYNTHESIS OF TRIS (THIOUREA) COPPER (I) SULPHATE and this serves to industrial chemistry students doing transition metal chemistry.
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South Africa is one of the first countries to implement full-scale mine water reclamation to drinking water quality. Reverse osmosis is already being used on full scale for desalination of mine water. However, with increased recycling of mine water, the result has been the increased generation of sludge. The Council for Scientific and Industrial Research (CSIR) has developed the Alkali-Barium-Carbonate (CSIR-ABC) process that can be used for neutralization and desalination of sulphate-rich effluents while recovering valuable by-products from the mixed sludges produced. A mixture of BaSO4 and CaCO3 sludge is produced as one of the by-products, which preferably needs to be separated into its components prior to thermal treatment. The aim of this study was to separate CaCO3 and BaSO4 from a CaCO3-BaSO4 mixed sludge through dissolution of CaCO3 as Ca(HCO3)2 in contact with CO2. Measured quantities of a simulated CaCO3-BaSO4 mixed sludge from the CSIR-ABC process were fed into a reactor vessel containing deionized water and pressurized CO2 was introduced. The effects of temperature and pressure with time were investigated while monitoring alkalinity, pH and calcium concentration. The findings of this study were: (1) The dissolution rate of CaCO3 was rapid i.e. from 0 to 2000mg/L in the first 20 minutes; (2) Ca(HCO3)2 had a high solubility of about 2 600 mg/L when in contact with CO2 at 1 atm., while BaSO4 was almost completely insoluble; (3) The solubility of Ca(HCO3)2 increased with decreasing temperature and increasing pressure; (4) CaCO3, after conversion to Ca(HCO3)2, was separated from BaSO4 in a CaCO3-BaSO4 mixed sludge; (5) Visual MINTEQ model is a powerful tool that can be used to predict the solubilities of CaCO3 and BaSO4 when contacted with CO2.
Willie Nelson Net Worth: A Journey Through Music, Movies, and Business Venturesgreendigital
Willie Nelson is a name that resonates within the world of music and entertainment. Known for his unique voice, and masterful guitar skills. and an extraordinary career spanning several decades. Nelson has become a legend in the country music scene. But, his influence extends far beyond the realm of music. with ventures in acting, writing, activism, and business. This comprehensive article delves into Willie Nelson net worth. exploring the various facets of his career that have contributed to his large fortune.
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Introduction
Willie Nelson net worth is a testament to his enduring influence and success in many fields. Born on April 29, 1933, in Abbott, Texas. Nelson's journey from a humble beginning to becoming one of the most iconic figures in American music is nothing short of inspirational. His net worth, which estimated to be around $25 million as of 2024. reflects a career that is as diverse as it is prolific.
Early Life and Musical Beginnings
Humble Origins
Willie Hugh Nelson was born during the Great Depression. a time of significant economic hardship in the United States. Raised by his grandparents. Nelson found solace and inspiration in music from an early age. His grandmother taught him to play the guitar. setting the stage for what would become an illustrious career.
First Steps in Music
Nelson's initial foray into the music industry was fraught with challenges. He moved to Nashville, Tennessee, to pursue his dreams, but success did not come . Working as a songwriter, Nelson penned hits for other artists. which helped him gain a foothold in the competitive music scene. His songwriting skills contributed to his early earnings. laying the foundation for his net worth.
Rise to Stardom
Breakthrough Albums
The 1970s marked a turning point in Willie Nelson's career. His albums "Shotgun Willie" (1973), "Red Headed Stranger" (1975). and "Stardust" (1978) received critical acclaim and commercial success. These albums not only solidified his position in the country music genre. but also introduced his music to a broader audience. The success of these albums played a crucial role in boosting Willie Nelson net worth.
Iconic Songs
Willie Nelson net worth is also attributed to his extensive catalog of hit songs. Tracks like "Blue Eyes Crying in the Rain," "On the Road Again," and "Always on My Mind" have become timeless classics. These songs have not only earned Nelson large royalties but have also ensured his continued relevance in the music industry.
Acting and Film Career
Hollywood Ventures
In addition to his music career, Willie Nelson has also made a mark in Hollywood. His distinctive personality and on-screen presence have landed him roles in several films and television shows. Notable appearances include roles in "The Electric Horseman" (1979), "Honeysuckle Rose" (1980), and "Barbarosa" (1982). These acting gigs have added a significant amount to Willie Nelson net worth.
Television Appearances
Nelson's char
Characterization and the Kinetics of drying at the drying oven and with micro...Open Access Research Paper
The objective of this work is to contribute to valorization de Nephelium lappaceum by the characterization of kinetics of drying of seeds of Nephelium lappaceum. The seeds were dehydrated until a constant mass respectively in a drying oven and a microwawe oven. The temperatures and the powers of drying are respectively: 50, 60 and 70°C and 140, 280 and 420 W. The results show that the curves of drying of seeds of Nephelium lappaceum do not present a phase of constant kinetics. The coefficients of diffusion vary between 2.09.10-8 to 2.98. 10-8m-2/s in the interval of 50°C at 70°C and between 4.83×10-07 at 9.04×10-07 m-8/s for the powers going of 140 W with 420 W the relation between Arrhenius and a value of energy of activation of 16.49 kJ. mol-1 expressed the effect of the temperature on effective diffusivity.
Artificial Reefs by Kuddle Life Foundation - May 2024punit537210
Situated in Pondicherry, India, Kuddle Life Foundation is a charitable, non-profit and non-governmental organization (NGO) dedicated to improving the living standards of coastal communities and simultaneously placing a strong emphasis on the protection of marine ecosystems.
One of the key areas we work in is Artificial Reefs. This presentation captures our journey so far and our learnings. We hope you get as excited about marine conservation and artificial reefs as we are.
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Natural farming @ Dr. Siddhartha S. Jena.pptxsidjena70
A brief about organic farming/ Natural farming/ Zero budget natural farming/ Subash Palekar Natural farming which keeps us and environment safe and healthy. Next gen Agricultural practices of chemical free farming.
WRI’s brand new “Food Service Playbook for Promoting Sustainable Food Choices” gives food service operators the very latest strategies for creating dining environments that empower consumers to choose sustainable, plant-rich dishes. This research builds off our first guide for food service, now with industry experience and insights from nearly 350 academic trials.
growbilliontrees.com-Trees for Granddaughter (1).pdf
Exp 8
1. 58
EXPT. 8 IODOMETRIC DETERMINATION
OF AVAILABLE CHLORINE IN A
SAMPLE OF BLEACHING POWDER
Structure
8.1 Introduction
Objectives
8.2 Principle
8.3 Requirements
8.4 Solutions Provided
8.5 Procedure
8.6 Observations and Calculations
8.7 Result
8.1 INTRODUCTION
In the previous experiment you learnt about and performed iodimetric determination
of ascorbic acid in a tablet of Vitamin C. In this process we recalled from Unit 10 of
the Basic Analytical Chemistry course (Section 10.7.1) that the I2/2I‒
couple is of
medium oxidising power.Molecular iodine is a weak oxidant, whereas the iodide ions
are relatively weak reductant. Accordingly, the I2/I–
redox couple can be used for the
determination of reductants as well as the oxidants. In the previous experiment you
used I2 (generated in situ from acidification of KIO3) as the oxidizing agent to
determine the reductant, ascorbic acid. In the present experiment you will be using
iodide ions (from KI) to determine available chlorine in bleaching powder. Such a
determination wherein iodide ions are used as a reducing agent is termed as
iodometric determination.
Bleaching powder, also known as chlorinated lime, is a yellowish-white powder
having a smell of chlorine and is readily soluble in water. It is prepared by passing
chlorine gas over slaked lime at a temperature of 35-450
and consists of a mixture of
calcium hypochlorite Ca(OCl)2 and calcium chloride CaCl2; in addition some amount
of free slaked lime i.e. Ca(OH)2.H2O is generally present. Of these, Ca(OCl2) is
responsible for the bleaching action of bleaching powder . On treatment with glacial
acetic acid, it liberates chlorine gas (Cl2) as per the following reaction.
( ) ( ) 222332 CIOHCOOCHCaCOOH2CHOCICa ++→+ ….(8.1)
The amount of chlorine liberated by the action of an acid on bleaching powder
(CaOCl2) is termed as available chlorine. The chlorine content of bleaching powder
varies from 35 – 40%. Besides bleaching action it has got strong germicidal and
disinfectant properties also. Accordingly, it finds application as a disinfectant for
drinking water or swimming pool water. Industrially, the bleaching powder finds
major use in chemical, paper, textile and oil industries. The bleaching, oxidizing or
disinfecting potential of a sample of bleaching powder depends on the percentage of
chlorine liberated on action of acid. We may define available chlorine to be the grams
of chlorine liberated from 100 g of the bleaching powder on treatment with dilute acid.
Due to its hygroscopic nature, bleaching powder absorbs moisture from atmosphere
and evolves chlorine as per the following reaction
( ) 222
2-
CIOHCaOHCaClOCl +→+++ +−
….(8.2)
Due to this deterioration, a sample of bleaching powder may always contain lesser
amount of chlorine than expected and therefore a sample of bleaching powder needs to
be analysed for its effective or available chlorine. In the next experiment you would
2. 59
learn about precipitation titrations and perform a precipitation titration for the
determination of chloride ions in a solution.
8.2 OBJECTIVES
After studying and performing the experiment, you should be able to:
• define available chlorine,
• define iodometric titrations,
• state and explain the principle of iodometric titrations with reference to the
determination of available chlorine in a sample of bleaching powder,
• state the reasons for using acetic acid to liberate chlorine from bleaching
powder,
• prepare a standard solution of potassium dichromate and use it to standradise a
solution of sodium thiosulphate,
• write the chemical equations involved in the titration of a solution of bleaching
powder solution with sodium thiosulphate,
• prepare a solution of bleaching powder from the given sample,
• perform the determination of available chlorine in the solution of bleaching
powder, and
• calculate the amount of available chlorine in the solution of bleaching powder.
8.3 PRINCIPLE
As mentioned in the introduction, a sample of bleaching powder liberates chlorine gas
(Cl2) on treatment with glacial acetic acid, as per the following reaction.
( ) ( ) 222332 CIOHCOOCHCaCOOH2CHOCICa ++→+ …(8.1)
The amount of chlorine so liberated is termed as available chlorine. The liberated
chlorine can be used to oxidize KI (taken in excess) in presence of acid and liberate
out an equivalent amount of iodine as per the following equation:
22 I2KCl2KICl +→+ …(8.3)
This iodine can then be determined by titrating against a standardised solution of
sodium thiosulphate using freshly prepared starch solution as an indicator. The
chemical reactions involved can be given as follows
2NaIOSNaIOS2Na 6422322 +→+ …(8.4)
The overall reaction between the chlorine liberated from the bleaching powder and
sodium thiosulphate mediated by potassium iodide can be obtained by adding eq. 8.3
and eq. 8.4 can be written as follows,
22 I2KC2KICl +→+ l …(8.3)
2NaIOSNaIOS2Na 6422322 +→+ …(8.4)
ll CK22NaIOSNa2KICOS2Na 6422322 ++→++ …(8.5)
The sodium thiosulphate can be standardized by titrating against a primary standard
solution of potassium dichromate. (alternatively, you can use potassium iodate for the
purpose as described in the previous experiment)
Sodium thiosulphate,
Na2S203.5H20, can be obtained
chemically pure. However, a
standard solution of
thiosulphate cannot be made
by exact weighing as it reacts
with atmospheric O2 and also
the CO2 dissolved in water.
More so, even some
microorganisms can
decompose thiosulphate
3. 60
The standradisation of sodium thiosulphate by using potassium dichromate is also
based on iodimetric titrations. The reaction between potassium dichromate and sodium
thiosulphate is mediated through the participation of iodide ions provided by
potassium iodide as explained below.
In acidic medium, Cr2O7
2-
ions gets reduced to Cr (III) ions as per the following
equation
O7H2Cr6e14HOCr 2
3-2
72 +→++ ++−
…(8.6)
The iodide ions from KI on the other hand can get oxidised to I2 as follows:
−−
+→ 2eI2I 2 …(8.7)
In order to maintain the electron balance, we can multiply equation 8.7 by 3 to get the
following,
−−
+→ 6eI36I 2 … (8.8)
Adding equations 8.6 and 8.8, we get the overall ionic equation for the reaction
between potassium dichromate and potassium iodide as :
O7H3I2Cr6I14HOCr 22
32
72 ++→++ +−+−
… (8.9)
Thus, from Eq. 8.9, one mole of potassium dichromate reacts with 6 moles of
potassium iodide and liberates 3 moles of iodine in the process.
The liberated iodine, in turn, reacts with sodium thiosulphate solution as per the
following equation
−−−
+=+ 2
64
2
322 O3S6IO6S3I …(8.10 )
The iodide ions are regenerated back. The net chemical reaction involving a titration
of potassium dichromate and sodium thiosulphate in the presence of excess potassium
iodide can be written by combining Eq. 8.8 and Eq. 8.9, as shown below,
O7H3I2Cr6I14HOCr 22
32
72 ++→++ +−+−
... (8.9)
−−−
+=+ 2
64
2
322 O3S6IO6S3I ... (8.10)
O7HO3S2CrO6S14HOCr 2
2
64
32
32
2
72 ++→++ −+−+−
… (8.11)
We see from Eq. 8.11 that one mole of potassium dichromate is equivalent to 6 moles
of sodium thiosulphate. Therefore, the molarities are related by the following
relationship.
6 MDichromateVDichromate = MThiosulphateVThiosulphate … (8.12)
You would be using this equation to compute the molarity of the given solution of
sodium thiosulphate.
8.4 REQUIREMENTS
Apparatus Chemicals
4. 61
Volumetric flask (100 cm3
) – 1
Burette (50 cm3
) – 1
Pipette (10 cm3
) – 1
Weighing bottle – 1
Burette stand with clamp – 1
Conical flasks (100 cm3
) – 2
Funnel – 1
Beakers (250 cm3
) – 2
Bleaching powder
Potassium dichromate
Potassium iodide
Sodium thiosulphate
Sodium carbonate
Sulphuric acid
Sodium bicarbonate
Acetic acid
Starch
8.5 SOLUTIONS PROVIDED
1. ~0.05 M Sodiun thiosulphate: It is prepared by dissolving about 7.9 g of
sodium thiosulfate pentahydrate in about 200 cm3
of distilled water taken in a
1.0 dm3
volumetric flask and adding about 0.1 g of sodium carbonate to it. The
solution is then diluted to the mark with distilled water.
2. 0.5% Starch indicator solution: It is prepared by mixing 0.25g of soluble
starch with 50 cm3
of distilled water taken in a 100 cm3
conical flask or beaker
and heating it with stirring at about 80o
C for about 5 minutes. The solution is
then allowed to cool to room temperature.
3. 10% Potassium iodide solution: It is prepared by dissolving 100g of KI in
about 200 cm3
of distilled water taken in a 1 dm3
beaker or conical flask and
stirring well to dissolve it. It is followed by making up the volume to 1 dm3
by
adding more distilled water.
8.6 PROCEDURE
The determination of available chlorine in a sample of bleaching powder using
iodometric titration consists of the following steps:
a) Preparation of potassium dichromate primary standard
b) Standradisation of sodium thiosulphate solution
c) Preparation of the solution of the bleaching powder sample
d) Determination of available chlorine in the above solution by iodimetric
titration
Follow the instructions given below in sequential manner
a) Preparation of potassium dichromate primary standard
• Accurately weigh about 0.3g of potassium dichromate in a clean dry
weighing bottle, and transfer the same to a clean conical flask of 100 cm3
capacity through a glass funnel.
• Add about 20 cm3
of distilled water and swirl the contents of the flask
until all the potassium dichromate is dissolved.
• Make the volume upto the mark by adding more distilled water.
b) Standradisation of sodium thiosulphate solution
Sodium carbonate is added to
adjust the pH to
approximately 9.3 so as to
inhibit the formation of
thiosulfonic acid.
5. 62
• Pipette out 10 cm3
of potassium dichromate solution in a 100 cm3
conical
flask, add 10 cm3
of dilute sulphuric acid and 1 g sodium hydrogen
carbonate with gentle swirling to liberate carbon dioxide.
• Add 10 cm3
of 10% KI solution, swirl, cover the flask with watch glass
and allow the solution to stand for about 5 minutes in a dark place.
• Titrate the liberated iodine against the sodium thiosulphate solution taken
in the burette until the solution acquires a light pale yellow colour.
• Add about 2 cm3
of starch solution and continue adding sodium
thiosulphate dropwise until the violet colour of the starch iodine
complex just disappears.
• Repeat the standardization procedure at least three times and record your
observations in Observation Table 8.1.
c) Preparation of the solution of the bleaching powder sample
• Accurately weigh about 3-4 g of the bleaching powder and put it into a
clean glass mortar. Add a little water, and rub the mixture to a smooth
paste.
• Add a little more water, triturate with the pestle and allow the mixture to
settle.
• Pour off the milky liquid into a 500-cm3
volumetric flask.
• Grind the residue with a little more water, and repeat the operation until
the whole of the sample has been transferred to the flask either in solution
or in a state of very fine suspension, and the mortar washed quite clean.
• Make the volume upto the mark by adding more distilled water.
d) Determination of available chlorine in the above solution by iodometric
titration
• Wash the burette with distilled water and rinse with standard solution of
sodium thiosulphate and then fill the burette with the same.
• Carefully pipette out 10 cm3
of homogenous solution of bleaching powder
and transfer into a 100 cm3
conical flask.
• Add about 10 cm3
of 10% potassium iodide (KI) solution and about half
test tube of glacial acetic acid to the flask.
• Keep the flask in a dark place for about 5 minutes
• Titrate the liberated iodine against the sodium thiosulphate solution taken
in the burette until the solution acquires a light pale yellow colour.
• Add about 2 cm3
of starch solution and continue adding sodium
thiosulphate dropwise until the violet colour of the starch iodine
complex just disappears.
• Repeat the standardization procedure at least three times and record your
observations in Observation Table 8.2.
8.7 OBSERVATIONS AND CALCULATIONS
Sodiu
carbon
an atm
CO2 i
which
air an
oxidat
from a
6. 63
a) Preparation of standard solution of potassium dichromate
Mass of weighing bottle + potassium dichromate = m1 g = ..............g
Mass of weighing bottle (after transferring potassium dichromate)
= m2 g = .............. g
Amount of potassium dichromate transferred = m1 – m2 = m g = ............. g
Molar mass (Mm) of potassium dichromate = 294.18 g mol−1
Volume of potassium dichromate prepared = 100 cm3
Molarity of standard potassium dichromate solution =
K Cr O2 2 7
1000 10
...........
100 294.2 294.2
m m
M M
×
= = =
×
b) Standardisation of sodium thiosulphate solution
Volume of standard K2Cr2O7 solution taken in conical flask, Vdichromate = …cm3
Volume of 10% KI added : 10 cm3
Volume of dilute sulphuric acid added : 10 cm3
Solution in the burette: Sodium thiosulphate
Indicator used: Starch
Observation Table 8.1: Standardisation of sodium thiosulphate
S.No. Volume of potassium
dichromate (in cm3
)
Burette reading
Initial Final
Titre value (in cm3
)
(Final-initial reading)
1
2
3
Concordant reading
The concentration of the given sodium thiosulphate solution can be determined as
follows.
The reactions involved:
O7HO3S2CrO6S14HOCr 2
2
64
32
32
2
72 ++→++ −+−+−
Molarity equation: 6MDichromateVDichromate = MThiosulphateVThiosulphate
Thiosulphate
6 Dichromate Dichromate
Thiosulphate
M V
M
V
=
Substituting the values, the molarity of thiosulphate =
The molarity of given thiosulphate solution is = ……….M
c) Preparation of the solution of the bleaching powder sample
7. 64
Mass of bleaching powder taken =
d) Determination of available chlorine in the given sample of bleaching
powder
Volume of bleaching powder solution taken in conical flask, = 10 cm3
Volume of acetic acid added : 10 cm3
Volume of 10% KI added : 10 cm3
Solution in the burette: Sodium thiosulphate
Indicator used: Starch
Observation Table 8.2: Determination of the amount of available chlorine in the
solution of given bleaching powder
S.No. Volume of bleaching
powder solution (in
cm3
)
Burette reading
Initial Final
Titre value (in cm3
)
(Final-initial reading)
1
2
3
Concordant reading
The molarity of the iodine liberated from KI solution (which in turn is equal to the
amount of chlorine liberated from the bleaching powder on the action of acetic acid)
can be determined as follows.
The reaction involved:
ll 2C2NaIOSNa2KICOS2Na 6422322 ++→++
Molarity equation: 2MChlorine VChlorine = M Thiosulphate V Thiosulphate
Thiosulphate Thiosulphate
2Chlorine
Chlorine
M V
M
V
=
Substituting the values, of the molarity and the volume of thiosulphate used, the
molarity of chlorine is found to be: ......M=
The mass of chlorine liberated = molarity × molar mass = ….M × 70.90 g mol−1
= ….×70.90 g = P g dm-3
The mass of bleaching powder dissolved per liter = 2 ×w g
(the solution was w g/ 500 cm3
)
Thus, the amount of available chlorine in 2 w g of bleaching powder = P g
• The amount of available chlorine in 100.0 g of bleaching powder = 50 P / w g
• The available chlorine (the grams of chlorine liberated from 100 grams of the
bleaching powder on treatment with dilute acid) = 50 P/w g
8.8 RESULTS
The available chlorine (the grams of chlorine liberated from 100 g of the bleaching
powder on treatment with dilute acid) = ….. g