This document provides background information on two titrimetric methods for analyzing chloride: a weight titration method using a chemical indicator and a volumetric titration method using potentiometric detection. The weight titration method involves standardizing a silver nitrate solution and then titrating samples to determine the mass of silver nitrate needed to reach the equivalence point. The potentiometric method uses a silver ring electrode to monitor the titration potential and determine the endpoint volume. Procedures for both the Fajans indicator method and potentiometric titration of samples are described.
This presentation gives us idea about Gravimetric Analysis which is widely used in chemistry. Hope This Helps !
For More Information - 19103083@student.hindustanuniv.ac.in
What is Gravimetric analysis, stepes invloved in gravimetry, Filteration medium in gravimetry, gravimetric factor, application, organic and inorganic prepecating agents
Titration - principle, working and applicationSaloni Shroff
A brief introduction to the titration technique used to know the concentration of unknown solutions. different types, indicators used and its application in foods and nutrition is also described.
This presentation gives us idea about Gravimetric Analysis which is widely used in chemistry. Hope This Helps !
For More Information - 19103083@student.hindustanuniv.ac.in
What is Gravimetric analysis, stepes invloved in gravimetry, Filteration medium in gravimetry, gravimetric factor, application, organic and inorganic prepecating agents
Titration - principle, working and applicationSaloni Shroff
A brief introduction to the titration technique used to know the concentration of unknown solutions. different types, indicators used and its application in foods and nutrition is also described.
This is a general presentation about Argentometric Titration or well known as Precipitation Titration. Contain Mohr Methods, Volhard Methods, and Fajans Methods.
Titrimetric analysis is a method of analysis in which a solution of the substance being determined is treated with a solution of a suitable reagent of exactly known concentration. The reagent is added to the substance until the amount added is equivalent to the amount of substance to be determined.
more chemistry contents are available
1. pdf file on Termmate: https://www.termmate.com/rabia.aziz
2. YouTube: https://www.youtube.com/channel/UCKxWnNdskGHnZFS0h1QRTEA
3. Facebook: https://web.facebook.com/Chemist.Rabia.Aziz/
4. Blogger: https://chemistry-academy.blogspot.com/
Physical Chemistry
Errors - pharmaceutical analysis -1, bpharm 1st semester, notes, topic errors
full details and answer about error
TN DR MGR UNIVERSITY
by Kumaran.M.pharm, professor
Learning objectives
Introduction
Conditions For Volumetric Analysis
Terms In Volumetric Analysis
Primary Standard
Methods Of Expressing Concentrations In Volumetric Analysis
Types of Titration Methods
Classification Of Titrimetric Or Volumetric Methods
Conclusion
References
This is a general presentation about Argentometric Titration or well known as Precipitation Titration. Contain Mohr Methods, Volhard Methods, and Fajans Methods.
Titrimetric analysis is a method of analysis in which a solution of the substance being determined is treated with a solution of a suitable reagent of exactly known concentration. The reagent is added to the substance until the amount added is equivalent to the amount of substance to be determined.
more chemistry contents are available
1. pdf file on Termmate: https://www.termmate.com/rabia.aziz
2. YouTube: https://www.youtube.com/channel/UCKxWnNdskGHnZFS0h1QRTEA
3. Facebook: https://web.facebook.com/Chemist.Rabia.Aziz/
4. Blogger: https://chemistry-academy.blogspot.com/
Physical Chemistry
Errors - pharmaceutical analysis -1, bpharm 1st semester, notes, topic errors
full details and answer about error
TN DR MGR UNIVERSITY
by Kumaran.M.pharm, professor
Learning objectives
Introduction
Conditions For Volumetric Analysis
Terms In Volumetric Analysis
Primary Standard
Methods Of Expressing Concentrations In Volumetric Analysis
Types of Titration Methods
Classification Of Titrimetric Or Volumetric Methods
Conclusion
References
Pairwise Keys Generation Using Prime Number Function in Wireless Sensor NetworksIDES Editor
Providing security in wireless sensor networks is
a very crucial task. Because of its dynamic nature (no fixed
topology) and resource constraint devices. Which has limited
computational abilities, memory storage and physical
restrictions. Advancement in the field of intrusion and
evaesdroping has increased challenges for a secure
communication between nodes. So, establishments of pair wise
keys in a wireless network becomes a vital issue. Hence,
securely distributing keys among sensor nodes is a
fundamental challenge for providing seamless transmission
and security services. Having little resources in our hand,
it is always a tough task to design and implement protocols.
But this paper proposes a new robust key pre-distribution
scheme which resolves this issue without compromising
security. This paper presents a new mechanism to achieve
pair wise keys between two sensor nodes by using the
algebraic, exponential, logarithm functions and prime
numbers. The resilience method under this scheme is based
on discontinuous functions which is hard to be spoofed.
this eperiment was done by
Anet Mengesha Dube
at addis ababa university
addis ababa institute of tecnology
school of bio &chemichal_engineering
2nd year student
Which titration technique is best fit to detect what type of analyte?Zubayar Rahman
The act of adding standard solution in small quantities to the test solution till the reaction is complete is termed titration.
The basis of this process is the reaction between the analyte and solution of known concentration(titrant).
The analyte is taken in a conical flask using a pipette and the standard solution of known concentration is taken in a calibrated burette.
Scanned with CamScanner1 STANDARIZATION OF A B.docxtodd331
Scanned with CamScanner
1
STANDARIZATION OF A BASE
AND TITRATION OF A VINEGAR SOLUTION
ADDITIONAL READING
The concepts in this experiment are also discussed in sections 3.6 AND 17.3 of Chemistry and Chemical Reactivity by
Kotz, Treichel, Townsend and Treichel, and in sections 4.3b, 17.3a, and 17.3b of Mindtap General Chemistry by Vining,
Young, Day, and Botch
ABSTRACT
This experiment is divided into two parts. Each student is expected to perform the experiment individually.
In Part A, you will prepare a NaOH titrant solution, then standardize it (determine its exact concentration) using the acid
primary standard, potassium hydrogen phthalate, KHC8H4O4, frequently abbreviated as KHP. Note KHP is not a chemical
formula.
In Part B you will use your standardized NaOH solution to determine the molar concentration of vinegar (an acetic acid,
CH3COOH, solution), and convert this concentration unit to a mass percent concentration unit, and finally compare your
measured mass percent concentration to the value reported on the bottle.
BACKGROUND
TITRATIONS
One of the most useful strategies in analytical chemistry is to use a known reagent (known composition or concentration)
as a standard to analyze an unknown substance. A titration is an analytical procedure in which a solution of known
concentration, the standard solution, is slowly reacted with a solution of unknown concentration. The concentration of
the unknown solution can be easily calculated. Titration is often used to measure the concentration of an acid or base,
but it can also be used for any chemical reaction if the stoichiometry is known.
EXPERIMENTS 6 AND 7 ARE BOTH ACID BASE TITRATION EXPERIMENTS, QUITE SIMILAR TO EACH OTHER.
THE REASONS FOR DOING TWO TITRATION EXPERIMENTS
A. TO GIVE STUDENTS PLENTY OF OPPORTUNITY BOTH TO PERFECT THEIR TITRATION TECHNIQUE AND
TO LEARN TO DO THE CALCULATIONS;
B. TITRATION IS THE MOST IMPORTANT TECHNIQUE LEARNED IN CHEM 1033 LAB.
YOU WILL DO A PRACTICAL LAB EXAM AT THE END OF THE SEMESTER; IT WILL BE A VERY SIMILAR
TITRATION.
IT IS IMPORTANT TO REALIZE THAT TITRATION IS AN ACQUIRED SKILL, REQUIRING PRACTICE. MOST
STUDENTS ARE NOT PROFICIENT AT FIRST, BUT IF YOU WANT TO BECOME EXPERT AT IT, YOU WILL GET
THERE WITH PRACTICE.
It is critical that there be an observable change that signals that the titration is complete. This is called the endpoint,
since it signals the end of the titration, when the equivalents of titrant added just equal the equivalents of the analyte
unknown. When performing an acid-base titration, we commonly use an acid-base indicator that has one color before the
endpoint but changes sharply to a different color at the pH of the endpoint.
Titrations are carried out using a specialized piece of glassware called a buret, which is long tube with a dispensing valve.
The buret scale has graduated marks in units of 0.01 mL or 0.02 mL. You can apply the techniques used for readi.
What is the Rate Law for the Crystal Violet Reaction327-43.docxalanfhall8953
What is the Rate Law for the Crystal Violet Reaction?
3/27-4/3/2014
Section 10th
TA: Jinwei Zhang
Group 6
Daylin Morgan
Ahmed Alsharif
Shili Tong
Chang Chuan
Introduction
The main goal of this experiment was about observing the reaction between crystal violet and sodium hydroxide, CV+ + OH- -> CVOH. The objectives of this experiment are to monitor the absorbance of the crystal violet solution as a function of time, and determining the order of the reaction with respect to CV+. The pseudo rate constant k’ in this reaction is derived from the knowledge that OH- and the rate constant can be combined to a single constant. The Beer’s Law relationship between absorbance and concentration for CV+ is used to calculate the concentration in a solution given the Absorbance and a calculated constant. The half-life for this reaction with respect to CV+ and the rate law for this reactionare derived from total data.
Materials & Procedure
Materials
2.5*10-5M CV+(aq)
2.5*10-5 M OH-(aq)
Volumetric measuring equipment
Beaker
Cuvette
Stirring Rod
Spectrophotometer
Each student in a group will measure kinetics of the reaction at different concentration of sodium hydroxide. Before starting kinetic measurements, you should measure the spectrum of the crystal violet in the aqueous solution and establish the wavelength suitable for absorption measurements. Of course, this wavelength is the same for the whole class, so there is no reason to establish it once and once again.
Created 4 different solution of H2O and Crystal Violet at specific concentration. Measured the absorbance of each of these concentration using spectrophotometer and noted absorbance.
Graphed the absorbance vs. concentration, and found line of best-fit with an intercept of 0 to find value of m= εb.
Prepared spectrophotometer for kinetics measurements (separate instructions will be provided for each group).
Pour 10 mL of NaOH solution into 10 mL beaker. CAUTION: Sodium hydroxide solution is caustic. Avoid spilling it on your skin or clothing.
Pour 10 mL of 2.0 X 10-5 M crystal violet solution. CAUTION: Crystal violet is a biological stain. Avoid spilling it on your skin or clothing.
Initiated the reaction, simultaneously poured the 5-mL portions of crystal violet and sodium hydroxide into a 25-mL beaker and stirred the reaction mixture. Rinsed the cuvette with ~1-mL amounts of the reaction mixture and then filled it 3/4 full. Placed the cuvette in the cuvette slot of the spectrophotometer, and clicked "Collect" button. The program collected the absorbance data.
Analyzed the data graphically to decide if the reaction is zero, first, or second order with respect to crystal violet.
Results
Conc.(M)
A
0.000125
1.609
0.0001
1.244
0.000075
1.019
0.00005
0.53
*Measured with λmax= 600nm
Determining Beer-Lambert’s Law
A=εbC
Using the linear-fit line above εb was determined to equal 12695.
Determining the order wrt [CV+]:
To find molarity of CV+ used Beer-Lambert’s Law and value for εb.
Volumetric analysis is a quantitative analytical method which is used widely. As the name suggests, this method involves measurement of the volume of a solution whose concentration is known and applied to determine the concentration of the analyte.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
The Art of the Pitch: WordPress Relationships and SalesLaura Byrne
Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
UiPath Test Automation using UiPath Test Suite series, part 4DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 4. In this session, we will cover Test Manager overview along with SAP heatmap.
The UiPath Test Manager overview with SAP heatmap webinar offers a concise yet comprehensive exploration of the role of a Test Manager within SAP environments, coupled with the utilization of heatmaps for effective testing strategies.
Participants will gain insights into the responsibilities, challenges, and best practices associated with test management in SAP projects. Additionally, the webinar delves into the significance of heatmaps as a visual aid for identifying testing priorities, areas of risk, and resource allocation within SAP landscapes. Through this session, attendees can expect to enhance their understanding of test management principles while learning practical approaches to optimize testing processes in SAP environments using heatmap visualization techniques
What will you get from this session?
1. Insights into SAP testing best practices
2. Heatmap utilization for testing
3. Optimization of testing processes
4. Demo
Topics covered:
Execution from the test manager
Orchestrator execution result
Defect reporting
SAP heatmap example with demo
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
JMeter webinar - integration with InfluxDB and GrafanaRTTS
Watch this recorded webinar about real-time monitoring of application performance. See how to integrate Apache JMeter, the open-source leader in performance testing, with InfluxDB, the open-source time-series database, and Grafana, the open-source analytics and visualization application.
In this webinar, we will review the benefits of leveraging InfluxDB and Grafana when executing load tests and demonstrate how these tools are used to visualize performance metrics.
Length: 30 minutes
Session Overview
-------------------------------------------
During this webinar, we will cover the following topics while demonstrating the integrations of JMeter, InfluxDB and Grafana:
- What out-of-the-box solutions are available for real-time monitoring JMeter tests?
- What are the benefits of integrating InfluxDB and Grafana into the load testing stack?
- Which features are provided by Grafana?
- Demonstration of InfluxDB and Grafana using a practice web application
To view the webinar recording, go to:
https://www.rttsweb.com/jmeter-integration-webinar
UiPath Test Automation using UiPath Test Suite series, part 3DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 3. In this session, we will cover desktop automation along with UI automation.
Topics covered:
UI automation Introduction,
UI automation Sample
Desktop automation flow
Pradeep Chinnala, Senior Consultant Automation Developer @WonderBotz and UiPath MVP
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
Key Trends Shaping the Future of Infrastructure.pdfCheryl Hung
Keynote at DIGIT West Expo, Glasgow on 29 May 2024.
Cheryl Hung, ochery.com
Sr Director, Infrastructure Ecosystem, Arm.
The key trends across hardware, cloud and open-source; exploring how these areas are likely to mature and develop over the short and long-term, and then considering how organisations can position themselves to adapt and thrive.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
91mobiles recently conducted a Smart TV Buyer Insights Survey in which we asked over 3,000 respondents about the TV they own, aspects they look at on a new TV, and their TV buying preferences.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf
Argentometric titration
1. TITRIMETRIC ANALYSIS OF CHLORIDE
Introduction
The purpose of this experiment is to compare two titrimetric methods for the analysis of chloride in a
water-soluble solid. The two methods are:
• a weight titration method using a chemical indicator;
• a volumetric titration method using potentiometric detection.
The most important difference between the methods is how the endpoint is determined. In the first
case, the color change of the indicator signifies that the titration is complete, while the second method
generates a titration curve from which the endpoint is determined. For the potentiometric method, an
automatic titrator will be used to perform the titration, and to obtain the titration curve.
Background
Argentometric Titrations
In order for a titrimetric method to be viable, the titration reaction (1) must be complete (i.e., Ktitration is
large) and (2) should be rapid. There are many precipitation reactions that can satisfy the first
requirement, but far fewer that satisfy the second. Precipitation reactions of silver salts are usually quite
rapid, and so argentometric titrations, which use AgNO3 as the titrant, are the most common
precipitation titrations. Argentometric titrations can be used to analyze samples for the presence of a
number of anions that form precipitates with Ag+
; table 7-1 in Harris lists some of these.
Weight Titrations
The goal of any titrimetric method is to determine the number of moles of titrant needed to reach the
equivalence point of the titration reaction:
titration reaction aA + tT → product(s)
where a and t are the stoichiometric coefficients in the reaction between titrant and analyte. In a
titrimetric analysis, solution of titrant is added until the equivalence point of the titration reaction is
reached. At the equivalence point, neither analyte nor titrant is present in excess. By definition, the
equivalence point is the point during the titration at which the following relationship is true:
equivalence point
nA
a =
nT
t
where nA is the number of moles of analyte originally present in the sample solution, and nT is the
number of moles of titrant that must be added to the sample to reach the equivalence point.
From this last expression, we see that, in order to determine the number of moles of analyte originally
present in the sample solution, we must (a) know the stoichiometry of the reaction, and (b) determine
how many moles of titrant are needed to reach the endpoint. In order to meet this last requirement, we
must somehow keep track of the quantity of titrant solution that is added to the sample solution.
Page 1
2. In volumetric titrations, the volume of the titrant solution is used to calculate nT. By simple
dimensional analysis,
nT = mol T
vol soln
! vol added soln = CT ! VT
where CT is the concentration of the titrant solution in M, and VT is the volume of titrant solution
needed to reach the equivalence point.
By contrast, in weight titrations, the mass of the titrant solution is used to determine the value of nT:
nT = mol T
mass soln
! mass added soln = CT ! mT
where mT is the mass of titrant solution delivered to reach the equivalence point, and CT is the
concentration of the titrant solution in units of mol/kg. A concentration that is expressed in these units
is sometimes called the weight molarity of the solution1
, and is abbreviated MW. Note that, since for
most solutions 1 L ≈ 1 kg, the numeric values for molarity and weight molarity are similar.
In order to calculate the number of moles of analyte, nA, in the dissolved sample, the titration procedure
must consist of the following two steps:
1. Standardization, in which concentration of the titrant solution is determined. In weight titrimetry,
the concentration of titrant is determined in units of mol/kg.
2. Titration of sample(s), where the quantity of titrant solution that must be delivered to the sample
solution to reach the equivalence point is measured. In weight titrimetry, the mass of delivered
titrant solution is measured.
Endpoint Detection for Argentometric Titration
Another requirement of titrimetric analysis is that there must be some method of determining when the
titration reaction has reached its equivalence point. In this experiment, you will compare two methods
of endpoint detection, one using a chemical indicator and another using potentiometric detection. We
will now describe the common methods of endpoint detection for argentometric titrations.
Chemical Indicators
There are three common chemical indicators that are associated with argentometric titrations:
1. The chromate ion, CrO4
2−
(the Mohr method);
2. The ferric ion, Fe3+
(the Volhard method);
3. Adsorption indicators such as fluorescein (the Fajans method).
In this experiment, we will be using dichlorofluorescein, a Fajans (adsorption) indicator, to detect the
endpoint chemically; however, it is useful to briefly describe all three methods of endpoint detection.
Titrimetric Analysis Background
Page 2
1
the weight molarity is easy to confuse with another measure of concentration, the molality of the solution. Molality is
mass solute per mass solvent, while weight molarity is mass solute per mass solution. Both, however, have units of
mol/kg.
3. The Mohr Method
The Mohr method is based on the following reaction between the titrant and the indicator:
Mohr indicator reaction 2Ag+
+ CrO4
2−
! Ag2CrO4(s)
titrant indicator red precipitate
The concentration of titrant rises sharply near the equivalence point, and the solubility of Ag2CrO4 is
exceeded. The appearance of red precipitate marks the endpoint. The applicability of the Mohr method
is limited compared to either of the other chemical indicator methods: it can be used to analyze for Cl−
or Br−
anions.
The Volhard Method
The Volhard method of Ag+
determination is associated with argentometric titrations even though the
titrating agent is actually SCN−
:
Volhard titration rxn Ag+
+ SCN−
! AgSCN(s)
analyte titrant
The indicator in Volhard titrations is Fe3+
, which reacts with titrant to form a red colored complex:
Volhard indicator rxn Fe3+
+ SCN−
! Fe(SCN)2+
(aq)
indicator titrant red complex
This is a good method for the analysis of Ag+
in solution. We can extend the applicability of this
method to anions such as I−
through the procedure known as back-titration. A measured excess of Ag+
is added to the dissolved sample:
Ag+
+ I−
"""""! AgI(s)
excess analyte
reagent
After the precipitation of AgI is complete, the concentration of excess Ag+
titrant is determined by a
Volhard titration. The number of moles of I−
analyte originally present in the solution is easily
calculated:
# mol I−
= # mol Ag+
originally added to solution − # mol Ag+
as determined by Volhard titration
In a similar manner, the Volhard titration method can be used to analyze for a number of anions.
The Fajans Method
Adsorption indicators function in an entirely different manner than the chemical indicators described
thus far, and they can be used in many precipitation titrations, not just argentometric methods. Let’s
imagine that we wish to analyte Cl−
in a sample solution by titrating with Ag+
; the titration reaction
would be
Ag+
+ Cl−
! AgCl(s)
Silver chloride forms colloidal particles. Before the equivalence point, the surface of the precipitant
particles will be negatively charged due to the adsorption of excess Cl−
to the surface of the particles. A
Titrimetric Analysis Background
Page 3
4. diffuse positive counter-ion layer will surround the particles. When the equivalence point is reached,
there is no longer an excess of analyte Cl−
, and the surface of the colloidal particles are largely neutral.
After the equivalence point, there will be an excess of titrant Ag+
, some of these will adsorb to the solid
AgCl particles, which will now be surrounded by a diffuse negative counterion layer. The next figure
illustrates this concept.
before equiv. point after equiv. point
excess Cl analyte excess Ag titrant
surface charge: negative positive
titration
Adsorption indicators are dyes, such as dichlorofluorescein (shown below), that usually exist as anions
in the titration solution.
O O
Cl
O
Cl
COO-
dichlorofluoroscein
The doubly charged dichlorofluoroscein anion is attracted into the counterion layer immediately
following the equivalence point, when the surface charge of the particles changes from negative to
positive. For reasons that are not fully understood, the closer proximity of the dye to the particles
changes the color of the molecule, providing a visual indication of the titration endpoint. In the case of
dichlorofluorescein, the indicator changes to a pinkish color (see Harris color plate #2).
Potentiometric Endpoint Detection
The progress of the reaction as the titrant is added to the analyte solution can be followed
potentiometrically using an indicator electrode. A schematic for the general setup is shown in the next
figure.
Titrimetric Analysis Background
Page 4
5. Ecell
titrant added
to analyte
stir bar
indicator electrode
reference
electrode
The analyte solution is part of an electrochemical cell that can be represented by
reference electrode || analyte solution | indicator electrode
The reference electrode usually contains a liquid junction that completes the electrical circuit. The
potential of this cell can be written as
Ecell = Eind − Eref
where Eind is the half-cell potential at the indicator electrode due to species in the analyte solution and
Eref is the half-cell potential of the reference electrode. The reference electrode is chosen to be stable:
Eref is assumed to be constant during the titration. Any changes in measured cell potential are due to
changing species concentrations in the analyte solution.
Let’s imagine that we wish to monitor the course of the argentometric determination of Cl−
. The
titration curve in argentometric titrations is sometimes represented by a plot of p[Ag] vs added titrant,
and the curve should be sigmoidal in shape.
mass added titrant, g
pAg
Titrimetric Analysis Background
Page 5
6. We will now show that we observe the same sigmoidal shape if we plot Ecell instead of p[Ag] as the
x-axis, so long as we use the proper indicator electrode to measure Ecell. If we use a bare silver wire as
our indicator electrode, our electrochemical cell can be represented as
reference || Ag+
, Cl−
, AgCl(s) | Ag(s)
At the indicator electrode, the dissolved Ag+
will have a certain tendency towards reduction to the
silver metal:
Ag+
+ e−
! Ag(s) Eind
The potential of this half-reaction will depend on the concentration [Ag+
] in the analyte solution,
according to the Nernst equation:
Eind = Eind
0
− 0.0592
n logQ
Since n = 1 and Q = [Ag+
]−1
, we may write for this cell
Ecell = K + 0.0592 " log[Ag+
] = K − 0.0592 "p[Ag+
]
where K is a constant that accounts for various constant contributions to the cell potential, such as the
reference half-cell potential. Thus, as we see, the measured cell potential is directly related to p[Ag+
],
and can be used to follow the course of the titration reaction. A plot of Ecell vs added titrant will yield a
sigmoidal titration curve similar in appearance to the one in the previous figure. The endpoint, which is
usually taken as the inflection point of this curve, can be estimated from a plot of the first or second
derivative of the titration curve.
References
Titrimetry (general): Harris 7
Precipitation titrations: Harris 7.4-7.7
Titrimetric Analysis Background
Page 6
7. TITRIMETRIC ANALYSIS: Procedure
General
There is one titrator that is to be shared by everyone. You will use the titrator in order of your unknown
numbers (i.e., alphabetical order). While waiting for the titrator, you should proceed with the Fajans
titration described below.
By the time it is your turn to use the titrator, you should have your three titrator samples prepared and
ready to go (steps 1-3 on the next page). Each person will take 10-15 minutes to analyze their samples
with the titrator. If your samples are not ready when it is your turn, you will lose your place in “line!”
The first few people should prepare their titrator samples immediately, before beginning the Fajans
titration.
Handling of Titrant (AgNO3) Solution
Aqueous silver nitrate is photosensitive and should not be exposed to light any more than is necessary
during this procedure. It should be stored in darkened storage bottles, and be kept in your drawer
except when being used.
Fajans Method of Endpoint Detection
Chemicals and materials:
Silver Nitrate, 0.07 - 0.10 MW
Dextrin, 2%
Dichlorofluorescein, 0.1%
1. Dry the sample and NaCl primary standard for at least one hour at 110 °C. Cool in a desiccator.
2. Weigh by difference three 0.1 g samples of the pure NaCl (to the nearest 0.1 mg) into three separate
250 mL Erlenmeyer flasks. Weigh by difference three 0.1 g samples of the unknown sample into
another three 250 mL Erlenmeyer flasks. Add approximately 100 mL of deionized water to each of
the six beakers to dissolve the solid.
3. Add 5 mL of 2% dextrin solution and 10 drops of 0.1% dichlorofluorescein solution to the first
flask. The purpose of the dextrin solution is to stabilize the colloidal suspension of AgCl(s) formed
once the titration begins, and the dichlorofluorescein is the adsorption indicator.
4. Titrate with AgNO3 solution at a fairly rapid rate, using continuous swirling. When the rate of
fading of the pink color becomes slow, reduce the rate of addition to a drop-wise rate, swirl
constantly, and continuously observe the color of the suspension to detect the endpoint, which is a
change from a light peach color to a darker “Pepto Bismol” pink. Color plate 2 in Harris shows the
expected endpoint.
5. Repeat steps 3 and 4 for the other five flasks.
After completing your titrations, dispose of the AgCl(s) and titrating solutions by pouring them into the
waste bottles in the hood that are marked “AgCl(s)Waste.” Also return any unused titrant solution to
the instructor. Anything that contained AgNO3 should be rinsed thoroughly before being put away.
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8. Potentiometric Method of Endpoint Detection
Chemicals and materials:
Silver Nitrate, approximately 0.3 M
Nitric acid, 6 M
solid KNO3
1. Dry the sample for at least one hour at 110 °C. Cool in a desiccator.
2. Weigh three approximately 0.1 g samples of the “unknown” into your plastic titrator sample
beakers. The sample masses should be recorded to the nearest 0.0001g using the analytical
balances. Add 0.5 g potassium nitrate; this can be massed using the top-loader balances on the lab
benches.
3. Add about 40 mL of deionized water to each beaker and stir until dissolved. Rinse your stir rod into
the sample solution (i.e., you do not want any analyte chloride to leave the solution). Also add a
few drops of 6M nitric acid into each beaker.
4. You will titrate your sample solutions with the Mettler-Toledo DL58 titrator using a silver ring
indicator electrode to follow the progress of the titration. For your first sample, your instructor or a
TA will show you how to use the titrator.
5. Repeat the titration for your other samples. Be sure to wash the titrator thoroughly after each
titration. Dispose of the silver chloride waste in the appropriate container (found in the HOOD).
When you are finished, wash your titrator sample beakers thoroughly and rinse with deionized
water.
6. You will be provided with data from three titrations that were used to standardize the titrant
solution just prior to the experiment.
For each of your samples, the titrator will print out its estimate of the endpoint volume, as well as the
raw data (potential as a function of added titrant solution volume). Plot your titration curves and
include at least one of them as a figure in your lab report. Please turn in copies of your data and your
titration curves with your data sheet - this material is supplemental to your lab report.
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9. DATA SHEET: Fajans Method
Directions: fill in this sheet and turn it in with your lab report.
Name: Unknown #:
estimated analyte conc
(as a confidence interval)
1: g
2: g
1: g
2: g
1: g
2: g
Titration of sample
(1) initial mass titrant soln
(2) endpoint mass titrant soln
1: g
2: g
1: g
2: g
1: g
2: g
Titration of NaCl
(1) initial mass titrant soln
(2) endpoint mass titrant soln
1: g
2: g
1: g
2: g
1: g
2: g
dry sample mass
(by difference)
1: g
2: g
1: g
2: g
1: g
2: g
dry NaCl mass
(by difference)
CBA
10. DATA SHEET: Potentiometric Method
Directions: fill in this sheet and turn it in with your lab report. You should also turn in your titration
curves and your raw data (you can xerox the titrator printout). I do not need the standardization data - I
already have a copy. Also turn in plots of your titration curves with your data.
Name: Unknown #:
estimated analyte conc
(as a confidence interval)
Endpoint: Titration of sample, mL
Endpoint: Titration of NaCl, mL
(from handout)
1: g
2: g
1: g
2: g
1: g
2: g
dry sample mass
(by difference)
dry NaCl mass
(from handout)
CBA
Results from Hypothesis Testing
Conclusion
Observed value for F
Comparison of Precision of Methods
Conclusion
95% CI for d
Comparison of Accuracy of Methods
11. TITRIMETRIC ANALYSIS: Data Treatment
Effect of Standardization Measurement Error
A requirement for quantitative analysis by titration is that the titrant concentration is known. In many
cases, including this experiment, titrant solution concentration is itself determined (standardized) in a
separate set of titrations. The titrant concentration is thus subject to random measurement error
comparable in magnitude to that of the sample titration.
When calculating a confidence interval for the analyte concentration in your “unknown” sample, you
will have to use the titrant concentration. A propagation of error approach can be used to account for
the effect of standardization error on the final, calculated value for analyte concentration in the sample.
Let’s assume that you have one set of standardization titrations and another set of titrations of the
sample solution:
• from the standardization titrations, you calculate the mean titrant concentration, CT, and its standard
deviation (i.e., the standard error of the mean)
• from the endpoints of the sample solution titrations, you can calculate the mean analyte concentration,
, and its observed standard deviation, . This standard deviation does not include the effectCA sobs(CA)
of uncertainty in CT; it is calculated directly from the endpoint volumes of the sample titrations.
A propagation of error approach yields a value for RSDA, the true relative standard deviation of the
point estimate ( ) of analyte concentration.CA
RSDA
2
= RSDT
2
+ RSDobs
2
where andRSDT =
s(CT)
CT
RSDobs =
sobs(CA)
CA
Note: assume that the value you calculate from this procedure contains 2 degrees of freedom. Although
this is not strictly true, it is a conservative estimate of the true degrees of freedom contained in the
estimate of standard error.
Comparison of the Accuracy and Precision of Titration Methods
One of the primary goals of this experiment is to compare the ability of two titrimetric methods –
weight titration with chemical indicator, and volumetric titration with potentiometric detection – to
measure the chloride content of a soluble, solid sample. In particular, it would be meaningful to
compare the relative accuracy and precision of the two methods.
For each method in this experiment, you essentially obtain two results (which you combine into a
confidence interval):
• a point estimate of the analyte concentration, which represents your best estimate of the true analyte
concentration. In this case, the point estimate will be the mean of three independent measurements.
The difference between the point estimate and the true analyte concentration is a measure of the
accuracy of the method.
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12. • the standard error of your point estimate: the standard deviation of the mean of three independent
measurements (corrected for standardization error, as explained above). The magnitude of the
standard error indicates the precision of the method.
Statistical theory provides a procedure, called hypothesis testing, that can be used to objectively
compare the accuracy and precision of the two methods in this experiment. You will need to apply this
procedure to your results. Hypothesis testing is discussed at length in Chemistry 300, but a very brief
summary will be given here of procedures that you may use (since the Full Report for this experiment
may be due before the subject is covered!). More detail on hypothesis testing is given in the lecture
notes for Chemistry 300.
Comparison of Accuracy
Concerning the accuracy of the two titrimetric methods, there are three general possibilities:
1. Neither method gives biased estimates of analyte concentration;
2. One method is biased but the other is not;
3. Both methods are biased.
In order to determine if bias exists, the true analyte concentration must be known. Since it isn’t (to you,
anyway!), all you can do is compare the bias of the two methods. A relatively simple procedure for
doing this is as follows.
Let’s define a random variable d, as the difference between the point estimates for the analyte
concentration obtained from the indicator and potentiometric methods:
d = Cind − Cpot
This value is the difference between two random variables, and so it too must be a random variable.
Use error propagation to calculate the standard deviation of the difference, sd, and then calculate a 95%
confidence interval for µd (assume d is normally distributed, and 2 degrees of freedom in sd). If the
confidence interval does not contain zero, then there is at least a 95% probability that there is a
statistically significant difference in the bias of the two methods. That means that either possibility #1
(only one of the methods has bias) or #3 (both methods have bias, but of different magnitude) must be
true.
Comparison of Precision
Let’s define a random variable F as follows:
F =
seA
2
seB
2
where seA and seB are the standard errors of the point estimates obtained using titrimetric method A and
method B. Which method is A and which B? You should choose them so that the ratio of the squared
standard errors is a value greater than one (F > 1). In other words, method A is the one with the larger
standard error.
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Titrimetric Analysis Data Treatment
13. The value F is the ratio of two sample statistics, so it is a random variable. If the measurement
precision of the two methods is the same, then the population mean of this variable should be equal to
one (i.e., µF = 1 if σA = σB). Values of F that are much larger than one suggest that perhaps method A is
less precise than method B.
Hypothesis testing allows us to determine what the “cutoff point” (the critical value) should be before
we can consider one method to be definitely less precise than the other. For this experiment, the critical
value for this hypothesis test is 39.0. If F > 39.0, then there is at least a 95% probability that the
precision of method A is worse than that of method B.
Why is the critical value so large? The reason is that there are only two degrees of freedom in our
standard error values, so that there is a lot of uncertainty in both seA and seB (and even more in their
ratio). So it will be very hard to “prove” a difference in precision for this experiment. If you wanted to
get a smaller value for the critical value, more degrees of freedom (i.e., more measurements) are
needed. For example, with six measurements for each method, the critical value would be 7.15.
“Within-Student” and “Between-Student” Variability
When comparing precision, you should be aware of the difference between what we can call
“within-student” and “between-student” sources of random error. We can illustrate the difference
between these sources by considering a titration using a chemical indicator (like the Fajans method):
• within-student variability will be due to the uncertainty a single student experiences in determining
the color change from sample to sample. This source of variability is reflected in the spread of each
student’s measurements about the mean.
• between-student variability is due to the fact that different students will interpret the endpoint color
slightly differently. This source of variability is reflected in the spread of the measurement errors of
all the students in the class.
The difference between these sources of variability is almost certainly quite significant for the Fajans
method – there will be much more between-student variabilty than within-student variability. There is
probably not too great a difference in the case of the potentiometric method, though.
Since you won’t have access to the data of your classmates when you write this laboratory report, there
is not much you can do to assess the true variability of the Fajans method. You should be aware the you
are actually comparing “between-student” variability when you compare the precision of your point
estimates.
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Titrimetric Analysis Data Treatment