CHM3120L
Introduction to Analytical Chemistry
Lab Manual
Modernized chemistry laboratory preparing
students for careers in science/health/other
Dr. Joseph Lichter, Senior Instructor
Dr. Justin Carmel, Assistant Professor
Contents
Page Number
Section 1- Analytical Chemistry: Why Is This Important?
What is Analytical Chemistry?
The revised 3120L manual
Goals for CHM3120L
The Chemical Analysis Method
Safety
Learning How to Work in a Laboratory
Laboratory Notebook
Laboratory Reports
Written lab reports
Poster presentation
Oral presentation
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Section 2 – Laboratory Equipment, Instruments, Computation
Laboratory Equipment
Test tubes
Beakers
Vials
Erlenmeyer Flasks
Buchner Flask (also called a vacuum flask)
Volumetric Flasks
Buret
Pipet
Funnels
Spatula
Measuring devices
Graduated cylinder
Heating devices
Stirring hotplate
Bunsen burner
Laboratory Instruments
Laboratory Balance
pH meter
Ion selective electrodes
Spec 200 UV-Vis spectrophotometer
Computation
Microsoft Excel
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Section 3 – Laboratory Techniques
Preparing an experiment
Sampling and Sample preparation
Filtration
Gravity filtration
Vacuum Filtration
Volume delivery by Pipet
Making and Diluting Solutions
Titration (volumetric analysis)
Standardizing a Titrant
Performing a titration of an unknown
Gravimetric Analysis
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Calibration Curves
Quality Assurance
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Section 4 - Projects
Project 1: Investigation of Phosphorus Content in Fertilizers
Project 2: Investigating Kombucha Fermentation
Project 3: Measuring calcium in supplements
Project 4: Fluoride in our Drinking Water
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Section 5 – Experiments
Experiment 1: Review of lab techniques
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Section 1- Analytical Chemistry: Why Is This Important?
What is Analytical Chemistry?
Analytical chemistry focuses on the identification and quantification of individual chemical components
from larger, more complex systems.
If you take the words Analytical Chemistry and define them individually we see the word analysis means
“breaking up a complex topic into smaller parts for a clearer understanding”. The word originates from
the ancient Greek analusis (ana meaning “up, throughout” and lysis meaning “a loosening or breaking”).
So, analytical chemistry is breaking up more complex chemical systems into their smaller chemical
components and identifying and/or quantifying them.
Analytical chemistry is most often broken into two subsections: Qualitative analysis focuses on solving
the identity of an unknown substance while quantitative analysis focuses on calculating how much of a
substance is present. In this laboratory, we will explore both areas but there will be a large emphasis on
quantitative analysis, as evidenced by the goals of the projects you will be involved in.
The revised 3120L manual
This manual is a revision of the original CHM3120L used at FIU for almost 30 years. The authors intention
to revise the previous manual was to improve CHM3120L using evidence in the chemistry education
literature for effective teaching laboratory techniques, student feedback from previous semesters,
teaching assistant feedback, and discussions with faculty both here at FIU and from a variety of
universities in the country.
Why did we change the way the analytical chemistry laboratory had been taught?
The older manual was more of a cookbook. The recipes (i.e. the experiments) were listed step by step
and then students had to answer questions about what they did. While there were some techniques
learned and some sharpening of laboratory skill, there was a lacking in developing the skills of the
scientific process. The new lab gives students the potential to develop good questions they want to
know, design their own procedures, and/or review their results in the context of the hypotheses that
they craft. One of the key parts of a career in science is being able to think through the type of processes
necessary to answer questions of interest. The newer model of the course intends to help prepare you
(the student) for your career, by providing you with that experience.
The laboratory manual is now split up into 4 sections:
1. Introduction section on the what and why about analytical chemistry
2. A reference section of laboratory equipment, instruments and computation
3. A reference section on laboratory techniques you will use
4. The projects you will engage in for this class
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The way you should use this lab manual will be to read through the introduction to understand what are
the goals of this course, the methods used, the safety you need to concern yourself with, and then how
to record and report your results to be able to submit for a good grade.
The reference sections can either be read in full or you can reference them depending on what project
you are doing. At the onset of each project there will be a small section indicating what types of
equipment and technique you should review.
The weekly activities will be found as projects. For all of these you will have to research the topics
(citations will be provided as a starting point) and you will have to design procedures to follow through.
All of the procedural design and experimental follow through will be done in groups. The projects will
generally last 2-3 weeks long. The reports for these projects will sometimes be in the form of a written
report, poster presentation or an oral presentation. You will read more about recording and reporting
results at the end of this introduction.
Goals for CHM3120L
The revised manual has goals to prepare you as a scientist while meeting the framework for science
education (National Research Council. 2012. A Framework for K-12 Science Education: Practices,
Crosscutting Concepts, and Core Ideas. Washington, DC: The National Academies Press.)
Students will:
1. read scientific literature to obtain and evaluate the info related to each project
2. ask their own question and develop a plan to carry out the investigation
3. analyze and interpret the data using mathematics and computation
4. construct explanations for the problems they sought to understand
5. use some of the more commonly used analytical chemistry tools in preparation for careers in
science/health
6. develop an understanding of analytical chemistry in context of other sciences (food science,
materials science, biochemistry)
7. learn how to work in an analytical chemistry laboratory
The Chemical Analysis Method
Almost every laboratory manual will remind students to think about the scientific method. This is the
method used by scientists that ensures an organized approach to trying to solve a scientific problem. For
instance, you wouldn’t want to try and ask a question without having a procedure to use. Or vice versa,
you wouldn’t devise a procedure without having a problem to solve.
In analytical chemistry, there is a slightly modified version of the scientific method to account for the
fact that chemical species are under investigation (as compared to say humans in biological studies or
strictly numbers as in mathematics). Here is a side by side comparison of the chemical analysis method
and the “traditional” scientific method:
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Chemical Analysis Method
Ask a question
Conduct background research
Formulate a hypothesis
Select/design procedure
Sampling and Sample preparation
Perform experiment/analysis
Reporting and interpreting results
Draw conclusions
“Traditional” Scientific Method
Ask a question
Conduct background research
Formulate a Hypothesis
Select/design procedure
Perform experiment/analysis
Reporting and interpreting results
Draw conclusions
As can be seen, the chemical analysis method is almost the same as the “traditional” scientific method
except for the addition of sampling and sample prep.
Sampling is the process of choosing your materials to analyze in a way that is representative of the
material as a whole. For example, if you wanted to analyze sugar content in a commercially available
soft drink, you might collect samples from bottles of the soft drink sold in different stores to ensure you
have samples that are representative of the many places the drink is sold. If you only measured it from
one store, you would not have a representative sample of the soft drink, you would have a more
localized set for that store. What if that sample was slightly higher than the average for all the soft drink
sold nationwide? Unless you sampled other stores, it would be difficult to ascertain whether the sample
set is representative of the product as a whole and not just a localized sample.
Sample preparation is the process of converting your sample into a suitable form for the analysis you
chose. For instance, if you wished to study the sugar content in the soft drink as above, you might want
to remove the carbonation if it would interfere with your analytical technique. When you consider the
analytical procedure, you have to investigate what other species exist in the sample you have collected
and whether they are going to mask the species you wish to study. You may also have to modify the
concentration of your sample to fit within the lower and maximum detection limits of your analysis.
While the chemical analysis and “traditional” scientific method are similar, as an analytical chemist we
need to learn the importance of how we collect our samples and whether they represent the analyte as
a whole or as a subset of the whole, and as well we want to be sure to prep the sample for whichever
analysis we use.
In the laboratory equipment, instruments, computation (section 2), and technique sections (section 3)
you will find example of the various types of instruments and analyses that can be done. You will notice
that some will work on solids/liquids/or gases, some will work with ions or neutral molecules, and some
might work for acids or bases. Depending on your type of analysis, you must consider how you might
prep your samples.
Safety
Safety in the laboratory is of the utmost importance. As a student in a chemistry laboratory, you should
consider safety as an essential part of your educational experience. If you should choose a job working
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as a scientist you will be expected to know safety procedures and regulations on the job. Many
companies will require regular safety certification as part of the job training and on-going education.
As part of the CHM3120L course, you need to be aware of the safety regulations below as you will be
graded on how well you heed to them. Note that for some of the time in the lab you will be in
“planning” mode and for sometimes the class will be in “chemistry” mode. There are modifications to
the safety depending on that.
A. Safety goggles and protective clothing (long sleeves, long pants) must be worn whenever
chemistry is being done in the lab. In the periods where planning is going on, it is okay to not
wear them.
B. If you have long hair it must be tied back in a ponytail.
C. Turn your cell phones off while performing an experiment. It is okay to use during the planning
periods, but not during an experiment
D. It is highly recommended that students do not wear contact lenses in the lab.
E. All accidents must be reported to the teaching assistant immediately.
F. No eating, drinking, chewing gum, smoking, or applying make-up in the lab. A water bottle
packed in your backpack is allowed, and if you must drink you should step outside of the lab.
G. Never leave an experiment unattended. If you must use the restroom or have a sip of water,
please let your TA know.
H. Clean up any spills immediately. Do not leave your area contaminated.
I. Dispose of excess chemicals and wastes in their appropriate waste containers. If you are not
sure where a chemical should be disposed, ask the TA or a lab assistance.
J. Avoid unnecessary physical contact with chemical materials used in the lab.
K. Use caution when using glassware in the lab. Do not force glass tubing into rubber stoppers
L. Broken glass needs to be placed in the appropriate container.
M. Exercise caution when using hot plates, Bunsen burners, or any equipment that produces a lot
of heat.
N. Always turn off your equipment when finished, and clean up your area after the experiment is
done.
Learning How to Work in a Laboratory
One of the goals mentioned above is for students to learn how to work in an analytical chemistry
laboratory. While this may seem like an obvious thing, there needs to be attention brought to this. Here
we will answer some important questions
1. What is different between working in laboratory and working in an office?
An office is typified by computers, desks, books, paper files, decorations and what not. A
laboratory is going to have sinks for water, instrumentation to perform experiments, fume hoods
to work with chemicals that may be volatile, safety measures that must be considered (see the
section on safety above). As a result, there needs to be proper dress and behavior in a
laboratory, maintaining safety instruments from being mishandled, broken or exposed to
harmful elements and as well it will be of importance to label things so that other who work in
this shared space will know what certain things are.
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If and when you are to take a position in a lab sometime in the future be it for graduate school or
your career, you will need to have respect for the laboratory and the organization of
instruments, tools, chemicals, and overall organization. Things should never be left in disarray
and any chemical or instrument that is not known what it is or how to be used, should be
refrained from being used until proper education of the substance or instrument has been
received. It is generally good practice to ask more senior members of a laboratory to show you
how to operate an instrument if you have never used one. In CHM3120L, your laboratory
teaching assistant will be of assistance with this.
2. What are the most important skills required for a laboratory?
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Analytical skills
Independence, but capability of working in teams
Good written reports as well as oral explanations
Time management
Attention to details
If you do work in a laboratory, these are the skills that will make you efficient.
Your TA will be assessing your laboratory technique as part of your grade in the course.
3. What are things that someone starting to work in a laboratory should know before entering one?
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what are the main instruments in the laboratory and how do they work
where are the safety showers and the first aid kit in event of an emergency
where are all the material safety data sheets (MSDS) for chemicals in the lab
who are the senior staff or scientists that can be talked to for consultation and instruction on
things that are yet known by the person starting in the lab
Laboratory Notebook
The laboratory notebook is the only official record of laboratory measurements and observations. For
the researcher, a properly maintained notebook can be a source of useful information for many years.
In an industrial or governmental laboratory, a notebook may serve as evidence in court. In the clinical
setting, good records must be kept to help guarantee the safety of patients. Therefore, it is essential to
learn and practice proper record keeping in the laboratory.
The book should be permanently bound with consecutively numbered pages (if necessary, the pages
should be hand-numbered before any entries are made). Do not crowd entries in a page.
The first few pages should be used for identifying the laboratory or project this is with respect for, the
individual who is responsible for the notebook and a table of contents that is updated as entries are
made.
All data and observations must be made in ink directly into the notebook.
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Each page of the notebook should have the date the entry was recorded.
Each entry or series of entries should have a heading with the title of the experiment (Example:
Calibration of the Pipet #99).
Never erase or obliterate an incorrect entry. Instead cross it out with a single horizontal line. The new
entry should be written close by.
e.g.
MgCl2
MnCl2
Never remove a page from the notebook.
The laboratory notebook is NOT intended to be a neat piece of artwork, with rewritten versions of other
people’s procedures and ideas in your handwriting. The laboratory notebook IS intended to be where
you write out the procedure you come up with, record your observations in an organized and easy to
follow fashion so that if someone wanted to understand what you did, they could open your notebook
and figure it out.
A great video about the lab notebook from the perspective of a graduate student can be found here:
https://youtu.be/sW9YBcDAAvI
Laboratory Reports
Reporting the work done is part of the chemical analysis/scientific method. There are a few different
ways to report results: written lab reports, poster presentations, and oral presentations. In CHM3120L
you will be completing all 3 of the above.
Written lab reports
Lab reports should be typed and should be organized in the following way:
1. Title page
Title page will include the title of the project, your name, your lab section and your TA’ s name,
justified to the center of the page. The title of the project can be as simple as the project itself or
you can elaborate a bit more. For instance, for the statistics of food, you might either write “the
statistics of food” or if you were conducting a study on breads you might write “Evaluating the
texture of various breads using objective and subjective measurements”
At the bottom of the title page you should include in italics the following statement followed by a
signature: “My signature indicates that this document represents my own work. Excluding shared
data, the information, thoughts and ideas are my own, except as indicated with any references.”
While the laboratory work will be done in groups, the reports will all be written independently
and should not therefore contain any copied words from another classmate. This goes for the
introduction, experimental section, results, and conclusion. You may use some of the same
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references but should not be writing the same thing as others in your group. In the event that
you do copy either all or part of another student’s lab report verbatim, you will be violating the
academic conduct code.
2. Introduction
The introduction is a brief overview of the project you are investigating. Here is a good point to
cite any of the important work done prior that helped you to decide on your project procedure.
You will want to explicitly say the goal of the experimental procedure and any hypothesis you or
your group has come up with respect to the analysis to come. You will explain why this is an
important thing to investigate. For this introduction section you are encouraged to consider any
of the journal articles or reading that are assigned for the project in the research component as
well as any of the research questions posed. You do NOT need to start describing the
experimental procedure here in the introduction, that will be in the next section.
3. Experimental Procedure
Here you will provide step-by-step what you did to achieve the analysis for your project. You will
include procedures of both the validation components and then your project based component.
So, if you investigate one fertilizer with the whole class in the first part of project 1 and then you
bring in from a store for the second part, you will explain the experimental procedure for both.
You should describe the procedure in a way that others could read your lab report and be able to
duplicate your experiment if they followed the procedure. For many of the procedures you will
be coming up with for your projects you will be gaining ideas from other experimental sections
from journals, so keep an eye out to see how the authors for those journal articles present their
experimental section.
When it comes to the style of writing the experimental section you should always write in past
tense, 3rd person and passive voice. For example to say that your final solid product was weighed
you would write it as: “the precipitate was weighed”; NOT “we weighed the precipitate” (1st
person) or ‘weigh the precipitate” (future tense).
4. Results and Discussion
This section should provide data in the form of any measurements taken, calculations, graphs
constructed, and an analysis of the data. You should include any error or statistical analysis here
as well.
Numerical data should be presented in tabular form while any relationships between sets of data
should be represented in graphs. If you want to include drawings or figures that help to explain
your analysis, you may do so. Your graphs, drawings, or images should be labeled as figure 1, 2,
etc. and your tables should be labeled as table 1, 2 , etc. When you discuss them in your
discussion you can then more easily refer to the tables and figures. Be sure to embed your
figures and tables close to where you will be discussing it in the paper so that your reader can
follow your ideas.
Along with the data/results, is the interpretation of them in the form of the discussion. The
discussion about results is a critical part of your report. It is in this section that you can explain
the numbers, tables and figures you have made so that they make sense to the reader. Given
that papers only include a few figures, they are usually an important portrayal of what was done.
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To accompany these figures there needs to be a great explanation of the figure in case it doesn’t
explain itself on its own.
The discussion should basically answer the following: what did you do? what did you see? and
what can you claim from what you did and what you see? How do your results answer the
problem that you originally sought to answer? If the questions above don’t already do so, the
discussion MUST address any of the post-project questions provided.
5. Conclusion
Your conclusion section should be no more than one paragraph that sums up the discussion. Use
this paragraph to explain the results in a concise manner, even if in your discussion you were a
bit more in-depth with your analysis of your data and results.
6. References
In your introduction and your discussion, if you used any previously done work or ideas of others
you must reference it in the end of the paper.
Each of the references should be numbered consecutively within the text as superscripted
footnotes, and then on the last page of the report you should have them listed numerically and
cited using the ACS style.
For journals: author (last name, first initial), Journal title, year, volume number, starting page
number.
For books: author (last name, first initial), Title of book, publisher: city, year, page number.
Your citations should be sought from primary sources. Should you find a page from the internet
from a professional society or governmental page or another reputable source, you may cite that
as well. When citing you should give the URL, host institution and the date of your visit.
Poster presentation
The purpose of the poster presentation is to communicate what you have been doing in a larger visual
format that takes less time to read through than a written lab report, and also allowing the author to
present a poster at a conference or a meeting. Poster sessions are very common at conferences, where
companies and labs (both public and private) present work they are doing in a social manner where
attendees walk around and view posters while the poster presenters are around to answer any
questions that may arise. Everything that is in a lab report (such as an intro, procedure, results and
discussion, references) can be included in the poster presentation but formatted in a way that highlights
the important things found. In a paper titled “Ten Simple Rules for a Good Poster Presentation” in PLOS
Computational Biology (written by Thomas Erren and Philip Bourne) they highlight the following tips
(article doi: 10.1371/journal.pcbi.0030102):
1. Define the purpose. What do you want the person reading your poster to walk away with? What
is the plotline for the story of your work? Make that clear.
2. Sell your work in 10 seconds. First impressions are everything.
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3. The title is important. Should be concise and understandable.
4. Poster acceptance means nothing. Just because your poster is accepted to a conference (or for
the class) doesn’t mean that your work is automatically good. You need to have done good
science and present it well.
5. Many of the rules for writing a good paper apply to posters too.
6. Good posters have unique features not pertinent to papers. Does not have to have as much info
as a paper and can take advantage of the visual presentation.
7. Layout and Format are critical
8. Content is important but keep it concise.
9. Posters should your (or your group’s) personality
10. The impact of a poster happens both during after the poster session.
For more of making a poster (and the how-to), please see the following video:
https://youtu.be/IIr22p0jWjQ
Oral presentation
The oral presentation is intended for an audience who specifically will want to hear about what you did,
along with seeing some visual aids to help understand what your work is about. It is more similar to the
poster presentation, in that there will be presenting of a visual aide, but in the case of an oral
presentation you should present a set of presentation slides (either through Microsoft PowerPoint or
Prezi or another slide presentation type of formatting).
When it comes to the oral presentation you will have to put time into preparing and presenting.
Tips for the preparation:
1. Organize your presentation before you start to make slides. Decide what your title will be and
how you will present to your audience the importance of what you did and the findings.
2. Use an easy to work with presentation program to develop your slides for the talk. If you work
with Powerpoint regularly, use Powerpoint. If you use Prezi regularly, use Prezi. If you have never
used either one of those programs, you should use YouTube to find some tutorials on how to use
those programs effectively.
3. Your slides should be easy to read. Avoid color schemes that may be blinding or hard to see.
Avoid font types that are difficult to read. Avoid font sizes that are small and hard to read. Avoid
putting too many words on a screen giving your audience a difficult time in trying to read
everything on the slide while you are talking to them.
4. Start strong. If your presentation slides are boring from the start, people will lose interest pretty
quickly. Make sure you have intro slides that will pull your audience in.
5. Finish strong, too. This doesn’t mean to suggest the middle portion should be weak, but there is
a possibility that the longer the presentation you have the more likely there will be some
audience that loses attention. If you can regain their attention with a strong conclusion that
summarizes well what you did, then the audience may have been saved from not learning
anything.
6. Practice your presentation. Have a friend who is willing to be a practice audience and practice in
front of them. See that in practicing, your talk will not take longer than the time you are allowed.
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Tips for the presentation:
1. Speak confidently and with excitement. Not too much excitement. But make sure your voice is
not monotone.
2. Make eye contact with the audience. Let the people who you are talking to, know that you are
talking to them. If you stare at a wall while you present, it will look funny. If you speak to your
audience directly they will feel more comfortable, and you will too.
3. Pause. Sometimes we have a tendency to just keep talking through our slides. Leave some room
for people to look at your slides and to ask a question if they want.
4. Be prepared for questions. You should know what type of questions may come up and be
prepared to answer as best as you can. If you do not know the answer, take a pause to think
about it and if you still can’t figure it out then say you are not sure, but take the time to thank
the person for asking a good question.
5. Use a pointer when necessary. You don’t need to have a laser pointer going through your entire
talk, but it may be helpful for some of your slides.
6. Avoid speaking too relaxed and with the everyday vernacular. Filler words such as “like”, “um”,
“you know”, “right” should be avoided.
7. Relax. Even though you should avoid speaking too relaxed, you should FEEL relaxed. May be
easier said than done, but one way to lower your anxiety is to have practiced speaking your
presentation in front of others so that you know what you will say and how the presentation may
go.
8. If you are in a group, allow everybody to be involved. Do not make the order of speaking, right
before you get up to speak. Practice how you will share the load of the presenting and be sure
that everybody is involved.
9. Acknowledge all the people who helped you with your research.
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Section 2 – Laboratory Equipment, Instruments, Computation
Laboratory Equipment
Containers (TC on glassware: “to contain”)
Test tubes
Test tubes are finger like tubes made of
glass that are used to contain small sample
sizes of material. They are shaped
cylindrical with an open top to add samples
and a concave closed bottom. Test tubes
are found measured by the cylindrical
diameter and their length, with a variety of
widths (mostly ranging from 10-20 mm)
and lengths (mostly ranging from 50-200
mm). These can be used for either solids or
liquids and for most cases in your
laboratory they will be used to either carry out small scale reactions, test for solubility of compounds,
test for impact of temperature, and/or other tests for properties (colorimetric, viscosity, etc.). The
volume contained by a test tube can range generally from 1-20 mL. When holding a test tube, be aware
that if you intend to heat the test tube you should use a clamp or tongs to avoid the heat transfer from
the tube to your hand. You might also consider a stopper to put on top if your sample may be volatile.
Note that test tubes do NOT measure the volume of samples; you would have to use a pipet or a buret
to transfer a volume into the test tube to properly know the volume.
Beakers
Beakers (like test tubes) are cylindrical
containers used to contain a liquid or volume,
but unlike a test tube they are shaped with a
greater width and a smaller length. There is
usually a small pouring spout at the top of the
cylindrical opening. Like test tubes they are
made out of glass and are safe for heating. The
sizes of beakers range from a small 5 mL
beaker to larger ones ranging the liter
quantity. These are good for containing larger solutions that perhaps need stirring so you can add a stir
bar to the bottom of the beaker and put on a stirring plate. Similar to a test tube, these are NOT used to
measure volumes even though some beakers will have approximate gradations for the volume of the
container.
Vials
Vials are small cylindrical bottles made of glass or plastic, that contain a top that can be
sealed shut. This makes this type of container excellent for storing samples for a long
time, especially those needed to be kept under sealed conditions. Vial sizes range
similarly to those of test tubes and beakers. Historically, vials have been used to hold not
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just scientific samples, but also medicines. In the event that a sample needs to be frozen or refrigerated,
a vial is a good sample container to ensure that the sample does not spill while in a refrigerator or a
freezer.
Erlenmeyer Flasks
Erlenmeyer flasks are conical shaped glass containers with a
narrower opening than a beaker. This has the advantage to
add liquid samples with a slightly higher volatility so that the
flask can keep most of the liquid from escaping. Because of the
narrow shape these are also mostly used for containing
liquids. Common uses for these include recrystallization,
reactions, and for heating solutions.
Buchner Flask (also called a vacuum flask)
There is a flask that looks very similar to the Erlenmeyer flask except besides
the conical opening on top it will have a smaller side glass opening that
points parallel to the table by which it sits. That type of glassware is referred
to as either a vacuum flask or Buchner flask. The intention for that type of
flask is that you can connect a tube from the side opening to a vacuum and
use that flask to draw out liquid from a solid during vacuum filtration. While
it is similar to the Erlenmeyer flask, you would ONLY want to use it when
connecting it to a vacuum to collect the liquid from a recently precipitated
solid.
Volumetric Flasks
Another type of flask you will find in the lab are volumetric flasks. These will
have very long necks that rise up from the wider bottom portion to the opening
at top. These have very accurate gradations for a specific type of volume. These
are generally used for making solutions of a specific volume, you could use that
gradation as the point to fill to and then you could properly measure the
volume of your solution. This type of flask is specific for containing solutions,
often for a stock solution from which you might want to make serial dilutions
for analyses.
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Transferring devices (TD on glassware, “to deliver”)
Buret
A buret is a very long thin cylindrical
glassware with a wider opening on top
to add volume, and at the bottom there
is a small pinhole type opening (also
described as a capillary tip) that can be
controlled by a stopcock which is either
a Teflon or glass device that you turn in
order to allow a solution to come out of
the buret. These are used in volumetric
analyses where the buret can deliver the
solution to separate container at the
bottom, and the volume of the buret can
be read before delivery and at the point of ending the delivery and that volume can be recorded. Usually
burets will contain gradations to the 0.1 mL and can therefore be read with accuracy to the 0.01 mL.
Burets are very often used for titrations. When using a buret you will want to be sure to clamp it to
either a stand or to a secured position so that it does not fall and risk the potential to break. Also, when
using burets you want to be sure to remove any residue of previously used solutions, while also being
sure to wash it out good before returning it to its drawer in the lab. To wash it, you should first wash and
rinse it with water, and then rinse with some of your solution that you intend to use (so that when you
add the solution to fill the buret it does not dilute your solution with any residual water). When you
have washed it through with your solution, you may then fill the buret with your solution above the zero
line with the stopcock closed, and then ensure there are no air bubbles in the capillary tip by releasing
some solution and looking for a steady stream. If you can visually see air bubbles, you can release them
by lightly tapping on the buret with your finger.
While doing a titration, be careful to dispense the solution as much as needed. If you open the stopcock
all the way you will release a stream of solution which could release mL at a time. If you doing a titration
you want to try not to miss the end point so it is good practice to try and estimate the endpoint either
with an indicator first and then go back with a pH meter and try to very accurately release drop by drop
near the end point. Always be sure to read the bottom of the meniscus when taking volume
measurements with a buret.
When you have finished using the buret, be sure to wash it through with water. Depending on the type
of solution you have used you may want to use soap to wash the buret first. If the solution you used was
rather dilute, you may be able to rinse with tap water a few times and then be sure to use a few rinses
with distilled water.
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Pipet
Pipets are thin delivery tools (somewhat pen-shaped) used to dispense solutions of one specific volume.
Unlike a buret these do not need to be clamped to anything since they are handheld and usually deliver
one specific volume instead of delivering a steam of solution.
There are quite a few different types of pipets you will see in a laboratory. They vary not just by the
volume that they can deliver but also in terms of their accuracy, use of samples (either chemical and/or
biological), and the mechanisms by which the solutions are drawn into the pipet and dispensed out.
Pasteur Pipets are pipets that are used for the
transfer of small amounts of liquid. These are not
calibrated nor do they have any accurate
measurement of volume. To use one, you connect a
bulb (that is separate of the glass) to the larger
opening of the pipet, then you hold the rubber bulb
with your thumb and index finger to squeeze out
air and then pull in solution you want, being careful
not to pull in too much volume to absorb into the
bulb. Then you can release the solution you have
collected into a separate container by squeezing
the bulb while holding the pipet over that
container.
Volumetric pipets are pipets that are used to transfer a specific type of volume of liquid. Like the Pasteur
pipet they are shaped with a long stem but they will have a portion of the pipet that can contain the
volume you need. There are either larger bulbs to use (if the volumes are large) or a manual propipetter
which functions by wheel mechanism that you may use to collect and then release the solutions. These
volumetric pipets will have gradations similar to that of the volumetric flask that make these very
accurate for dispensing one specific volume. For instance if you have a 25-mL volumetric pipet, the only
volumes you can dispense accurately are 25 mL. Using that pipet you might be able to make solutions of
25 mL (1 dispense), 50 mL (2 dispenses), or any multiple of 25 mL.
Graduated pipets are pipets that have a series of volumetric gradations on the pipet that will allow you
to dispense a variety of volumes. Historically, the accuracy of the volumetric pipet is better than that of
the graduated pipet, however the graduated pipet still offers a more accurate dispensing than a Pasteur
pipet. There a few different types of graduated pipets including the Mohr pipet and the serological pipet
which differ by the position of the last gradation as shown in the image below.
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NEVER use your mouth on a pipet as a means of collecting a solution.
Funnels
Funnels in the chemistry lab are similar in function to funnels used in automotive industry or in the food
industry. It is a device that allows for the guiding of a larger volume of solution to be poured from one
container into the next. There exist a few different types of funnels depending on the
type of transfer.
Gravity funnels are used to transfer a solution from one container to the next simple
allowing gravity to take the solution into the second container. Filter paper can be
added to the gravity funnel to allow for the collection of any solid from getting into
the 2nd container.
A Buchner funnel is often used in conjunction with the Buchner flask (read
above about flasks) which allows for vacuum filtration. The Buchner
funnels has some a conical shape but a flat surface with pores on which a
piece of filter paper should be added. When doing a vacuum filtration, you
connect the Buchner funnel to the Buchner flask and you can pull as much
of the liquid out of your solid. This is very useful when trying to collect a
solid and removing all of the liquid from it. You may also do some washes
of the solid that you collect in the precipitate to ensure that you remove all solvent.
Spatula
These are small metal devices that come in a variety of different forms and sizes
that allow for the transfer of solids from one place to the next. They can be used to
put solids into a weighing boat, weighing bottle. These are NOT the same as a
kitchen spatula.
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Measuring devices
Graduated cylinder
These are common lab equipment used to measure the volume of a
liquid. Graduated cylinders are either made with plastic or glass. As the
name implies, it’s a cylinder with gradations for volume on the cylinder
which allow the user to pour some solution into the cylinder and
measure how much they have poured in. Some graduated cylinders will
have the letters “TD” and some will have “TC”. This indicates that it is
not specific for containing or delivering. In reality the use of these are to
make measurements of a volume that can then be delivered to another
container, but there are cases where one might just want to contain the
measured volume, perhaps to use of a gravimetric analysis. Graduated
cylinders are more accurate than flasks and beakers but are NOT more
accurate than the volumetric flask. If you are performing a volumetric
analysis you would prefer to create solutions in the volumetric flask.
Heating devices
Stirring hotplate
When mixing solutions, it is often desirable to use a stirring hotplate.
These work by providing a ceramic plate that both heats up and provides
a magnetic field to allow for a magnetic stir bar to be added to a
flask/beaker/container and rotate at a certain RPM “(rotations per
minute”). Usually the plate is made of ceramics and there is a heating and
magnetic component embedded within that needs to be plugged into an
electrical outlet in the lab. There should be two knobs (one for heating
and one for magnet) and they should have numbers or
temperatures/RPMs listed on the knobs. These should be used with
caution for accidental burns. Do not just grab these by the plate head.
Make sure to turn the knobs off when finished and if you are intending to
use one, you should ask to see if the one you want to use has been used
recently. The ceramic plates are usually pretty easy to clean and they
should be cooled down properly before being cleaned.
Bunsen burner
The Bunsen burner is one of the most common laboratory equipment found
in a chemistry lab. Named after the inventor of this heating device (Robert
Bunsen) these are a small metal tube that is connected to a gas source in
the lab and requires a spark or a match to light. The hose that is connected
to the burner will release a stream of flammable methane that can be
controlled by a handle at the gas nozzle. Once the spark or match is brought
towards the top of the burner, a flame will begin. the flame can be
controlled at the base of the burner where there is generally a mechanism
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that acts to let more or less air into the burner. Similarly to the hot plate, this should be used with
caution since there is an open flame. In order to heat something with the Bunsen burner, a ring stand
with either a metal ring or a clamp should be used to keep the container that is being heated in place.
Laboratory Instruments
Laboratory Balance
A laboratory balance (also referred to as an “analytical
balance”) is used to measure the mass of an object. In
analytical chemistry, the laboratory balance is used for
gravimetric analyses, where the determination of an
analyte can be found by measuring its mass or the mass
of a synthesized or complexed product. This can be
useful especially in the event that you produce a
complex from an originally unknown amount of analyte
and want to use the mass of the product and any of the
chemical reactions to determine what the amount of
your unknown analyte is.
There are several types of laboratory balances but the
ones we have in the CHM3120 lab balance room are
the digital, top loading balances. The sensitivity of
these balances can be found in the number of places
past the decimal that are shown on the balance. The
balance is enclosed with a draft shield. The purpose of the shield is to remove the influence of any air
currents in the room and to keep dust or any other contaminants getting into the balance. The way that
electronic analytical scales work is to actually measure the force of the object placed on the scale and
how much must be countered by the balance to maintain the position. This requires that balances be
calibrated correctly to allow for that force measurement to be done correctly.
Please use the balances with care and respect. Keep them clean and never put chemical directly on the
balance but instead use weighing vessels such as weighing paper, bottle, weighing boats or a watch
glass.
In order to use the balance correctly be sure after you turn on the balance that you tare (set it to zero) it
first before adding anything. If you are using a weighing bottle you can add sample to your weighing
bottle and measure the mass of the weighing bottle with your sample. Then you can remove some
sample from the weighing bottle
One of the most important rules of weighing is that the sample must never come in direct contact with
the balance pan. The best way to keep the balance pan clean and to ensure that the sample is kept
dried and not contaminated is to use the method of “weighing by difference.”
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In weighing by difference, a sample is placed in a weighing bottle in order to be dried before weighing.
The weighing bottle is kept closed through the whole process. The weighing bottle plus sample is
weighed, then the required weight of sample is removed to a suitable receiver, and the weighing bottle
and remaining sample is reweighed. The weight of the sample in the receiver is simply the difference in
the two weights. Both weights must be recorded (in your lab notebook) – not just the difference! The
notebook entry of this procedure would look something like this:
initial weight of W.B. plus cement sample = 24.5678 g
final weight of W.B. minus cement sample = 24.1357 g
weight of cement sample = 0.4321 g
The sample is removed from the weighing bottle by gently tapping on the weighing bottle with its cap to
allow a controlled amount of sample to be transferred to the receiver. To prevent fingerprints from
changing the weight of the weighing bottle, it is usually handled with a Kim-wipe or “paper loop.”
If, by accident, too much sample was removed, that sample will be discarded. The discarded sample
should not be returned to the weighing bottle. Of course, in the case of very expensive or otherwise
irreplaceable reagents, a discarded sample should be saved and re-dried.
The method of weighing by difference may at first seem cumbersome, but with practice, samples can be
weighed efficiently. This method is used because:
1. The balance pan is kept clean, because only the clean, dry weighing bottle touches the pan.
2. The sample is kept clean and dry, because it remains in a capped weighing bottle as much as
possible.
3. The exact zero of the balance is not critical, because only the difference of the weight is used.
4. The sample can be weighed into a wet “receiver.”
5. Time is saved when several samples are weighed from an initial amount, because the final weight
for the first sample becomes the initial weight for the second sample, etc.
An alternative approach that is common in modern analytical chemistry is the use of disposable
weighing boats and weighing paper in conjunction with the tare function that is available on digital
analytical balances. The weighing boat/paper prevents the sample from coming into contact with the
balance pan. The weighing boat/paper is placed on the analytical balance, and the tare (or “zero”)
function subtracts the weight of the boat/paper to make the starting weight read as zero. Therefore,
there is no need to subtract the weight of the boat/paper from the final weight to determine the weight
of the sample. The disadvantages of this approach include (in addition to the need for non-reusable
weighing boats/paper) the inability to weigh directly into wet receivers and possibility that sample may
adhere to the weighing boat/paper causing inaccuracy in the weight.
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pH meter
As the name implies, the pH meter will be used to measure the pH of
a solution but it is not measuring pH directly. The pH meter is
actually built of two electrodes (a reference and a glass electrode)
which measures the potential between these two electrodes. Once
the potential is measured, the pH meter can convert from millivolts
into pH if the pH meter has been calibrated correctly. The calibration
component allows the pH meter to say that a certain millivolt is
equivalent to a buffer of pH = 4, 7 and 10 and then creates a
calibration curve that allows the millivolts read in an unknown
solution to be set towards a particular pH.
The pH meters we have in the laboratory can be calibrated as follows:
1. Check to see that the electrode filling solution is level.
2. Take electrode out of solution (or take cap off), rinse with deionized water and dry with a
kimwipe
3. Immerse the electrode in pH 7 buffer (these buffers can be found in the laboratory), swirl and
press the cal button
4. The meter should auto-endpoint and display 7.00
5. Rinse the electrode with deionized water, dry with a kim wipe.
6. Immerse pH meter in the pH 4 or pH 10 buffer solution. Depending on whether your pH range is
within 4-7 or 7-10, you should choose the correct buffers to calibrate with. If you are using a
range from 4-10, then you can either use the pH 4 and 10 and do a 2-point calibration OR use pH
4, 7 and 10 by doing a 3-point calibration.
7. Swirl, and press cal button and wait until the pH gets as close to 4 as possible. The meter should
auto-endpoint at or near pH 4.00
8. Remove the electrode, rinse it with deionized water and dry with a kimwipe.
9. Place electrode in sample you wish to measure pH
10. Swirl and read pH
11. After done using pH meter, rinse with deionized water and place back in solution or with cap.
Once you have calibrated your pH meter, you are now ready to use it to measure the pH of your
solution. It is good practice to rinse the electrode with distilled water whenever you transfer it from one
solution to another. Wipe it down with a kim wipe so that you do not then add any drops of distilled
water to the solutions you then place the electrode. Once you have finished using the pH meter, be sure
to wash the electrode tip with distilled water and place it in the buffer solution that it was originally
stored in. The electrode should never be left to sit out dry as that will impact the efficiency of the
electrode tip.
A helpful video for how to use the pH meter correctly can be found here:
https://youtu.be/vwY-xWMam7o
Ion selective electrodes
Ion selective electrodes (ISE) are electrodes that are specific for one type
of ion and can be used to measure the activity of that ion when in solution.
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There are a variety of different types of ion-selective electrodes based on their design and what they
measure.
1) Glass membrane ion electrodes are made from an ion-exchange type of glass that allows for a
difference to be measured between an internal reference electrode and the external ion
selective electrode. The pH meter is an example of a glass membrane electrode specific for H+.
2) Crystalline membrane ion selective electrodes have a crystallite structure at the tip of the
electrode that is specific to only one type of ion. The Fluoride ion selective electrode is an
example based on a LaF3 crystallite electrode. In our laboratory we have fluoride ion selective
electrodes that are for your use. When using the fluoride ion selective electrode you will need to
connect a reference electrode in the reference terminal and the fluoride selective electrode into
the indicator terminal. You will place both probes into a solution and measure the voltage read
by the ISE. Similarly to the pH meter, you should consider calibrating the fluoride ion selective
electrode with standardized solutions of F-. The pH 4,7, and 10 solutions
Spec 200 UV-Vis spectrophotometer
Spectrophotometry measures how much light is absorbed by a
chemical substance by measuring the intensity of light that passes
through a sample. The principle behind this technique is that
chemical compounds contain electrons and based on the energy
levels/orbitals for those electrons and how much energy is
required to promote to higher energy levels, a compound will
absorb certain wavelengths of light. The measurement not only
shows how much absorption is there, but also allows for
quantification of how much of that substance is there through
Beer’s law which says:
A = e*C*l
where A = absorbance; e = molar absorptivity (a constant specific
for each compound at a specific wavelength); C = concentration; l
= pathlength of the light travelling through the substance
(measured by the length of the cuvette, usually 1 cm)
The spectronic 200 is a spectrophotometer, which operates at wavelengths between 340 and 1000 nm.
To read more about the one we have in the laboratory you are encouraged to go to the manufacturer’s
site and read the brochure: http://www.thermofisher.com/order/catalog/product/714-039400 .
Key things to note when using the spectrophotometer:
1) If you are unsure of where a chemical species absorbs light, you may place a sample into the
cuvette and do a scan of the wavelengths from 340 to 1000 nm and get the continuous
spectrum. This type of spectrum is often done at the onset of measurements to ensure that if a
wavelength is used to monitor the absorbance of a compound, it should be an absorbance
maximum so that all concentrations, especially lower concentrations, can be read.
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2) Once you have the absorption spectrum for a compound you may want to create a calibration
curve using standard solutions so that you can then use that calibration curve as a way to identify
the concentration of unknown quantities (which is what we will be using the spec200 for most
regularly)
3) The handling of cuvettes is extremely important. Often two cuvettes are used simultaneously,
one for the “blank” solution and one for the sample to be measured. Yet any variation in the
cuvette (change in width, curvature of the glass, stains, smudges or scratches) will cause varied
results. Thus, it is essential, in dealing with cuvettes, to follow several rules:
•
•
•
•
•
•
•
Do not handle the portion of a cuvette through which the light beam will pass
Always rinse the cuvette with several portions of the solution before taking a measurement.
Wipe off any liquid drops or smudges on the lower half of the cuvette with a clean kimwipe
before placing the cuvette in the instrument. Never wipe cuvettes with towels, handkerchiefs, or
shirts. Inspect to ensure that no lint remains on the outside and that no small air bubbles are
clinging to the inside walls.
When inserting a cuvette into a sample holder:
To avoid any scratching, insert the cuvette with the index line facing toward the front of the
instrument
After the cuvette is in place, line up the index lines exactly. The cuvette should be removed in the
reverse manner (pointing the cuvette index toward the front of the instrument before
withdrawing it).
When using 2 cuvettes simultaneously, use one of the cuvettes always for the blank and the
other for your sample. Do not interchange the two.
Computation
Microsoft Excel
In CHM3120L there is going to be loads of data that you will collect in your projects. Organizing the data
into easy to read tables and graphs, and doing calculations on large sums of data can all be done in
relatively quick and easy fashion using a spreadsheet program. The most common spreadsheet program
that is used today by students is Microsoft Excel. Excel provides spreadsheet capability for all types of
operating systems; importantly it has crossover availability between Windows and Mac systems. The
program itself provides grids of cells that you can use to insert calculations/functions, graphing tools,
and other useful processes.
An entire course could be dedicated to the use of Microsoft Excel and to the various editions of the
program that exist.
Listed here in your reference manual are a variety of YouTube videos that will help you to understand
how to do some basic functions on Microsoft Excel.
1) Basic usages of excel including page view, formatting, inserting into a document:
https://youtu.be/jisHP2JGXUQ
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2) How to make a scatter plot in excel, add a best fit line and display equation:
https://youtu.be/nfu6CrRK-Co
3) Plotting an absorption spectrum using UV-Vis data: https://youtu.be/dpm8bnijVvY
4) 10 useful function in excel: https://youtu.be/X12oQeJWpEs
5) Descriptive statistics for one data set, done quickly: https://youtu.be/4_9vGqQaCFk
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Section 3 – Laboratory Techniques
Preparing an experiment
A central component of CHM3120L is the ability to prepare an experiment. You will be investigating the
topic for each of the 6 projects listed. The experiment will NOT be given to you, but you will have to
prepare one that will investigate the topic. You will be working in groups for each project, and so you
will find the following in your technique guiding questions:
“Write out a plan for ______________. Think about what materials you might need, consider two
methods of analysis, the number of measurements you might need in total, and what type of
containers and instruments you might use. Think about how each member of your group will
contribute to the experiment. Materials are provided in the chemical fume hoods. Once you have
completed this preliminary plan please show your TA and they will review it, and upon their approval
you may proceed.”
Each project will be different, so consider looking here each time your group needs to set up a new plan.
To help you determine how to come up with a plan here are some central questions for you and your
group to consider. Use these questions as a way to check that you are on track:
1. What is the purpose of the experiment? This will be specific for each project. You want to be sure
that you have a specific purpose (i.e. “to quantify the mass percent of phosphate in Scott’s turf
builder fertilizer”). After deciding on the purpose, you will want to be sure your analytical
method is going to work. Which leads to the second question...
2. What type of analysis is going to be used for the experiment? There will be multiple methods for
quantifying analytes. You want to be sure you have thought through which type is going to be
best suited for your experiment’s purpose. For all the projects, you will be encouraged to look at
research articles that have studied the same topic and you will need to check their methods and
materials and see what they have done. This is common practice in science, so you will be gaining
this skill. For some of the projects you will be required to do two types of analysis, to help
corroborate your evidence and improve the confidence in what you find. This means you may
have to find more than one research group’s work to find more than one analysis method
(though some research article will have presented work with multiple types of analyses).
3. What reagents will you be using for the experiment? In our labs, we will have chemicals in the
fume hood for you to use so you will want to look at those, and if something else is needed you
may ask the TA to see if that reagent is available in the stockroom.
4. Have you looked at the material safety data sheet for the reagents you will be using? You need
to be aware of any safety precautions and special disposal instructions for any of the reagents
you will be using.
5. What equipment will you need to do your experiment? Is it available in the CHM3120L lab or do
you need to request it from the stockroom?
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Once you have answered those questions and have started to put together a plan. Here are some tips to
consider to make your experiment go smooth.
1. Be sure to write everything down in the process of planning. This means the procedure you
want to do, any calculations as to how you determined how much of a reagent you want to use,
and anything else that you need to have for the planning to be successful. If you leave out details
during the planning, you may have a difficult time during the experimental process to remember
what your planned procedure was going to be or why you used a certain amount of something.
Refer back to section 2 on the lab notebook for more about how to write things down.
2. Always consider starting with a small-scale reaction first to ensure that it works. For most of the
projects you will be asked to provide an error with your quantification and so you will have to do
replicate measurements. Rather than set up replicate measurements that you aren’t sure of their
compatibility or success, it would be to your group’s advantage to try a reaction or quantification
first on a smaller scale and then scale it up. The small-scale reactions don’t need to be done in
replicate if you will be doing them for testing purposes.
3. Make sure you have everything ready before you start the actual experiment. This means know
where all the reagents are that you need, and if some need to be kept in the fume hood, be
aware of that.
4. Make sure that you divide the work evenly amongst the group. Working in a group is often hard
for students because some want to do more than others and some don’t want to do anything
and coast by. If you are finding difficulty with your group, the best idea is to speak openly to
everybody in the group to ensure that everyone tries to assert themselves and work equally. If
you are having major issues with your group you may speak to your TA in private.
Sampling and Sample preparation
As explained in section 1, sampling and sample preparation are critical in analytical chemistry
experiments. Sampling is the process of choosing your materials to analyze in a way that is
representative of the material as a whole. Sample preparation is the process of converting your sample
into a suitable form for the analysis you chose.
When you are deciding upon your sample to be investigated you want to ask the following questions.
1. Where are you getting the sample from? If the stockroom is providing you your reagents and
chemicals you wish to study can you verify that the sample you have chosen is representative of
a larger sample as a whole?
2. What conditions does my sample need to be kept at? This could include things like the particular
temperature, amount of light it receives, whether it is kept in liquid or needs to be dried. If it’s a
chemical reaction (such as a fermentation reaction), how do you stop the reaction? Do you use
26
temperature to stop the reaction or a chemical reagent? How will this affect your analysis of the
sample?
3. Is your sample homogeneous (uniform substance throughout) or is it heterogeneous (varying in
substance)? If you do replicate measurements of this substance can you insure that you have
made all the replicate samples the same in terms of their homogeneity or heterogeneity?
4. If you have to prepare your sample for analysis, what type of preparation is necessary? Things to
consider are filtration to separate some of the components, boiling off or evaporating away
solvents, centrifuging to collect the heavier particles, making a concentrated stock solution by
which you can dilute your sample as necessary.
Filtration
As mentioned above, filtration is one of the key components for sample preparation. The purpose of
filtration is to separate mixtures of liquids and solids. There are two main types of filtration that you will
consider using: gravity filtration and vacuum filtration.
Gravity filtration
Gravity filtration is used generally when it is desirable to remove unwanted solids from a desired
solution. The process will require a funnel with a piece of conical filter paper in the funnel, to be placed
over an Erlenmeyer flask to collect the solution. The purpose of using filter in this situation is to remove
the solid by letting it collect in the filter paper. Filter papers are categorized by pore sizes. In general, the
smaller the pore size the faster the flow rate for the filter paper. An excellent guide to the types of filter
paper used in chemistry can be found here:
http://www.simada.co.il/images/filters/Whatman_filter_paper_guide_en.pdf .
The procedure for setting up gravity filtration is to put your filter paper into the funnel. If no conical
filter paper is available it may be necessary to fold over circular filter paper and place in the funnel.
A visual video explanation for folding filter paper into “fluted” filter paper can be found here:
https://youtu.be/caXpfoVqqXo
Once you have the filter paper in the funnel and the funnel placed in
the collecting vessel, you may wet the filter paper to have it set in
place in the funnel. Then add the solution you wish to filter, being
careful not to add it so that the fluid level rises higher than the filter
paper. That will risk solid getting through the funnel. Repeat this
process until you have all the solid in the filter paper. if you have
some solid still in the original flask, pour some of the filtrate into the
solid and swirl to ensure you can pour the remainder into the filter
paper and collect. Wash the solid in the filter paper with a small
amount of cold solvent. For most gravity filtration, you won’t need
the solid, but if you decide to keep it for further analysis, collect it
carefully and place somewhere to dry with the filter paper still with
it.
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A video on gravity filtration as well as decanting (pouring off a liquid from a solid, without needing to
filter), can be found here: https://youtu.be/tLmh_rMQu7M
Vacuum Filtration
The purpose of vacuum filtration is generally the contrary to
gravity, where here the solid component of a solution is desired
so it is collected through connection to a vacuum so as to
remove any solvent from the solid.
Setting up a vacuum filtration, you will need the Buchner funnel
(ceramic white funnel) and the Buchner flask (which look just
like an Erlenmeyer flask but has the tube coming out of the
side) and circular filter paper. Before you even begin the
process, make sure to weigh the filter paper and watch
glass/beaker you will use to collect the material! The filter
paper will not be removed from your dried product so you need
to subtract the weight of the filter paper to be able to efficiently
calculate how much solid you produce. You may also find that
you need to keep the recovered product on a watch glass or
beaker so you may want to measure that too in the event you
need to subtract those values from your final dried product on filter paper and watch glass.
Attach the Buchner to the Buchner flask with the addition of a rubber adapter that allows for the funnel
to have a tight seal in the flask. Connect the Buchner flask to the vacuum in the lab using a rubber hose.
Place a piece of circular filter paper inside the Buchner funnel. Unlike the gravity filtration, this paper
should fit perfectly so that no solid will go through the holes in the Buchner funnel. Wet the paper with
some solvent, and then turn on the vacuum so that there is suction. You will then add your solution to
the Buchner flask, being sure that your solution is mixed so that none of the solid you wish to collect is
left in the flask you are adding it from. Wash out any of the solid that remains in the flask you are
transferring from, using remaining solvent. Once you have collected all the material on the filter paper
you can wash it with cold solvent to ensure you remove any unwanted impurities. Collect the product in
either a beaker or a watch glass and let it dry for the necessary time before you measure it. Remember
to subtract the measurement of the filter paper and watch glass when you do measure it.
A video showing how to set up and perform a vacuum filtration can be found here:
https://youtu.be/yvAT4C3-U7k
Volume delivery by Pipet
The most accurate volume delivery in the CHM3120L laboratory will come from the use of volumetric
pipets. Here is a procedure you could follow to ensure good laboratory practice with a pipet
1. Decide which volumetric pipet will work best for the volume you need delivered. If you intend to
deliver 50 mL to a solution, you may either use a 50mL pipet or a 25 mL pipet twice. You want to
28
ensure that you don’t use a 1 mL pipet 50 times because this will introduce error from so many
measurements, and it will be a waste of time.
2. Rinse out the pipet you intend to use with a small portion of your solution. If you are using a 50
mL pipet, you might rinse it out two with 10mL of your solution. If you have a 25 mL pipet you
might use 5 mL portions. In order to rinse, you will attach a rubber bulb, squeeze air out of the
bulb, and then withdraw some of the solution into your pipet and then discard. This will ensure
that the pipet does not have any contamination of your actual sample dispensed, nor will the
concentration change due to any water left in pipet from previous use.
3. To collect the volume of your interest, you will follow the same procedure by expelling air out of
the bulb, dipping the pipet tip into the surface of the solution without scratching the bottom
surface of your flask/beaker/container. Release your grip from the bulb slowly, allowing liquid to
fill up until the liquid is ~1 cm above the calibration mark.
4. Remove the bulb, and quickly put your index finger to cover the tip of the pipet. Wipe the
outside of the tip with a kimwipe. Using your finger to control, you should dispense out the
excess past the calibration mark back into your original solution, until the bottom of the
meniscus in the pipet reaches the calibration mark.
5. Place the pipet into the container you wish to dispense and release your finger to allow the
solution to drain. Be careful not to splash or leave any of the volume in the pipet. If some
remains you may gently tap (do not blow on the pipet).
A video explaining how to use a pipet can be found here: https://youtu.be/VKaJ4G29Tnc
Making and Diluting Solutions
In most of the procedures for which you will be analyzing substances with any type of solutions, it will be
important to make the solution with the correct concentrations. The following procedure could be
followed for making a solution of a known concentration starting from solid material:
1. Based on the experimental needs, decide on the concentration you want to make. For examples
let’s assume you wanted to make a 0.1 M Kill solution
2. Calculate the molecular weight of the compound using the chemical formula (KCl = 74.551 g/mol)
3. Use a volumetric flask to make a stock solution. Depending on how much you need you might
use a 25mL, 50mL, 100mL, 250mL, 500mL, or 1L flask.
4. Weight out accurately your compound needed. If you wished to make 1L of a 0.1 M KCl solution
the calculation would be:
(1 L) * (0.1 mol KCl/1 L) * (74.5513 g KCl/ 1mol) = 7.455 g NaOH
5. Place the weighed compound into the volumetric flask. Be sure to put all of the compound into
the flask. Then add enough of the solvent to dissolve the solute. Swirl around to ensure that you
have mixed the solution completely. Then add enough volume of solvent to fill the volumetric
29
flask. You should read the bottom of the meniscus when making sure the volume is as desired.
For the example above the ~7.455g of KCl could be dissolved with approximately 250 mL of
water. Once the solute has dissolved you should add enough water to the volumetric flask to
ensure that the correct volume has been made
For a video on how to make solutions from a solid sample please see the following:
https://youtu.be/A2YyIo8vSCA
If starting with an aqueous solution, it is possible that you will be given a solution of an already known
molarity. In order to make the desired solution you would have to do a dilution. Dilutions function by
taking an existing solution of a known molarity (M1) and using a starting volume (V2) add more solvent
to that volume to make a final volume (V2) with a new molarity (M2).
M1*V1 = M2*V2
So if we were trying to create a 1 L (V2) solution of 0.100 M NaOH (M2) and we had a stock solution of
10.0 M NaOH (M1), we would need to do the calculation:
(1 L) *(0.100 M) = (10.0 M) *(Volume of NaOH stock solution needed)
Volume of NaOH stock solution = 0.01 L or 10 mL
Therefore we would take, 10 mL of the stock solution and need to dilute it to 1.000 L with the addition
of water.
NOTE: If the original solution has a concentration of more than 3 M for an acid or a bas, you should add
the acid/base to water, rather than pouring the acid in to the flask and then adding water. The reason
for this is that the mixing of acid and water is an exothermic reaction, and rather than have the contact
be done with an equal amount of water and acid it would be best to have a large amount of water to
dilute the acid instead of having contact of a lot of the acid/base with a small amount of water.
For a video on how to dilute solutions from a stock solution see the following:
https://youtu.be/MG86IFZi_XM
Titration (volumetric analysis)
The most common form of volumetric analysis in the analytical chemistry lab
is that of titrations. It is useful for determining the concentration of an
unknown solution.
The general principle behind a titration is that if you react a chemical species
with another compound and can monitor the reaction with either an
indicator/pH meter/color change, then it is possible to say when the two
chemical species react fully and therefore have equimolar concentrations.
That point where the two chemical species react fully is called the end point.
If you know the concentration and volume of one species, and the volume
30
for your other species, you can quantify the concentration for that second species. This means it is
critical to have a known concentration of solution to titrate against your unknown. While it is possible to
calculate the concentration of a solution, a better method to finding the concentration is to standardize
a solution by titrating it against a known amount of a primary standard (a solid of known mass and
molecular weight) Standardizing the known concentration is common practice in the CHM3120L and will
be described below.
Standardizing a Titrant
The purpose of standardizing a solution is to be sure what the concentration REALLY is.
You might think that if I need 0.1 M HCl, I should just try to be sure to weigh out 1 mol of HCl and put it
in 10 mL of deionized water, and that should be equivalent to 0.10 M. However in the analytical
chemistry lab we want to be sure with as much precision as possible. Is the solution 0.0999 M OR 0.1010
M? So how do we do it.
Depending on what your solution is, you will pick the opposite species to standardize against: if it is an
acid you might use sodium carbonate as your primary standard base, and if it you are standardizing a
base you might use potassium hydrogen phthalate, KHC8H404 (often referred to as just KHP).
Here is a basic outline of a procedure for standardizing a solution of 0.10 M NaOH using KHP.
1. Determine how much volume of your NaOH solution you need. If you are doing titrations with
the NaOH solution, think about how many titrations you need to do and whether you want to do
them in triplicate or more, and what the volume of each titration is. For instance if we intend to
do 10 titrations that are going to be done in triplicate and will be about 50 mL each, we would
need at least
10 titrations*3 measurements*50mL each = 1500 mL or 1.5 L of NaOH
2. Prepare 1.5 L of 0.10 M NaOH (See section on making solutions)
3. To standardize the NaOH (i.e. “to find out the concentration to more decimal places) you will be
titrating the NaOH with the KHP primary standard. Given the 50 mL volume of the buret, you
should try to standardize the NaOH solution with an amount of KHP that will be within the 050mL range of NaOH (optimum being towards the 25 mL dispensed).
4. Calculate the mass of KHP required to react with 25 mL of a 0.1 M NaOH. KHP is a strong acid
reacting in a 1:1 manner with the NaOH. So the calculation would be:
(0.1 mol/L NaOH)*(0.025 L NaOH)* (1 mol KHP/1mol NaOH)* (204.2g KHP/1 mol KHP) =
= 0.5105 g of KHP
5. Accurately weigh out the amount of KHP you measured, and dissolve it into 25-50 mL of distilled
water in a 250 mL beaker. The amount of water is somewhat indifferent in that the moles of KHP
is what react, not the molarity! So the water works to ensure that the solution is fully dissolved
and ready to be titrated. Add a magnetic stir bar to the beaker and put it on a stir plate. You may
add 5-6 drops of an indicator such as phenolphthalein so that you may be able to visualize the
change in pH of your solution.
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6. Set up a pH meter (see the section on pH meters). Though you have the indicator present, the
pH meter will be a more accurate way to read the pH change.
7. Wash a buret and rinse with distilled water and then some of your base solution that you wish
standardize.
8. Fill the buret to 1 cm above the top marker on the buret and then be sure to dispense the excess
up to the point where the bottom of the meniscus is at the 0 mL mark. The buret is now ready to
dispense the base to your 250 mL beaker containing the KHP solution.
9. Slowly add the base to the KHP solution and titrate until you are 4-5mL past the point where the
solution has change from clear to pink (as a result of the indicator). Be sure to collect pH
measurements regularly throughout the standardization (0.5-1mL increments)
10. Plot the titration curve (volume of base added on x-axis, pH on y-axis) and determine the
equivalence point using either a 1st derivative, 2nd derivative or gran plot.
11. You can calculate the concentration of your standardize solution by noting that the volume
dispensed * the molarity of the base = moles of KHP in the beaker (which you can get from the
mass you put there and then molecular weight)
Video of the standardization of NaOH w/KHP can be found here: https://youtu.be/J8gDdy6y_j8
Performing a titration of an unknown
Upon standardizing your titrant (whether it be an acid or a base or a metal solution or EDTA), you are
now ready to perform a titration with an unknown to help identify the concentration of that solution.
The procedure to perform a titration of an unknown is very similar to that of the standardization
technique except for the lack of the primary standard. Instead you will have a solution of unknown
concentration in the beaker you are titrating into, and you will try to use the knowledge of the reaction
you are doing and the tools you have to figure out when the reaction reaches an end point and
therefore what the concentration of your unknown is.
An outline for a procedure for doing this can be found here:
1. Make sure you have the right equipment at hand: the buret, a standardized titrant, an indicator
or a pH meter, a beaker/flask to collect, and your unknown solution
2. Pipet a volume of your unknown into the collection flask or beaker. Add in drops of an indicator
based on what will be able to identify the pH change. If you know what your unknown species is
you make look to see what the acidity constants are to know how what type of pH will be seen
when you reach the ½ of equivalence and at equivalence. You may also use a pH meter and
simply measure the pH change with that.
3. Fill a buret with your standardized titrant.
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4. The best idea is to do one trial rapidly with an indicator to see roughly how much volume needs
to be dispensed. if you were to do the first trial of an unknown slowly and the end point volume
is around 50 mL, you may be wasting valuable time in the lab to do so. Once you do the first
rapid trial with an indicator, you may go ahead and make note of the end point volume and then
do successive trials where you are most accurate near the endpoint so you can collect pH data
not just along the titration curve but also close enough to the endpoint to visualize it graphically
5. Repeat the trials once you have an estimate of the end point and try to more accurately collect
the pH measurements nearest the end point.
6. Make sure to do titrations in replicate to ensure good precision with your data.
7. You can calculate the concentration of your unknown solution by noting that the volume
dispensed * the molarity of the standardized titrant = volume of your unknown in flask
*unknown concentration
Videos about performing titrations with indicator and pH meter, and how to do the calculations can be
found here:
• Principles of titration: https://youtu.be/d1XTOsnNlgg
• Performing a titration with indicator: https://youtu.be/sFpFCPTDv2w
• Determining concentration of unknown in titration: https://youtu.be/2z4mlE6MK0U
• Data analysis of pH data from titration: https://youtu.be/l2Z8gK4adqk
Gravimetric Analysis
Determining the amount of an analyte by measuring mass is known as gravimetric analysis. As you might
imagine, it’s somewhat similar to the volumetric analysis just described previously, except now we will
be using the analytical balance to measure the mass of a compound that can allow us to calculate the
amount of analyte we are looking for.
Often in gravimetric analyses we might react an unknown analyte with other chemical species in a
manner that we know we have kept the unknown analyte as the limiting reagent of the reaction so that
the product that is formed can be used to calculate the analyte we started with (using the stoichiometry
of our chemical reaction).
An example of such a reaction could be the precipitation of an ion in solution to form an insoluble salt.
Once the insoluble salt is formed, filtration of the salt can be achieved using vacuum filtration, and the
product could be weighed to determine the amount formed. Using the formula of the compound
formed and the stoichiometry with the analytes you start with, you may go back and determine the
moles of analyte and/or grams if desired.
A video describing the process in a bit more detail can be found here: https://youtu.be/WBg-yh8qk94
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Calibration Curves
Another way to find an unknown concentration for an analyte is to make a calibration curve. The
concept for a calibration curve is that if your analyte is detectable someway (i.e. using uv-vis
spectrophotometry, conductance, potentiometry, fluorescence) AND you have the analyte you are
investigating available to create “standard” solutions (i.e. solutions by which you know the
concentration) then you can make a few standards of varied concentrations, measure those standards
for a detectable signal and then plot on a graph the concentration of your standards (on the x-axis) and
the detectable signal (on the y-axis). Once you plot the values for your standards you may fit the plot to
a best fit curve which can often be done within the linear range of detection for the instrument and the
analyte of interest. Sometimes it may be necessary to take the log of your concentrations in order to get
the best fit line. With having the best fit line for your data, you may then take measurements of your
unknown and see whether the measured signal falls within the line. If an unknown that is measured has
a detectable signal that falls too high or too low to be detected, you might consider using more dilute or
concentrated solutions of your original solution and then doing dilution calculations to determine the
analyte concentration in the sample you begin with.
An example of a calibration curve is shown here for the log of concentration of an ion compared to the
potential voltage reading. Given that the x-axis is in log concentration, this would suggest that the
concentrations used were 10-7, 10-6, 10-5, 10-4, 10-3, 10-2 M:
Given that the equation of the line is given, this calibration curve can be used to solve for an unknown
within the range of 10-7 to 10-2 M. If an analyte of unknown concentration were measured using the
electrode used here and the response were -150 mV, then the calculation to solve for the unknown
concentration would be:
-150 mV = -96.714x – 388.38
x = -2.465
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and because the x axis is in log concentration we have to take the antilog (or 10x) and therefore the
concentration would be 10-2.465 M or 3.43 x 10-3 M
In the event that the sample we measured was a dilution of a stock solution made, we would have to
consider any dilution factors used in order to determine the concentration of analyte in our original
stock solution.
For instance, let’s assume for that solution you just measured to have a -150 mV response, the electrode
was dipped into a 250 mL solution for which was made by first taking out 2.0 mL from a stock solution
(of say 1.0 L volume), and diluting it to a 250 mL volume with solvent, you would have to use the same
type of dilution formula you have used previously to say:
M1V1 = M2V2
(3.43 x 10-3 M) * (250 mL) = (??? M) * (2 mL)
The original stock solution is therefore calculated to be 0.429 M.
(NOTE: The volume of the original stock solution is not important in the dilution equation because you
don’t use all 1.0 L of the stock volume in the dilution! Be aware of what volumes are most important
when you are doing dilution formulas)
For more on how to use calibration curves, the following videos may be useful:
1) Find concentrations of solutions using UV-Vis Spectrophotometry and calibration curves:
https://youtu.be/Il9hlMT0aUQ
2) Making calibration curves using an ion selective electrode: https://youtu.be/XMJtdBzsWVY
Quality Assurance
The final area to consider in terms of your laboratory techniques is not so much a technique itself but a
system of checking that your processes are all being done with the highest quality. This term quality
assurance is critical in laboratory settings. Your textbook for the analytical chemistry course includes an
entire chapter on it, which will be covered by the instructor. There are employment positions at
laboratories and companies worldwide that are called QA and QC positions for Quality assurance and
quality control. The two are similar though the assurance is more process oriented (i.e. people and
process involved) and the control is more product oriented (i.e. the product that comes out of the
process). Both work together to ensure the highest quality laboratory production.
So how does this transfer into the laboratory techniques you should be employing in the CHM3120L.
Here is a list of a few of the critical quality assurance steps you should be considering. For the success of
your projects and ultimately your grade, you will want to be sure to think about these steps.
1) Personal safety. Always wear the protective clothing required of the laboratory when performing
any experiments or if others around you are performing experiments within close vicinity. Be
aware of your surroundings. Be aware of any of the hazards or risks with the materials that you
are intending to use. There will be times in the laboratory when you will be planning out your
35
course of action and you may not necessarily need your goggles on. However, you must be
prepared at all times with your safety gear when you do perform experiments or when others
near you will be.
2) The use of validated methods for your analytical techniques. Method validation is the process by
which you confirm that the procedure you are using is suitable for its purpose. You might
consider trying your method on a known standard and seeing whether or not the value produced
is what is listed on the standard. The standards for method validation differ depending on the
type of lab you are working in, but the concept remains the same: is your process a valid one for
quantifying what you intend to quantify.
3) Performance characteristics for your validated method. Are the instruments calibrated? Have
you been able to determine what the minimum and or maximum detectable limit for the analysis
technique you are using? Often times you may read the maximum on analytical devices like
burets and pipets or even on some digital devices like your laboratory balances, but being certain
that you know these characteristics before you engage in the experiment will be of utmost
importance.
4) Reproducibility of your data. The confidence in your data in a laboratory is not just on whether
the value is close to what you predict, but more about the ability to reproduce the data to a very
high level of precision. Consider how many sample replicates you may be able to do with the
materials you have in the laboratory and for the analysis you intend to use. You might also
consider the importance of intra-laboratory comparison studies (different members within the
laboratory working on the same material).
5) Control samples. Have you been able to use your method on a sample that may contain solvent
but does not contain analyte and do you receive any detectable signals for that control sample?
Knowing how to use blanks for your measurements
There are quite a few more important practices that are used for QC/QA in laboratories but the ones
listed here are to be considered for your practice in the CHM3120L lab.
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Section 4 - Projects
37
Project 1: Investigation of Phosphorus Content in Fertilizers (revised Fall 2021)
Background: In order for plants to grow and thrive, they require a few basic chemical elements (listed
below in order of importance):
Elements
Carbon (C), hydrogen (H), oxygen (O)
Nitrogen (N), phosphorus (P), potassium (K)
Sulfur (S), calcium (Ca), magnesium (Mg)
Boron (B), chlorine (Cl), manganese (Mn), iron
(Fe), zinc (Zn), copper (Cu), molybdenum (Mo)
Source/Information
Readily obtained from water, carbon dioxide, and soil
Found in soil, considered primary macronutrients
Found in soil, considered secondary macronutrients
Found in soil, considered micronutrients
As you can see from the table, soil generally provides the
macro and micronutrients. The primary macronutrients
(N, P, and K) are so crucial for plant growth and survival,
that plants can deplete soil of these nutrients during early
stages of growth. In order to ensure the supply of these
vital nutrients for a plant’s lifetime, fertilizers containing
varying amounts of these primary macronutrients are
added to the soil, replenishing what the growing plant has
removed.
When you purchase a bottle of fertilizer, the amount of
primary macronutrients is often labelled with a 3 number
ratio, referred to as the N-P-K value. The N-P-K value is
the mass percent of nitrogen, the mass percent of
phosphorus (in the form P2O5)1 and the mass percent of
potassium (in the form K2O)1 in the fertilizer. In Figure 1, a
bottle of the Green Light SuperBloomä fertilizer is shown
and we see the numbers 12-55-6 written on the bottle.
These numbers mean that the SuperBloomä fertilizer is
guaranteed to contain 12% nitrogen, 55% phosphorus (in
the form P2O5) and 6% potassium (in the form K2O). The
remainder of the fertilizer is usually other macro and
micronutrients along with fillers, dyes, and other
anions/cations to balance the charges of the chemical
components.
Figure 1: Super Bloom fertilizerä indicating the N-P-K
ratio of 12-55-6 suggesting a composition of 12%
nitrogen, 55% phosphorus, and 6% potassium
Project Goals:
(1) Learn the techniques of filtration and weighing-by-difference.
(2) Quantify the mass percentage of phosphorus in a store-bought fertilizer and compare with the
product label.
1
The reason that phosphorus is expressed as P2O5 and potassium is expressed as K2O is because in earlier quality control studies of
fertilizer, scientists would do gravimetric analyses after igniting samples and then measure the oxidized components of the fertilizer, P2O5
and K2O.
38
Techniques you may need to learn or review:
• Sampling
• Sample preparation
• Filtration
• Gravimetric Analysis
• Microsoft Excel
Pre-Lab Research (to be done individually)
Refer to Liu et. al. “Magnesium ammonium phosphate formation, recovery and its application as
valuable resources: a review” J Chem Technol Biotechnol 2013; 88: 181–189
1. Phosphorus exists in what is known as “P rock” with large deposits in South Africa, China and
Morocco. What form of phosphorus is found in this “P rock”?
2. What is the chemical formula for Magnesium Ammonium Phosphate (MAP)?
3. Give 2 reasons MAP could be used as a fertilizer?
4. Reactions 1, 2 and 3 in the Liu paper show how to make MAP. What is the difference between
reaction 1, 2 and 3.
5. Under what conditions are MAP formed?
6. List the reagents used in MAP formation and their purpose.
7. How might you make MAP using store bought plant fertilizer that has phosphorus in it?
8. If a researcher has used 0.500 g of sodium phosphate (in the Na2HPO4 form) with an excess
amount of all the other ingredients (the magnesium and ammonium), what would the predicted
amount of MAP be?
9. If a researcher has used 0.500 g of sodium phosphate (in the Na2HPO4 form) to form MAP and
then measured their product collected on a piece of filter paper (measured before 1.015 g and
after 1.685 g), what was the % yield for the product?
Procedural design (to be done as a group)
As a group you shall write up a procedure for the following:
• A validation step that you can make MAP from a known source of phosphate (think about what
type of phosphate salt you might want to use)
• How would you calculate the percentage of phosphate that was successfully turned into MAP
from your original source. Keep in mind the reactions you wrote down in your pre-lab questions
• After validating that you could make MAP from a phosphate source, you must then consider a
question you wish to ask about a commercial fertilizer. Suggest a fertilizer/s that you want to
investigate and why did you want to choose that one/those ones? This step is a critical one.
• Determine what your question is that you wish to ask (review the section 3/pgs. 25-26 in this
manual).
• Write out the procedure for what you might do to answer your question.
o Things to consider for all the steps above: what question do you want to ask, what
materials would you use, what glassware, what volumes, what concentrations, how
many reactions would you run, how would you calculate values.
o If you have any questions, you should ask and/or email your TA during the week and they
will be able to provide you with some guidance
39
Project Summary questions (to be provided as part of your discussion in your lab report or
presentation)
1. How successful was your validation step? Were you able to recover the amount of phosphate
that you started with?
2. What question did you ask about the commercial fertilizers present?
3. How did calculated percentages of phosphorus (as P2O5) for your fertilizer samples studied
compare with the N-P-K values given on the fertilizer bottle?
4. What was the error associated with the replicate measurements you took? Was it a relatively
large or small error?
5. What are some of the possible sources of error AND what could you do in further experiments to
reduce the amount of error in your measurements/calculations?
6. Is this technique suitable for a quantitative analysis of phosphorus in a fertilizer? Explain your
reasoning.
40
Project 2: Investigating Kombucha Fermentation
Background: Kombucha is a drink made through
fermentation of black or green tea. It has grown in
popularity over the course of the last 10 years,
showing up in health food stores first and making
its way into more popular supermarkets
Fermentation is one of the most commonly used
methods of food processing. The process uses
microorganisms like yeast or bacteria to convert
carbohydrates into alcohols or organic acids. For
instance, with production of kombucha, a
symbiotic culture of bacteria and yeast (often
referred to as SCOBY) is added to a solution of
Figure 2: Kombucha being brewed in jars; look
black tea leaves and water and given time to
closely and you can see on the top there is the
convert the sugar to the corresponding organic
SCOBY (symbiotic culture of bacteria and yeast)
acids. The reasons fermentation is so popular
where the reactions are being catalyzed
include: 1) the production of alcohol, 2)
preservation of perishable foods, 3) enriching existing foods with nutrients produced in the process and
4) it became an additional method of food preparation other than cooking by heat and/or eating raw
foods.
Probably one of the more famous examples of fermentation in food processing is the production of wine
from grapes. To make wine, grapes are covered with a combination of bacteria, mold and yeast under
anaerobic (“no oxygen”) conditions causing sugars inside the juice from the grapes to be converted into
alcohol and CO2.
A stepwise explanation (with chemical reactions) for the fermentation of ethanol from glucose grapes
are shown here:
1. Glucose is converted into pyruvate through the glycolysis pathway in yeast/bacteria utilizing 10
enzymes and the following substrates: adenosine diphosphate (ADP), inorganic phosphate (Pi)
and oxidized nicotine adenine dinucleotide (NAD+):
C6H12O6 + 2 ADP + 2 Pi + 2 NAD+ → 2 CH3COCOO− + 2 ATP + 2 NADH + 2 H2O + 2 H+ (reaction 1)
2. The pyruvate molecules are converted to acetaldehyde by pyruvate decarboxylase
CH3COCOO− + H+ → CH3CHO + CO2
(reaction 2)
3. Lastly the alcohol dehydrogenases in the yeast/bacteria will convert acetaldehyde into ethanol
and regenerate the oxidized NAD+
CH3CHO + NADH+H+ → C2H5OH + NAD+
(reaction 3)
41
The fermentation reactions shown above are specifically for ethanol, however there are quite a
substantial amount of foods we eat that are processed through fermentation and therefore similar
processes. Popular fermented foods include:
-
Dairy products (utilizing lactic acid producing microorganism which take the milk sugars, known
as lactose, and turn them into lactic acid, giving the products a more acidic taste): Yogurt,
Cheese, Sour Cream
Meat products (converting carbohydrates found in the meat mixtures into lactic acid): dry
sausages, salami, chorizo, prosciutto
Fruit or vegetable products: olives, sauerkraut, pickles
In this project, you will make kombucha through the fermentation of black tea and you will evaluate the
fermentation kinetics. As a reminder, chemical kinetics studies the speed of reactions. You want to
investigate the speed at which the fermentation process takes place in your kombucha as well as
whether there is an optimum time frame for the fermentation (i.e. can it ferment too short or too long).
You should consider what type of chemical compounds you could measure in order to report the
fermentation kinetics. This will give you an opportunity to both experiment with fermentation
(biological chemistry) as well as with quantitative analysis of some component of your kombucha
mixture through analytical means (analytical chemistry). The recipes for brewing kombucha can be
found online but you will want to think about what kind of methods you might use to analyze
fermentation kinetics. Because we will be using laboratory glassware and materials, the kombucha you
make is NOT for consumption.
Project Goals
(1) learn how to perform fermentation of food products
(2) use acid-base titrations to evaluate the acid content of kombucha being fermented
(3) create a curve showing fermentation kinetics (fermentation vs. time)
(4) use a calibration curve to be able to identify the approximate age of a store bought kombucha
(5) gain experience in interdisciplinary research of analytical chemistry with biology
Techniques and equipment/instruments/computation you may need to learn or review:
• Sampling
• Sample prep
• Titrations
• Calibration Curves
• pH meters
• High performance liquid chromatography
42
Pre-Lab Research (to be done individually)
For questions 1- 4, please refer to the following paper:
Villarreal-Soto,S et.al. (2018) Understanding Kombucha Tea Fermentation: A Review. J. Food Science. 83,
3 580-588
1. What is the difference between a journal article, a communication or a review article and how
would you describe this paper and why?
2. Draw and label the 5 main organic acids found in the formation of kombucha.
3. What does Table 1 tell us? Explain it in a few sentences.
4. What is a SCOBY and what specific molecule is formed in the fermentation process that helps the
SCOBY grow into a large gelatinous biofilm?
5. Write out a procedure for making Kombucha and cite your source for making it.
6. What volume of Kombucha might be good for this lab and why?
7. Provide 2 distinct ways that you might try to measure the fermentation of Kombucha?
8. Below you will find a table with titration data of a sample from a batch of Kombucha that is being
titrated with a standardized NaOH solution of 0.01000 M. From this data below, determine the
volume of the end point using a first derivative plot. Notice that with this data set, the volumes
being read are from a buret and the initial volume shown here is the starting point.
Vol (mL)
pH
1.1
3.47
1.5
4.21
1.75
4.54
2
4.89
2.25
5.42
2.5
6.66
2.6
9.01
2.7
9.2
2.8
9.31
2.9
9.41
3
9.51
3.1
9.76
3.2
9.81
3.4
9.85
43
3.55
9.9
3.7
9.91
3.85
9.92
4
9.92
Procedural design
1. Write out a plan for fermenting kombucha and analyzing the fermentation kinetics. Think about
what materials you might need, the brewing process, the collection of samples and how
regularly, consider methods of measuring the acidity of the kombucha, the number of
measurements you might need in total, and what type of containers you might use. Materials are
provided in the chemical fume hoods. Once you have completed this preliminary plan please
show your TA and they will review it, and upon their approval you may proceed with the
fermentation.
Investigating Guiding Questions
1. Based on the products formed in fermentation that you found in question #1 of your pre-lab
research and the papers you have read in your investigation, discuss with your group what
analytes you would want to quantify in order to create a fermentation kinetics curve (i.e. analyte
concentration vs time)
2. How will you collect samples for creating a fermentation curve? What days will you collect? What
volumes will you collect? And how will you store them?
3. How will you analyze these samples?
Project Summary Questions (to be included in your report/presentation)
1. Provide your fermentation kinetics curve.
2. Discuss how long it took your kombucha to reach its maximum fermentation based on your
quantitation of analyte.
3. Comparing a store bought kombucha to your fermentation kinetics curve, what can you
conclude?
4. If you chose more than one method to evaluate the analyte of interest, can you discuss your
comparison of the two methods and whether they gave similar results or not?
44
45
Project 3: Measuring calcium in supplements
Background: Most of the nutrients that human beings need
to live a healthy life are received through a well-balanced
diet. But for some people there may be deficiencies that
require supplements to maintain a healthy life.
A common supplement found at supermarkets and health
food store is that for calcium. The daily recommended
intake for calcium is 1,000 mg for an adult. Often food labels
(as seen in the figure for whole milk) will present the
calcium content in percent of this recommended value,
whereby if you got 30% calcium in one serving of milk that
would be the equivalent of getting 300 mg of calcium in that
glass.
Figure 3: Milk nutritional label with the
In this project you are asked to use the Lewis base
ethylenediamine tetraacetic acid (EDTA) to identify how
much calcium is in a store-bought supplement.
macronutrients listed by gram and percentage,
yet the micronutrients which include calcium
are only listed by percent daily value. In this
sample the milk serving will provide 30% of the
daily value or 300 mg calcium.
EDTA is an acid (that’s what the “A” in EDTA stands for) with 6 protons, and when all the protons are
deprotonated (referred often as the Y4- form, as compared to the fully protonated H6Y2+ form) you have
a very strongly binding Lewis base as shown in the figure below. The deprotonated EDTA forms very
stable 1:1 complexes with practically every metal (except for the univalent ions such as Li+, Na+, and K+).
In order to promote this 1:1 complex, the pH must be kept high enough to deprotonate the EDTA but
not too high as to form metal hydroxide salts of the metal you wish to
investigate.
Therefore, metal-EDTA titrations are generally performed in the
presence of a buffer system to keep the pH of the solution alkaline and
constant.
We can look at both the equilibrium reaction and associated
equilibrium constant equation to solve for the amount of metal present
or metal complex formed.
The reaction and equilibrium expression are shown as follows:
Mn+ + EDTA <---------> MYn-4
(reaction 1)
KF = [MYn-4]/[Mn+]aY4-[EDTA]
(equation 1)
Figure 4: EDTA forming a metal
binding complex with a metal.
Notice the coordination is of an
octahedral format.
Mn+ = metal and its charge n
MYn-4 = metal EDTA complex with its charge of n-4
KF = formation constant of the metal EDTA complex
46
aY4- = the fraction of EDTA in the completely deprotonated form (impacted by the pH, temperature and
ionic strength of the solution; often found as reference tables in your analytical text or online)
So for example if we buffered a system at pH=10, we have to use the fraction of EDTA at that pH (aY4- at
pH 10) which can be solved mathematically or looked up in reference tables. At pH=10 (and 25°C,
µ=0.10) the fraction of EDTA is equal to 0.30. You can therefore input the [EDTA] concentration you had
and your metal concentration and solve for the complex, or depending on the variables you have you
can solve for one of the missing variables.
When doing these metal-EDTA complex titrations it will be necessary to use a metallochromic indicator
These indicators will form a colored complex with most metal ions but have properties that make them
colorful based also on the pH of a solution.
Eriochrome black T is a triprotic acid (abbreviated as H3In). The fully protonated structure is shown here:
The fully protonated state is virtually non-existent in solution due to an equilibrium constant of 1. Here
are the other two equilibria and the associated constants:
Equilibrium reaction
H2In- <-----> HIn2- + H+
(purple red)
2-
HIn
(blue)
(blue)
<-----> In3- + H+
(yellow)
Equilibrium constant
K2 = 5.00 x 10-7
K3 = 2.82 x 10-12
Eriochrome black T forms stable 1:1 complexes with most metal ions and at pH =10, it will change from
the singly protonated (blue) to the doubly protonated (purple-red) states. A very small speck of
eriochrome black should be used (very small!) because if you add too much the color exhibited will be
too dark and it will be difficult to discern between the purple-red and the blue.
Project goals
(1) standardize a solution of EDTA and understand the importance of standardization
(2) use a standardized EDTA solution to perform a titration with supplements to identify how much
calcium is in the supplement
Techniques and equipment/instruments/computation you may need to learn or review:
• How to deal with an unknown
• Weighing liquids and solids
47
•
•
•
Volume delivery
Filtration
Titration
Pre-Lab Research (to be done individually)
1. Using EDTA as the titrant and a free metal in solution is called a direct titration. This can be
measured using an indicator that changes color when the metal is no longer in solution. What
are the other types of EDTA titrations that can be done and why would you choose to do one of
those?
2. What is the formation constant for calcium with EDTA? Are there any challenges with doing a
direct titration with Ca2+? If so what would be the alternative titration to do (see your answers
for #1)
3. List and explain some of the commercial uses for EDTA.
Refer to the following article for questions 4-6:
Garvey, S et. al. (2015) Determination of Calcium in Dietary Supplements: Statistical Comparison of
Methods in the Analytical Laboratory. JCE. 92:167-169.
4. What two methods are being investigated in this paper.
5. What statistical tests are used to compare the two methods and what did their results find.
6. In their supplementary information they provide the methods that they used. What do you think
is the reasoning behind using the Milli-Q2 water?
Procedural design
You should write up a procedure that will include
1. A plan to standardize an EDTA solution. Think about what materials you might need and what
type of containers you might use. also think of what each person will do and what data they will
record. Materials are provided in the chemical fume hoods. Once you have completed a
preliminary plan please show your TA, they will review it, and upon their approval you will follow
through with your experiment
2. A calcium supplement that you want to investigate. This step is a critical one. Determine what
your question is that you wish to ask (review the section 3/pgs. 25-26 in this manual)
3. How do you plan to ensure fair sampling of this supplement?
4. How do you plan to sample prep so that you can evaluate just the calcium found in the
supplement?
5. A plan for your experimental procedure to measure the calcium in your supplement. Indicate
what each person in the group will do to sample, sample prep and quantify the mass of calcium
48
in the supplement and what data will everybody record. Once you have completed a preliminary
plan please show your TA, they will review it, and upon their approval you will follow through
with your experiment.
6. Based on your plan:
a. what calculations will you use to find the mass of calcium in your supplement?
b. what statistical analyses will you use to ensure that your values are valid?
Project Summary Question (to be included in the discussion in your report/presentation)
1. What was the mass of calcium you found in the supplements you studied?
2. What was the error associated with your replicate measurements? Was it a relatively large or
small error?
3. What are some of the possible sources of error AND what could you do in further experiments to
reduce the amount of error in your measurements/calculations?
4. How did the mass of calcium you found compare with the value given on the supplement tablet
you investigated?
5. Is this technique a good one for a quantitative analysis of calcium in supplements? Explain your
reasoning.
49
Project 4: Fluoride in our Drinking Water
Background: Your tap water has fluoride in it. It is there to help you. The United States was actually the
first country to adopt the fluoridation of its public water sources in an effort to reduce the prevalence of
dental cavities (also called “caries). Dental science identified the importance of fluoride in tooth enamel
in as early as the turn of the 19th century. A full recount of the history of fluoridation can be found here
at the National institute of Health’s Institute of Dental and craniofacial research:
https://www.nidcr.nih.gov/OralHealth/Topics/Fluoride/TheStoryofFluoridation.htm. What is interesting
about the process of determining fluoride concentrations in drinking water, was that optimal levels were
found to lower the prevalence of dental cavities but also limited the potential for brown teeth stains
(which can be caused by high levels of fluoride).
Figure 5: Worldwide map showing countries receiving fluoridated water: 80–100% 60–80% 40–
60% 20–40% 1–20% < 1% unknown (taken from Table 31 (pp. 35–6) of: The British Fluoridation
Society; The UK Public Health Association; The British Dental Association; The Faculty of Public Health (2004)
"The extent of water fluoridation" in One in a Million: The facts about water fluoridation (2nd ed.), pp. 55–80
The process of fluoridating drinking water involves the addition of fluoride compounds such as sodium
fluoride, fluorosilic acid or the base form sodium fluorosilicate into the main water sources.
Project goals
(1) use ion-selective electrodes to quantify fluoride content in water
(2) develop calibration curves with standard fluoride solutions
(3) using a calibration curve to determine the amount of fluoride in sample of water from various
sources
Techniques and equipment/instruments/computation you may need to learn or review:
• Sampling
• Ion selective electrodes
• Calibration Curves
• Microsoft Excel
50
Pre-Lab Research (to be done individually)
1. What is the biochemical role of fluoride in your teeth?
For questions 2-5, Refer to Rum et. al. “Applications of a U.S. EPA-Approved Method for Fluoride
Determination in an Enviornmental Chemistry laboratory: Fluoride Detection in Drinking Water” J
Chem Ed. 2000; 77: 1604–1606
2. What do you think is the purpose of the Journal of Chemical Education? What audience does this
journal target and what might they provide to the audience?
3. Based on the article, what is the optimum range of fluoride in drinking water (here in the USA)
and what was the source that the authors cited?
4. Write out in a “flow chart” format the process by which the authors have set up this experiment.
5. What were the results that the authors found for El Paso water?
Procuedural Design
In your group you should put together a procedure for the following things:
1. A plan to create a calibration curve for fluoride in water. Indicate what each person in the group
will do for this validation and what they will record. You are welcome to look at the methods and
supplemental work in the Rum et. al. paper, and/or research more methods online. Once you
have completed a preliminary plan please show your TA, they will review it, and upon their
approval you will follow through with your experiment.
2. Water samples that you wish to investigate. This step is a critical one. Determine what your
question is that you wish to ask (review the section 3/pgs. 25-26 in this manual)
3. How do you plan to ensure fair sampling of the water?
4. Are you planning to prep the water prior to the measurements and if so how do you plan to
sample prep?
5. Experimental procedure to evaluate the fluoride in the water samples you wish to investigate.
Indicate what each person in the group will do to quantify the fluoride, any calculations you may
need and what data everybody will record. Once you have completed a preliminary plan please
show your TA, they will review it, and upon their approval you will follow through with your
experiment.
51
Project summary questions (to be included as part of your discussion in your lab report)
1. What was the fluoride concentration in your water samples?
2. What was the error associated with the replicate measurements you took? Was it a relatively
large or small error?
3. What are some of the possible sources of error AND what could you do in further experiments to
reduce the amount of error in your measurements/calculations?
4. How do the values of fluoride in your water samples compare to the amount of fluoride allowed
in such samples (you might want to look up the standards for fluoride in public water samples as
well as the manufacturer’s listed amount of fluoride in their water)?
5. Is this technique a good one for a quantitative analysis of fluoride in water? Explain your
reasoning.
6. Can you think of other methods that might work to analyze fluoride content in water?
52
Section 5 – Experiments
53
Experiment 1: Review of lab techniques
1.1 THE ANALYTICAL BALANCE AND WEIGHING TECHNIQUES
Although it may not seem true to students, the analytical balance (balance that weighs to 4 decimal
places, i.e. 1/10th of milligram) is one of the most precisely built and expensive tools that she/he will use
in an analytical chemistry course. It is essential that the balance be used correctly, and that all steps be
taken to keep the balance in proper working order.
In an analytical experiment procedure, a typical weighing instruction reads something like this: “Weigh a
sample of about 0.5 g with a precision of 0.1 mg” or “Weigh accurately a sample of about 0.5 g.” This
statement means that a sample of 0.5 grams is to be weighed in the analytical balance to four decimal
places (i.e. 0.0001 g = 0.1 mg) with an accuracy of ± 10% (i.e. the sample weight should be in the range
of 0.4500 - 0.5500 g).
Weighing By Difference:
One of the most important rules of weighing is that the sample must never come in direct contact with
the balance pan. The best way to keep the balance pan clean and to insure that the sample is kept dried
and not contaminated is to use the method of “weighing by difference.”
In weighing by difference, a sample is placed in a weighing bottle in order to be dried before weighing.
The weighing bottle is kept closed through the whole process. The weighing bottle plus sample is
weighed, then the required weight of sample is removed to a suitable receiver, and the weighing bottle
and remaining sample is reweighed. The weight of the sample in the receiver is simply the difference in
the two weights. Both weights must be recorded (in your lab notebook) – not just the difference! The
notebook entry of this procedure should look something like this:
initial weight of W.B. plus cement sample = 24.5678 g
final weight of W.B. minus cement sample = 24.1357 g
weight of cement sample = 0.4321 g
The sample is removed from the weighing bottle by gently tapping on the weighing bottle with its cap to
allow a controlled amount of sample to be transferred to the receiver. To prevent fingerprints from
changing the weight of the weighing bottle, it is usually handled with a Kim-wipe or “paper loop.”
If, by accident, too much sample was removed, that sample will be discarded. The discarded sample
should not be returned to the weighing bottle. Of course, in the case of very expensive or otherwise
irreplaceable reagents, a discarded sample should be saved and re-dried.
The method of weighing by difference may at first seem cumbersome, but with practice, samples can be
weighed efficiently. This method is used because:
1. The balance pan is kept clean, because only the clean, dry weighing bottle touches the pan.
2. The sample is kept clean and dry, because it remains in a capped weighing bottle as much as
possible.
3. The exact zero of the balance is not critical, because only the difference of the weight is used.
4. The sample can be weighed into a wet “receiver.”
54
5. Time is saved when several samples are weighed from an initial amount, because the final weight
for the first sample becomes the initial weight for the second sample, etc.
An alternative approach that is common in modern analytical chemistry is the use of disposable
weighing boats and weighing paper in conjunction with the tare function that is available on digital
analytical balances. The weighing boat/paper prevents the sample from coming into contact with the
balance pan. The weighing boat/paper is placed on the analytical balance, and the tare (or “zero”)
function subtracts the weight of the boat/paper to make the starting weight read as zero. Therefore,
there is no need to subtract the weight of the boat/paper from the final weight to determine the weight
of the sample. The disadvantages of this approach include (in addition to the need for non-reusable
weighing boats/paper) the inability to weigh directly into wet receivers and possibility that sample may
adhere to the weighing boat/paper causing inaccuracy in the weight.
1.2 THE BURET AND VOLUME DELIVERY
Volumetric methods of analysis depend on a volume of a standard solution. Usually, this solution is
delivered from a buret. When recording volume data obtained using a buret, it should be done in the
following manner:
Example:
Titration of 24.95 mL of HCl 0.09678 M vs. NaOH
#1
#2
#3
Final Buret Reading (mL)
35.87
34.45
35.90
Initial Buret Reading (mL)
0.74
0.34
0.78
Volume Delivered (mL)
35.13
35.11
35.12
The initial buret reading should not be 0.00; it should be anywhere between 0.00 and 1.00. If you are
reading the buret correctly, the last digit of the number is almost always going to be different (as in the
example above).
1.3 PRE-LAB QUESTIONS (Include these answers in your lab report)
1. According to the manual, what is an important component of both volumetric flasks and weighing
bottles?
2. What is density? Explain in your own words.
3. How do you use density to calculate volume?
4. What do “ppt” and “ppm” stand for? Write out the calculation for both.
5. If the instruction says “weigh by difference 0.4 g sample with a precision of 0.1 mg”, how much
sample are you going to weigh out?
6. Draw a flow chart for this experiment. (A flow chart should show the basic flow of your
experimental design with arrows. It should NOT be the procedure written out over again. See
the preface for more details.)
1.4 LABORATORY EXERCISE: CALIBRATION OF 25-ML PIPET
55
This laboratory exercise is designed to familiarize you with some essential volumetric techniques, as well
as to review some basic calculations. The results will be entered into a computer, specifically using the
Microsoft Excel® software, providing practice on how to use this software to analyze data and report
analytical results.
In your laboratory drawer, you have a 25-mL pipet. You need to calibrate the pipet to know the exact
volume that this pipet delivers. The average value of your calibration (obtained with a precision of 1
part per thousand [ppt] or less) will be used as the actual pipet volume throughout the semester.
Procedure:
1. Obtain three (3) clean 50-mL volumetric flasks from the laboratory instructor. Label each one so
that you can tell them apart.
2. Weigh each flask, including the stopper (a volumetric flask is worthless without its correct
stopper), with a precision of 0.1 mg. Record each weight in your lab notebook.
3. Practice using your 25-mL pipet until you are comfortable with your technique. Follow the
correct procedure demonstrated by your instructor.
4. After your instructor has checked your pipetting technique, pipet 25-mL aliquots of deionized
water into each of the three 50-mL volumetric flasks. Stopper each flask immediately.
5. Reweigh the flasks and water in the same balance as before. Record each weight in your lab
notebook.
6. Record the temperature (to the nearest 1 °C) of the water in the flasks.
7. Determine the density of water at the recorded temperature(s). Consult the Handbook of
Chemistry and Physics (available in the laboratory), and/or Table 1.1 (below) that gives the
density of water at various temperatures.
8. Return the clean flasks and stoppers to the instructor.
TABLE 1.1 DENSITY OF WATER AT VARIOUS TEMPERATURES
Temperature (°C)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Density (g/mL)
0.99973
0.99963
0.99952
0.99940
0.99927
0.99913
0.99897
0.99880
0.99862
0.99843
0.99823
0.99802
0.99780
0.99756
0.99732
0.99707
Temperature (°C)
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Density (g/mL)
0.99681
0.99654
0.99626
0.99597
0.99567
0.99537
0.99505
0.99473
0.99440
0.99406
0.99371
0.99336
0.99299
0.99262
0.99224
Calculations:
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1. Calculate the weight of each aliquot delivered.
2. Calculate the volume of each aliquot delivered. Remember that the pipet is calibrated to four
(4) significant figures only.
3. Calculate the average volume that the pipet delivers.
4. Find the difference (as absolute value) or deviation between the average volume and each
volume delivered.
5. Add the deviations, and divide this value by the number of deliveries. This gives you the average
difference or average deviation.
6. Divide the average deviation by average volume, and multiply it by 1000. This gives you the
relative average deviation (R.A.D.) in parts per thousand (ppt).
7. If the precision, expressed in terms of R.A.D., is greater than 1.0 ppt, perform more calibration
determinations. If there is less than 20-30 minutes remaining before the class period is over,
stop performing calibration determinations.
1.5 LABORATORY EXERCISE: PREPARATION OF A STANDARD POTASSIUM CHLORIDE (KCl) SOLUTION
Procedure:
1. Find the approximate weight of your weighing bottle in the top-loader balance.1 All samples in a
quantitative analysis laboratory are weighed by difference from the weighing bottle.
2. Transfer about one gram of the oven dried KCl primary standard solid (from the desiccator) to
your weighing bottle. Use the top-loader balance to determine the weight.
3. Weigh (by difference) into a 50- or 100-mL beaker a 0.4 g sample of the KCl from your weighing
bottle with a precision of 0.1 mg.
4. Using the procedure demonstrated to you by your instructor, transfer quantitatively the KCl
sample to a 250-mL volumetric flask. Dilute to the 250-mL mark with deionized water, and shake
for at least 5 minutes.
Calculations:
1. Calculate the grams of KCl transferred to the beaker.
2. Convert to grams of KCl per liter of solution.
3. Calculate the molarity (M) of the solution.
4. Calculate the concentration of the solution in terms of ppm of K+ (i.e. mg K+ per liter).
1.6 LABORATORY EXERCISE: USE OF BURET AND PREPARATION OF DILUTED KCL SOLUTION
Procedure:
1. Obtain one 50-mL volumetric flask.
2. Rinse your buret three (3) times with small portions of your KCl solution.
3. Fill the buret with the KCl solution being careful to fill the tip of the buret; look for air bubbles in
the tip and eliminate them (follow your instructor’s demonstration on how to get rid of air
bubbles in the buret tip).
4. Deliver from the buret into the 50-mL volumetric flask a volume between 10 and 25 mL of the
KCl solution. Read the buret to 2 decimal places. Have the instructor check one of your readings
to be sure you are reading the buret volumes correctly.
1
Just as the volumetric flasks, the weighing bottles are not useful without their tops, and they should be weighed with their
tops.
57
5. Dilute to the 50-mL mark with deionized water and shake well.
6. Clean the volumetric flask and return to the instructor.
Calculations:
Calculate the molar concentration (M) of your diluted KCl solution
58
59