Isolation of Caffeine from Tea

 

EXAMPLES OF HARVARD REFERENCING FOR WEBSITES

The format for creating a Harvard reference for a website is:

AUTHOR(S) (Year of publication or last update) Title of Page [viewed date]. Available from:
URL

Sample Reference:

SOUTHAMPTON SOLENT (2014) Southampton Solent University new build animation [viewed
28 July 2015]. Available from: http//www.youtube.com/watch?v=yQJDLiP-GyY

NOTE: Some Websites don’t provide all the details you may need – include as much
information as you can. If no author is given, use the provider of the website as the author (this
may be the name of a University, a company, a newspaper, or just a website name.

Sample Reference:

DEAKIN UNIVERSITY (2010) The Literature Review [viewed 6 May 2008]. Available from:
http://www.deakin.edu.au./library/findout/research/litrev.php

Sample Citation (when details are missing from the website)

This approach has been outlined by Deakin University (2010).

Often the date that the website was published is not available. You may find a note at the
bottom of the page a note of when it was last updated – give this as the date. If no date is
provided you should use n.d.

 

Chemistry 1223
Isolation of Caffeine from Tea: Part 1 and
Purification and Identification of
Caffeine Part 2 Combined Lab Report

Informal Report- Evening Class

 

1: Title Page:
Include all 7 components.

2: Introduction:
Purpose only. Please state the purpose for both parts of the lab.

No equations required this time!

3: Experimental Method:
Follow the format in the handout – please remember to properly cite the
lab manual.

4: Results:
Data table for weights from Part 1
Data table for distances and Rf values from Part 2
Sample calculation of Rf values

5: Questions:

!!Read the lab thoroughly and answer any questions/assignments!!
Look carefully some of the questions are hard to find.

Additional Questions.
Describe how you can confirm that caffeine is present from the TLC.
Describe how you can determine if your product is pure from the TLC.

6: Conclusions:
Please provide a short restatement of what was done in both parts.
Remember to report your yield.

7: References:
Please follow the guidelines in the lab report format handout.

Data: Collected Online Jan 19th

Quiz: Completed Online by Jan 18th 11:59 pm
Report Due Feb 9th 11:59 pm

 

Chemistry 1121/1223 Lab Report Format

Following is the format for the informal and formal lab reports. Please note the following:

• The report should be typed (12 pt font, Times New Roman, double spaced) on
8 ½ x 11 paper.

• Equations and calculations may be hand written.

• Present all sections in the order given.

• The lab report is about the work you did, therefore the discussion and conclusions must be based on results obtained in the
lab.

• (Academic Misconduct) Copying, manipulation/fabrication of data, plagiarism, content similarities etc. will not be tolerated and
will be heavily penalized. There will be no distinction between those who copy and those who let others copy them.

• Any changes to these guidelines will be announced.

• Important: Make a backup copy of your lab before handing it in.

Format for an Informal Report

1: Title Page
2: Introduction – Purpose and relevant equations (chemical and mathematical)
3: Experimental Method
4: Results
5 : Conclusions
6 : Questions
7 : References

 

Format for a Formal Report

1 : Title Page
2 : Abstract
3: Introduction – Background and Purpose
4: Materials and Method
5: Results
6: Discussion
7: Conclusion
8: Questions
9: References

Title Page
Your title page should include all of the following:

• Title of the report

• Your name

• Name(s) of your lab partner(s)

• Your instructor’s name

• Course name (including section number)

• Date of the lab and date that the lab is due.

• Location at which the lab took place

The title page should be typed (minimum 12 font). Use the entire page and ensure that it is readable and interesting. Optional: If
you have suitable graphics that can be incorporated, please do so.

Abstract

In one paragraph, state the purpose of the lab and the major findings. Your abstract should be concise, yet complete; it should
provide an overview of your scientific investigation. By reading the abstract, your reader should have a general idea regarding the
nature of the work, the main experimental findings and the relevance of these finding to the scientific literature. In general, your
abstract should be one paragraph and no more than 250 words; it should stand-alone. Avoid references in the abstract.

When writing the abstract you should consider the following:

 

• Why was the study performed?

• What was the purpose of the experiment?

• What basic methods were used?

• What results were obtained?

• What were the major findings?

Hint: People often find it easier to write the abstract last after the entire report is completed.

Introduction – Background and Purpose

The Introduction is presented in paragraph form. The intention of the introduction is to “introduce” the topic of the paper. For the
formal report it should provide a brief overview of the literature (background) such that the reader can evaluate and understand the
rational for conducting the experiments. It should not be considered as an exhaustive review of the literature.

Within the body of the introduction and for the informal lab report, the experimenter should define the purpose of these experiments.
The purpose should clearly define the problem. Note: if the problem is not clearly defined the reader will not understand why this
work was carried out.

To get a better idea of what is required, it is recommended that you review some recently published chemistry articles. Be sure to
consider the following:

• Why was the study necessary and how did you resolve it?

• What techniques/protocols were used?
Following are few points to consider when writing this section.

Background

 

• Definitions may be included in this section as long as they do not define something that the reader is already familiar with.

• Do not make references to anything that comes as a result of doing the experiment.

 

Note: You may find the information provided in the lab manual insufficient to draft a good background. Other sources of information
can be included in this section. Please ensure that they are properly cited in the text and references are included at the end of the
report.

Purpose

• Here the objectives of the experiments are provided.

• Remember to include all important chemical equations.

Experimental Method

Cite the source of the experimental procedure. Diagrams and a list of materials are not required. Note any changes or omissions.
Remember to reference the source at the end of the report.

Example: The source of the experimental method can be found on pages??? – ??? of the Chemistry 1223 Laboratory Manual
(Marotta et. al, 2014).

The instructor omitted question 4 and Step 5 was modified by the addition of 5 mL of 1.0 M hydrochloric acid to the beaker before the
titration.

Materials and Methods

The information presented within the Materials and Methods section should provide a list of all of the reagents that were used as well
as a summary of the methods that were used. The information should be presented in a fashion that allows a competent scientist to
duplicate the results you obtained. You should ask yourself whether someone else could follow your procedure and perform the
same experiments.

Note:

• The methods section can be presented in point form for clarity.

• Indicate and describe any changes made to the original protocol (new procedure, omitted section, modification to the
experimental settings).

 

Results

Your experimental findings should be presented in a chronological fashion that ultimately leads the reader towards the solution to the
problem. If your logic is sound, the reader will easily understand why you preformed certain measurements and will be interested in
the actual data obtained.

Your experimental findings should be presented either in the form of tables or graphs each of which must be able to stand alone.
That is, the reader should be able to read the title and legend and understand what the result demonstrates. Note: Graphs are a
type of figure and will be referred to as such in these guidelines.

Be sure to focus on the defined question that you are attempting to address in your studies. Make sure you do not repeat the
experimental details described in the materials and methods section.

Here are some general points to consider when preparing your tables/figures.

Data Tables

 

• Framing: The tables should be framed with borders.

• Titles: Include titles for the data tables. Example: Table 1: Titration data for Standardization of NaOH

• Description: If necessary include a brief description of the table to enhance clarity. A general description provides sufficient
information to understand the data, which is presented. All abbreviations should be defined in the description.

• Column Headings: Within each column heading include the quantities and units. Do not write the units down the columns of
your data table.

• Layout: The title should appear at the top and description below.

• Correct Significant Figures: Record all data to the correct number of significant figures.

• Sample Calculations: Show numerical examples for each different calculation following your data table, not in your data
table. Don’t describe your calculations in words. The general formula for a sample calculation is as follows:

(quantity) = (formula)= (substitution step) = (answer)

Example:

Heating Rate = (T/t) = (26.4 – 25.1) oC/10 s = 0.13 oC/s

 

Graphs (if required)

• Paper: Use metric graph paper. Note: If correctly presented, computer generated graphs will be accepted.

• Scaling: Scale both axes at even intervals. Choose a scale that allows all data points to be presented clearly. Don’t use
scale factors. Remember: a good scale is easy to read and allows you to plot points quickly. Aim for a presentation that uses
as much of the paper as possible and is clear and easy to read. Scales do not have to begin at 0 when the data points are far
removed from 0. The axes should begin from the lower left corner.

• Labeling of axes: Label both axes with quantity and units. The quantity must be spelled out in full. Example: Mass (g)

• Sideways Graphs: If your graph is plotted on the side, make sure the graph is right side up as seen by a viewer on your
right.

• Titling: Title your graph (e.g. Figure 1: Time vs. Temperature Graph)

• Data Point Markers: Clearly plot your data points using markers like “o” or “+”. Do not label each data point with its value.
The data point should be no larger than 1 mm in diameter.

• Multiple Graphs on the same page: Use a legend or some other method to differentiate between the graphs.

• Linear Graphs: If the data points suggest a linear relationship between the plotted variables, do not construct a join-the-dots
graph. Draw the line of best fit using a ruler. The line of best fit is chosen so that an equal number of data points lie on either
side of the line. The line of best fit is not joining the first data point to the last data point. Do not force the graph through the
origin when the data points suggest otherwise. Once drawn, only the points, which lie on the line of best fit, are used in
further calculations (e.g. slope calculation, etc.)

• Linear Graph – slope calculation: For linear graphs, the slope should be computed on the graph. Choose two points ON
the line of best fit. Using a slope triangle determine slope using the rise over run method. Do not forget the units of the slope.
(The units of the slope are equal to the units of the y-axis quantity divided by the units of the x-axis quantity.)

• Curves: If the data points suggest a curve, then draw the best-fit curve through the data points. For this a flexible drawing
curve is of some assistance.

• Legend: The legend should be description; it should provide sufficient information such that the reader can understand what
the figure represents.

• Layout: The Title and Legend appear below the figure.

Note: Present information in the Figures and Legend as if this were all the reader would see for this point.

 

Further Calculations

If additional numerical calculations are to be preformed on the data put them in this section.

 

• (% Error Calculation) Show how you calculated the % error, indicating what two numbers you were comparing. For example,
for experiments with a true value for comparison,

% Error = your value – true value X 100
true value

Averaging Multiple Data Points

It is acceptable to present data for several runs in the Tables. If you have more than one data point for a given experiment it is best to
use the average value for that point for calculations. Remember to pay close attention to significant figures in calculations involving
experimental data.

Discussion

The discussion section is presented in paragraph form. When writing your discussion you should take into consideration the
following:

• This is the most important part of the lab. It connects the purpose and the results and leads the reader to the conclusion
drawn.

• Present the interpretation of your findings as clearly as possible. Be sure to provide a summary for each of your major
findings.

• Discuss/interpret the results for each part of the lab. Everything was done for a reason, present the logic behind the design of
the experiment to your reader.

• For each graph discuss:
o What was graphed.
o What type of graph resulted.
o What does it show.
o If the graph is linear, what is does the slope represent?

• Support your statements with numerical figures.

 

• Do not phrase your sentences as questions in your lab report.

• Do not show calculations in this section, however you should mention the final values calculated in your discussion.

• Possible errors: Be specific to the experiment when stating sources of error; avoid generic statements like measurement
error, crude equipment, etc.

o What caused the measurement error?
o If there was a reading error what caused it?
o What could have affected the accuracy of the data recorded?
o Make note of difficulties that occurred in the experiment.

• Your discussion should always consist of more than one paragraph. For example, if your lab consists of three parts, you
should write one paragraph for each part, and then another one for the sources of error.

• Compare and contrast the results you have drawn from your experiments with those published within the scientific literature.

• Discuss the implications of you work and highlight future experiments that may be of interest.

Conclusion

The conclusion should restate you findings. The concluding remarks should be concise and clear as the reader most often
remembers this section.

• Make brief statements that summarize the whole experiment.

• The conclusion is not that you can do something; rather it is what was actually found.

• No new information is to be presented here.

Questions

Any questions or exercises assigned in the lab manual should be included here.

• Give specific answers and explain your answers.

• Read the questions carefully.

• Show your work for calculation type questions. Include the appropriate units.

 

References

Using bibliographical format, list the references that you used. Examples include the textbook, a library book, the lab manual, a
periodical or a web site.

References are listed alphabetically. Remember to cite to the reference within the body of the lab report.

Data Sheet and Flow Chart

These are checked by the instructor during the lab. It is your responsibility to ensure that these are recorded in order to receive
credit for this portion of the lab.

Miscellaneous

Writing style: Lab reports in the past have been written in the passive voice past tense. The literature is changing and the active
voice is now acceptable. Find copies of recent papers for examples of scientific writing in the active voice.

Background reading/research: Read all the background information related to the experiment. It is a good idea to look in your
textbook for more information on the topic. Hint: Use the INDEX to locate topics. Research the topic in the library or on the Internet.

Important: Make a backup photocopy of all your labs before handing them in.

Study habits: The course moves fast. Have your labs completed by the due date.

Academic Misconduct: Copying, manipulation/fabrication of data, plagiarism, content similarities etc. will not be tolerated and will
be heavily penalized. There will be no distinction between those who copy and those who let others copy them.

• Don’t lend your lab report to anyone before handing it in or after you get it back. Don’t throw rough copies away.

• Don’t fix your data.

• Cite your references if you used other sources.

 

Citations and References:

Citing References in Text – some useful expressions
Introducing someone’s ideas:
Smith (2012) suggests/argues/states/believes/concludes/proposes that —

Smith (2012) expresses/holds the view that —
Smith (2012) draws attention to —
Smith (2012) describes X as —
Smith (2012) describes how —
Smith (2012) refers to —
Smith (2012) takes the stance that —
Smith (2012) emphasizes/stresses the need to/the importance of—
According to Smith (2012) —
As stated/suggested/argued/proposed by Smith (2012) —
There is a view/theory/argument that — (Smith, 2012).
It has been suggested/stated/argued/proposed that — (Smith, 2012)
One view/theory/argument/suggestion/proposal is that — (Smith 2012)
One view, expressed by Smith (2012) is that —

Introducing an idea/theory that agrees with/has built on another:
This is supported by Jones (2013).
in line with the view/theory/suggestion of Jones (2013).
reflects the “ “ “
Jones (2013) accepts/supports/agrees with/concurs with this view/suggestion/theory.
A similar view is held by Jones (2013)
A similar stance is taken by Jones (2013)
This idea/theory has been extended/developed/taken further/built upon by Jones (2013).

Introducing an idea/theory that disagrees/contrasts with another:
This conflicts/contrasts with/is contrary to the view held by Carter (2013) that —
This is not accepted by/has been challenged by Carter (2013), who argues that —
Carter (2013), on the other hand/however/in contrast, suggests that —
An alternative view/suggestion is that — (Carter, 2013)
The opposite/a conflicting view is expressed by Carter (2003)

 

Harvard Referencing
Source General Format Example

Book
(1 author)

FAMILY/SURNAME, Initials. (Publication year in brackets)
Book title – italicised or underlined. Series title and volume
if applicable. Edition – if not the first.
Place of publication: publisher.

SMITH, C. (2012) The Complete Guide to Referencing.
3nd Ed. Edmonton: Open University Press.

Book
(2 to 3 authors)

FAMILY/SURNAME, Initials., FAMILY/SURNAME, Initials.
And FAMILY/SURNAME, Initials. (Publication year in
brackets) Book title – italicized or underlined. Series title
and volume if applicable. Edition – if not the first. Place of
publication: Publisher

BRAD, I., COYLE, J. and BORSE, A. (2004) Scientific
Principles .Harlow: Prentice Hall. Note: Use either “and”
or “&” between authors’ names as dictated by the book’s
own presentation.

Book
(4 or more
authors)

It is discretionary as to whether you list all authors and
also whether you use ‘et al.’ or ‘and others’ as below:
FAMILY/SURNAME, Initials. et al. or and others.
(Publication year in brackets) Book title – italicized or
underlined. Series title and volume if applicable. Edition – if
not the first. Place of publication: Publisher.

BELL, N. A. et al. (2008) Biology. 5th Ed.London:
Pearson.

Book (Editor/s)

FAMILY/SURNAME, Initials. (ed.) or (eds.) – in brackets
for editor(s). (Publication year in brackets) Book title –
italicised or underlined. Series title and volume if
applicable. Edition – if not the first. Place of publication:
Publisher.

FONTANA-GIUSTI, G. (ed.) (2008) Designing Cities for
People: Social, Environmental and Psychological
Sustainability. London: Earthscan.

Chapter in an
edited
book

FAMILY/SURNAME, Initials of the author writing the
chapter. (Publication year in brackets) Title of chapter. In:
FAMILY/SURNAME, Initials. of author or editor of book
(ed.) or (eds.). Book title – italicized or underlined. Series
title and volume if applicable. Edition – if not the first. Place
of publication: Publisher.

MARSH, W. A. (1978) The Child as a Mirror of his Brain’s
Development. In SANTS, J. & BUTCHER, H. J. (eds.).
Development Psychology. Seattle, Bucks: Mazell Catson
& Vimey Ltd.

Corporate Includes publications by Government departments, NORTHERN IRELAND. DEPARTMENT OF ENERGY.

 

authors
(groups,
committees,
companies)

Committees: COUNTRY. NAME OF ISSUING BODY.
(Year of publication in brackets) Title of publication – in
italics or underlined. Place of publication: Publisher.
(Report Number – if applicable in brackets).

(1971) Tidal Power Barrages in the Severn Trent
Estuary: Recent Evidence on their Feasibility. Belfast: H.
M.S. O. (Energy Papers 21)

E-Book

FAMILY/SURNAME, Initials. (Publication year in brackets)
Book title – italicized or underlined. [Online] Series title and
volume if applicable. Edition – if not the first. Place of
publication: Publisher. Available from – URL. [Accessed:
date].

SALLER, P. (2006) Strategic Management. [Online]
Sterling. VA Kogan Page. Available
from:http://www.netlibrary.com/reader/. [Accessed: 6th
May 2013].

Films [DVD],
[VHS],
[Blu-ray Disc]

Title – in italics or underlined. (Year of distribution in
brackets) Material type. Directed by – name of director(s).
[Format of source in square brackets] Place of distribution:
Distribution company.

Chicken Run. (2000) Animated Film. Directed by Peter
Lord and Nick Park. [VHS] UK: Pathe Distribution.
Requiem for a Dream. (2000) Film. Directed by Darren
Aronofsky. [DVD] UK: Momentum Pictures.

 

EXPERIMENT 9: Organic Chemistry Laboratory

ISOLATION OF CAFFEINE FROM TEA – Part 1


DATA:

 

Weight (g)

Weight of Tea in 2 Tea Bags

6.3757 g

Weight of Empty Beaker

102.9325 g

Weight of Beaker + Crude Caffeine

62.8622 g

Weight of Crude Caffeine

0.0461 g

Mass of 100 mL Beaker: 62.8161 g

CALCULATIONS Part: 1

1. Calculate the theoretical mass of caffeine in tea (tea contains 4% caffeine by weight).

2. Calculate the percentage yield of crude caffeine: mass of crude caffeine % yield crude caffeine = ————————————– x 100%

theoretical mass of caffeine in tea.

109.3802 g)

Notes:
– The boiling was done beforehand. The concentrated tea solution has been pre-prepared.
– The two liquids are immiscible.
– Hissing of gas vapour release when mixing solutions in step 5. (Emulsion)
– Bottom layer dichloromethane holding the caffeine product and it must be kept in the 150 mL beaker that it was transferred to.
– We add a second aliquote of dichloromethane to extract more caffeine from the aqueous solution.
– Both lower layers are collected and combined.
– At this point the tea solution has been decaffeinated.
– The colorless dichloromethane layer has our caffeine sample.
– The brown layer can be disposed of and the separatory funnel cleaned before continuing on with the separation.
– The light brown in the middle is the emulsion.
– The dichloromethane and water are still separating from each other.
– We leave the emulsion behind as we don’t want to carry over any impurities.
– We wait until the emulsion has separated before collecting the dichloromethane.
– We are now cleaning the separatory funnel before continuing on with the separation.
– We will now remove some of the impurities that transferred over with the caffeine.
– Yes, it’s ok to have some water in the separatory funnel to clean it. We are still using water in the next steps of the separation.
– The aqueous NaOH solution removes impurities that are converted to ions in base.
– The base converts the impurities to forms that are now less soluble in dichloromethane and very soluble in the base solution.
– The caffeine stays behind in the dichloromethane.
– The top layer contains the base soluble impurities.
– The yellow aqueous layer is impurities.
– We do one last wash with cold water to remove any lingering aqueous soluble impurities.

– This reduced our overall yield but increases our purity. The sample is quite pure and it is ok to really shake the mixture. We won’t have to wait long for it to separate.

– The bottom layer contains our product. Be very careful not to discard it.
– If you leave some dichloromethane behind the yield will be decreased but your product will be purer.
– Dichloromethane is very volatile and will boil off quickly when heated.
– The last few mL will boil off quickly. The caffeine solid starts to show up just near the end of the solvent evaporation step.
– We can start to see the solid white caffeine. It looks like we have an excellent yield.
– We are going to cool the beaker and weigh it.
– We can calculate the theoretical yield from the mass of the tea bags.
– We can determine the actual yield from the mass of the beaker with and without the caffeine.
– We can determine the % yield by taking the ratio of the two values. What % of tea leaves is caffeine?

We combine three beakers of caffeine into one flask to get enough sample to do a sublimination.
TLC – Thin Layer Chromatography
The crude and pure caffeine are not interchangeable. (Crude caffeine has impurities pure caffeine is purified)

Different compounds are attracted to the silica in different amounts. Compounds which are not attracted very much move up the plate with the solvent. Compounds which are strongly attracted to the silica stay near the bottom of the plate.
Mass of the beaker + caffeine = 62.8622 g

yes, a photo will be provided. You will measure the Rf from the photo.

So, each compound has a unique Rf.

– By doing a TLC with standards we can determine the Rf for caffeine under these solvent conditions.
– We also determine the Rf for theophylline (a common impurity in this extraction) you will need to print out the photo and measure the distances on your own.
– If the Rf of two spots on two different TLC is the same we can safely assume that we have the same compound.
– In reality it is not possible to control the development conditions enough and the Rfs vary a bit.
– Still the way to identify an unknown is to compare the Rf to a known standard.
– So, caffeine will have the same Rf as a caffeine standard.
– We can over spot standards that the Rf for each standard will not change.
– This way we can determine the identity of an unknown even if we have a mixture.
– The Rf of a compound will not change when we are doing the TLC for a sample that has more than one compound.
– I’m not sure if you can see the plate in the sealed bottle but the solvent is travelling up the plate.
– The solvent now evaporates off and we are ready to analyze the plate.
– If we had done the sublimation we would have used the sample as the pure caffeine. We do have a sample of crude caffeine.
– So for plate 3 we spot the crude caffeine 5 times crude caffeine is on spot F
– We are going to use a sample of pure caffeine for spot E plate 3. Typically, we would have made this sample in class. We have a source of pure caffeine and so can replicate this material for this lab activity.

Plate 1 is dried. We will look at it under the UV light.
Plate 2 and 3 will be developed in the solvent, dried and then analyzed under the UV light.
The silica gel on the plate has been treated with a chemical that glows green in UV light
The spots from our samples do not glow green.

We are able to see our spots using UV light

One for caffeine plate 1 spot A – One for theophylline plate 1 spot B

Now we are looking at plate 3 spots E and F

We see one spot for plate 3 spot E pure caffeine and one spot for plate 3 spot F

yes, the spot indicates how much material we have. More material larger spot. Plate 2 looks great. We have one long spot for plate 2 spot C and two spots for Plate 2 over spotted D These look great. We need to measure the distance the solvent travels and the distance the spots travel. We measure for the center of the spots. We determine the Rf for each spot. Not the average.

Plate 1 Rf Total Travel: 3.5 cm => 1B – 1.56 cm Theophylline 1A – 2.2 cm Caffeine
Plate 2 Rf Total Travel: 3.5 cm => 2D – 1.75 cm Theophylline Lower, 2.25 cm Upper & 2C – Extract 2.0 cm
Plate 3 Rf Total Travel: 3.6 cm => 3E – 1.75 cm Purified Caffeine 3F – 2.0 cm Crude Caffeine

 

CALCULATIONS

For each chromatographic plate measure the distance traveled by the compound (represented

by each spot) and the distance traveled by the solvent in the same amount of time. Measure

the center of the spots to the nearest 0.5 mm!

The Retention Factor (Rf) for each spot is calculated as:

Distance moved by Spot

Rf = ————————————-

Distance moved by Solvent

Identify the spots by comparing the Rf values of the spots of the samples with the Rf values

for the standard solutions provided. Discuss the number and position of the spots for each of

the samples. The position or Rf of the spot indicates only the identity of the compound

(usually compared to the Rf of a known compound). The Rf value is not related to the purity

of the compound.

REPORT

Appropriate presentation, labeling and discussion of the thin layer chromatography

plates are necessary for a good report.

1

CONTENTS

 

SUBJECT PAGE

Laboratory Information 2

 

Laboratory Safety 3

 

Laboratory Reports 8

 

Significant Figures 9

 

Experiment 1: Kinetics- The Rate of Reaction of Peroxydisulfate Ions

with Iodine Ions. Part I – Effect of Concentration

11

 

Experiment 2: Kinetics- The Rate of Reaction of Peroxydisulfate Ions

with Iodine Ions. Part II – Effect of Temperature and Part III – Effect of a

Catalyst

17

 

Experiment 3: Recycling Aluminum: The Synthesis of Potassium Alum

From Aluminum. Part A: The Synthesis of Potassium Alum.

23

 

Experiment 4: Recycling Aluminum: The Synthesis of Potassium Alum

From Aluminum. Part B: Determination of Yield and Purity of the Alum.

27

 

Experiment 5: Heat of Chemical Reactions 33

 

Experiment 6: Determination of the Molar Mass of a Solid Acid 39

 

Experiment 7: Measurement of pH: pH Titration of Strong and Weak

Acids and pH Measurement of Buffers.

47

 

Experiment 8: Quantitative Determination of Vitamin C by Redox

Titration

56

 

Experiment 9: Isolation of Caffeine from Tea – Part 1 64

 

Experiment 10: Purification and Identification of Caffeine – Part 2 71

 

 

2

CHEMISTRY 1223 LABORATORY INFORMATION

 

Welcome to Chemistry 1223. The Chemistry 1223 laboratory is a continuation of the

Chemistry 1121 laboratory which covered the basics of introductory chemistry laboratory

techniques and built a strong foundation in chemical safety. Good chemistry laboratory

techniques and lab safety are still expected to be practiced while performing these ten

exercises chosen to demonstrate laboratory principles in chemical thermodynamics, kinetics,

inorganic synthesis and organic chemistry. Your course outline provides substantial

information regarding the laboratory component of this course; please refer to it for the exact

dates of the laboratory sessions and current course policies. We hope that you enjoy the

course.

 

Laboratory Attendance

Laboratory attendance is essential and mandatory, as missed labs cannot normally be made up

due to time constraints. Students are expected to be in the lab on time as necessary safety and

procedural information is provided at the beginning of the lab. Exceptions (make-up labs) will

only be made in extraordinary circumstances and with advance notification. Make up labs

have to be scheduled with the instructor – otherwise a “zero” will be granted without

exception. Lab missed due to illness will require a note from a physician. It is current policy

to have only one day at the end of term to complete any missed labs.

 

Pre-Laboratory Preparation

For each experiment, you may be required to prepare a flowchart that outlines the

experimental steps that will be conducted during the course of the lab. Note: In the past

instructors have required a flowchart for each of the labs which must be signed during the lab.

Please ensure you are aware of your instructor’s current policy.

 

Laboratory Quizzes

There may be a quiz at the beginning of a lab. Please check with your instructor regarding

their policy on lab quizzes.

 

Laboratory Note Books and Data Sheets

Instructors have required that students collect their data in a bound note book. Remember to

record data in ink in your lab book as you do the experiment. All data must be labeled and

have both the correct units and number of significant figures for that measurement. Please ask

for clarification if you are unsure how information should be recorded. Your data

sheet/notebook may need to be signed by one of the instructors at the end of the lab period to

receive a grade for each lab report. This not only validates the data but also allows the

instructor to check if you have recorded all the information needed to complete the lab report.

Please ensure that you are aware of your instructor’s expectations.

 

3

 

CHEMISTRY 1223 LABORATORY SAFETY

Policy on Safety and Breakage

Before working in the laboratory portion of the course, every student must read the

“Laboratory Safety” rules in the laboratory manual plus any Departmental Rules and agree in

writing to abide by these rules. It is imperative for your safety that you and everyone around

you strictly adhere to the Safety Rules. Before you are able to participate in the course

laboratories a SAFETY CONTRACT and CONTACT LENS SAFETY CONTRACT will

need to be signed.

 

Failure to comply with the safety regulations (e.g., by not wearing eye protection at all times;

by wearing open-toed shoes, short skirts or shorts without also wearing a lab coat or apron; by

running an unauthorized experiment; or by removing chemicals or equipment from the lab)

may result in not being allowed to perform the laboratory exercise or dismissal from this

portion of the course.

 

You will be utilizing equipment furnished by the Chemistry Department. It is your

responsibility to properly maintain the equipment while it is in your care. If equipment that

has been entrusted to you is not returned in satisfactory condition, you will be held

responsible for it.

 

General Rules of Safety
1. Act responsibly, concentrate on the activity, listen and be aware of potential hazards in the

classroom to you and your partners.

2. If you have any questions regarding chemicals, flames, the use of glassware, equipment
etc. please ask!

3. Inform your instructor or laboratory demonstrator of any accidents or incidents.

Location of Eyewash Station, Emergency Shower and Fire
Extinguisher/Blanket
1. An eyewash station is located in the classroom. This station will be demonstrated to you

before you begin your first lab activity. If chemicals get in your eyes they must be flushed

with water for at least 20 minutes.

2. The emergency shower is located in room 3256. There is a door in room 3252 to allow
access to the emergency shower. The emergency shower is to be used in case of a large

spill to the body.

3. A safety drench hose is located in room 3252. Use of this drench hose will be
demonstrated to you before you begin your first lab activity.

4. Fire extinguishers are available in case of fire. If a fire alarm goes off follow your
instructor out of the building and gather outside at China Creek Park.

5. A fire blanket is also available to extinguish clothes fires. Stop, Drop, Roll! Is the
preferred method of extinguishing fires to the body. Wrap the blanket around the person

and smother the flames.

 

4

First Aid and Emergencies

Inform your instructor or lab demonstrator of any accidents or injuries. If necessary, they will

contact campus security (security phones are installed in the laboratory) for first aid or other

medical emergencies.

 

Personal Protective Equipment

 

 

1. Adequate eye protection is required for all individuals working in the laboratory. Do not
remove your eye protection until you have physically left the laboratory room. Safety

goggles, that will form a tight seal to your face, are the required form of eye protection. If

you must wear prescription glasses wear them under safety goggles.

 

NOTE: Contact lenses are a proven hazard and should not be worn in the laboratory area. If

chemicals are splashed into the eyes, they can become trapped under hard lenses or absorbed

by soft lenses. Some chemicals can cause coagulation of the protein in the eye within seconds.

Similarly, chemical vapors can be trapped under hard lenses or dissolve into soft lenses. It is

also extremely difficult to remove lenses if something has been splashed into your eyes.

 

Contact lens wearers have two options in the teaching laboratories:

 

A. Remove the contact lens before entering the lab and wear safety goggles or prescription
glasses under safety goggles.

B. If you cannot replace the contact lens with prescription glasses and you cannot see well
enough without the lens, you can wear the contact lens into the laboratory under a pair of

safety goggles but you must inform your instructor that you are wearing the lens in the

laboratory. WE MUST KNOW THIS FACT IN THE EVENT OF AN INJURY TO

YOUR EYES. This is the least desirable option.

 

For some laboratories (particularly organic), where exposure to toxic or irritating fumes is a

real problem, contact lens even under safety goggles are not recommended.

 

NOTE: Safety goggles will be provided.

 

2. Lab coats must be worn. These can be obtained from the bookstore. Lab coats should not
be worn outside the laboratory. Lab coats should be stored separately from other clothing

or personal belongings when not in use. Lab coats should be laundered separately on a

regular basis.

 

EYE PROTECTION MUST BE WORN AT ALL TIMES WHILE

YOU ARE IN THE LABORATORY. STUDENTS WILL NOT BE

ALLOWED TO DO AN EXPERIMENT WITHOUT SAFETY GOGGLES.

 

5

3. Gloves are provided. Gloves should be worn when handling corrosive materials, toxic
materials and organic materials. Note: The use of gloves can introduce a hazard as they

can reduce one’s ability to perform delicate manual tasks, cause one to exert increased

force or cause skin irritation. Work carefully when wearing gloves.

 

Spills and Emergencies

Accidental release or spills of chemicals or other hazardous materials must be controlled

immediately and cleaned up under the supervision of persons knowledgeable in the hazards

involved and the precautions to be taken during the clean up.

 

1. Work carefully when pouring solutions or weighing solids to avoid spills. Clean your
hotplate/magnetic stirrer after using it to avoid leaving chemical spills for the next student.

Chemical and water spills must be wiped up before other people could accidentally come

into contact with them.

 

2. If you spill a large quantity of chemicals report it to your demonstrator or instructor for
clean up. If you find an unidentified chemical spill report it to your demonstrator or

instructor for clean up.

 

General Do’s and Don’ts

1. Only perform the assigned laboratory during the lab session. Do not work alone. Do not
deviate from any of the procedures in the manual without explicit directions from your

instructor.

 

2. Never taste, touch or smell chemicals.

3. No smoking, eating or drinking is allowed in the laboratory.

4. Food for consumption must not be kept in the laboratory, and laboratory glassware,
vessels and containers must not be used to prepare or store food or beverages for

consumption.

 

5. Always label glassware to indicate the contents. Many solutions look the same and it is
important that the contents be clearly identified.

 

6. If chemicals come into contact with your skin they must be washed off immediately with
copious amounts of cold water. If chemicals come into contact with your eyes you must

irrigate them with water for at least 20 minutes (know the location of the eye showers)

and summon help. Report any such incidents to your instructor.

 

7. Wash your hands thoroughly before leaving the laboratory area, before taking a break and
at the end of the lab. Use the soap and water provided to wash your hands.

 

8. Wash your bench top thoroughly before and after completing each laboratory.

 

6

 

9. Use a mechanical pipetting device when pipetting. NEVER pipette by mouth.

10. Coats, knapsacks, brief cases and other bags can cause tripping accidents if left on the
floor (especially dangerous to people carrying glassware). Store them safely out of the

way.

 

11. Keep floors dry. Clean up any liquids, refuse or waste materials that spill or accumulate
on the floors.

 

Proper Waste Disposal

Our lab demonstrators are trained in the proper segregation and disposal of chemicals. Always

follow disposal procedures given in the manual and by your instructor. Do not pour chemicals

down the sink unless you are told that it is safe to do so.

 

1. Some waste streams are separated for safety and disposal cost reduction. Only put waste
in the proper container. Solid wastes must be discarded in the waste containers provided

and not in the garbage. Certain liquids must also be disposed of in special waste

containers. When in doubt always ask your instructor before disposing of chemical solids

and solutions.

 

2. Never put broken glass in the waste paper bins (to prevent dangerous accidents to our
janitorial staff). Special bins marked “Broken Glass Only” are provided to contain broken

glass only. Use these bins for broken glass only (no waste paper). Do not clean up broken

glass by yourself, have the instructor or lab demonstrator do so.

 

Centrifuges

1. Centrifuge loads must be balanced by sample distribution.
2. Do not open the access cover until the centrifuge has stopped spinning.

Glassware

1. Check tubes for cracks or broken lips and discard into the glassware discard bucket.
2. Clean glassware before putting away.
3. Never pick up broken glassware with your hands. Inform your instructor or lab

demonstrator and we will sweep it up for you.

 

Chemical Safety

1. Never smell a chemical by putting your nose over the container.
2. Never touch, taste or smell a chemical unless instructed to do so.
3. Always add acids to water (not water to acids).
4. Do not mix tube contents by inverting with your thumb over the tube. Instead grip the tube

in between the fingers of one hand, and gently flick the tube with the other hand.

 

7

 

Face and Hand Safety

1. Always wear your protective goggles. Do not remove them even to check a measurement.
2. Do not bend down or squat to the level of the bench when pouring solutions into beakers

or measuring solutions. Pour first, and then check the amount. You put yourself at risk

when the solution you are pouring is higher than where your eyes and face are.

3. Point test-tubes or bottles that are being heated away from you or others. This protects
against chemicals boiling out of the tubes or propellant objects under compression from

the heat.

 

Fire/Bunsen Burner/ Hotplate Safety

1. Check your glassware for chips or cracks and discard into the glassware discard bucket.
Do not heat glassware that is damaged as it may break.

2. When heating anything in a test tube, be careful not to point the open end towards yourself
or anyone else.

3. Avoid wearing garments with loose fitting sleeves.
4. Never reach across a flame.
5. Always set up and check your work area so that the burner, when ignited, will not burn

anything.

6. Ensure that the power cord for the hot plate is not a tripping hazard.
7. Use clamps, tongs, or gloves to handle hot objects.
8. Remember glassware and equipment looks the same hot or cold. Work carefully with hot

equipment and glassware.

 

8

LABORATORY REPORTS

The laboratory portion of the course is worth 35% and you will be required to prepare reports

as well as attend and complete the laboratory. Your instructor will provide detailed

instructions as to how to prepare the laboratory reports. As well your instructor will provide

information regarding their late policy in the course outline. Please remember to ask for

clarification if you are unsure of any of these details. All lab reports must be completed in

order to obtain a final grade in the course.

 

A Note on Plagiarism

Plagiarism is easy to do but can come with harsh consequences – from a zero (0) grade to an

expulsion with academic misconduct on your record. Your submitted lab report must reflect

information obtained by you while in the laboratory and recorded on your data sheets. When

working in groups make sure each group member submits their own unique lab report, written

in their own words. Always use a reference list to identify any information, images, etc.

gathered from other sources.

 

Report Style

Detailed guidelines regarding the preparation of lab reports will be provided by your

instructor. Please refer to these when preparing your reports. In the past the following

guidelines were used when writing up a laboratory report for submission. The format of

write-up will be indicated in the schedule for each experiment.

 

Informal Lab Report Formal Lab Report

Title Page Title Page

Experimental Purpose Introduction

Hypothesis Material and Methods

Experimental Method Results

Results Discussion

Conclusions Conclusion

References References

 

All reports should be kept together and retained in the event that the instructor needs to

review your work. It is recommended that you photocopy each report in the event that a report

is lost.

 

Note: Both the laboratory and lecture sections must be passed individually in order to

pass the course.

 

9

SIGNIFICANT FIGURES

Many operations in the chemistry laboratory involve measurements of some kind. Examples

include weighing a compound, measuring the volume of a liquid, etc. The number of figures

recorded for a measured quantity must reflect the precision with which the measurement has

been made. Therefore, a degree of certainty can be attributed to a reported value.

 

All the figures reported must be significant; the value must provide as much usable

information as is possible but must also avoid giving misinformation. By employing the

correct number of significant figures, the accuracy of the apparatus will be indicated.

 

Consider the recorded mass of an object to be 12.346 g. There are 5 significant figures with

the last digit representing a degree of uncertainty. In this case, this result was weighed to the

nearest thousandth (0.001 g) of a gram. This means that the last digit has been estimated and

the exact mass is between 12.3455 g and 12.3465 g. Significant figures refer to those digits

we know with certainty plus the first doubtful or estimated digit.

 

Leading zeros in a number are not significant and trailing zeros are significant only if the

number contains a decimal point.

 

Examples:

 

0.0001234 has 4 significant figures

0.00012340 has 5 significant figures

 

600 has 1 significant figure but if written as 6.00 x 102, it has 3 significant figures.

 

If one measures 250 mL to the nearest milliliter, it is more informative to write this volume as

0.250 L or 2.50 x 102 mL; making all three digits significant.

 

Calculations must also be recorded with the correct number of significant figures required to

indicate the precision of the experiment.

 

Integers, such as stoichiometric ratio, and other “whole numbers” have infinite, significant

figures.

 

Significant Figures in Calculations

In any calculation in which experimental results are used, the final result should contain only

as many significant figures as is justified by the experiment. Thus, the least precise

measurement dictates the number of significant figures that should be present in the final

answer.

 

1. Addition and Subtraction: In addition and subtraction, retain only as many decimal places

in the results as there are in that component with the least number of decimal places.

 

10

121.1 + 2.035 + 6.12 = 129.255 Becomes 129.3

 

2. Multiplication and Division: In multiplication and division the answer should contain only

as many significant figures as are contained in the factor with the least number of significant

figures.

 

21.71 x 0.029 x 89.2 = 56.159428 Becomes 56

 

3. Logs and Antilogs: One significant figure is gained when you take the log of a number

greater than 1 x 10-10 and one significant figure is lost for the antilog of a number below 10.

For logarithms, the mantissa keeps the same number of significant figures as there are in the

original number.

log (3.000 × 104) = 4.4771 and log (3 × 10 4) = 4.5

For anti-logarithms, the result has as many significant figures as the mantissa in the logarithm.

antilog (2.301) = 2.00 x 102 and antilog(2.30) = 2.0 x 102

Note: For a real number X, the mantissa is defined as the positive fractional part. For

example, for x = 3.14159, the mantissa is 0.14159

 

11

 

EXPERIMENT 1: Chemical Kinetics Laboratory

KINETICS – THE RATE OF REACTION OF PEROXYDISULFATE IONS WITH IODIDE
ION

PART I – EFFECT OF CONCENTRATION

The purpose of this experiment is to study the kinetics of the reaction between iodide, I-, and

peroxydisulfate, S2O82-, ions:

S2O82- + 2 I-  I2 + 2 SO42- … (1)

The rate of this reaction is equal to the rate of disappearance of S2O82-, – [S2O82-] /t,

which equals the rate of formation of iodine, [I2] /t. The rate law expression has the form:

rate = – [S2O82-] =
[I2] = k [S2O82-]

x [I-]y

t t

The experiment involves determining the rate of the reaction with differing concentrations of

S2O82- and I- present by measuring the rate of formation of I2. From the data you will

calculate:

(1) “x”, the order of the reaction with respect to S2O82-

(2) “y”, the order of the reaction with respect to I-, and

(3) “k”, the specific rate constant for the reaction.

Iodine, I2, is produced continuously by the reaction being studied:

S2O82- + 2 I-  I2 + 2 SO42-

The rate of formation of I2 (which equals the rate of the reaction) is determined by measuring

the time required, t, for a measured amount of iodine,I2, to be formed. This is carried out

by adding a measured amount of another reagent, sodium thiosulfate, Na2S2O3, which reacts

extremely rapidly and stoichiometrically with the I2 as fast as it is formed according to the

reaction:

I2 + 2 S2O32-  2 I- + S4O62- … (2)

An indicator in the solution changes color as soon as the measured amount of thiosulfate has

reacted. From the amount of S2O32- added to the solution, the amount of I2 formed, (I2), in

the time taken for the indicator to change color, (t), can be calculated.

The indicator used is starch which becomes dark blue in the presence of free iodine, I2 is

being continuously produced by reaction (1) but as fast as it is produced it is consumed by the

thiosulfate according to reaction (2). There will be no free I2 in the solution as long as there is

thiosulfate present but when all the thiosulfate present is used up, free I2 will then begin to

accumulate in the solution and the indicator will cause the solution to turn blue.

 

12

The experiment is carried out by mixing definite concentrations of the reactants, together with

the indicator, and starting the timer. An aliquot of the thiosulfate is then added. The indicator

will turn blue at the instant all of the thiosulfate present in the aliquot has reacted. The time of

the appearance of the blue color is noted. This time, t, is the time taken for an amount of I2,

equivalent to the amount of thiosulfate present in the aliquot to react. A second aliquot of

S2O32- is then added. This will react with the I2 that has been accumulating in the solution

and the blue color will disappear. When this second aliquot of S2O32- has all reacted, the

solution will again turn blue, and the time will again be noted. This second time will

correspond to the time required for the amount of S2O32- in two aliquots to react. This

process is repeated until five aliquots have been added and five times recorded. This process

is then repeated with a new reaction mixture containing different concentrations of the

reagents S2O82- and I- (note 1).

 

Graphical Determination of the Rate

The more rapidly the aliquot of S2O32- is consumed, the faster the reaction is. To determine

the rate of reaction, a plot is made of moles of S2O32- that have reacted versus the time

required for the reaction, and a best-fitting straight line drawn through the points. The slope of

this line corresponds to the average number of moles of S2O32- that are being consumed per

second, and is proportional to the rate of reaction of peroxydisulfate, S2O82-, in moles per

second at that time, (-S2O82-/t).

Since the rate of the reaction corresponds to the change in concentration of S2O82- per

second, dividing the moles of S2O82- that are reacting per second by the volume of the

solution yields the rate of disappearance of S2O82- in moles per litre per second, which is the

rate of the reaction. The rate depends upon the concentrations of the reactants present at that

instant. However, these concentrations may be taken as the initial amounts present divided by

the volume of the solution at the time the rate is measured, since the amount of iodide does

not change (note 1) and although the actual amount of S2O82- in the reaction mixture is

decreasing with time due to reaction (1), the amount reacting during the experiment is

negligible compared to the initial amount present.

CHEMICAL LABORATORY TECHNIQUES

 Careful preparation of solutions

 Precise measurement of reaction time

 Correct handling of chemical glassware and equipment

CHEMICAL SAFETY

Good chemical safety practices were reviewed in the introductory chemical safety lecture and

should always be used. The following points highlight some safety concerns specific to the

 

13

lab and does not constitute a comprehensive list of safety procedures. Always work carefully

thereby taking responsibility for your safety and the safety of those around you. Remember,

you can ask your instructor or lab demonstrator for help and information.

 

Safety Procedures for Working with Hazardous Materials

NOTE: The following information is provided for the pure substances, not diluted solutions

of the compounds. Often by diluting, the hazardous effects of a material are reduced.

Nonetheless, a spill of a diluted solution will dry to form the pure compound, therefore care

must be taken when working with all compounds in the chemistry laboratory.

 

 Ammonium persulfate is listed as an oxidizing material.

 Potassium iodide is listed as amaterial causing other toxic effects (VERY TOXIC).

 Potassium nitrate is listed as an oxidizing material.

Always wear personal protective equipment (PPE) when performing an experiment. PPE

includes a labcoat, safety goggles and gloves. Always wash your hands before and after

performing an experiment. Always wash your laboratory bench top after performing an

experiment. Always ensure that spills are cleaned up from benches and analytical balances so

that others do not come in contact with them.

Chemical Disposal

Our lab demonstrators are trained in the proper segregation and disposal of chemicals.

Dispose of all chemicals only as directed by your instructor or lab demonstrator. Do not pour

chemicals down the sink unless you are told that it is safe to do so.

PROCEDURE

Obtain 100 mL of KNO3 solution in a clean and dry 250 mL beaker. From the appropriate

dispenser, dispense 25 mL Na2S2O3 solution into a clean and dry 50 mL beaker (This is

enough for half of the runs that have to be done). Also obtain a 1 mL graduated plastic pipet

(to measure 1.0 mL Na2S2O3 aliquots), a glass stir rod, and a stopwatch.

 

Kinetic Experiments

Three separate runs are to be carried out, differing only in the initial concentrations of

reactants. You will need the following: a 25 mL graduated cylinder for KNO3 solution, a

100 mL beaker for KI solution, and another 100 mL beaker to be used as the reaction beaker.

Note that it is important that the glassware be clean for this experiment (note 2). Before first

use, the graduated cylinder and the 1 mL graduated plastic pipet should be rinsed two times

with small amounts of the solutions to be measured.

 

The first kinetic run (Run 1, Part I) is carried out as follows:

 

14

1. a) Dispense 10.0 mL of (NH4)2S2O8 solution into a clean and dry 100 mL reaction

beaker.

Note: the dispenser is set to deliver 10.0 mL of liquid – do not adjust its settings.

b) Add 1.0 mL of the 0.5% starch solution to the reaction beaker.

c) Add 27.0 mL of KNO3 solution to the reaction beaker (note 3).

d) Add one drop of EDTA solution to the reaction beaker and mix well.

2. Dispense 10.0 mL of KI solution into a clean and dry 100 mL beaker. Note: the dispenser

is set to dispense 10.0 mL of liquid – do not adjust volume settings.

You are now ready to start the actual kinetic run.

Read the following four steps before proceeding with the actual run.

3. Pour rapidly the 10.0 mL of the KI from the 100 mL beaker into the reaction beaker (the

100 mL beaker containing the other reagents) and simultaneously start the stopwatch.

This corresponds to zero time for the run.

4. As soon as it is conveniently possible after the two solutions are mixed, add an aliquot of

exactly 1.0 mL of the Na2S2O3 solution to the reaction mixture, using the 1 mL graduated

plastic pipet. Mix the solution well. The color should disappear as soon as the Na2S2O3 is

added. Watch the reaction mixture and immediately record the time when the …

 

 

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