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Note: This file is also available via Canvas Files. Students are also strongly encouraged to check out
the more detailed “FORMAL_REPORT_INFORMATION” file and a sample formal lab report, both
available via Canvas Files.
FORMAL LAB REPORT, General
A formal lab report is required in conjunction with some of the experiments in each chemistry
course. It is your chance to demonstrate to your professor or TA how well you understand the
experiment and the chemical principles involved. A formal report is different than a term paper. It
should be written in a scientific style, which is not the same style used for English or philosophy
papers.
The keys to effective technical writing are organization, brevity, clarity, and an appreciation of the
needs of the reader. You must write clearly and be thorough, but concise. Do not ramble. The best
way to avoid rambling is to first prepare an outline of the report and stick to it. Always use complete
sentences. Bulleted lists are okay in a lab notebook but are unacceptable in a formal report. Formal
reports must be typed. Use 1.5 line spacing, 1-inch margins, 12 pt font and 8.5×11 inch paper. Only
use third person, past tense. Also, proofread well.
While report sheets may be a joint effort, formal reports must be individually written.
FORMAL LAB REPORT PRACTICE – Results and Discussion
This section is the meat of a formal report as it is where you demonstrate your understanding of the
experiment and its results. It is also the most difficult to write, should take the most time, and is
generally worth the most points in your score.
Begin this section with a statement of results. When you have finished working up your data,
look it over to decide what conclusions may be drawn. State your results briefly, using the past
tense. Write something about each table or figure, keeping in mind that they present the data but
they do not state the results. Do not simply offer the data as your results. Be sure to introduce all
your results in this section.
This section will also contain error analysis. Before one can draw conclusions from data, one
must assess the precision and accuracy of the results. A result is only as good as the accuracy to
which it was measured. To evaluate your data you must know how reliable it is. Acquiring data on
a brand-new instrument does not mean that there is no error in the data, nor are computer calculated
results error free.
There is always some error in your measurements. In the discussion of each error, a discussion of its
effect on the experimental outcome/results should be included. Listed below are some common
sources of error, all of which should be considered in assessing your data.
•
Errors in measurement: It is easy to misread an instrument, particularly when using an
analog device with several scales located on a single meter. Make sure you are reading the
right scale. Make sure you know what the units are when recording data from an instrument.
Other common measurement errors might be misreading a buret, not zeroing a balance, or
incorrectly taring a balance. It is common to take 3-5 readings and use the standard deviation
of the readings to estimate the uncertainty.
•
Errors in Recording or Recopying: It occasionally occurs that numbers are transposed or
decimal points lost when entering data in your notebook or copying them to a table. This
type of error is hard to catch unless the number is totally unreasonable or well removed from
an observed trend in the other measurements. Examples might be a pH of 23 or a series of
repeated measurements where four out of five readings gave values between 0.2 and 0.8, but
the firth reading gave 3.9; clearly there is a problem with the fifth measurement.
•
Errors in Computation: Double check your calculations. Don’t assume your answer is
wrong if it did not agree with your lab partner’s or the literature. Watch your units and unit
conversions! Make sure they are consistent. Once you have completed your calculations,
consider if the answer is reasonable. Always evaluate your calculations, particularly your
units.
Once you have assessed the reliability of your data, you can discuss and interpret your results. You
should first consider whether you accomplished what was proposed in the introduction and if your
results were successful. What are the significant sources of error in the experiment? At least three
procedural errors should be identified. How might they be minimized in the future?
Begin the “Results and Discussion” section with your interpretation of the results, and then perhaps a
comparison of them with expected values. Always try to put a positive spin on your results if
possible. You must also discuss the reliability of your data, how the reported uncertainty was
determined and what its primary source was.
Things may go wrong in lab. However, even if your results are questionable, it is still possible to
write a good lab report. Begin by stating what should have happened, then discuss what actually
happened and why the experiment went wrong. Never begin your discussion with what went wrong.
It is important that you demonstrate that you understand both what should have happened and what
might have gone wrong. Note also that there is a big difference between a null result and a failure to
get results.
Assignment: Practice writing a “Results and Discussion” section on the lab
specified in the syllabus and submit on the date indicated there. Should be typed in
word document and submit electronically!
Steps in writing Results and Discussion section:
1. Results statement: what key conclusions you can draw from your experimental data?
2. Identify 2-3 sources of errors and analyze
a. Their impacts on the experimental result;
b. How they can be eliminated and/or reduced in future attempts.
C125/C126 FORMAL LAB REPORT
FORMAL LAB REPORT, General
A formal lab report is required in conjunction with some of the experiments in each
chemistry course. It is your chance to demonstrate to your professor or TA how well you
understand the experiment and the chemical principles involved. A formal report is
different than a term paper. It should be written in a scientific style, which is not the
same style used for English or philosophy papers.
The keys to effective technical writing are organization, brevity, clarity, and an
appreciation of the needs of the reader. You must write clearly and be thorough, but
concise. Do not ramble. The best way to avoid rambling is to first prepare an outline of
the report and stick to it. Always use complete sentences. Bulleted lists are okay in a lab
notebook but are unacceptable in a formal report. Formal reports must be typed. Use 1.5
line spacing, 1-inch margins, 12 pt font and 8.5×11 inch paper. Only use third person,
past tense. Also, proofread well.
The general structure of a formal lab report follows that of a scientific paper. It is:
Title and Author (s)
Introduction
Experimental Information
Data and Calculation
Results and Discussion
Conclusion
References
Results and discussion sections are combined into one single section. Different
instructors may have specific formats that they want you to follow. You should always
defer to the instructions given to you by your course. Presented here are general
guidelines for writing formal lab reports and scientific papers.
Before writing your first report, visit the library and examine several journal articles. Pay
close attention to the style of the prose and the contents of each particular section.
Several common journals to investigate are:
The Journal of the American Chemical Society
The Journal of Physical Chemistry
Analytical Chemistry
Biochemistry
Initialed and dated laboratory notebook pages of the experiment must be submitted.
While report sheets may be a joint effort, formal reports must be individually written.
A schedule of reports and dates on which they are due is given in the course laboratory
schedule. We highly recommend that reports be completed prior to the day of
submission to allow time to proofread, and thus avoiding loss of points due to last minute
problems. Lost data or the inability to print reports is not acceptable excuses for
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incomplete or missing reports. You will be informed when notebook pages will be
collected before the report is due.
FORMAL LAB REPORT – Title and Author(s)
State the title of the experiment, your name, the date and your laboratory section number,
if applicable. Also state the name of your lab partner(s). This information should be at
the top of the first page.
FORMAL LAB REPORT – Introduction
The Introduction states the purpose of the study and introduces the reader with new ideas
and topics. It also provides any background necessary to acquaint the reader with the
problem being addressed, as well as providing the reader with references to previous
relevant work.
Although a portion of a formal report, it is sometimes easier to view this section as a
short essay, one in which the writer describes the importance of his work, and the
possible application of his work to other areas of interest to the reader. As in an essay,
the Introduction begins with a broad description of the principles being discussed in the
report, and funnels down, becoming more specific along the way, to a statement of the
specific objective of the study. It should acquaint the reader with the main topics and
ideas discussed in the experiment, and should include definitions of key terms that are
new.
In your Introduction, you will need to choose the relevant facts from your textbook, lab
manual or other materials available to you, organize them in your own words, and present
them in a logical order that highlights and supports the proposed experiment.
Definitions of significant terms should be included. In general, your introduction should
be two to three paragraphs long, concluding with the statement(s) of purpose.
FORMAL LAB REPORT – Experimental Information
Here you must give a concise description of what occurred in lab with sufficient detail to
allow the reader to repeat the study. However unlike the audience for a laboratory text
book, the audience for a formal report does not need to be told to wash the beakers or to
insure there are no air bubbles in the buret tips. It is essential, therefore, that the writer be
careful not to insult the intelligence of the audience when writing the Experimental
section.
Another difference between formal Experimental sections and laboratory text books is
that laboratory texts are generally written in second person past tense, i.e., “Open the lab
drawer and take out your notebook.” Formal Experimental sections, on the other hand,
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are written in the third person, past tense, i.e., “The KHP solution was titrated with NaOH
until a slight pink color permeated the solution.”
Preparing for this, it may help to summarize the procedure into a bulleted list of about
five main procedural steps and then to convert the list to complete sentences. Be sure to
mention any significant deviations from the procedure as stated in the lab manual.
In this section you should state significant information: amounts of starting materials and
products, reagents used and their concentrations, instruments used, including their make
and model, and significant observations of chemical reactions. Give a synopsis of what
went on.
In general, remember that the audience would like to know what was done, not what to
do. In a report you must write in complete sentences. Write in the third person past
tense. One final note, be forewarned that step-by-step cookbook instructions are
unacceptable in formal lab reports.
FORMAL LAB REPORT – Data and Calculations
The first step in completing this section is to use your data and generate any tables or
graphs necessary for the analysis. This should be done in your lab notebook. Data may
be graphed or tabulated. Whether the results are graphed or tabulated will depend on the
data and the conclusions you draw. You need to use your judgment.
Then examine your data and select the appropriate, pertinent items for your formal report.
Not everything in the data tables in your notebook will necessarily go into tables in your
report. In your notebook you might have recorded initial and final buret readings, but in
your report you would only state the volume of titrant used, i.e., the difference between
the initial and final buret volumes. Once the reliability of your data has been assessed,
you may tabulate your results. Having achieved this, you can discuss and interpret your
results.
Conclusions you draw from your data must be presented in a clear, concise manner.
Tables and figures (graphs are considered figures) should be integrated into your text, as
you would find them in your textbook or in a journal article. You should introduce data
tables and figures with words using complete sentences. Refer to figures and tables
sequentially as they are introduced. Figures and tables should be identified with a
separate series of number.
FORMAL LAB REPORT – Results and Discussion
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This section is the meat of a formal report as it is where you demonstrate your
understanding of the experiment and its results. It is also the most difficult to write,
should take the most time, and is generally worth the most points in your score.
Begin this section with a statement of results. When you have finished working up your
data, look it over to decide what conclusions may be drawn. State your results briefly,
using the past tense. Write something about each table or figure, keeping in mind that
they present the data but they do not state the results. Do not simply offer the data as
your results. Be sure to introduce all your results in this section.
This section will also contain error analysis. Before one can draw conclusions from data,
one must assess the precision and accuracy of the results. A result is only as good as the
accuracy to which it was measured. To evaluate your data you must know how reliable it
is. Acquiring data on a brand-new instrument does not mean that there is no error in the
data, nor are computer calculated results error free.
There is always some error in your measurements. In the discussion of each error, a
discussion of its effect on the experimental outcome/results should be included. Listed
below are some common sources of error, all of which should be considered in assessing
your data.
•
Errors in measurement: It is easy to misread an instrument, particularly when
using an analog device with several scales located on a single meter. Make sure
you are reading the right scale. Make sure you know what the units are when
recording data from an instrument. Other common measurement errors might be
misreading a buret, not zeroing a balance, or incorrectly taring a balance. It is
common to take 3-5 readings and use the standard deviation of the readings to
estimate the uncertainty.
•
Errors in Recording or Recopying: It occasionally occurs that numbers are
transposed or decimal points lost when entering data in your notebook or copying
them to a table. This type of error is hard to catch unless the number is totally
unreasonable or well removed from an observed trend in the other measurements.
Examples might be a pH of 23 or a series of repeated measurements where four
out of five readings gave values between 0.2 and 0.8, but the firth reading gave
3.9; clearly there is a problem with the fifth measurement.
•
Errors in Computation: Double check your calculations. Don’t assume your
answer is wrong if it did not agree with your lab partner’s or the literature. Watch
your units and unit conversions! Make sure they are consistent. Once you have
completed your calculations, consider if the answer is reasonable. Always
evaluate your calculations, particularly your units.
Once you have assessed the reliability of your data, you can discuss and interpret your
results. You should first consider whether you accomplished what was proposed in the
introduction and if your results were successful. What are the significant sources of error
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in the experiment? At least three procedural errors should be identified. How might they
be minimized in the future?
Begin the “Results and Discussion” section with your interpretation of the results, and
then perhaps a comparison of them with expected values. Always try to put a positive
spin on your results if possible. You must also discuss the reliability of your data, how
the reported uncertainty was determined and what its primary source was.
Things may go wrong in lab. However, even if your results are questionable, it is still
possible to write a good lab report. Begin by stating what should have happened, then
discuss what actually happened and why the experiment went wrong. Never begin your
discussion with what went wrong. It is important that you demonstrate that you
understand both what should have happened and what might have gone wrong. Note also
that there is a big difference between a null result and a failure to get results.
FORMAL LAB REPORT – Conclusion
The purpose of the Conclusion section is to summarize the pertinent concepts discussed
in the R&D section. Always begin your Conclusion by clearly stating your results and
the “goodness” or significance of your results, and relating them to ideas presented in the
introduction. In other words, if the objective of the study was to determine the percent
calcium carbonate in an unknown sample, you should restate the percentage, with its
uncertainty, in this Conclusion section.
Important observations may go in this section as well. Discuss the significance of the
results. When possible, compare your results with literature values. Discuss significant
errors and suggest improvements to the procedure or possible ideas for additional
experiments that could further support your conclusion.
Then make a concluding statement(s) and relate your conclusion to the ideas presented in
the introduction. Note: Stating that “overall the experiment went well” or that “I learned
how to use a piece of equipment” are not strong conclusions.
The conclusion is not to be a lengthy discourse. One paragraph (about four to seven
sentences) is the amount to be presented in conclusion.
FORMAL LAB REPORT – References
Always cite any literature and websites used in preparing your lab report. “Verbal
Communications” may also be cited as such. The specific format used to cite references
varies from journal to journal. You should always reference the lab manual. You may
have others if you cite literature values or refer to your textbook for clarification of ideas.
Generally, all citations include the author’s last name and first initial, an abbreviated
form of the journal title, the volume number, the first page number of the article and the
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year published. In citing a scientific paper, the title need not be given. In citing a book,
begin with the author’s name, followed by the title of the book, the publisher, where
published and the specific edition.
Examples
N. E. Triggs, M. Zahedi, J. W. Nibler, P. A. DeBarber and J. J. Valentini, J. Chem.
Phys., 96, 1822 (1992).
J. A. Halstead, N. Triggs, A. L. Chu, and R. Reeves in Gas Phase Chemiluminescence
and Chem-ionization, A. Fontijn (ed.), p. 307-334, North-Holland, (1985).
FORMAL LAB REPORT – Formatting Guidelines for lab reports
Clarity and Style
Observe the rules of good grammar, spelling, and punctuation. It is expected you will
write in complete sentences. Proofread your report before you turn it in. There is no
bigger turn off when grading a report than to find sloppy grammar and incorrect spelling.
It sets the tone “expect the worst” and it will surely be reflected in your grade.
Reports must be typed and the use of a word-processor is encouraged. Use 1-inch
margins, 12-point font for text and 1.5-line spacing. Choose a font that is easy to read.
Equations
Equations are presented as part of the sentence structure of the text and are numbered for
future reference. All symbols are defined where first used. In formal reports, the first
time an equation is presented, it is identified by a number. Each use of that equation is
then referenced by that number, whether in the section introduced or in later sections.
Sample calculations and results in any section may refer to equations previously
introduced, or new equations may be presented. Equations are not grouped together, but
are presented only when needed during the course of discussion.
A very useful tool for inserting equations into your documents is the equation editor
available in many word processor packages.
“The molarity of HCl was calculated from Equation 1, where M and V are
molarity and volume (mL) respectively. The mean molarity of HCl for the
three trials was 0.0985 M, and the standard deviation, calculated with
Equation 2, was ± 0.0002 M.”
M HCl =
M NaOH VNaOH
VHCl
i =n
(x − x )
(1)
2
i
SD =
i=1
n −1
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(2)
Figures
One figure that is often used in Chemistry is a graph. The type of graph you compose
will depend on your data. Chemists most commonly use an x-y scatter plot with the
dependent variable on the y-axis and the independent variable on the x-axis. All axes
should be labeled – the reader does not necessarily know what you are plotting. And be
sure to include the units for each axis, for example, “time (secs)” or “Fe3+ concentration
(moles/liter)”. (You will be penalized if you leave axes labels out.) Pay attention to
your axes’ scales and make sure your data fills the graph. The same data can look very
different depending on how it is scaled. Always consider whether it is important to show
that your data passes through the origin, or if it s more important that your data fills the
scale.
Generally on an x-y scatter plot, you do not connect the dots, but simply draw the best
straight line or curve through the data. If you plot more than one set of data on the same
axis, you must include a legend to identify each series. Error bars are also important and
helpful in judging the significance of the data. Usually these are only included for the
dependent variable.
Figures (graphs) should be at least one-half of a page in size and regression statistics also
included if calculated. They need to be numbered sequentially and include a relevant
title. Ex: Figure 1. Density of Metal, Volume (mL) vs. Mass (g)
Tables
Tables are used when graphs are inappropriate and the data cannot be introduced in a
single sentence of text. Each table should have a title at the top and a table number by
which it can be cited in the text. Arrange your data by column rather than by row. It is
much easier to read down than across. Do not include a column containing all the same
numbers. Footnotes are frequently used to convey specifics about a subset of data within
the table. Uncertainties in results should be presented with the data in the table. Tables
are sequentially numbered, independent of Figures.
Abbreviations
Well-known abbreviations, such as mL, M.W., etc., may be used without explanation.
Otherwise, spell out the words the first time they are used, followed by the abbreviation
in parenthesis, and use the abbreviation thereafter:
“Potassium hydrogen phthalate (KHP) was used as the primary standard.”
Subtopic: Symbols
Many quantities have accepted symbols, i.e., pressure (P) or temperature (T). It is often
convenient or efficient to define symbols for calculated or measured values.
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Name:
Partner:
Formal Laboratory Report
C125 Experimental Chemistry I
Section 5975
IUPUI
July 21, 2005
Determination of Purity Using Titration
INTRODUCTION
A common problem in chemistry is determining whether or not a substance is
impure and to what extent it is impure. Chemicals used in experiments or for commercial
purposes often need to be pure to ensure safety and efficiency during reactions, but
determining whether or not a given substance is pure can be difficult. If the chemical is
an acid or a base, titration with a standardized solution can be used to assess its purity.
In a generic titration, “one solution of known concentration is used to determine
the concentration of another solution through a monitored reaction.”1 An acid-base
titration works on the principle that the acidic solution will combine the basic solution to
neutralize, altering the pH of the solution.
H3O+(aq) + OH- (aq) → 2H2O(l)
(1)
Eq. 1 shows that when equal moles of the H3O+ion and the OH- ion are present, the
solution is completely neutralized. 2 When this dynamic equilibrium occurs in a titration,
it is called the equivalence point, and at that point a given reaction has a characteristic
pH. Thus, indicators, substances that can change color depending on the pH, are valuable
tools for monitoring the progress of titration reactions. A few drops of indicator are added
to one of the solutions and the other solution is added dropwise. When the moles of acid
and base are equivalent, the equivalence point is reached and adding one more drop of the
titrant will cause the indicator to change color, signaling the end point of the reaction.
The end point occurs just after the equivalence point, but the extra titrant required to
reach the end point is negligible in calculations.
The titration method is useful in determining purity only if a standardized
solution, one with a known molarity, is available for the titration. If a known volume of
standardized solution is used in a titration, then the moles of both acid and base can be
determined. From the moles, the mass of the pure substance can be determined and
compared to the mass of the impure substance to find the percent purity.
In this experiment, a sodium hydroxide, NaOH, solution was standardized by
titration with pure hyrdrochloric acid, HCl.
HCl (aq) + NaOH (aq) → H20 (l) + NaCl (aq)
(2)
This reaction was monitored using phenolphthalein indicator, which changes from clear
to pink near a pH of 8, corresponding to the pH at the reaction’s equivalence point. Once
the molarity of the standard NaOH solution was known, the solution was used to titrate
an impure sample of industrial grade muriatic acid, HCl, again using phenolphthalein
indicator, and the purity of the muriatic acid sample was determined.
EXPERIMENTAL
25 mL of pure 1.000 + 0.003 M HCl was measured using a 25.00 mL graduated
pipet and added to a 250 mL flask along with 2 drops of phenolphthalein indicator. Next,
an NaOH solution of approximately .1 M was created by diluting 75 mL of 1 M NaOH to
750 mL with DI water. The NaOH solution was then placed in a 50 mL buret and added
dropwise to the HCl solution until the indicator in the solution turned pink. The above
procedure was repeated three times to standardize the NaOH solution, at which point
three samples of approximately 35 mL impure muriatic acid were prepared and titrated
again using the NaOH solution and phenolphthalein.
DATA
The results obtained from the above procedure may be found in Data Tables 1, 2,
and 3. In Table 1, the moles of HCl were obtained from the measured volumes and then
equated to moles of NaOH. The molarity of the NaOH solution was calculated by
dividing the moles of NaOH by the volume of liters of NaOH delivered during titration.
Moles HCl = Moles NaOH=Molarity x Liters HCl
(3)
Molarity, NaOH = Moles Solute/ Liter Solution
(4)
Table 1: Standardization of NaOH Solution
Volume, pure
Moles of Pure
Volume of
Molarity of
6M HCl (L)
HCl and of
NaOH
NaOH Solution
NaOH (mol)
Delivered (L)
(M)
Trial 1*
0.02450
2.450 * 10-3
.02600
9.45201 * 10-2
Trial 2
0.02450
2.450 * 10-3
.02622
9.39698 * 10-2
Trial 3
0.02460
2.460 * 10-3
.02560
9.60353 * 10-2
Trial 4
0.02450
2.450 * 10-3
.02586
9.47289 * 10-2
In Table 2, the volume of the impure muriatic acid was measured using a volumetric
pipet, but the number of moles of HCl in the samples was determined by equating the
moles of NaOH used to titrate to the moles of HCl. The percent purity of the sample was
the mass of the HCl in the sample divided by the total sample mass. Moles of pure HCl
in the standard HCl and moles of muriatic acid were converted to grams present and the
% purity calculated according to Eq. 5.
% Purity = Mass of Pure Substance / Mass Standard x 100%
(5)
Table 3 summarizes the results of Tables 1 and 2: the mean and standard deviation for
NaOH Molarity and HCl purity.
Table 2: Percent Purity of Impure Muriatic Sample
Volume of
Volume of
Moles of
Mass of HCl
Purity of the
Impure
NaOH
NaOH =
present in
Impure HCl
Muriatic
Delivered
Moles of
Impure
Sample (%)
Acid (L)
(L)
HCl (mol)
Sample (g)
Trial 1
.03410
.01155
.0010973
.2240913
31.64685
Trial 2
.03490
.01152
.0010944
.2235093
31.78912
Trial 3
.03520
.01153
.0010954
.2237033
31.95305
*
Over-titrated, trial not used in calculation of mean or standard deviation
Table 3: Statistcal Analysis of NaOH Molarity and KHP Percent Purity Results
Molarity of NaOH (M)
% Purity of KHP Sample
Mean
.094911
31.79634
Standard Deviation
+ .00104
.153
Mean +/- Std. Dev.
.095 + .001
31.8 + .2
RESULTS AND DISCUSSION
The molarity of the NaOH solution was determined to be .095 ± .001 M and the
percent purity of the muriatic acid sample was determined to be 31.8 ± .2 %. In
determining the molarity of NaOH solution, the first trial was not used because it was
visibly over-titrated. Trial 3 used a higher volume of muriatic acid than trial 1, but needed
less titrant, indicated, in addition to the visible evidence, that trial 1 was over-titrated.
Trials 2, 3, and 4 appear consistent: the trial with the highest volume required the most
NaOH and the trial with the lowest volume required the least NaOH.
In the second part of the experiment, only three trials were performed because
none of the solutions appeared over-titrated. However, trials 2 and 3 are not consistent:
trial 2 used more HCl than trial 3, but needed less NaOH. Trial 2 may have been slightly
under-titrated or trial 3 may have been slightly over-titrated. All of the trials in the second
part of the experiment required less NaOH than the trials from the first part, even though
a greater volume of HCl was used. This was a clear indication that the samples in the
second phase were highly impure.
The most probable cause of error in this experiment was over-titration. It is
difficult to add extremely small drops toward the end of titration; often the last drop or
splash added causes the solution to change from clear to dark pink rather than a pale pink.
If over-titration occurred in only the first phase of the experiment, it would deflate the
molarity of the NaOH and subsequently the percent purity of the muriatic acid. If overtitration occurred in only the second phase of the experiment, it would inflate the percent
purity of the HCl.
Another problem was losing drops of NaOH solution: drops of solution stuck to
the sides of the flask, occasionally slipped out of the loose-fitting stopcock, and often a
single drop lingered on the buret’s tip at the end of titration. Losing drops of NaOH
would make the volume of NaOH used too high, having the same effect on the results as
over-titration. In order to reduce these effects, the sides of the flask were rinsed with DI
water, the stopcock was held tightly on the buret, and the buret was turned off quickly at
the end point instead of slowly to avoid drop formation.
Problems may also have occurred if any HCl was lost during measurement with
the pipet. The volume on graduated pipets can be difficult to read because the meniscus
level of measured liquid is often difficult to steady. Overestimating the amount of
hydrochoric acid in the flask only in the first part of the experiment would inflate the
molarity of the NaOH solution and subsequently the percent purity of the HCl. If HCl
were lost only in the second part of the experiment, the calculated percent purity of the
HCl would be too low.
CONCLUSION
The molarity of the NaOH solution was determined to be .095 + .001 M and the
percent purity of the muriatic sample was determined to be 31.8 ± .2 %. Though the true
molarity and percent purity were unknown, the standard deviation in these numbers was
fairly low, indicating precise, if not accurate, results. The accuracy of this experiment
could be improved by running more trials with both the pure and the impure muriatic
acid. This experiment is significant, because being able to determine accurately and
precisely the molarity of a solution is an important step in many experiments, and
determining the percent purity of a sample is necessary in
