# University of Central Oklahoma Gravimetric Determination of Chloride Report

Gravimetric Determination of ChlorideHan Doan
Date of Experiment : 02/03/2021
Date of Submission : 03/12/2021
Submitted to Dr. Skiles
Gravimetric Determination of Chloride
Calculations and Results
Standard brass weights were used to calibrate the analytical balcance. These results were further utilized in the propagation a mass
error
N is the number of trial and x, or average is:
x=
xi 2.0002 g + 1.9999 g + 2.0001 g + 2.0004 g + 2.0002 g
=
= 2.0002 g
n
5
Standard deviation of balance number 4:
S=
S=
(xi−x)2
n−1
(2.0002−2.0002)2+(1.9999−2.0002)2+(2.0001−2.0002)2+(2.0004−2.0002)2+(2.0002−2.0002)2
5−1
= 0.0002g g
Below are the calculations utilized to determine the percent chloride in the soluble chloride unknown.
The mass of silver chloride in crucible 1:
Cfinal − Cempty = 17.2979g − 16.8767g = 0.4212 g
The uncertainty in the mass of the unknown was obtained by the following calculation utilizing the balance error for the 2.0 gram
weight:
efinal = e21 + e22 + e23 + . . . + e2n
Where e1 ,e2, and up to en are the uncertainty of measurement 1 to n respectively
eunknown =
(0.00026)2 + (0.00026)2 = 0.00037 g
The standard uncertainty for each element was calculated to determine the error in the formula weight of silver
chloride as follows:
Ag: 107.8682 ±
0.0002
3
g/mol = 107.8682 ± 0.0001 g/mol
Cl: 35.453 ±
0.002
3
g/mol = 35.453 ± 0.001 g/mol
The formula weight of AgCl and the standard uncertainty were obtained as followed:
Formula weight of AgCl: 107.8682 g/mol + 35.453 g/mol = 143.321
Standard uncertainty: e = (0.0001)2 + (0.001)2 = 0.001 g/mol
The reaction stoichiometry was utilized to convert to moles of chloride from the weight of silver chloride:
Mole of Cl:
grams of AgCl
= mole of Cl
molar mass of AgCl
0.4212g
= 0.002939 mol Cl
143.321 g/mol
%e =
absolute uncertainty
× 100
obtained value
0.00037
× 100 = 0.088%
04212
0.001g
%e of AgCl =
× 100 = 0.00007%
143.321g
%e =
%efinal = (0.088)2 + (0.00007)2 = 0.088%
efinal =
0.088
× 0.002939 mol Cl = 2.6 × 10−6 g = 0.00003g
100
Mass of Chloride in Crucible 1:
Mass of Cl: 0.002939 mol Cl × 35.453g/mol = 0.1042g
%eChloride =
0.001g
× 100 = 0.003%
35.453
%efinal = (0.003)2 + (0.088)2 = 0.0876%
0.0876
× 0.1042 g Cl = 0.00009
100
0.1042g + 0.1260g + 0.1163g
Average mass of Chloride =
= 0.1155g
3
efinal =
Uncertainty: (0.000047)2 + (0.000047)2 + (0.000047)2 = 0.000081g
The percent of Chloride in crucible 1:
0.1042
× 100 = 66.75%
0.1561
%e = (0.087)2 + 0.1163)2 = 0.146%
e=
0.146
× 66.75 = 0.0974
100
Unknown: #351
Balance used #4
Table 1: Uncertainty for #4 Analytical Balance
Trials
Obs. Weight for 2.0g (g) Analytical
Obs. Weights for 20.0 Analytical
Weight (g)
Weight (g)
1
2.0002
20.0003
2
1.9999
20.0006
3
2.0001
20.0001
4
2.0004
20.0003
5
2.0002
19.9999
Uncertainty for Analytical Weight
±0.0002 g
±0.0003 g
Table 2 : Raw and Calculated Data
Trial 1
Trial 2
Trial 3
Unknown mass
Mass of crucible +
Mass of Crucible
Mass of AgCl
(g)
AgCl (g)
(g)
(g)
0.1561±0.0002
17.2979±0.0003
16.8767±0.0003
0.4212±0.0004
0.1753±0.0002
0.1535±0.0002
17.6771±0.0003
17.7658±0.0003
17.1678±0.0003
17.2956±0.0003
0.5093±0.0004
0.4702±0.0004
Mole of Cl(mol)
Mass of
Cl(g)
0.0029
0.1042
±0.00003
±0.0001
0.0046
0.1260
±0.00003
±0.0001
0.0012
0.1163
±0.00003
±0.0001
Table 3 : Percent of chloride in crucibles with Absolute and Relative Uncertainty
Crucibles
Percent of Chloride
Absolute Uncertainty (with
Relative Uncertainty (with
error )(%)
error) (%)
1
66.75
0.09742
0.1462
2
71.87
0.09081
0.1260
3
75.77
0.01083
0.1422
Average percent of chloride
71.46
0.09864
0.1383
with error
Quantitative Chemical Analysis
Writing Guidelines
As you make your way in the world of your scientific profession, it is inevitable that you will be called upon
to write reports. Different supervisors and organizations will want reports done in different ways. However,
as an example, we will make the report in the form of an ACS journal article. This is to teach you to be able
to communicate in writing with your supervisor effectively, and pass on what you have found in your studies.
If you cannot write and transmit your information that you discover, you will not succeed in science since
the transmission of the information is the bottom line of science. THE LAB REPORTS WILL BE WRITTEN
IN THE STYLE OF THE PEER REVIEWED JOURNAL “ANALYTICAL CHEMISTRY”.
This class will include 2 formal lab reports. These lab report is identical in form to that required to submit a
scientific paper to the journal “Analytical Chemistry” (here are the actual guidelines for their authors:
http://pubs.acs.org/paragonplus/submission/ancham/ancham_authguide.pdf )
Journal Articles normally have the following parts: We will focus this class on writing only the bold
sections. It will likely feel like you are repeating yourself at times and also like you are missing key
information (methodology).

Title and Bibliographic Information
Abstract
Introduction
Experimental/Methodology
Results
Discussion
Conclusion
References
Supplemental Information
1
Report Writing Guidelines
This class will follow the guidelines established in the ACS Style Guide. A full PDF of this book is available
online (https://pubs.acs.org/isbn/9780841239999 ); additionally several copies can be found in the
chemistry department or the campus library. The following is a simplified miniature version to get you
started.
The full lab reports will be broken into the sections outlined below:
1. Cover Page
 Title
o

Use specific and informative titles with a high keyword content. Avoid acronyms
and subtitles. Either the title or the abstract must contain the name(s) of the
central measurement methodology used in the paper.
Author
Date of Experiment
Date of Submission
Submitted to Instructor (i.e. Dr. Skiles-Jones)
2. Abstract
Abstracts (80–250 words) should describe briefly and clearly the purpose of the research, the principal
results, and the major conclusions. Remember that the abstract will be the most widely read portion of the
paper. An abstract summarizes, in one paragraph, the major aspects of the entire paper in the following
prescribed sequence:
 Purpose
o state the purpose very clearly in the first or second sentence
 Experimental design and methods used
o clearly express the basic design of the study
o Name or briefly describe the basic methodology used without going into excessive detailbe sure to indicate the key techniques used
 Key results
o major findings including key quantitative results
o identify trends, relative change or differences, etc.
 Conclusions
o clearly state the implications of the answers your results gave you
Limit your statements concerning each segment of the paper (i.e. purpose, methods, results, etc.) to one
or two sentences, if possible. The abstract is ONLY text with no references. Use the active voice when
possible, but much of it may require passive constructions. Write your abstract using concise, but complete,
sentences, and get to the point quickly. Use past tense.
3. Calculations / Data Tables/ Results
Presentation of data in chart or graphical form (this will be lab dependent) with appropriate
labeling. Calculations should have a general equation and a sample. Everything should have
UNITS and correct significant figures.
This section includes the typed and formatted data tables, correctly labeled and printed graphs, and sample
calculations.
2
Data Tables: This should include all of the data that you actually collect in the laboratory. You
should transfer this data into typed data tables as you prepare your report to turn in. Be sure to
include the concentration of solutions, any masses that you weighed, and any other data that you
collect.
Graphs: Graphs may be prepared using Excel or similar program. Regardless, graphs should
include an appropriate title, axis labels, and units. Be sure to utilize good graphing techniques. Any
lines used to interpret the graph should be shown on the graph and labeled.
Sample Calculations: At least one example of every calculations you performed in lab must be
shown. Be sure to include units and proper significant figures.
REMEMBER: Do not “create” or “discard” significant figures! If you measured to only
hundredths of grams, do not add a trailing zero (3.13 -> 3.130 g). On the other hand, if
a beaker weighed 45.217 g full of reagent and 41.137 g after adding the reagent to the
flask, you added 4.080 g to the flask, not 4.08 grams. Many points are lost on labs
because of improper use of significant figures, and that can add up over a semester.
4. Discussion
This is the most important section of the laboratory report. This section is where you explain and interpret
All information in the Discussion must be based on observations and/or data that is recorded. For
example, do not refer to the appearance of a solid if you did not record its appearance in your notebook.
Additionally, any references to a book or other source must be properly cited.
As a rule, the quality of your Discussion indicates how clearly you understand the objectives of the
experiment and how you interpreted your results. A Discussion that contains inaccurate or poorly
supported claims, illogical reasoning, or which leaves out key information, suggests that you do not
understand the experiment. Conversely, even if an experiment is unsuccessful, a well-written and wellreasoned Discussion can earn more points than a poorly-written one describing a successful experiment.
The results may be presented in tables or figures; however, many simple findings can be
presented directly in the text with no need for tables or figures.
The discussion should be concise and deal with the interpretation of the results. Walk
through the calculations and explain them. Discuss the meaning of the results. How
the “known” was used to verify the method and to correct the unknown for method
error. This section should include the major results. They should discuss possible
sources of error, (not doing what they should in lab in not a good example of error!!)
a.
b.
c.
Explanation of results, what do the numbers mean, where did they come from
Observations that you have made that can explain why data may appear “off’
Interpretation of the quality of your data to include statistical analysis, Q-testing, standard
deviation, etc…
The Discussion of Results should follow the “Four-C Principle”. The Discussion should be:
Correct: The information should be accurate and data interpreted correctly. Calculations should be
correct.
Complete: Do not leave out relevant information, even if some of may seem contradictory.
3
Concise: Avoid being “wordy” or including irrelevant information.
Clear: Use proper grammar and terminology, write neatly, and break the Discussion into paragraphs.
5. Conclusion
This is generally a single paragraph. It is written very similar to the abstract. This is not the place
for new ideas or discussion of error.
a.
Response to answering the “statement of the lab”
b.
Answer to the unknown in the form (Average ± Standard deviation)
c.
Frame your results to state what broader impact this has. (Why do we care?)
6. References
You are required a minimum of 2 peer reviewed references. Although 2 is likely insufficient to
complete a well written report. References from the internet are not acceptable, and will count
against you.
Advice: Use the UCO Web of Science Data Base to find articles.
https://libguides.uco.edu/az.php?a=w
If the journals cannot found on the “White List” they are likely very obscure or predatory journals
and need to be avoid. http://www2.cabells.com/journals
References to notes/comments and to the permanent literature should be numbered in
one consecutive series by order of mention in the text with each reference individually
numbered. Reference numbers in the text must be superscripted. Use Chemical Abstracts
Service Source Index abbreviations for journal names (http://cassi.cas.org/search.jsp )
and provide article title, publication year, volume, and page number. For work published
online (ASAP, Just Accepted, in press), the DOI should be furnished in addition to the
standard bibliographic information.
Examples of the reference format:
(1) Ho, M.; Pemberton, J. E. Alkyl Chain Conformation of Octadecylsilane Stationary
Phases by Raman Spectroscopy. 1. Temperature Dependence. Anal. Chem. 1998,
70, 4915–4920.
(2) Bard, A. J.; Faulker, L. R. Electrochemical Methods, 2nd ed.; Wiley: New York,
2001.
(3) Pratt, D. A.; van der Donk, W. A. Theoretical Investigations into the Intermediacy of
Chlorinated Vinylcobalamins in the Reductive Dehalogenation of Chlorinated
Ethylenes J. Am. Chem. Soc. 2004, DOI: 10.1021/ja047915o.
7. Page Numbers- Located at the bottom right of each page. Page number can be omitted
from the cover page.
4
Tips for Preparing for Lab and Writing Reports
1. Preparing for lab is absolutely essential. Know what you are supposed to do, what chemicals you will
use, what glassware you must set up, etc. Good preparation leads to neater notebooks, which
makes it easier to find information when writing the Discussion.
2. Summarize procedural steps to save time for you. Remember to include any additions or changes to
the procedure—including things like re-doing steps, performing additional extraction, re-distilling
your product or even restarting the whole experiment.
3. The amounts of chemicals you list in the Procedure are approximately what you will need. Record
the exact masses and volumes you use in your Observations. Record the appearances of your
solvents, reagents, the colors of solutions, changes in appearance or texture during heating or
cooling, colors of the layers when performing extractions, colors and appearance of products, etc.
4. When performing calculations, use significant figures correctly.
5. Present data from spectra in tables. Try to interpret all relevant signals. “Relevant” is loosely defined
as a signal or peak that is probably from either the product, starting material or a solvent. Consult
your instructor if you need some help.
6. Be concise. Wordiness can be confusing, and it takes too much time to write (and read!).
7. Avoid slang or jargon, and use correct scientific terms. (e.g., the plural of “spectrum” is spectra, not
spectrums. Use “percent yield” and “percent recovery” appropriately.
8. Carefully check your spelling and grammar to make sure what you say makes sense. You may want
to have a friend or classmate read your report to help locate mistakes and parts that should be
revised. All compound names, terms, etc. that appear in the manual should always be correctly
spelled.
9. For “typed” parts of your report, do not use the “MATH” SYMBOLS such as *, E-21, 10^5 or other
obsolete computer shortcuts. You have full publishing capabilities on your computer. Use regular
scientific notation: Ex: 5 x 10-2.
10. Use common sense in your Discussion. If you spill a sample that cannot result in a higher
percent yield.
claims. Reading it aloud—or even better—having someone else read it can help spot problems
such as flawed reasoning, contradictory sentences, poor grammar and so forth.
12. Edit your own paper for content, grammar, English, and most importantly readability. Editing
your paper takes time. After you write your paper, go through it several times to correct it so that it
conforms to the form (pay attention to the 3rd person, past tense, passive voice rules). Again, having
give the impression of sloppiness or that you did not proofread your work. These impressions will
5
General Rubric of Sections
Abstract
Appropriate length/
Spelling/ Grammar
Completely Satisfies
Partially Satisfies
Does Not Satisfy
Perfect amount of
detail. Great spelling
and grammar.
Slightly too little or too
much detail. A few
grammar and spelling
mistakes.
Stated the purpose, but
could have been more
concise.
Very short or long.
Grammar and spelling
mistakes throughout.
Did not indicate the
basic design or the
experiment. Or only
named the methods,
but did not describe the
basic methodology.
Did not name or
describe the basic
methodology of the
experiment.
Report the results but
do not include context,
units or significant
figures.
Results are not
reported.
Data tables are present
but lacking key
information, statistics,
or units.
Did not include data
tables.
Sample calculations for
each area are typed
and relatively
organized. They
include most units, and
equations, but are
missing some.
Did not include sample
calculations.
Sample calculations
are handwritten.
Results are included
but are not clearly
explained. Minor issues
with significant figures,
units or statistics.
Results not included.
Purpose
What problem did you
study and why is it
important? Stated the
purpose clearly.
Methods
What methods did you
use to study the
problem? Clearly
express the basic
design of the study.
Name or briefly
describe the basic
methodology used
without going into
excessive detail.
Key Findings
Report the result that
the experiment.
Numerical results with
correct units and
significant figures
reported. Identify any
trend, relative changes
or difference you
notice.
Data Tables and Sample Calculations
Data Tables
Data tables are well
formatted and include
all necessary
information including
statistics, significant
figures, and units.
Sample Calculation
Sample calculations for
each area are clearly
typed and organized.
They include all units.
Results/ Discussion
Results
Results are clearing
indicated in the text.
Appropriate units and
significant figures are
used. Statistics are
used where needed
Did not state the
purpose.
6
Discussion of
calculations
Discussion of Data
Quality/ Error analysis
Conclusion
Purpose of the Lab
Major results
Impacts
References
Minimums
Formatting
Completely Satisfies
The logic behind the
calculations is clearly
explained using
scientific theory and
chemical reactions.
Discuss major sources
of error. Error trends
statistics. Explain how
this could be improved.
Partially Satisfies
Calculations are
discussed but the logic
behind the calculations
is flawed.
Does Not Satisfy
Calculations are not
discussed.
Discuss major sources
of
error,
but
it
to higher product yields.
No discussion of error.
Human error is the only
mentioned error.
Clearly reframe the
purpose of the
experiment.
Major results are
reported with the
correct units and
significant figures.
Generic restatement.
Missing the purpose.
Results are reported
with errors in units
and/or significate
figures. Minor and
major results are
reported.
the results and
experiment preformed.
Results not reported.
Thoughtful conclusions
given. Attempt to relate
implications of the
results and experiment.
Meet the minimum
requirement for
accepted references.
Followed ACS
guidelines for
formatting references.
No conclusion given.
Did not meet
requirement.
References are
formatted, but may
have some consistency
errors.
Reference are not
formatted.
7
Writing Guidelines
Scientific writing, in particular, must be precise and unambiguous to be effective.
Voice: Use the active voice when it is less wordy and more direct than the passive. Use the passive voice
when the doer of the action is unknown or not important or when you would prefer not to specify the doer
of the action.
Tense: Simple past tense is correct for stating what was done, either by others or by you. Present tense
is correct for statements of fact. Present and simple past tenses may both be correct for results,
discussion, and conclusions. However, the use of present or simple past tense for results, discussion,
and conclusions should be consistent within a paper.
Person: Write in third person. Exceptions to this can be make when it helps keep your meaning clear
comparing your results to published works. First person is used very sparingly if at all.
Example: Smith reported xyz, but I (or we) found ….
Avoid slang and jargon.
Do not use contractions in scientific papers.
Do not use the “MATH” SYMBOLS such as *, E-21, 10^5 or other obsolete computer shortcuts. You have
full publishing capabilities on your computer. Use regular scientific notation: Ex: 5 x 10-2
Use correct notation for units. A liter is L not l.
Element/Compound names: these are not capitalized unless at the start of a sentence or a trademarked
compound.
You may paraphrase (NOT QUOTE) what a Peer Reviewed paper states, but you must still reference it.
Referencing enhances your paper and strengthens it.
Do not split a table/figure between two pages. If you must split the column headings must be repeated.
Originality: All labs will be turned in electronically via D2L with a TurnItIn type Plagiarism detector on
D2L. You must write all your reports individually. Although you may have experimental data in common,
your report must not resemble those of the other students or be copied or pasted from the literature. We
will set up a D2L system that will show you what percentage your report has in common with your
classmates, former students (including yourself if you are repeating the course), and online sources. This
percent should not be greater than 30%. Point deductions starts at 30%. A percentage above 50% gives
you an official warning, any subsequent time you are above 50% it is an automatic ZERO and an official
report to the university.
Be sure to READ WHAT YOU WRITE! That means Edit your own paper for content, grammar, English,
and most importantly readability! If I have to edit your paper, it will cost you points!
Editing your paper is hard! After you write your paper, go through it several times to correct it so that it
conforms to the form (pay attention to the 3rd person, past tense, passive voice rules). Make sure that the
paper says what you MEAN IT TO SAY. Finally, either get an English Major for a friend who will go over
your paper, or get an appointment at Tutor Central.
8
Gravimetric Determination of Chloride
Jane Doe
Date of Experiment: 8/2/18 & 8/9/18
Date of Submission: 9/23/18
Submitted to Dr. Skiles
1
Abstract
The objective of this experiment is utilizing gravimetric analysis to determine the percentage of
the chloride in an unknown soluble chloride sample. Gravimetric analysis is a method of
chemical analysis based on the weight of the final product. This experiment also investigates the
uncertainties in measuring the weight of the product at various stages. The uncertainty of one
measurement can affect the final uncertainty of the calculated value. A known mass of unknown
was weighed and reacted with aqueous silver nitrate. This created solid silver chloride precipitate
which was filtered to remove as much liquid as possible. The precipitate was dried in the oven and
weighed to obtain the final mass of AgCl. The percent of chloride was calculated by using
stoichiometry. The average percent of chloride found was 59.90% ±0.329%. The percent of
chloride in the three crucibles were significantly close to each other; as indicated by a low standard
deviation of the measurements. This means that the final average percent of chloride was relatively
precise in sample 339.
Calculations and Results
Standard brass weights were used to calibrate the analytical balance. These results were further
utilized in the propagation a mass error.
N is the number of trial and x̅, or the average is:
x̅ =
∑ xi
n
The average for the 2.0 grams analytical weight is:
x̅ =
2.0008g + 1.9993g + 1.9988g + 1.9930g + 1.9990g
= 1.9982g
5
Standard deviations of balance number 3:
(xi − x̅)2
s=√
n−1
The standard deviation for the 2.0 grams analytical weight is:
(2.0008−1.9982)2 +(1.9993−1.9982)2 +(1.9988−1.9982)2 +(1.9930−1.9982)2 +(1.9990−1.9982)2
s=√
5−1
= 0.0030g
Below are the calculations utilized to determine the percent chloride in the soluble chloride
unknown.
2
The mass of silver chloride in crucible 1:
17.0466𝑔 − 16.7075𝑔 = 0.3391𝑔
The uncertainty in the mass of the unknown was obtained by the following calculation utilizing
the balance error for the 2.0 gram weight1:
efinal = √e12 + e22 + e23 + ⋯ + e2n
Where e1, e2, and up to en are the uncertainty of measurement 1 to n respectively.
𝑒𝑢𝑛𝑘𝑛𝑜𝑤𝑛 = √(0.0010)2 + (0.0010)2 = 0.0014𝑔
The standard uncertainty for each element was calculated to determine the error in the formula
weight of silver chloride as follows:
Ag: 107.8682 ±
0.0002
√3
Cl: 35.453 ±
0.002
√3
g/mol = 107.8682 ± 0.0001 g/mol
g/mol = 35.453 ± 0.001 g/mol
The formula weight of AgCl and the standard uncertainty were obtained as followed:
Formula weight of AgCl: 107.8682 g/mol + 35.453 g/mol = 143.321 g/mol
Standard uncertainty: 𝑒 = √(0.001)2 + (0.0001)2 = 0.001 g/mol
The reaction stoichiometry was utilized to convert to moles of chloride from the weight of silver
chloride:
mole of Cl:
grams of AgCl
= mole of Cl
molar mass of AgCl
0.3391 𝑔
𝑔 = 0.002366 𝑚𝑜𝑙 𝐶𝑙
143.321
𝑚𝑜𝑙
%e =
absolute uncertainty
× 100%
obtained value
%𝑒 =
0.001414 𝑔
× 100 = 0.4170%
0.3391𝑔
%eAgCl =
0.001g
× 100% = 0.000697734 %
143.321g
3
%𝑒𝑓𝑖𝑛𝑎𝑙 = √(0.4170)2 + (0.000697734 )2 = 0.417058 %
𝑒𝑓𝑖𝑛𝑎𝑙 =
0.417058
100
× 0.002366 𝑚𝑜𝑙 𝐶𝑙 = 9.868 × 10−6 ≈ 0.00001 g
Mass of Chloride in Crucible 1:
𝑔
Mass of Cl: 0.002366 𝑚𝑜𝑙 × 35.453 𝑚𝑜𝑙 = 0.08388 g
%echloride =
0.001g
× 100% = 0.002821%
35.45g
%𝑒𝑓𝑖𝑛𝑎𝑙 = √(0.417058 )2 + (0.002821)2 = 0.4171%
𝑒𝑓𝑖𝑛𝑎𝑙 =
0.4171
× 0.083876 = 0.0003498g
100
Average Mass of Chloride:
0.083876𝑔+0.082169𝑔+0.112123𝑔
3
= 0.092723𝑔
Uncertainty: √(0.0003498)2 + (0.0003498)2 + (0.0003498)2 = 0.0006067g
The percent of chloride in crucible 1:
0.083876𝑔
× 100% = 54. 36%
0.1543𝑔
%𝑒 = √(0.417059 )2 + (1.94426 )2 = 1.98849
𝑒=
1.98849
× 54.3590 = 1.08092
100
Data
Unknown code: 338
Balance used: #3
Trials
Table 1: Uncertainty for #3 Analytical Balance
Observed Weight for 2.0g
Observed Weight for 20.0
Analytical Weight(g)
Analytical Weight(g)
1
2.0008
20.0013
2
1.9993
20.0017
3
1.9988
19.9997
4
1.9930
20.0004
5
1.9990
19.9993
Uncertainty for 2.0 Analytical Weight: ±0.0030g
Uncertainty for 20.0 Analytical Weight: ±0.0010g
Table 2: Raw and Calculated Data
4
Unknown
Mass (g)
Trial 1
0.1543 ±
0.0030
Mass of
Crucible +
AgCl (g)
17.0466
±0.0010
Mass of
Crucible
(g)
16.7075 ±
0.0010
Mass of
AgCl (g)
0.3391 ±
0.0014
Mole of
Cl
(mol)
0.0024 ±
0.00001
Trial 2
0.1510 ±
0.0030
18.6618 ±
0.0010
18.3296 ±
0.0010
0.3322 ±
0.0014
0.0023 ±
0.00001
Trial 3
0.2059 ±
0.0030
18.3729 ±
0.0010
17.9196 ±
0.0010
0.4533 ±
0.0014
0.0032 ±
0.00001
Mass of
Cl (g)
0.0839
±
0.0003
0.0822
±
0.0003
0.1121
±
0.0003
Table 3: Percent of chloride in crucibles with Absolute and
Relative Uncertainties
Crucible
Percent of
Absolute
Relative
chloride
Uncertainty
Uncertainty
(with error) (%) (with error)
(%%)
1
54.36
1.080924
1.988493
2
54.42
1.105668
2.031855
3
54.72
0.819173
1.497002
Average percent of chloride (without error): 54.50±1.749839
Average percent of chloride (with error): 54.4989±1.749841
Discussion
In this experiment, the chloride is extracted from the unknown sample in the solid form of AgCl
using excess AgNO3. A simple reaction of the chloride anion and silver nitrate is as followed1:
Cl− (aq) + AgNO3 (aq) →
NO3− (aq) + AgCl(s)
The chloride anion from the unknown and the silver nitrate react to form solid silver chloride.
The only available source of chloride in this reaction was the unknown soluble chloride,
therefore all of the chloride in the product came from the unknown. The silver chloride has the
Ksp value of 1.77×10-10, and it is insoluble in water and only sparingly soluble in acids2. To
ensure all chloride was reacted an excess of silver nitrate was used. This solid precipitate was
filtered and dried. Nitric acid is used in the reaction mixture as well as to wash the precipitates
formed. Washing with nitric acid ensures that the precipitates will be preserved because washing
with water may dissolve it.
5
Table 2 shows the raw and calculated masses throughout the experiment, including the masses of
pure silver chloride in each of the Gooch crucibles after filtration and drying in the oven. The
mass of the silver chloride in each crucible was obtained by subtracting the mass of the empty
crucible from the mass of crucible with the silver chloride. Since the masses of pure AgCl were
obtained, it was possible to calculate the mass of chloride in each of the Gooch crucible using
stoichiometry; one mole of AgCl is contains one mole of chloride. From this the mass of chloride
in each sample can be found and ratioed to the mass of the starting unknown to find the percent
chloide contained in the unknown sample.
The uncertainty, ±0.0010g, of the analytical balance was taken into account for masses close to
20.0 grams, as shown in Table 1. An uncertainty of ±0.0003g was utilized for the masses in the
range of 1 gram. The uncertainty in the molecular weight of AgCl was obtained by using the
standard uncertainty of the silver and the chlorine from the periodic table. The molar mass of
AgCl with uncertainty is 143.321 ±0.001 g/mol.
All initial masses of unknown have the same absolute error coming from the balance. This error
was propagated throughout the experiment. The moles of chloride in each crucible was
calculated using the molar mass of AgCl. The mole of chloride had taken into the account of
uncertainty in the molar mass of AgCl. The moles of chloride in each crucible is fairly close to
each other, therefore there is little to no variation in the error. The mass of chloride was obtained
by multiplying the moles of chloride in each crucible with the atomic mass of chlorine. Table 2
shows the masses of the chloride in the crucibles and their absolute uncertainty and uncertainty.
The uncertainty in the mass of chloride for crucible one was 0.1121±3.49819×10-4 g. The absolute
error tended to be greater in the crucible with larger mass of chloride. The percent of chloride
was obtained by taking the mass of the chloride in each crucible and dividing by the mass of
soluble chloride unknown.
The percent of chloride in all three crucibles was consistent with each other. The precision in the
results suggest that there was no significant loss of masses. Ideally, the percent of chloride in
three crucibles will have the same value; it is because the same unknown sample was partitioned
into three different trials. Some losses of product during the transfer from beakers to the
crucibles can account for the slight difference in percent of chloride. During the transfer of AgCl
from beaker 1 to crucible 1, there was some AgCl remained on the rubber policeman, and AgCl
stuck at the bottom of the beaker and created white streak. Hence, crucible 1 had a lower value,
54.36%, when compared to the other two. The average percent of chloride without error was
54.50±1.749839 %, and the average percent of chloride with error was 54.50±1.749841%.
Conclusions
The average absolute uncertainties in the percent of chloride was ±1.749841%. The average
percent of chloride in three crucibles was 54.50%. Therefore, it is reasonable to conclude that the
percent of chloride of the unknown sample #338 is in the approximated range of 53% and 56%.
There was a slight difference in the percent of chloride among the crucibles. However, the
difference was not deemed to be significant. Therefore, the AgCl in three beakers was transferred
to the Gooch crucibles without any significant loss. The presence of the uncertainty in the atomic
mass of the element did not create a significate difference in the uncertainty. Therefore, for most
calculations, the uncertainty in the atomic mass can be ignored.
6
References
1
Harris, D. Quantitative Chemical Analysis, W.H Freeman, New York, 8th Ed, pp, 21, 57, 58,
Front cover.
2
Haynes, William M., et al. “Fluid Properties.” CRC Handbook of Chemistry and Physics, CRC
Press, 2016, pp. 5-184, 5-178
7
Experiment – 02
Gravimetric Analysis, or Analysis by Weight and the use of the Propagation of Uncertainty (Error)
as the measure of the uncertainty.
This is the experiment that you will have to utilize the propagation of uncertainty presented in
Chapter 4. Review this and calculate the uncertainty in this manner for THIS LAB ONLY. All the
other labs can use standard deviation for uncertainty.
This deceptively easy experiment is one of the oldest techniques of analytical chemistry. It is simple, very
accurate and requires only a good analytical balance plus common laboratory glassware, if you are careful
with your laboratory technique. However, you must be extremely careful while working with the analysis as
there are many sources of error. One of the great disadvantages of this method is the relatively long time
required compared to most other quantitative methods. The method consists basically of the four steps:
 Precipitation of the species of interest
Remember that this lab
 Filtration to remove the liquid (impurities must be eliminated)
manual is NOT peer
 Drying of the sample
reviewed, so don’t quote it
 Weighing of the sample
 Determination of the % Cl in your sample.
In this case, the % Cl- will be determined by the precipitation of
available chloride ion in the unknown sample by Ag+ to produce
Why is AgCl solid? Ksp???
AgCl by the addition of a slight excess of AgNO 3 (aq) solution.
The resulting precipitate is collected on fiber glass filter mats.
Calculations are done through the use of stoichiometry. A known will not be done for this laboratory
meaning that you can’t get a measure of the BIAS of your error. (What is Bias?)
Remember, errors will accumulate if you lose weight, or gain weight. What could cause each event?
Remember that you will have to understand and report on what happened if one of your samples is too
heavy or too light! What is the most logical explanation. Note: If you keep extensive notes and
observations – such as “I couldn’t get some of the precipitant from sample 2 out of the beaker”, or “I spilled
some of sample 1 on the table and may not have retrieved it all!” These notes will help you write your report.
Procedure:
Period 1. (Be sure to write your own step-by-step procedure without all the explanations)
1. Obtain an unknown sample in a small labeled vial that has been dry to constant weight at ~110o C
What is constant weight? Why do we
dry it to constant weight?
2. Prepare 3 filter crucibles by placing fiber glass mats
in each and using suction filtration draw the mats
firmly down on the crucible bottom by passing 10-20
mL of water through the mats. (Question: are there
with your lab classmates to as little
dissolved solids in tap water? Should you use
space as possible…(stacking them in
Deionized (DI) water?) Place the crucibles in the
large labeled beakers is a good option)
110oC drying oven until the next laboratory period.
there are other labs and other students)
3. Prepare 100 mL of approximately 0.15 M AgNO3
solution. (exact concentration of this solution is not critical. Why? Think stoichiometry.)
4. Accurately weigh 3 portions of your unknown to be in the range of 0.15 to 0.20 g into 250 mL
beakers (well labeled) from which you will determine the weight by difference. Determine the
weight of the unknown accurately (as above).
5. Dissolve the 3 unknown ”runs” in 50 mL water
(tap?? Or DI?? Does exact volume matter? Think!)
by 25 mL of 0.15 M silver nitrate solution.
1
6. Mix the three solutions thoroughly, careful to maintain the integrity of the samples. A precipitate
forms (do you know what it is?). Avoid transferring precipitate from one beaker to another on the
stirring rod, and cover with Parafilm and store in your cabinet until the next lab period.
Period 2
1. Accurately weigh the empty three
(Q: What happens if you don’t get all the precipitate, and how
thoroughly dried cooled filter crucibles.
would this affect your results (bias?)? What is a “rubber
2. Filter the three precipitate samples using
policeman?” Could some of your ppt dissolve? How? What
filtration, wash the precipitate with about 10
if your precipitate is not dry? What could cause the precipitate
mL of ~0.01 M nitric acid (This is a 10 fold
to turn color? An impurity? Why wash with nitric acid? How
dilution for last week), then dry the
do you know if you have dried the ppt to constant weight?
precipitates at 110o C to constant weight,
THINK!) These are potential things that could go wrong with
which can take around 60 min. (Coffee
your results, and that you need to discuss in the discussion
Break!)
section.
3. Accurately determine the weights of the
precipitates. (THINK!) (What are these
precipitates?) WHAT DOES DRYING TO A CONSTANT WEIGHT MEAN?? HOW DO YOU DO
IT?
Calculate the %Cl- of the three unknowns to the maximum number of significant figures possible.
Determine the errors and the relative standard deviation in parts per thousand (ppt) (check your text!). Your
work should be under 2 ppt!
REMEMBER, FOR THIS LAB ONLY, YOU WILL CALCULATE THE UNCERTAINTY USING THE
PROPAGATION OF UNCERTAINTY. FOR ALL THE OTHER LABS, USE STANDARD DEVIATION.
2
Gravimetric Determination of Chloride
Han Doan
Date of Experiment : 02/03/2021
Date of Submission : 03/12/2021
Submitted to Dr. Skiles
Gravimetric Determination of Chloride
Calculations and Results
Standard brass weights were used to calibrate the analytical balcance. These results were further utilized in the propagation a mass
error
N is the number of trial and x, or average is:
x=
xi 2.0002 g + 1.9999 g + 2.0001 g + 2.0004 g + 2.0002 g
=
= 2.0002 g
n
5
Standard deviation of balance number 4:
S=
S=
(xi−x)2
n−1
(2.0002−2.0002)2+(1.9999−2.0002)2+(2.0001−2.0002)2+(2.0004−2.0002)2+(2.0002−2.0002)2
5−1
= 0.0002g g
Below are the calculations utilized to determine the percent chloride in the soluble chloride unknown.
The mass of silver chloride in crucible 1:
Cfinal − Cempty = 17.2979g − 16.8767g = 0.4212 g
The uncertainty in the mass of the unknown was obtained by the following calculation utilizing the balance error for the 2.0 gram
weight:
efinal = e21 + e22 + e23 + . . . + e2n
Where e1 ,e2, and up to en are the uncertainty of measurement 1 to n respectively
eunknown =
(0.00026)2 + (0.00026)2 = 0.00037 g
The standard uncertainty for each element was calculated to determine the error in the formula weight of silver
chloride as follows:
Ag: 107.8682 ±
0.0002
3
g/mol = 107.8682 ± 0.0001 g/mol
Cl: 35.453 ±
0.002
3
g/mol = 35.453 ± 0.001 g/mol
The formula weight of AgCl and the standard uncertainty were obtained as followed:
Formula weight of AgCl: 107.8682 g/mol + 35.453 g/mol = 143.321
Standard uncertainty: e = (0.0001)2 + (0.001)2 = 0.001 g/mol
The reaction stoichiometry was utilized to convert to moles of chloride from the weight of silver chloride:
Mole of Cl:
grams of AgCl
= mole of Cl
molar mass of AgCl
0.4212g
= 0.002939 mol Cl
143.321 g/mol
%e =
absolute uncertainty
× 100
obtained value
0.00037
× 100 = 0.088%
04212
0.001g
%e of AgCl =
× 100 = 0.00007%
143.321g
%e =
%efinal = (0.088)2 + (0.00007)2 = 0.088%
efinal =
0.088
× 0.002939 mol Cl = 2.6 × 10−6 g = 0.00003g
100
Mass of Chloride in Crucible 1:
Mass of Cl: 0.002939 mol Cl × 35.453g/mol = 0.1042g
%eChloride =
0.001g
× 100 = 0.003%
35.453
%efinal = (0.003)2 + (0.088)2 = 0.0876%
0.0876
× 0.1042 g Cl = 0.00009
100
0.1042g + 0.1260g + 0.1163g
Average mass of Chloride =
= 0.1155g
3
efinal =
Uncertainty: (0.000047)2 + (0.000047)2 + (0.000047)2 = 0.000081g
The percent of Chloride in crucible 1:
0.1042
× 100 = 66.75%
0.1561
%e = (0.087)2 + 0.1163)2 = 0.146%
e=
0.146
× 66.75 = 0.0974
100
Unknown: #351
Balance used #4
Table 1: Uncertainty for #4 Analytical Balance
Trials
Obs. Weight for 2.0g (g) Analytical
Obs. Weights for 20.0 Analytical
Weight (g)
Weight (g)
1
2.0002
20.0003
2
1.9999
20.0006
3
2.0001
20.0001
4
2.0004
20.0003
5
2.0002
19.9999
Uncertainty for Analytical Weight
±0.0002 g
±0.0003 g
Table 2 : Raw and Calculated Data
Trial 1
Trial 2
Trial 3
Unknown mass
Mass of crucible +
Mass of Crucible
Mass of AgCl
(g)
AgCl (g)
(g)
(g)
0.1561±0.0002
17.2979±0.0003
16.8767±0.0003
0.4212±0.0004
0.1753±0.0002
0.1535±0.0002
17.6771±0.0003
17.7658±0.0003
17.1678±0.0003
17.2956±0.0003
0.5093±0.0004
0.4702±0.0004
Mole of Cl(mol)
Mass of
Cl(g)
0.0029
0.1042
±0.00003
±0.0001
0.0046
0.1260
±0.00003
±0.0001
0.0012
0.1163
±0.00003
±0.0001
Table 3 : Percent of chloride in crucibles with Absolute and Relative Uncertainty
Crucibles
Percent of Chloride
Absolute Uncertainty (with
Relative Uncertainty (with
error )(%)
error) (%)
1
66.75
0.09742
0.1462
2
71.87
0.09081
0.1260
3
75.77
0.01083
0.1422
Average percent of chloride
71.46
0.09864
0.1383
with error

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