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 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 report those results which answer the questions you were asking 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 the results of your experiments. 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. 11. Critically analyze your Discussion and your reasoning to avoid making contradictory or nonsensical 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 someone else read your report can be very helpful. Similarly, misspelled words and poor grammar give the impression of sloppiness or that you did not proofread your work. These impressions will probably reduce your score. 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 answer the purpose of 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 Conclusions/ Broader 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 with your results and 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 contradicts your results. IE: Spilled sample leads 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. Some conclusion about the results and experiment preformed. Results not reported. Thoughtful conclusions given about the results given. Attempt to relate to the broader 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. Be brief. Wordiness obscures your message and annoys your readers. 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 in your report.  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 (Consolidate your well labeled crucibles 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 and add about 10 mL of ~0.1M HNO3 followed (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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