UMaine General Chemistry Laboratory Course Guide Fall 2013, Version 3.0 Includes info about Grading, Lab Reports, InterChemNet V3.0 Fall 2013
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Prepared for General Chemistry Students & Instructors
For students, this guide explains how to get started, how to use InterChemNet, the components involved in your grade, how lab reports are assessed, and instructions for writing lab reports. For instructors, this guide will be use as a reference for the standards across the general chemistry lab program.
Dr. Mitchell Bruce, General Chemistry Coordinator Fall 2013, Version 3.0
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Table of Contents Section 1: Getting started . . . . . . . . . . . . . . . 4 Section 2: Grading . . . . . . . . . . . . . . . . . . . . 12 Section 3: Laboratory reports . . . . . . . . . . . 16 Section 4: Laboratory report examples . . . . 21
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Section 1: Getting Started
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Required Course Materials 1. Chemistry: InterChemNet (ICN) Access Packet (includes: a laboratory notebook, ICN Access Code, and safety information) The ICN packet is purchased in the University Bookstore The ICN packet will be discussed during the safety and orientation session during the first week of classes. You will need to set up your account in order to accept (download) and submit (upload) a safety quiz. 2. InterChemNet Account To set up your account go to: http://icn2.umeche.maine.edu/newnav/NewNavigator/LoginForm.cfm The ICN access packet contains a code for setting up your account. After setting up your account, you will have access to lab procedures and your grades will be posted by your instructor. You must set up an account before performing the first lab experiment (during week two of the classes). This will allow you to obtain your pre-lab assignment for your first lab experiment.
-‐Purchase ICN Packet -‐Accept and submit safety quiz Attend safety & -‐Accept and -‐Hand in pre-‐lab orientation session complete pre-‐lab assignment -‐Conduct first lab Time line: -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐à -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐à First Week of Classes Second Week of Classes (first lab session) (second lab session)
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InterChemNet (ICN) Student Instructions Important highlights for Fall 2013: • The safety quiz is obtained online (downloaded) from your ICN progress page. After completing it, you upload it for grading by your lab instructor. • Lab assignments (lab experiments) are obtained online. • Lab reports are submitted for grading online (uploaded) either as Word or pdf files. • Lab report grades will be posted into your account and will include instructor feedback. The methods for grading the course are described in this guide: The UMaine General Chemistry Laboratory Course Guide, Fall 2013, V3.0. • Lab reports that are eligible for re-grading (available for the first few labs) are also submitted online. A. Logging into your progress page 1. Once your account is established, you log into ICN (http://interchemnet.com) by entering your username and password. 2. Upon logging in, you land on your progress page. At the top of the page is course and instructor information. 3. The lab sessions for your course are listed below in chronological order. Each session is named and will include information about the date, e.g. “First Week: safety quiz” or “Second Week: Dissolved Oxygen”. 4. From your progress page, you will accept assignments (download), answer pre- or post- questions (answering online), submit assignments (upload), look up course lab grades, and obtain instructor feedback for your submitted work.
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B. Assignment Basics 1. Your assignment may be different than someone else in your class. Therefore it’s important to always obtain your assignment through your ICN account. 2. In your ICN progress page, you can accept an assignment by clicking on the “Accept” hyperlink. The screen shot above shows an “Accept” hyperlink in the right most column of the assignment Lab Week 01. 3. When an assignment is accepted, you will gain access to the assignment and it will change the status from “Accept” to “Submit”. 4. The “Submit” status indicates that you have access to your assignment and that you will be able to perform the lab activity in the coming week(s). 5. The “Submit” status also will be used to electronically hand in the results of an assignment, as explained below. C. Laboratory Data 1. The data and observations in lab should reflect your work and participation. This information should be recorded in your lab notebook, on a page that has a date and your name on it. 2. If you work jointly with another student, you should record the name of your lab partner in your lab notebook. You can also establish that you participated in collecting data by making observations in your lab notebook. You need not copy all of the data collected by your lab partner and recorded in their notebook. You can reference this information in your lab partner’s notebook, including the page where the information can be found. 3. Data taken from other students can be used only if it is clearly marked as such, especially if it is used in lab reports. The reason for using another person’s data should also be clearly explained. For example, if you collected data from another student to compare to your own data, you can do this if you identify the student(s) and clearly mark it as someone else’s data. D. Electronic Submission of Assignments 1. Once an assignment is accepted, you will have time to work on it. This may take one or more weeks. During this time, the status in your ICN account will remain “Submit”. 2. The “Submit” status indicates that you will be able to submit the assignment when it is ready. 3. Normally, your assignment will be due after you complete it and before the next lab
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session. For example, when you attend a safety and orientation session during the first week, your quiz will be due before the start of your lab session in week two. 4. The due date for lab reports is similar. For example, in week 2, you will conduct an experiment called “Making Chemical Observations”. The lab work will be completed in your lab session in week 2, and the assignment will be due before your next lab session in week 3. 5. You will be asked to submit assignments like the safety quiz and (most) lab reports through your ICN account. E. Electronic Submission of the Safety Quiz Assignment 1. When the safety quiz is downloaded, it will be as a fillable pdf file. 2. You may need to download a program that reads pdf files such as Adobe Reader for Mac or PC (available at http://www.adobe.com/products/reader.html) 3. Off line, you will complete the quiz, making sure that the version you save contains your answers. 4. When you are ready to submit the safety quiz, you can click on “Submit”. This will take you to a new page, called “Submit Lab Assignment” (or Submit Lab Report”). 5. From this page, you will be able to choose a file on your computer to upload it. 6. There is also a place for you to write information to your lab instructor that may be helpful for grading your assignment. 7. Your file will be sent to a directory that your lab instructor has access to. He or she will be able to download your assignment, grade it, and post the results on your ICN account. 8. Once submitted, your assignment will get a date and time stamp. This will be used in grading your assignment. Late work may receive deductions, or after a certain date, may not be accepted at all.
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F. Lab Procedures and Pre-lab assignment. 1. Lab procedures for each experiment need to be downloaded. You have permission to print the lab procedures and bring a paper copy to lab. (Make sure the procedures come from your account. Different sections may use uniquely modified versions of the same procedure) 2. A pre-lab assignment, consisting of summarizing the lab, making a safety table of chemicals involved, and answering questions must be completed in your laboratory notebook (see experiment procedure for specifics). Pre-lab assignments are required for every lab. You will not be permitted to do the lab experiment if this is not completed prior to class for safety reasons. These are handed in at the beginning of lab directly to your lab instructor. G. Electronic Submission of the Lab Report Assignments 1. Lab reports will be submitted in a similar way, expect that you will create a Word or pdf file that contains your lab report. This will then be uploaded to your lab instructor. 2. You will need to submit some work that is scanned and incorporated into your lab report. There are worksheets that need to be submitted electronically. You may also want to annotate your lab reports with drawings. Some scanners are available on campus (e.g. Fogler Library) and the general chemistry program will also have several set up. Your lab instructor will tell you more about where these are located. H. Pre- or Post- Pop Up Questions When You are Obtaining or Submitting Assignments 1. Occasionally, there will be times when an online question(s) will appear. 2. A question may ask you about a concept that will be investigated in lab OR was just investigated in lab. Or it may ask you your opinion about an activity. 3. Your lab instructor will never see your responses and so your grade will never be affected. 4. However, this data is very important to us, in order to have information to improve the course. So, please answer these questions seriously. We’d like you to answer without asking anyone else or looking up information. 5. All student answers will be “aggregated”, which means we will look at trends in data, among groups, not individuals. This is one way we make improvements to the lab program over time and we thank you in advance for helping.
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I. The Accept, Submit, Grading, and View Feedback Cycle 1. After you submit an assignment, the assignment will change status again from Submit to Grading. This is your way of knowing that your assignment has been sent to your lab instructor. 2. Lab instructors will look at the assignments you submitted to make sure that there are not issues with reading the files. It is very important that you save every assignment throughout the semester in case it needs to be re-transmitted to your lab instructor. 3. You will notice that the next assignment (Second Week, Dissolved Oxygen) is also now available to “Accept”. 4. The Accept, Submit, and Grading cycle will be used for assignments. As you complete assignments, new assignments will appear. 5. The actual sequence, names, and nature of your assignments varies, so again it is important to obtain your assignment from your own account as well as submit your own work. 6. When your assignment is graded, your will be able to view feedback, by clicking on the “View Feedback” link as shown here. 7. The feedback page will contain your grade for the assignment as well as comments. An example is shown here. 8. You will be able to access these pages throughout the semester. The default mode is to hide this information. J. Resubmit Option 1. For the first few assignments, lab reports may be resubmitted to improve your grade. If this option is available, the “Resubmit” button will appear.
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K. Getting Help 1. If you experience problems related to the submission of lab assignments, please contact your lab instructor and Bob Kirk (
[email protected]) as soon as possible. 2. Places to get help: Your laboratory instructor: On the first day, make sure to find out your instructor’s name, how to contact them, where their office is, and times they are available to provide extra help. The FAQ (frequently asked questions) page: Found on the general chemistry website: http://umaine.edu/general-chemistry/faq/ Robert (Bob) Kirk: General Chemistry Laboratory Manager Office: 229 Aubert Hall E-mail:
[email protected] Dr. Mitchell Bruce: General Chemistry Laboratory Coordinator E-mail:
[email protected]
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Section 2: Grading
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Laboratory course grade The laboratory course receives a letter grade that is independent from your grade in the lecture course. Lab grades are earned for each experiment considering these factors: 75%: Laboratory report (see Section 3 on Laboratory Reports). Lab reports are graded on a 0-75 pt scale and will be posted on your InterChemNet page. 10%: Pre-lab assignment and pre-lab discussion Pre-lab assignments are checked (pass/fail) before lab starts 5%: Safe behavior in lab 5%: Lab work, including taking notes 5%: Post-lab discussion The remaining points (safety, lab work, and post-lab) are presumed, and a lab instructor will inform students only if they do not earn full credit. Deducted points are communicated by the time lab reports are returned. Typically students lose points when they do not attend pre- or post-lab discussions, do something unsafe in lab, or do not use their lab notebooks properly.
Pre-lab assignment and discussion (10%) Pre-lab assignments are found within the procedure for each week’s laboratory experiment. You will be asked to write a summary of the lab experiment’s goals and procedures, a safety table describing the hazards and safety precautions for each chemical required in the experiment, and sometimes, additional questions or calculations to prepare you for the lab. Pre-lab assignments MUST be completed prior to coming to lab and written in your laboratory notebook. If you do not have your pre-lab complete at the start of lab, you will be asked to leave. The pre-lab is worth 5%. During pre-lab discussions, your instructor will provide relevant background information. The instructor will ask the class questions. Pre-lab discussions are an opportunity for you, your classmates and the instructor to clarify sections of the procedure or concepts that are difficult. Participation is required. If you arrive late to lab, you will receive a no credit for the pre-lab discussion. Your participation in the pre-lab discussion is worth 5%.
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Safe behavior in lab (5%) You are required to attend a safety presentation at the very first lab meeting and pass a safety quiz in order to continue in the lab course. No work can take place in lab without understanding how to conduct the experiments safely. Carefully reading procedures prior to coming to class is vital to operating safely in the lab. Safety is everyone’s concern. If you ever see anything unsafe going on in lab please report it to your lab instructor. If you are unsure if you are doing something safely, please consult your lab instructor before you proceed. Your pre-lab assignment includes safety information. If you haven’t completed the safety section, you will not be allowed to start lab. Safe behavior is presumed and 5% is earned for each lab. If a student exhibits unsafe behavior, the lab instructor has the responsibility to ask students to correct the behavior and even to leave lab if the behavior persists. If you are asked to leave lab for safety reasons, the incident will need to be reviewed by the general chemistry coordinator and laboratory manager before you are permitted to re-enter.
Lab work including taking notes (5%) Successful lab work takes active planning and thinking. There is often room for creative and critical thinking in lab work. Lab procedures are sometimes designed to be incomplete. You may be asked to design an experiment to test a hypothesis. Designing experiments can be done in a number of valid ways. You should use the lab notebook to describe how you approach tasks, answer questions posed in the lab procedure, make observations, and to record important information like the mass of a chemical. Keeping thorough and detailed notes will help you remember what you did and what your calculations mean in your notebooks several days later when you are trying to write your lab report. Good notes are critical to producing good reports later. Lab instructors assign 5% of your grade from lab work. To earn the complete 5%, make sure you remain focused and are working productively for the duration of the lab period. Ensure that your notes are detailed enough so that your lab instructor (and you!) will understand them.
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Post-Lab discussion (5%) The post-lab discussion is an opportunity to get together with other lab groups and your instructor to make sense of the information gathered in lab (What happened? What does it mean?). Sometimes mistakes in lab will make drawing conclusions difficult. There is no requirement to get a certain outcome in your lab work, however, it’s important to figure out what kinds of conclusions and arguments you can make from different types of results. Timing of the post-lab discussion varies because not every group finishes lab at the same time. Your lab instructor will appreciate your help in forming groups of 4-8 students to discuss and compare results. Students can have this discussion without the lab instructor but everyone must check in with the instructor before leaving lab and have their lab notebooks signed. Write a short paragraph summarizing the post-lab discussion in your lab notebook, under the heading “post-lab discussion.” Recording the post-lab discussion will help you later when you are writing your report. If your lab instructor notices that you do not participate in the lab discussion and that you do not write the summary you will not receive credit for the post-lab discussion.
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Section 3: Laboratory Reports
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Building a scientific argument How your laboratory report will be evaluated Well designed experiments generate data that is analyzed to construct conclusions that answer scientific questions. Scientific arguments revolve around claims or assertions that have been developed as the overarching conclusions of an experiment. Claims are the answer to a scientific question. A claim is NOT a hypothesis. To support a claim, a report must present a sufficient amount of evidence that suggests the claim is valid. Finally, a scientific argument must include reasoning, or a persuasive explanation of how and why the evidence presented supports the claim. Your lab report will be evaluated on the strength of the scientific arguments you construct. Your lab instructor will analyze the evidence, reasoning, and claims you present to judge the strength of your argument. They will use a rubric (on the following page) to assess your work based on these factors.
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Laboratory report rubric Your lab instructor will evaluate your report and the scientific arguments presented according a rubric, which is a conceptual framework to identify required components in a report. For each component, the rubric describes the type of work that would fall into level 0 (poor), 1 (average), and 2 (excellent) work. Many of the lab experiments will have a specific rubric that will be used for a particular experiment. Below is a generic rubric, which will be used whenever a specific rubric is not provided. (The rubric inspired by the work of Dr. Joseph Krajcik) Lab Report Rubric Required Components Claim(s): Is a statement(s), derived from evidence, using scientific reasoning. (15 pts total) Evidence: Scientific data that supports the claim. The data needs to be appropriate and sufficient to support the claim. (30 pts total)
Reasoning: Scientific arguments that use evidence and appropriate scientific principles to make claims. (30 pts total)
Level 0
Level of attainment Level 1
Level 2
Does not make a claim, or makes an inaccurate claim. (05 pts)
Makes an accurate but incomplete claim. (6-10 pts)
Makes an accurate and complete claim. (11-15 pts)
Does not provide evidence, or only provides inappropriate evidence (Evidence that does not support claim). (0-10 pts)
Provides appropriate, but insufficient evidence to support claim. May include some inappropriate evidence. Evidence from other published sources may be mentioned. (11-20 pts)
Provides appropriate and sufficient evidence to support claim. Communicates and describes evidence from other published sources that adds significance to gathered evidence. (21-30 pts)
Does not provide reasoning, or only provides reasoning that does not link evidence to claim. (010 pts)
Provides reasoning that links the claim and evidence. Repeats the evidence and/or includes some scientific principles, but is not sufficient because it does not clearly explain underlying chemical concepts. May mention outside sources or studies.(11-20 pts)
Provides reasoning that links evidence to claim. Includes appropriate and sufficient scientific principles to explain underlying chemical concepts. Appropriately identifies and discusses outside sources or studies. (21-30 pts)
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Laboratory report sections Essential information to include at the beginning of the report: (1) title of the report, (2) your name, (3) lab partner(s) name, (4) your lab section, (5) your lab instructor’s name, and (6) the date you collected data and/or worked in lab Summary of claims: Provide a few sentences that state the major conclusion(s) of the experiment. These are your claims. You might wish to write this last. Introduction: Provide one to two paragraphs that briefly explain the purpose of the experiment (what you were trying to find out and how you went about it) and background information relevant to the experiment. Procedure: Explain how the experiment was performed. In cases where the procedure was followed exactly as specified in an InterChemNet Procedure, the InterChemNet procedure may be referenced with any modifications explained. If you designed your own experiment for a part of a lab, you will need to carefully explain the procedure you devised. The procedure is part of your evidence. Results: In the results section, present the information that you collected in lab that supports the claim you are making. This is your evidence. You may need to present quantitative data (for example: values that you measured such as masses or volumes) or qualitative data (for example: observations such as a striking color change in a solution or the sudden appearance of bubbles during a chemical reaction) Use graphs to demonstrate important relationships and trends (for example: how temperature changes over time in a chemical reaction) Use tables to present information that is repetitive and belongs in groups (for example: you present five different trials where you recorded an initial temperature, a final temperature, and the time elapsed) If you performed calculations, ALWAYS show how you calculated the values, including units. You will not receive full credit without showing your work. The key to a good results section is clarity and organization. Make sure everything you present is clearly labeled, includes units, and could be understood by someone who didn’t perform the lab. Tables and graphs should always have specific titles.
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Discussion: The discussion should provide reasoning, or a substantial explanation of why and how your evidence (from your results section) supports your claim(s). There are two parts to how your results support your claim: Why? What underlying chemistry explains your evidence? Part of your discussion should explain the underlying chemical concepts and techniques that are necessary to understand what your results mean and why they might have occurred. Your explanation should draw on information you have gathered from laboratory procedures, outside sources (textbooks, reliable internet sites), and/or from talking to your laboratory instructor. How? In what ways does your evidence support your claim? Explaining how your results support your claim involves reviewing the evidence and explaining the thinking and decisions you made about this evidence that led you to your claim. Provide a logical argument. Make sure you discuss specific evidence. Refer back to actual values from tables, figures, and calculations that you provided in your results. Also, it’s important to establish how you ruled out alternative explanations.
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Section 4: Laboratory Report Examples
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Claims and introductions Linus Pauling Lab partner: Robert Oppenheimer Section: 0042 T.A. Mary Lyon Experiment Date: September 15, 2013 September 22, 2013 Using paper chromatography to identify cobalt and iron ions in an unknown solution Summary of claims: We recorded the Rf values and colors of iron, cobalt, copper, and nickel ions through paper chromatography. Using this information as a basis for comparison, we determined that our unknown solution consisted of cobalt and iron ions. Introduction: Paper chromatography is a technique for identifying unknown components of mixtures. It uses two phases: a mobile phase consisting of a hydrochloric acid and acetone solvent and a stationary phase, consisting of chromatography paper. Different types of metal ions demonstrate different levels of attraction to each of these phases. As a result, they have different measurable retention factors (Rf values). The Rf value is a ratio of the distance the metal ion travels to the distance the solvent travels on the chromatography paper. Our goal was to use paper chromatography to identify the components of the unknown solution that we were assigned. This introduction provides some background about the chemistry involved in the experiment, the goal of the experiment, and briefly describes how the experiment was carried out. The claim (the identity of the unknown metal ion) is clearly stated. The report has a comprehensive title, specific to the experiment and the necessary information to identify the student at the top. Procedures Exhibit A. Procedure presented as a set of steps 1. Add first chemical to beaker 2. Stir in the indicator solution 3. Allow beaker to sit for five minutes 4. Slowly add acid drop by drop until solution turns green This procedure is vague. It would not be possible to perform the experiment. Also, do not write procedures as directions for someone else to follow. A good procedure is a specific description of what YOU did in laboratory. This procedure would not receive full credit.
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Exhibit B. A better procedure First, we added 15 mL of an unknown concentration of sodium carbonate solution to a beaker using a graduated cylinder. Then, we added three drops of bromocreosol green indicator to the sodium carbonate solution. The indicator turned the solution blue at first. Next, we added 0.102 M hydrochloric acid drop by drop with a buret until the solution turned green. This procedure contains specific enough information (e.g. concentrations, amounts) for someone to actually repeat the experiment. It is written in the past tense, reflecting that it is a summary of work that already took place.
Graphs 18" 16" 14" 12" 10" 8"
Series1"
6" 4"
The graph here is worthless because it lacks labels on the axes and a title. Graphs are considered to be figures in a report and should also have a figure caption below the figure. Also, it is unnecessary to label the series when there is only one shown. This graph would lose a substantial number of points.
2" 0" 0"
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Temperature)(degrees)Celsius))
Reac4on)temperature)over)4me) 25" 20" 15" 10" 5" 0" 0"
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Time)(s))
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This graph is better because the x and y axis are labeled, units for each are given, and the chart has a specific title. We can easily see the trend it establishes: as the reaction proceeds, the temperature increases linearly. Note the Figure 1 caption which describes the information contained in the figure. The figure should be understandable without reference to the text.
Figure 1. The temperature of the reaction sodium hydroxide and hydrochloric acid increases linearly over time. Graphs can be created using Excel or other graphing software. Graphs may also be hand-drawn carefully with graph paper. To receive full-credit on hand-drawn graphs, make sure that the scales for each axis are consistent and use a ruler.
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Tables Exhibit A. An unclear table Part one results 25 mL 24. 2 mL 25.6 mL
0.2 0.19 0.3
This table needs headings for each column and a specific title. It also is inconsistent with the number of significant figures used.
Exhibit B. A clearer table Table 1. Volumes of HCl used to titrate 0.1 gram samples of calcium carbonate and calculated concentration of HCl
Trial 1 2 3
Volume of HCl (mL) 25.0 24.2 25.6
Calculated HCl Concentration (M) 0.201 0.190 0.300
Here we can tell there were three trials performed. The headings clearly indicate what information is in each column. Note that the units appear in the headings of the table and not in every field. The title clearly summarizes the information presented. Also, notice that the number of significant figures is constant throughout the table.
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Example discussions Exhibit A. A discussion that does not provide sufficient reasoning When we mixed different amounts of polyvinyl alcohol and sodium borate we can tell that the more polyvinyl alcohol you add, the thinner and runnier the slime gets. The thinnest slime we observed was with the ratio of 1:10 (sodium borate: polyvinyl alcohol). This slime also had left over liquid surrounding it. We believe this liquid was polyvinyl alcohol based on its clear color. The 1:8 ratio was slightly more viscose. The thickest slime we made had a ratio of 1:4 (sb:pva). However, we also noticed that if the amount of sodium borate we added was exactly equal to the amount of polyvinyl alcohol we added, the slime was also very thin and runny. More testing would be necessary to better illustrate the effects of proportions. Either way, we can conclude that the proportions that the reactants are mixed in does effect the final consistency of the product, “slime.” This discussion doesn’t tell us anything about the underlying chemical concepts that would help us better understand why the proportions of the reactants might matter. This person could improve their discussion by providing an explanation of what they think is happening on the molecular level and providing some background information about how the two chemicals react. For example, these results seem to suggest that sodium borate can only crosslink a certain amount of polyvinyl alcohol at once because sometimes extra polyvinyl alcohol is left over that doesn’t react. One explanation for this would be that there are only so many sites on the polyvinyl alcohol molecules for cross linkages to occur. This could be confirmed by doing some research online, reviewing information in the procedure, or talking to a TA. This discussion would not receive full credit. ---> SCORE: Level 1 (see rubric): “Provides reasoning that links the claim and evidence. Repeats the evidence and/or includes some scientific principles, but is not sufficient. May identify and/or mention outside sources or studies.(11-20 pts)” Exhibit B. A discussion that provides sufficient reasoning Paper chromatography allowed us to determine the identity of our unknown solution by making comparative observations and measurements with the chromatography strips we produced. In paper chromatography, ions are placed on a strip of paper, called the stationary phase. A solvent, called the mobile phase, travels up the paper through capillary action. Different ions in a solution have different affinities, or attractions to the mobile phase or the stationary phase because of their chemical properties. Because of these different affinities, ions that are placed on the paper and exposed to the solvent will demonstrate different, characteristic retention factor (Rf) values. Rf values are a ratio between the distance the leading edge of the spot travels up the paper to the distance solvent travels up the paper. Additionally, we used
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ammonia vapors and DMG to further develop the spots. These chemicals form different kinds of complexes with different metal ions. Each of these different kinds of complexes has a distinct, vibrant color. After running ionic solutions with identities we know, we are able to use the retention factors and the colors to compare with values and colors on chromatography strips with unknown ionic components. We determined our unknown sample consisted of cobalt and iron ions by comparing the unknown sample’s chromatography strip with chromatography strips we produced with known ions. Our unknown sample separated into two unique spots with Rf values of 0.32 and 1.00 (see Table 2). Immediately, we knew that we could rule out the presence of nickel ions in our unknown because we did not observe any bright pink spots which we determined were characteristic of nickel ions (see Figure 1). The first unknown spot’s Rf value of 0.32 is similar to the Rf value we found for copper ions (0.42) and cobalt ions (0.38). However, the Rf value of the unknown seems to match closest with that of cobalt ions. Additionally, by comparing the color of the known spots of copper ions and cobalt ions to our first unknown spot, we found a greenish color is present in the copper ion spots that is not present in our unknown. Therefore, we concluded that the unknown sample most likely includes cobalt ions. The second spot’s identity was easier to determine because the Rf value matches exactly with the Rf value we measured for the iron ions we tested. The second unknown’s spot was also a dark yellow-brown color which matches closest to the color of the iron ion’s spot color. Therefore, we determined that the two spots we observed in the unknown sample’s chromatography strip indicated the presences of cobalt ions and iron ions in the unknown solution. This discussion explains the chemistry behind the experiment that someone would need to know to understand what the results mean (in the first paragraph). Next, it explains how the author used the evidence gathered to identify the unknown ions (in the second paragraph). Specific results are referenced and explained. This discussion would receive full credit.
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Evidence, reasoning, and claims in a scientific paper The claim is made right in the title. The intro gives back ground info to explain why the study was important
Ravishankara et al. Science, 326, 123-125, 2009. Cited over 385 times in other papers since publication (source: Web of Science, Accessed 8/29/2013). The full article can be downloaded from Fogler library.
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Evidence, reasoning, and claims in a scientific paper (cont.) The evidence is presented in a figure and explained and analyzed in the text.
The reasoning that leads to the author’s conclusion is clearly presented. Ravishankara et al. Science, 326, 123-125, 2009. Cited over 385 times in other papers since publication (source: Web of Science, Accessed 8/29/2013). The full article can be downloaded from Fogler library.
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Evidence, reasoning, and claims in a scientific paper (cont.)
Evidence from other studies is used in graphic form to put this study into a scientific context.
Ravishankara et al. Science, 326, 123-125, 2009. Cited over 385 times in other papers since publication (source: Web of Science, Accessed 8/29/2013). The full article can be downloaded from Fogler library.
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