A lesson designed to guide you through the process of composing a suitable lab report

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A lesson designed to guide you through the process of composing a suitable lab report. Report Writing Guide. Overview. - PowerPoint PPT Presentation

Transcript of A lesson designed to guide you through the process of composing a suitable lab report

Week 2*
A lesson designed to guide you through the process of composing a suitable lab report
Report Writing Guide
GenChem
Overview
This lesson will review the process you need to use to compose a proper report. Each section of the report is covered separately. The experiment covered is the first experiment performed this semester. For each section you will be presented with the questions you need to ask yourself as you compose your report.
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Section Order
The order in which the sections of the report should be composed is not the same as the order of the finished report.
Order of Sections in Report
Introduction
Procedures
Results
Calculation
Discussion
What were the major goals of today’s lab?
Determine the wavelength of maximal absorbance (λmax).
Determine the molar absorptivity at λmax ().
GenChem
Introduction
From p. 65 of your Technique Book:
Introduction. A description of what is already known, the plan of action and expected outcomes.
From p. 71 of your Technique Book:
Introduction. A description of:
Question to ask yourself:
For each goal, list the major techniques, formulas, and chemicals used:
λmax
Calipers- path length
Introduction: Goal 1
In a paragraph, introduce Goal 1. Include all items on your list.
Introduce Goal 1. Define λmax and give expected outcomes.
Plan of action. How was Goal 1 achieved? Introduce techniques/formulas/chemicals in context.
Relevance of results. What can you do with your newly found λmax?
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Introduction: Goal 1
*
Introduction: Goal 2
In a paragraph, introduce Goal 2. Include all items on your list.
Introduce Goal 2. Define ε and give expected outcomes.
Plan of action. How was Goal 2 achieved? Introduce techniques/formulas/chemicals in context.
Relevance of results. What can you do with your newly found ε?
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Introduction: Goal 2
Goal 2 was to find ε for the assigned dye. ε is a measure of how strongly a substance absorbs light at a particular wavelength and is a large value for dark colorful substances. In Beer’s Law, ε is the proportionality constant that relates absorbance to concentration (A=εbC).
To determine ε, Absorption Spectroscopy was used to measure absorbance values (at the λmax) of several dilutions of dye with known concentrations. An Excel graph of A vs. C was generated so slope=εb. The slope was given by the Excel trend line and the path length (b) of the cuvette was measured with calipers. ε can be used to determine the concentration of food dye in unknown solutions.
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Introduction
The first goal was to determine the λmax of the assigned food dye. The λmax of a substance is the wavelength of light with the highest absorbance and is the wavelength opposite the color seen by the human eye. The λmax was determined using Absorption Spectroscopy, a technique that measures the wavelengths of light absorbed by a colored solution. The λmax was then used to conduct a Beer’s Law analysis in Goal 2. 
Goal 2 was to find ε for the assigned dye. ε is a measure of how strongly a substance absorbs light at a particular wavelength and is a large value for dark colorful substances. In Beer’s Law, ε is the proportionality constant that relates absorbance to concentration (A=εbC).
To determine ε, Absorption Spectroscopy was used to measure absorbance values (at the λmax) of several dilutions of dye with known concentrations. An Excel graph of A vs. C was generated so slope=εb. The slope was given by the Excel trend line and the path length (b) of the cuvette was measured with calipers. ε can be used to determine the concentration of food dye in unknown solutions.
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Introduction: Helpful hints
Only include information that is known before lab. No results, observations, etc.
200 word maximum for one week lab.
Paragraph format. Subheadings okay.
Give items in context. No lists.
See Technique Book pp. 65, 67 and 71 for more help with writing an Introduction
See Technique Book pp. 52-55 for more help with scientific writing.
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Procedures
Also known as “experimental”. This section will be discussed with the next report.
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Calculations
Calculations. Examples of all calculations performed to manipulate the numerical data. Include one example for each type.
From p. 70 of your Technique Book:
One example for each type of calculation. Each example should consist of three parts:
The formula that describes the calculation
The formula in use
Question to ask yourself:
For each goal identify the important calculations that should be included.
Determine λmax
Determine at λmax.
Calculation of a value for .
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Calculations
Your presentation of your calculations should always use a three step format:
Write out the equation
Plug in your numbers
Give the answer
This method ensures that your instructor can follow your thought process during the calculation.
Do not forget to add units and watch significant figures during your calculations!
GenChem
Calculations: Goal 1
For a dilution the product of the concentration times the volume is constant.
C1V1 = C2V2
C2 = 5.37 x 10-5 M
*
Calculations: Goal 2
The first calculation of goal 2 is the same as that of goal 1: dilution. Since we have already shown this calculation, we do not need to show it again.
If we calculated the concentration a different way, then we would need to show a second calculation.
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Calculations: Goal 2
The second calculation we have listed is density. We obtained this value from the graph, but it would be helpful to make a note in the calculations so that the reader does not think you forgot one:
Density of known plastic: Determined from the slope of the graph
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Calculations: Helpful Hints
Include a calculation for all types of calculations that you do, but only include one example for the type of calculation
Watch significant figures and units
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Results
From p. 65 of your Technique Book:
Results. An organized presentation of the observations and calculated results. This section is frequently dominated by figures, tables and graphs. It will contain little to no text.
From pp. 67-8 of your Technique Book:
Results. An objective and clear description of experimental findings following an appropriate order and including relevant:
Tables
Graphs
Figures
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Question to ask yourself:
For each goal identify the important results and supporting data that should be included.
Determine λmax
Calculation of a value for .
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Results: Goal 1
Sometimes, it makes more sense to list numbers and answers in a clear order rather than putting them in a table.
Dye: Indigo carmine
λmax : 610 nm
Figure 1: Visible-UV spectrum of indigo carmine
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Results: Goal 2
For repetitive and/or related data a labeled table is best. Compile all of the items on your list in a logical order.
Table 1. absorbance of standard solutions
* Ratio of stock solution volume to final solution volume
** absorbance values measured at 610 nm
Dilution*
Results: Goal 2
It is often a good idea to display this information in a graph as well. If we plot the absorbance on the x-axis and the concentration on the y-axis, the slope will be the molar absorptivity of the dye.
Graph 1. absorbance vs concentration of standard food dye solutions.
at 610 nm = 5.50 x 105 abs/cmM
*
Results: Helpful Hints
Only include results that are important to the conclusions that you make
Be careful about the amount of significant figures you have, especially when copying tables that you’ve made from Excel
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Discussion
From your Technique Book:
Discussion. Analysis of the data and presentation of conclusions regarding original hypothesis. This should include a defense of the conclusions citing the results and a discussion of the reliability of the data used.
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What does it mean?
Does it make sense?
Is it consistent with your observations?
Comparisons to literature or peers.
If something went wrong: What were you expecting and why? What went wrong? How do you know? How could you fix it next time?
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Discussion: Goals
The λmax of Blue #1 was 610 nm which lies in the orange region of the visible light spectrum. As expected, the orange color absorbed is opposite the blue color observed.
Using the λmax, the ε for Blue #1 was found to be 55,000 M-1cm-1. This is a larger ε than the other three dyes, which means Blue #1 is the best at absorbing light. This is consistent with the observation that Blue #1 had the darkest appearance out of the four dyes.
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Discussion: Data quality
In a paragraph, discuss the quality and reliability of your data:
Discuss pros/cons/accuracy/precision of tools/techniques.
Be specific and give examples.
Suggest fixes for the problems you identify and additional experiments to improve findings.
Avoid discussing general human error. Only specific, documented errors should be addressed.
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Discussion: Data quality
The λmax value seems reliable because the spectrometer gives readings that vary by a maximum of 1 nm. Also, 610 nm is an exact match to the class average λmax. The ε value also came close to the class average ε of 55,000 M-1cm-1. The calipers used to measure the path length are accurate to 0.01 cm and the volumetric kit used for dilutions measures volumes accurate to 0.01 mL.
*
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Discussion