Transcript Report Writing Guide

GenChem
Report Writing
Guide
A lesson designed to guide you
through the process of composing a
suitable lab report
1
GenChem
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.
Overview
Section Order
GenChem
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
Recommended Order of
Composition
• Introduction
• Calculations
• Procedures
• Results
• Results
• Procedures
• Calculation
• Introduction
• Discussion
• Discussion
GenChem
Preparing to Write
First Question to ask yourself:
What were the major goals of today’s lab?
1.Determine the wavelength of maximal
absorbance (λmax).
2.Determine the molar absorptivity at λmax (ԑ).
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:
• the experimental objective(s)
• pertinent background information
• expected outcomes, if any
GenChem
Introduction: Outline
Question to ask yourself:
For each goal, list the major techniques, formulas, and
chemicals used:
1.λmax
• Absorption Spectroscopy
• Food dye
2.ε
•
•
•
•
•
Parallel dilution
Absorption Spectroscopy
Excel/trendline
Beer’s law (graph A vs C)
Calipers- path length
GenChem
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?
GenChem
Introduction: Goal 1
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.
GenChem
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?
GenChem
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.
Introduction
GenChem
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.
GenChem
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.
GenChem
Procedures
Also known as “experimental”. This
section will be discussed with the next
report.
GenChem
Calculations
• From p. 65 of your Technique Book:
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
– The answer
GenChem
Calculations: Outline
Question to ask yourself:
For each goal identify the important calculations
that should be included.
1.Determine λmax
• Dilution of stock dye solution
2.Determine ԑ at λmax.
• Parallel (or serial) dilution to produce standards.
• Calculation of a value for ԑ.
GenChem
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
• (5.37 x 10-3 M)(1.00 mL) = C2(100.0 mL)
• C2 = 5.37 x 10-5 M
GenChem
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.
GenChem
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
GenChem
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
Results
GenChem
• 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
GenChem
Results: Outline
Question to ask yourself:
For each goal identify the important results and supporting
data that should be included.
1.Determine λmax
• Identity of dye
• Concentration of dye
• Value for λmax
2.Determine ԑ at λmax.
• Parallel (or serial) dilution to produce standards.
• Calculation of a value for ԑ.
GenChem
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
Description: a clear, blue solution
Concentration: 5.37 x 10-5 M
λmax : 610 nm
GenChem
Results: Goal 1
Graphs are a good way to display data
Figure 1: Visible-UV spectrum of indigo carmine
GenChem
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
Dilution*
Concentration (M)
Absorbance (abs)**
none
5.37 x 10-5
0.943
8:10
4.22 x 10-5
0.782
6:10
3.16 x 10-5
0.577
4:10
2.11 x 10-5
0.392
2:10
1.05 x 10-5
0.181
* Ratio of stock solution volume to final solution volume
** absorbance values measured at 610 nm
Results: Goal 2
GenChem
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 yaxis, the slope will be the molar absorptivity of the dye.
Graph 1. absorbance vs concentration of standard food dye solutions.
concentration x 100000
6
y = 5.4953x + 0.0176
R² = 0.9979
5
4
3
2
1
0
0
0.2
0.4
0.6
Absorbance
0.8
ԑ at 610 nm = 5.50 x 105 abs/cm∙M
1
GenChem
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
GenChem
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.
GenChem
Discussion: General
Questions to ask yourself:
For each goal
–
–
–
–
–
–
–
–
What is the result? (Cite data/give examples).
What does it mean?
Does it make sense?
Explain the chemistry.
Is it what was expected?
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?
GenChem
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.
GenChem
Discussion: Data quality
In a paragraph, discuss the quality and
reliability of your data:
– Discuss pros/cons/accuracy/precision of
tools/techniques.
– Use technique book!
– 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.
GenChem
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.
The Absorbance values collected were all within the
spectrometer’s effective range of 0.1-1.0. Parallel dilutions were
chosen over serial dilutions to obtain a graph with well distributed
points. Parallel dilutions also minimize error propagation in consecutive
dilutions. The resulting calibration curve showed a strong linear
correlation with an R2 value of 0.99. And although the y-intercept
should be zero, the small value of 0.025 indicates minimal error.
GenChem
Discussion
• See Technique book pp. 68-69 for more
help with writing a Discussion.