More about Exp 1 report, graphs, sample calcs, etc.
Zellmer, Robert
zellmer.1 at osu.edu
Sun Jan 23 15:30:47 EST 2022
I always get a lot of questions about exp 1 and the report. I apologize to anyone
who's already completed or almost completed the report for exp 1. Here's what
you should be doing for the report sheet, sample calc., discussion, etc.
1) In exp 1 several types of glassware are used to measure volumes and masses
of water delivered to determine an experimental density. These exp values
are then compared to the actual density in order to determine which type of
glassware is the most accurate and with which you could be the most precise.
You will also be calculating the error and % error.
2) For the procedure section it's usually just a reference to the lab manual (see
our examples) and any changes which were made (the TA may tell you of
changes which need to be made).
3) For the data on the report sheet:
a) line 1: Average water temp. (page 15)
If you were taking data in lab you would have taken the temp
before using each piece of glassware and averaging those four
temps. Remember, temperature affects volumes and thus affects
the density. You can see how much a 10 degC difference makes
in the density by calculating it using the eqn. (1) for 20 C and 30 degC.
b) line 2: Accepted (actual) density (page 15)
Use eqn (1) on page 11 & footnote in the data table to calc. the
accepted density at your temp. This is an eqn for a straight line
relating density to temp. This eqn. is for the density of H2O between
20 and 30 degC.
Make sure you have the correct # of sig. fig. This can be tricky with
this eqn.
Show the calc. for this in the sample calc.
c) Data table:
Do the calculations and make sure your sig. fig. are correct.
You only have to show a sample calc. for the measured density, average density
error and % error for one line for one piece of glassware. You don't need to do it
for every single line for every piece of glassware. See item # 8 below.
For the errors and % errors, report them using the proper sign. For the average
error and % error use the absolute values of the errors and % errors.
The report sheet or report form is the "Data" in my report example outline on
the class web page. Use the Excel template for the report sheet on page 15
(you can find this on Carmen in the module for exp 1). Fill it in with your data
and program the proper eqns into the cells and let Excel do the calculations for
you (you still have to show sample calcs). Then include this Excel sheet as the
report sheet in your report (Word doc). You can certainly do all calculations by
hand and put them in the provided Excel sheet or you can create one in Excel or
Word. Even if you don't know how to use Excel, the time spent now to learn
how to have it do calc and graphs will save you a lot of time in the long run.
You always must make sure you have the correct sig. fig., even when using
Excel. It won't let you set sig. fig. but you can set decimal places to get the
correct sig. figs. I explain how to do this at the following link:
Using Excel for Calculations and Graphs<https://www.asc.ohio-state.edu/zellmer.1/excel/excel.txt>
You can find this link at the following link:
Using MS Excel for Reports<https://www.asc.ohio-state.edu/zellmer.1/excel/excel.htm>
4) Graphs
You must use Excel for graphs. You should not do any "hand-graphing"
on a piece of graph paper and scan it for the report. Do the graphs in
Excel and transfer to your Word doc. Do NOT take pictures or scans of
the graphs (or tables) and add to them to your Word doc.
You should set the margins for your graphs to zero in Excel and you
want them to stay that way when you import the graphs into your Word
document. One would think Word would do that automatically but it
doesn't, instead resetting the margins to agree with those set in Word.
You don't want it to do this and then simply drag the graph to expand
it's size since it can distort things. You'll find another link at the link
above explaining how to change the margins and page orientation on a
page in Word when importing another file into a Word document
(e.g. importing a graph or table from Excel) so the margins correspond
to what's in the imported file.
You should have 4 graphs, one for each piece of glassware. Make
sure your graphs look correct. They should take up pretty much the
entire page (0" margins) and the points should take up most of the space
on the graph (very little empty space). Always, one graph per page,
taking up the whole page.
Your axes should reflect the accuracy of the measuring device. For example,
for the buret since you should record the volume to 2 decimal places your
x-axis (volume) should show 2 decimal places for the labels.
You do NOT need a legend on any of these graphs since there's only one
set of data per graph so delete the legend so your graph can take up more
space on the page. Your title should include the piece of glassware being
used, but just having "Buret" or "Mass vs. Volume" is not an adequate title.
Pretend like your TA doesn't know anything about the exp. Thus, your title
should be fairly informative.
When using Excel have it print the eqn and R^2. The slope, intercept and
R^2 tell you something. Make sure your slope and intercept printed on
the graph have enough digits to show differences between the glassware
and you report them to the correct # sig. fig. in your report.
Look at my examples of good graphs. The 2nd one is the better example
since I needed some room on the first one for some extra things at the top
and bottom.
Sample Graphs<https://www.asc.ohio-state.edu/zellmer.1/sample_graphs.pdf>
a) Sample calc.
Even when using Excel you need to show a sample calc for the slope
Use pts from the line. Don't use your data pts for this. The pts on the
best-fit line are better than your data pts. Mark the points on the line
you use for the sample calc. There's a way to put symbols, text and
shapes on a graph. Go to "Insert" to see how. You don't need a ton of
grid lines, just major grid lines and a few minor grid lines. While we
want a sample calculation, the slope generated by your sample calc.
will not be used further. In your results and discussion section use the
slope and intercept generated by Excel.
You only have to do this sample calc for one of the graphs (not all four).
5) There is no Discussion or Conclusion section. Instead there are Report Questions.
Answer the report questions on pages 16-17 using the template for these you can
get from Carmen (SCM module). It is a Word document. This way you don't have
to type the questions. Include this in your Word document for the report.
For this exp. you will answer questions based on results from the table and graphs.
Which piece of glassware gave the smallest % error, which gave the largest? Were all the
% errors for a single piece of glassware really close to each other or not so much?
What does this imply about precision and accuracy? Think about it based on sig. fig.
Does the # of s.f. seem to effect your answers and what you think? Do they make sense?
Were they all errors positive or all negative? What might it mean if they are?
Report the slope, intercept and R^2 from all 4 graphs (pieces of glassware) in
question 5f. Think of the slope as being your average density for each piece of
glassware.
You will answer questions related to the graphs. What does the slope indicate
(m = D*v + b)? What does the R^2 indicate about your data? Remember, this
is the "correlation coeff" and the closer it is to "1" the better the fit (the closer
your points are to the line). How about the intercept? What should it be? What
is your intercept? What does your intercept mean if it's not the accepted intercept?
Think about what would happen to your eqn if the balance had been miss-calibrated
and was consistently reading a little too high? Would that affect the slope or intercept
or both? Would it affect the R^2? What if you weren't reading the volume correctly,
i.e. you didn't look straight on but at an angle but you made the same mistake each
time so your volume was incorrect by a certain specific amount due to this? Again,
would that effect the slope, intercept or R^2 or all of them.
How does the density calculated from the data points in your table agree with the
density from the graph? Which makes more sense?
There's questions about uncertainty (precision) and accuracy. Again, I've said
uncertainty rather than precision. Precision is how close repeated measurements
are to each other. You should have used volumes around 5, 10, 15 and 20 mL (20,
25, 30, 35 for the beaker). You weren't repeating anything. You need to look at
how close the densities are to each other. However, there is still a relationship
to precision since the more careful you were measuring your volumes the closer
your densities will be. In terms of precision look at your measured densities.
How do your graphs show precision and accuracy?
For example, the mass from a top loading balance can be reported out to 2
decimal places (e.g. 10.26 g). It has an inherent uncertainty of + or - 0.01 g. If
you are really careful when taking repeated mass measurements your precision for
your masses should be + or - 0.01 g (within the uncertainty of the instrument).
You couldn't get more precise than that. What on the graphs indicate your
precision and accuracy?
Discuss sources of error and how they might affect your results. Does the sig.
fig. (accuracy) of the balance cause any error? How about each piece of glassware?
If you have a bad data point on the graph you don't have to include it in your best-fit
line (a little harder to do in Excel than by hand). While there's not discussion, if you
have a bad data point you didn't include in the best-fit line you should include a short
discussion of the fact it was left out of the fit and why.
When you answer the question about error think about what types of error may
occur. You need to understand the difference between inherent sources of error
and human error. Inherent error is error which you have little control over due to
the equipment being used or the way we had you do the exp. This is not "I spilled
some water outside the beaker". That's an "oops, I better do this over" moment. It's
also not something like "there's errors in all equipment and chemicals used". That's
a cop out. You should be specific about the error, how it would affect your final
results, how could it be fixed. You will be asked to address inherent errors for
every exp.
Think about what you might have done in the lab. What errors might be introduced
if you added the water a little at a time to get the totals? For instance, to get
10 mL from the buret you could add 5 mL twice or start over and add 10 mL
once. Which would be better? Would it make a difference? Which way did
you do it? This may be something associated with the instrument (as in the # of
s.f. you can get from the instrument) but only if it affects the accuracy (s.f.) in
your final results. For instance, if you used the analytical balance for all the masses
(as you should have) does it affect your s.f. for any or all of the measured densities?
How about the s.f. for the volumes?
7) Conclusion
There's NO conclusion section for this exp. and the next several exps.
The first exp for which there's a Conclusion section is exp 14. Just so
you know what this is at this point it's explained below and in my report
outline and the other documents about the reports in the manual and my
web pages.
This is 5-7 sentences (depends on the exp) in which you come up with
what you can conclude from this exp. Essentially answer the purpose.
Think of this as a summary of the exp. and the results in sentence form,
essentially a summary of your Discussion section.
8) Summary of sample calc. (as shown on grading rubric).
Use the buret data for the sample calculations below, including for the slope calc.
for the graph in (f) below.
a) calc for the accepted density of water (eqn 1 on page 11 ).
b) calc. for measured density for one piece of glassware for one mass-volume pair
c) calc. for error for one piece of glassware for one mass-volume pair
d) calc. for % error for one piece of glassware for one mass-volume pair
e) calc of average for measured density for one piece of glassware
f) sample calc for slope from a graph (just using one of the four graphs):
1) slope calc using points from the best-fit line from one of your graphs
You only have to show a single sample calc for this for the graphs. You
need to report slope and intercept for each of the 4 graphs. This is
one reason to use Excel. Excel will give better results than you can likely
get by doing it by hand. You do a hand calculation for the slope using points
from the line as your sample calculation but use the Excel generated slope
to answer report questions.
I hope I haven't left anything out and I hope this helps. I also hope I've updated all
the page numbers and links. Again, if you find references I've made which don't
seem to coincide with the manual or broken links on my web pages let me know.
Dr. Zellmer
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