More about Exp 1 report, graphs, sample calcs, etc.
robert zellmer
zellmer.1 at osu.edu
Sat Aug 25 20:21:03 EDT 2018
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) The discussion section in manual gives an example of how you calculate
volume using density and the percent error using volume. In your exp
you used the measured volumes to determine an experimental density
and compare it to the actual density. You will be doing the % error
calculation for the density.
2) For the data on the report sheets:
a) line 1: Water temp. (page 9)
If you took the temp for each piece of glassware and it
differed significantly you can use each temp or take an
average temp if they were all about the same. There
were some labs in which the temp changed by a few degrees
degrees from the start of lab to the end of lab. If
you used
a single temp that would introduce error in the accepted
density of the water. If you took only one temp just use
that for your calc. You might think about how this could
affect your results. You can see how much of a 10 degree C
difference makes in the density by calculating it using
the eqn.
for 20 C and 30 C.
b) line 2: Accepted (actual) density (page 9)
Use the eqn on page 9 preceding 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
or H2O between
20 and 30 C. What if your temp was slightly below 20 C
or above
30 C? What can you do? You can go to the CRC Handbook
of Chem
and Physics and look up the table for the density of
water at diff. temps.
Can you still use the eqn on page 9? Well, I did a few
quick calc. based
on that eqn and the values in the CRC between 16 and 40
C. The errors
outside of the range of 20-30 C (given in the manual)
were about the same
as the errors within the 20-30 C range. So the gist of
it is, just use the eqn
on page 9 even if your temp is a little below 20 or
above 30 C.
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, 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.
You can fill out the report sheet from the manual and
include a scan or
picture in the report. This is your report page or sheet.
This is what I labeled
"Data" in my report example outline on the class web
page. If you use Excel
and make the data table in Excel you can include it as the
report sheet. You
don't need to copy all the data over to the data sheet from
the manual. However,
you should still include a picture of the report sheet from
the manual even though
it's blank. If for some reason you still wish to fill in
the report sheet and use
it in the report (a scan or picture) that's fine but turn
in your Excel sheets and
let the TA know which one they should grade for the report.
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>
3) Graphs
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 the 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, even if using Excel. 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.
If using Excel have it print the eqn and R^2. If doing it by
hand you should
figure out the slope and intercept and write those on the
graph. Both of
those and the 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
(results/discussion and conclusion section).
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.
If using Excel 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. Don't worry if you don't have
grid lines. We just
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.
If hand-graphing show a sample calc for the slope and
intercept. You will
use these in your results and discussion section.
You only have to do this for one of the graphs (not
all four).
4) Answer the two questions on page 10 on a separate page in the report
(after the
page with your Conclusion). You're suppose to copy the
questions on the page
and then answer them. It's easy to get these questions into the
report since there's
a PDF of the exp 1 manual on Carmen. You can copy them from the
PDF and
paste them into your Word document.
5) Results and Discussion (and graphs)
If you look at my report example I tell you what should go
here. Use the
Points to Consider on page 10 to help guide you.
For this exp. you should discuss the results from the table.
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).
Think of the slope as being your average density for each
piece of glassware.
You should discuss 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.
Discuss 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.
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. How about
the temp. of the water? Was it constant throughout the whole
lab period?
Did you measure it at different times to see if it stayed
constant? How much
might this affect your results? Does the sig. fig. (accuracy)
of the balance
cause any error? How about each piece of glassware? Did you
make a
mistake you know about which could have caused error? 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). Discuss the fact you
didn't include it.
How did you perform the experiment for each piece of
glassware? For instance,
for the buret, if you added ~ 5 mL each time to the weighing
beaker instead of
emptying and drying the weighing beaker before each volume
added (put in 5 mL,
weighed the beaker, emptied and dried it and then added 10 mL,
etc.) makes a
difference in terms of error and accuracy. How would the
different ways of doing
this make a difference? Were your graduated cylinders TD (to
deliver) or TC
(to contain)? What's the difference and how does that affect
your results? Did you
use the same grad. cyl. for all four measurements or switch
between the two types?
You should have seen the TD or TC at the top of the grad. cyl.
Make sure you have at least 2 inherent sources of error. This
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.
Think about what you did and how you did it. 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?
6) Conclusion
This is 5-6 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.
7) Summary of sample calc. (as shown on grading rubric).
a) calc for the accepted density of water (2nd line on report
sheet, page 9).
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 graphs (just using one of the four graphs):
1) slope calc whether by hand or using Excel (use points from
one of your lines)
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
for your discussion.
Please indicate which piece of glassware and lines for the table
you're using for the
sample calc. and indicate which graph you are using for the slope
calc.
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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