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I always get a lot of questions about exp 1 and the report. I
apologize to anyone<br>
who's already completed or almost completed the report for exp 1.
Here's what<br>
you should be doing for the report sheet, sample calc., discussion,
etc. <br>
<br>
1) For the data on the report sheets: <br>
<br>
a) line 1: Water temp. (page 8)<br>
<br>
If you took the temp for each piece of glassware and
it <br>
differed significantly you can use each temp or take
an <br>
average temp if they were all about the same. There
<br>
were some labs in which the temp changed by a few
degrees<br>
degrees from the start of lab to the end of lab. If
you used <br>
a single temp that would introduce error in the
accepted <br>
density of the water. If you took only one temp
just use<br>
that for your calc. You might think about how this
could<br>
affect your results. You can see how much of a 10
degree C<br>
difference makes in the density by calculating it
using the eqn.<br>
for 20 C and 30 C.<br>
<br>
b) line 2: Accepted (actual) density (page 8)<br>
<br>
Use the eqn on page 8 preceding the data table to
calc. the<br>
accepted density at your temp. This is an eqn for a
straight line<br>
relating density to temp. This eqn. is for the
density or H2O between<br>
20 and 30 C. What if your temp was slightly below
20 C or above<br>
30 C? What can you do? You can go to the CRC
Handbook of Chem<br>
and Physics and look up the table for the density of
water at diff. temps.<br>
Can you still use the eqn on page 8. Well, I did a
few quick calc. based<br>
on that eqn and the values in the CRC between 16 and
40 C. The errors<br>
outside of the range of 20-30 C (given in the
manual) were about the same<br>
as the errors within the 20-30 C range. So the gist
of it is, just use the eqn<br>
on page 8 even if your temp is a little below 20 or
above 30 C.<br>
<br>
Make sure you have the correct # of sig. fig. This
can be tricky with this eqn.<br>
After lecture on Mon. or Tue. (depending when you
have lecture) you should<br>
understand how to handle sig. fig. if you don't
already.<br>
<br>
Show the calc. for this in the sample calc. <br>
<br>
c) Data table: <br>
<br>
Do the calculations and make sure your sig. fig. are
correct. <br>
<br>
You only have to show a sample calc. for the measured
density, error and<br>
% error for one line for one piece of glassware. You
don't need to do it for<br>
every single line for every piece of glassware.<br>
<br>
You fill out this sheet and turn it in with the report.
This is your <br>
report page or sheet. This is what I labeled "Data" in
my report <br>
example on the class web page. If you use Excel and
make the data<br>
table up in Excel you can print it as the report sheet.
You don't need to<br>
copy all the data over to the data sheet in the manual.
However, you should<br>
still turn in the report sheet from the manual even
though it's blank. If for<br>
some reason you still wish to fill in the report sheet
and turn it in that's fine but<br>
turn in your Excel sheets and let the TA know which one
they should grade<br>
for the report.<br>
<br>
You always must make sure you have the correct sig.
fig., even when using<br>
Excel. It won't let you set sig. fig. but you can set
decimal places to get the<br>
correct sig. figs. I explain how to do this at the
following link:<br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/excel/excel.txt"><b>Using
Excel for Calculations and Graphs</b></a><br>
<br>
You can find this link at the following link:<br>
<br>
<a
href="http://chemistry.osu.edu/%7Erzellmer/excel/excel.htm"><b>Using
MS Excel for Reports</b></a><br>
<br>
2) Graphs <br>
<br>
You should have 4 graphs, one for each piece of glassware.
Make <br>
sure your graphs look correct, even if using Excel. They
should take up <br>
pretty much the entire page (0.1" margins) and the points
should take up <br>
most of the space on the graph (very little empty space).
Your axes<br>
should reflect the accuracy of the measuring device. For
example, for the<br>
buret since you should record the volume to 2 decimal places
your x-axis<br>
(volume) should show 2 decimal places for the labels. <br>
<br>
You do NOT need a legend on any of these graphs since
there's only one<br>
set of data per graph. Your title should include the piece
of glassware being<br>
used, but just have "Buret" (as shown in the example in the
manual) is not<br>
an adequate title. <br>
<br>
If using Excel have it print the eqn and R<sup
class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>.
If doing it by hand you should <br>
figure out the slope and intercept and write those on the
graph. Both of <br>
those and the R<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>
tell you something. Make sure your slope and intercept<br>
printed on the graph have enough digits to show differences
between the<br>
glassware and you report them to the correct # sig. fig. in
your report<br>
(results/discussion and conclusion section).<br>
<br>
a) Sample calc. <br>
<br>
If using Excel show a sample calc for the slope. Use
pts from the line. <br>
Don't use your data pts for this. The pts on the
best-fit line are better <br>
than your data pts. Don't worry if you don't have
grid lines. We just<br>
want a sample calculation. The slope generated by
your sample calc.<br>
will not be used further. In your results and
discussion section use the<br>
slope and intercept generated by Excel.<br>
<br>
If hand-graphing show a sample calc for the slope
and intercept. You will<br>
use these in your results and discussion section.<br>
<br>
You only have to do this for one of the graphs (not
all four). <br>
<br>
3) Answer the questions on page 10. Questions 1-3 should really be
addressed in the<br>
Discussion section. Questions 4-5 can be answered in the
Discussion section or<br>
on a separate sheet of paper. There's no need for you to
recopy the questions.<br>
<br>
4) Results and Discussion (and graphs) <br>
<br>
If you look at my report example I tell you what should go
here. Use the <br>
questions on page 10 to help guide you.<br>
<br>
For this exp. you should discuss the results from the
table. Which piece of <br>
glassware gave the smallest % error, which gave the
largest? Were all the <br>
% errors for a single piece of glassware really close to
each other or not so much?<br>
What does this imply about precision and accuracy? Think
about it based on sig. fig.<br>
Does the # of s.f. seem to effect your answers and what you
think? Do they make sense?<br>
<br>
Report the slope, intercept and R<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>
from all 4 graphs (pieces of glassware). <br>
Think of the slope as being your average density for each
piece of glassware. <br>
<br>
You should discuss the graphs. What does the slope indicate
(m = D*v + b)? <br>
What does the R<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>
indicate about your data? Remember, this is the "correlation <br>
coeff" and the closer it is to "1" the better the fit (the
closer your points are to the <br>
line). How about the intercept? What should it be? What
is your intercept? What <br>
does your intercept mean if it's not the accepted
intercept? Think about what <br>
would happen to your eqn if the balance had been
miss-calibrated and was <br>
consistently reading a little too high? Would that affect
the slope or intercept or both? <br>
Would it affect the R<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>?
What if you weren't reading the volume correctly, i.e. you <br>
didn't look straight on but at an angle but you made the
same mistake each time <br>
so your volume was incorrect by a certain specific amount
due to this? Again, <br>
would that effect the slope, intercept or R<sup
class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>
or all of them. <br>
<br>
Discuss uncertainty (precision) and accuracy. Again, I've
said uncertainty <br>
rather than precision. Precision is how close repeated
measurements are <br>
to each other. Most everyone used volumes around 5, 10, 15
and 20 mL (20,<br>
25, 30, 35 for the beaker). You weren't repeating
anything. (You can look at<br>
how close the densities are.) However, there is still some
relationship to precision. <br>
The mass from a top loading balance can be reported out to 2
decimal places <br>
(e.g. 10.26 g). It has an inherent uncertainty of + or -
0.01 g. If you are <br>
really careful when taking repeated mass measurements your
precision for <br>
your masses should be + or - 0.01 g (within the uncertainty
of the instrument). <br>
You couldn't get more precise than that. What on the graphs
indicate your<br>
precision and accuracy?<br>
<br>
Discuss sources of error and how they might affect your
results. How about <br>
the temp. of the water? Was it constant throughout the
whole lab period? <br>
Did you measure it at different times to see if it stayed
constant? How much <br>
might this affect your results? Does the sig. fig.
(accuracy) of the balance <br>
cause any error? How about each piece of glassware? Did
you make a <br>
mistake you know about which could have caused error? If
you have a bad <br>
data point on the graph you don't have to include it in your
best-fit line (a little <br>
harder to do in Excel than by hand). Discuss the fact you
didn't include it.<br>
<br>
How did you perform the experiment for each piece of
glassware? For instance,<br>
for the buret, if you added ~ 5 mL each time to the weighing
beaker instead of<br>
emptying and drying the weighing beaker before each volume
added (put in 5 mL,<br>
weighed the beaker, emptied and dried it and then added 10
mL, etc.) makes a<br>
difference in terms of error and accuracy. How would the
different ways of doing<br>
this make a difference? Were your graduated cylinders TD
(to deliver) or TC<br>
(to contain)? What's the difference and how does that
affect your results? Did you<br>
use the same grad. cyl. for all four measurements or switch
between the two types?<br>
You should have seen the TD or TC at the top of the grad.
cyl.<br>
<br>
Make sure you have at least 2 inherent sources of error.
This is error which <br>
you have little control over due to the equipment being used
or the way we <br>
had you do the exp. This is not "I spilled some water
outside the beaker". <br>
That's an "oops, I better do this over" moment. What errors
might be introduced<br>
if you added the water a little at a time to get the
totals? For instance, to get<br>
10 mL from the buret you could add 5 mL twice or start over
and add 10 mL<br>
once. Which would be better? Which way did you do it?
This may be something<br>
associated with the instrument (as in the # of s.f. you can
get from the instrument)<br>
but only if it affects the accuracy (s.f.) in your final
results. For instance, if you used<br>
the analytical balance for all the masses (as was best to
do) does it affect your s.f.<br>
for any or all of the measured densities? How about the
s.f. for the volumes?<br>
<br>
4) Conclusion <br>
<br>
This is 5-6 sentences (depends on the exp) in which you come
up with <br>
what you can conclude from this exp. Essentially answer the
purpose. <br>
Think of this as a summary of the exp. and the results in
sentence form.<br>
<br>
<br>
5) Summary of sample calc. (as shown on grading rubric). <br>
<br>
a) calc for the accepted density of water (2nd line on report
sheets, page 8).<br>
<br>
b) calc. for measured density for one piece of glassware for one
mass-volume pair<br>
<br>
c) calc. for error for one piece of glassware for one
mass-volume pair <br>
<br>
d) calc. for % error for one piece of glassware for one
mass-volume pair <br>
<br>
e) sample calc for graphs (just using one of the four graphs): <br>
<br>
1) slope whether by hand or using Excel (use points from one
of your lines)<br>
<br>
You only have to show a single sample for this for the
graphs. You <br>
need to report slope and intercept for each of the 4 graphs.
This is <br>
one reason to use Excel. Excel will give better results
than you can likely<br>
get by doing it by hand.<br>
<br>
Please indicate which piece of glassware and lines for the table
you're using for the<br>
sample calc. and indicate which graph you are using for the
slope calc.<br>
<br>
I hope I haven't left anything out and I hope this helps.<br>
<br>
Dr. Zellmer
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