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We are starting exp 14 this week on Tuesday.<br>
<br>
I have help files for exp 14 for both pre-lab and post-lab for the
graphs<br>
and report. Don't attempt the pre-lab until you've read the manual,<br>
the e-mails I'm sending and the information at the following links,<br>
<br>
<a
href="https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/lab_1250.htm"><b>Laboratory</b></a><br>
<br>
<a
href="https://www.asc.ohio-state.edu/zellmer.1/chem1250/faq/exp14.txt"><b>Exp
14 - Help for Exp 14</b></a><br>
<br>
For the first link pay close attention to the volumes you should be
using depending<br>
on what compound you have. You won't know which known compound
until<br>
lab. There are 5 volumes for each compound. These are approx. You
are supposed<br>
to get close to one of these and then hold it there for awhile
(about 30-60 seconds by<br>
adjusting the flame) and then read the volume and temperature.<br>
<br>
At the help link I've been quite specific about s.f. (especially for
logarithms),<br>
what should be in your discussion section, sample calculations,
etc. LOOK at<br>
this LINK.<br>
<br>
For the calculations you need to calculate the pressure of your
sample in the<br>
syringe. You will use eqn 6 on page 89 for the Ps values from the V
& T data.<br>
Often people will get negative Ps values. They can NOT be
negative. I've<br>
discussed this at the help link. It's because you used Celsius and
not kelvin.<br>
Remember,<br>
<br>
<big><font size="2"><big> </big></font></big><font size="+1"
color="#ff0000"><b>KELVIN, KELVIN, KELVIN</b></font><big><font
size="2"><big><br>
<br>
<br>
</big></font></big> There is no pre-lab quiz on Carmen.<br>
<br>
<b>HOWEVER, there is an on-line data input prelab at the following
link,<br>
<br>
</b><a href="https://uglabs.cbc.osu.edu/1250/pre-postlabs.php"> <b>https://uglabs.cbc.osu.edu/1250/pre-postlabs.php</b></a><br>
<br>
This is the SAME site as for the Gatekeeper quiz and exp 5. You can
get to it via<br>
the module for exp 14 on Carmen (it takes you to the same site).
You need read the<br>
discussion and data analysis section carefully. Watch the exp 14
video (there's a<br>
link on my web pages for videos). You can watch the video in the
pre-lab and then<br>
get out. As long as you don't submit you can restart it. Read my
help files (see the<br>
"Laboratory" link on my class web page). Then write the procedure
and do the pre-lab.<br>
<br>
Read the instructions on the landing page before clicking on the
"Prelab" link.<br>
Once you get to the prelab click on the Policies and Procedures link
at the<br>
very bottom, <br>
<br>
<a href="https://uglabs.cbc.osu.edu/1250/pre-postlabs.php">https://uglabs.cbc.osu.edu/1250/pre-postlabs.php</a>
<br>
<br>
Also, click on the "<font color="#ff0000">Instructions</font>" box
near the upper-left hand corner of the<br>
page. This will give some general instructions and ones more
specific to this<br>
exp.<br>
<br>
For the pre-lab the data given is supposed to be similar to what you
will obtain<br>
in the lab for your unknown. You are given 5 temp/vol data points,
just like<br>
you'll get in the exp. You use eqn 6 for this to calculate the
Ps. There are two<br>
boiling points, one determined at the barometric pressure for the
day (as given<br>
in the data) and the other is the normal b.p. You do NOT use eqn 6
for these.<br>
Boiling occurs when the vapor pressure (VP) of the liquid equals the
prevailing<br>
atmospheric (barometric) pressure. The normal b.p. is when the VP
equals the<br>
prevailing barometric pressure when it is 1 atm. Both of these are
given for the<br>
pre-lab. For the exp you'll obtain a b.p. the day of lab at the
barometric pressure<br>
for that day and look up the normal b.p. in the CRC (see my web
page).<br>
<br>
You will need to graph the points for the pre-lab and determine the
slope of the<br>
resulting best-fit line (linear fit must be used). The easiest
thing to do would be<br>
to use Excel for this while doing the pre-lab. You will have two
b.p. data points<br>
on the graph, the literature value and exp value, as explained
above. Your graphs<br>
for the report will have 7 data points. You'll see the same for the
pre-lab.<br>
<br>
The sig. fig. for ln(P) are tricky. It's explained in my help file
for exp 14 (see<br>
above link) and another help file I have specifically about logs and
s.f. I've sent<br>
both links out before but here they are again. Sig. fig. for
logarithms is also<br>
explained in Appendix A of the textbook.<br>
<br>
<a
href="https://www.asc.ohio-state.edu/zellmer.1/chem1250/faq/sig_fig_logs.txt"><b>Manipulating
Logs and Sig. Figs.</b></a><br>
<br>
<font size="+1" color="#ff0000"><b>Finally, the method of obtaining
the boiling point has changed<br>
from what is shown in the video.</b></font> <br>
<br>
We now use a sand bath rather than a boiling water bath. However,
you are<br>
still looking for the bubbles coming from the inverted capillary
tube and for<br>
the liquid to go back up into the capillary tube after removal from
the sand<br>
bath, as shown in the video. You'll see bubbles and then it appears
to start<br>
boiling. Do NOT record the temp at this point. The best thing to do
is watch<br>
the thermometer until the temp stabilizes (it will inc. rapidly and
then stop inc.).<br>
Then remove the test tube. Then don't watch the thermometer,
instead watch for<br>
the liquid to go up the capillary. When it does, read the
temperature. Ask your<br>
TA if it looks reasonable. You do at least three b.p.
determinations in the lab and<br>
average the best three and report this average as the experimental
b.p. <br>
<br>
Dr. Zellmer
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