Exp 14 pre and post-lab help (including Ps values from eqn 6 and s.f. for logs)

[robert zellmer]

We are starting exp 14 this week on Tuesday.

I have help files for exp 14 for both pre-lab and post-lab for the graphs
and report.  Don't attempt the pre-lab until you've read the manual,
the e-mails I'm sending and the information at the following links,

*Laboratory* 
<https://www.asc.ohio-state.edu/zellmer.1/chem1250/lab/lab_1250.htm>

*Exp 14 - Help for Exp 14* 
<https://www.asc.ohio-state.edu/zellmer.1/chem1250/faq/exp14.txt>

For the first link pay close attention to the volumes you should be 
using depending
on what compound you have.  You won't know which known compound until
lab.  There are 5 volumes for each compound.  These are approx.  You are 
supposed
to get close to one of these and then hold it there for awhile (about 
30-60 seconds by
adjusting the flame) and then read the volume and temperature.

At the help link I've been quite specific about s.f. (especially for 
logarithms),
what should be in your discussion section, sample calculations, etc.   
LOOK at
this LINK.

For the calculations you need to calculate the pressure of your sample 
in the
syringe.  You will use eqn 6 on page 89 for the Ps values from the V & T 
data.
Often people will get negative Ps values.  They can NOT be negative.  I've
discussed this at the help link.  It's because you used Celsius and not 
kelvin.
Remember,

*KELVIN, KELVIN, KELVIN*


There is no pre-lab quiz on Carmen.

*HOWEVER, there is an on-line data input prelab at the following link,

**https://uglabs.cbc.osu.edu/1250/pre-postlabs.php*

This is the SAME site as for the Gatekeeper quiz and exp 5.  You can get 
to it via
the module for exp 14 on Carmen (it takes you to the same site). You 
need read the
discussion and data analysis section carefully.  Watch the exp 14 video 
(there's a
link on my web pages for videos).  You can watch the video in the 
pre-lab and then
get out.  As long as you don't submit you can restart it.  Read my help 
files (see the
"Laboratory" link on my class web page).  Then write the procedure and 
do the pre-lab.

Read the instructions on the landing page before clicking on the 
"Prelab" link.
Once you get to the prelab click on the Policies and Procedures link at the
very bottom,

https://uglabs.cbc.osu.edu/1250/pre-postlabs.php

Also, click on the "Instructions" box near the upper-left hand corner of the
page.  This will give some general instructions and ones more specific 
to this
exp.

For the pre-lab the data given is supposed to be similar to what you 
will obtain
in the lab for your unknown.  You are given 5 temp/vol data points, just 
like
you'll get in the exp.   You use eqn 6 for this to calculate the Ps.  
There are two
boiling points, one determined at the barometric pressure for the day 
(as given
in the data) and the other is the  normal b.p.  You do NOT use eqn 6 for 
these.
Boiling occurs when the vapor pressure (VP) of the liquid equals the 
prevailing
atmospheric (barometric) pressure.  The normal b.p. is when the VP 
equals the
prevailing barometric pressure when it is 1 atm.  Both of these are 
given for the
pre-lab.  For the exp you'll obtain a b.p. the day of lab at the 
barometric pressure
for that day and look up the normal b.p. in the CRC (see my web page).

You will need to graph the points for the pre-lab and determine the 
slope of the
resulting best-fit line (linear fit must be used).  The easiest thing to 
do would be
to use Excel for this while doing the pre-lab.  You will have two b.p. 
data points
on the graph, the literature value and exp value, as explained above.  
Your graphs
for the report will have 7 data points.  You'll see the same for the 
pre-lab.

The sig. fig. for ln(P) are tricky.  It's explained in my help file for 
exp 14 (see
above link) and another help file I have specifically about logs and 
s.f.   I've sent
both links out before but here they are again.  Sig. fig. for logarithms 
is also
explained in Appendix A of the textbook.

*Manipulating Logs and Sig. Figs.* 
<https://www.asc.ohio-state.edu/zellmer.1/chem1250/faq/sig_fig_logs.txt>

*Finally, the method of obtaining the boiling point has changed
from what is shown in the video.*

We now use a sand bath rather than a boiling water bath.  However, you are
still looking for the bubbles coming from the inverted capillary tube 
and for
the liquid to go back up into the capillary tube after removal from the sand
bath, as shown in the video.  You'll see bubbles and then it appears to 
start
boiling.  Do NOT record the temp at this point. The best thing to do is 
watch
the thermometer until the temp stabilizes (it will inc. rapidly and then 
stop inc.).
Then remove the test tube.   Then don't watch the thermometer, instead 
watch for
the liquid to go up the capillary.  When it does, read the temperature.  
Ask your
TA if it looks reasonable.  You do at least three b.p. determinations in 
the lab and
average the best three and report this average as the experimental b.p.

Dr. Zellmer
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