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<big><font size="2"><big>I've received some questions about exactly
what you need to do for the<br>
first lab this week. The TAs should cover at least some of
what I have<br>
below in lab. I addressed some of this in my previous
e-mails, at least<br>
in general. One particular question I've been asked is about
the data<br>
table for the notebook.<br>
<br>
For exp 1 you should have your purpose, procedure and a data
table in<br>
your notebook when you go to your first lab. </big></font></big><big><font
size="2"><big><big><font size="2"><big>There is no on-line
prelab.<br>
<br>
</big></font></big>The data table on the report sheet has
mass of water and volume of water.<br>
However, in the lab you will not get the mass of the water
directly from a<br>
single measurement. This may also apply to the volume
(particularly<br>
when using a buret).<br>
<br>
You will be using a weighing beaker which you need to weigh
(just once)<br>
when it's dry. You will add water to the beaker and reweigh
it getting the<br>
total mass of the beaker and water. Thus you may want to
have another<br>
column in your data table for the total mass of water and
beaker and<br>
then a column just for the mass of the water (which you will
calculate).<br>
You may need another column for the volume of water depending
on how<br>
you do things. For the buret you may not start your water
right on zero,<br>
and even if you do, you should be recording the initial buret
reading and<br>
the final buret reading. The amount added would be the
difference<br>
between the two. If you start the water right on 0 you
should record this<br>
(with the correct # of sig. fig.). Then the amount you add
can go directly<br>
into your data table as the volume of water. However, if you
don't start<br>
right on zero you will need to record the initial and final
volumes<br>
somewhere and then write the difference in your data table for
the volume<br>
of water added. You can write down some of these numbers
elsewhere in<br>
the notebook and put just the needed numbers (mass of water
and volume<br>
of water) in the data table in your notebook. However, keep
things<br>
organized so someone (besides you) could pick up your notebook
and find<br>
these numbers and understand just what you did.<br>
<br>
Please read Appendix D of the lab manual about how to use the
buret and<br>
pipet and pay attention to the number of sig. figs. (and
decimal places) which<br>
you should be recording in the notebook. Always record your
data to the<br>
correct # of s.f. and use units.<br>
<br>
You should use the analytical balance for all your masses.
While for certain<br>
pieces of glassware the top-loading balance would suffice, if
you use the<br>
analytical balance, which is more accurate and gives more
decimal places<br>
(and thus sig. fig.), you won't need to worry whether it's
safe to use the<br>
top-loading balance. Plus, then the s.f. in the density will
be due to the<br>
piece of glassware used to measure the desired volume of water
and make<br>
for a more direct comparison of the accuracy of a particular
piece of<br>
glassware.<br>
<br>
Pipets and burets are meant "to deliver", assuming you use
them correctly.<br>
<br>
Beakers are meant "to contain" the amount in the beaker.<br>
<br>
Graduated cylinders can be tricky. Look at the top of the
graduated<br>
cylinders. There you will find either a "TD" or "TC". You
should write<br>
this down in the notebook. The "TD" means "to deliver" while
the "TC"<br>
means "to contain". This can make a difference and you want to
record<br>
this so you can discuss this in your report and how it might
affect your results.<br>
<br>
Also, while the measured density is a calculated value you may
want<br>
to do this calculation and record the numbers in your
notebook. For each<br>
piece of glassware the density you obtain for each mass and
volume should<br>
be the same. Thus, if three of them are very close and one
isn't something is<br>
wrong and you may wish to at least redo the one which is very
different than<br>
the others. Also, the density of water should be close to 1
g/mL. If what you<br>
obtain is noticeably different you may have made a mistake.
You want to do<br>
this before putting everything away and leaving lab.<br>
<br>
Finally, the lab manual on pages 5 and 6 in the Discussion
addresses using<br>
the density to calculate the volume and compare this volume to
the one<br>
you measured in the lab. This is just an example. You'll
actually be using your<br>
measured mass and volume to calculate a density. You will
then compare your<br>
calculated density (based on the measurements in lab for mass
and volume)<br>
and then get the error and % error for this density and the
"actual" density<br>
at the temperature of interest calculated from the equation
page 9, right above<br>
the table.<br>
<br>
Dr. Zellmer</big></font></big>
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