exp 1 information and data table in notebook

[robert zellmer]

I've received some questions about exactly what you need to do for the
first lab this week. Everyone is doing exp 1 the first week of class.

The TAs should cover at least some of what I have below in lab.  I
addressed some of this in my previous e-mails, at least in general.
You should also look at the exp 1 help link in the "Helpful Tidbits"
link on my class web page (not Carmen).  This link has several
items which will help with the lab report and data analysis.
One particular question I've been asked is about the data
table for the notebook.

When you look at some of the experimental write-ups in the
manual you will see questions throughout the discussion and
maybe even the procedure.   For exp 1 you have questions
on pages 3 and 4.   We do not collect these.   They are actually
answered at the end of the write-up for the exp (page 11 for
exp 1). They are supposed to be there to for you to answer
so you know if you are understanding what you're reading.

In exp 1 you are using several different types of volumetric
glassware. The manual states to use volumes between 5 mL
and 25 mL and then instructs you to look at the figure.*Use**
**volumes of around 5, 10, 15 and 20  (mL) for the buret, pipet*
***and**graduated cylinder.   For the beaker use volumes of around**
**20, 25, 30 and 35 (in mL).*

What should be written in the notebook?  There are some things
which you do before lab.  Everything done in lab is recorded
directly in the notebook and nowhere else.

For exp 1 you should have your purpose, procedure and a data table in
your notebook when you go to your first lab. There is no on-line prelab.

The data table on the report sheet has mass of water and volume of water.
However, in the lab you will not get the mass of the water directly from a
single measurement.  This may also apply to the volume (particularly
when using a buret).

You will be using a weighing beaker which you need to weigh (just once)
when it's dry.   You will add water to the beaker and reweigh it getting the
total mass of the beaker and water.   Thus you may want to have another
column in your data table for the total mass of water and beaker and
then a column just for the mass of the water (which you will calculate).
You may need another column for the volume of water depending on how
you do things.   For the buret you may not start your water right on zero,
and even if you do, you should be recording the initial buret reading and
the final buret reading.   The amount added would be the difference
between the two.   If you start the water right on 0 you should record this
(with the correct # of sig. fig.).   Then the amount you add can go directly
into your data table as the volume of water. However, if you don't start
right on zero you will need to record the initial and final volumes
somewhere and then write the difference in your data table for the volume
of water added.   You can write down some of these numbers elsewhere in
the notebook and put just the needed numbers (mass of water and volume
of water) in the data table in your notebook. However, keep things
organized so someone (besides you) could pick up your notebook and find
these numbers and understand just what you did.

Please read Appendix D of the lab manual about how to use the buret and
pipet and pay attention to the number of sig. figs. (and decimal places) 
which
you should be recording in the notebook.   Always record your data to the
correct # of s.f. and use units.

You should use the analytical balance for all your masses.   While for 
certain
pieces of glassware the top-loading balance would suffice, if you use the
analytical balance, which is more accurate and gives more decimal places
(and thus sig. fig.), you won't need to worry whether it's safe to use the
top-loading balance.  Plus, then the s.f. in the density will be due to the
piece of glassware used to measure the desired volume of water and make
for a more direct comparison of the accuracy of a particular piece of
glassware.

Pipets and burets are meant "to deliver", assuming you use them correctly.

Beakers are meant "to contain" the amount in the beaker.

Graduated cylinders can be tricky.   Look at the top of the graduated
cylinders.   There you will find either a "TD" or "TC".   You should write
this down in the notebook.   The "TD" means "to deliver" while the "TC"
means "to contain". This can make a difference and you want to record
this so you can discuss this in your report and how it might affect your 
results.
You should use the one(s) marked with "TD" when possible for this exp.

Also, while the measured density is a calculated value you may want
to do this calculation and record the numbers in your notebook.   For each
piece of glassware the density you obtain for each mass and volume should
be the same.   Thus, if three of them are very close and one isn't 
something is
wrong and you may wish to at least redo the one which is very different than
the others.   Also, the density of water should be close to 1 g/mL.  If 
what you
obtain is noticeably different you may have made a mistake.  You want to do
this before putting everything away and leaving lab.


Dr. Zellmer
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