Lab Report - Results/Discussion/Conclusion

[robert zellmer]

I received a question about what should be in these sections.   I give a 
short
synopsis in my on-line example.  There's information in the manual and on
Carmen and the Undergrad web site where you do you pre-labs.  Make sure
you address the Points to Consider,  at a minimum.  Here's what should
essentially be in each section:

Results/Discussion:

In this section you will have essentially 3 paragraphs:

        1) Discuss what was done in a general way w/o giving 
experimental details
                of the procedure.   Don't list every little step you did.

                For instance, for exp 5 (coffee-cup calorimetry exp) you 
might have something like:

                "In this experiment a coffee-cup calorimeter was used to 
determine the heats
                of reaction for two experiments.   The heat capacity of 
the coffee cup was
                first determined.   The cup was then used to determine 
the heat of reaction for
                a strong acid-strong base neutralization reaction and 
the heat of reaction between
                magnesium and HCl.   These heats of reaction were used, 
along with those for
                other reactions given in the manual, to determine the 
heats of reactions for two
                additional reactions using Hess's Law."

                Something along these lines should be done for each exp.

        2) The most important results should be given in the 2nd 
paragraph.   You don't need
                to give every single number you obtained.   You should 
have a discussion of the
                results.   Were they correct?   If you can't tell, were 
they at least reasonable?   How
                do you know they were reasonable.

                In exp 5 (CAL) you determined heats of reaction. Were 
they reasonable?   Heats of
                reaction are on the order of 10's to 1000's of kJ/mole. 
Were the ones you determined
                in this range.   Were they positive or negative and does 
it make sense?   Was the heat
                capacity of the coffee-cup negative?   The manual told 
you to set it to zero if you got
                a negative heat capacity.   Why did it tell you to do 
this? What could have made it come
                out negative?

                For exp 2 (dTf) you should be discussing whether the MW 
values are reasonable.
                Where the freezing points obtained for the different 
trials reasonable (follow what
                would be expected with inc. solute conc.)?  Does your 
average MW makes sense?
                Would a MW of 20 amu (g/mol) make sense?  How about 
10,000 amu (g/mol)?
                Look at the "Points to Consider".

                If you had more than one trial how well did the results 
for the trials agree.   If you are
                taking an average of 3 or more trials and one of the 
trials was very different than the
                others you could leave it out and just average the 
others. You would discuss that
                in this paragraph.   You technically should do an error 
analysis to see if it's okay to
                leave out that piece of data (see the link "Treatment of 
Numerical Data" at the
                "Laboratory" link on my web page or in Appendix F of the 
manual).   This should be
                explained here or in the next paragraph about errors.

        3) Errors.   You need at least 2 inherent sources of error. 
These are errors which are
                pretty much beyond your control due to the way we've 
designed the exp.   It doesn't
                mean there's no human element.   These are errors that 
would have affected your
                results.   How could they affect your results?  How 
could they be fixed?

                For instance, in exp 5 (CAL) a single coffee cup was 
used as the calorimeter.   While
                it actually does a pretty decent job heat can escape or 
get in, especially through the lid.
                Normally, one uses a double-walled Styrofoam cup 
(essentially two cups together) with
                a special lid made of cork (which doesn't easily allow 
the transmission of heat through
                it).  Sometimes people state "the water wasn't swirled 
before each temperature reading".
                That is NOT an inherent error.   That's your error. I've 
seen "a little water splashed
                out of the cup when the copper cylinders were dropped 
in".   Again, that's your error
                (a "do-over" error) not an inherent error. Another 
inherent error in exp 5 would be
                some heat was lost when the Cu cylinders were 
transferred from the boiling water bath
                to the cup.   If you did this transfer quickly enough 
not much would have been lost but
                some had to be lost no matter how quickly you 
transferred the cylinders.

                Can you put such errors (your errors) in this section?   
Yes, but you have to have at least
                two sources of inherent error.

                What else might go here?   If you've left a data point 
out of the best-fit line because it
                seemed to be way out of line with the other data points 
a discussion of this being done
                would go here.

                You should always discuss how these errors may have 
occurred and affected the results.


*Remember, you need to address the Points to Consider at a minimum**.
***
Conclusion:

         This is one paragraph of about 4-6 lines.   I't's more or less 
a summary of the Discussion.
         It's a one or two sentence summary of what was done 
(essentially summarize the first
         paragraph in the Discussion section).   You should have the 
most important result listed
         again (e.g. the average of the trials).   You should answer the 
purpose/objectives.

Remember, you shouldn't use "I" or "we".   In other words, don't say "I 
used a coffee-cup
calorimeter...".   Don't say "My results were ..."

We don't accept one word answers in lab reports.   You should always 
have an explanation.
The same generally goes for questions on quizzes.

I hope this helps.

Dr. Zellmer
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