Lab Report - Results/Discussion/Conclusion

[robert zellmer]

I received a question about what should be in these sections.  I gave a very
short synopsis in my on-line example.  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 6 (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 the correct?  If you can't tell, were they at 
least reasonable?  How
         do you know they were reasonable.

         In exp 6 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 14 you should be discussing whether the Hvap values are 
reasonable.
         Was the correct order obtained for the Hvap values for the 
three known compounds
         based on the attractive forces present?  What were those 
attractive forces?  Which
         compound should have the strongest AF and thus the highest 
Hvap?  Does this agree
         with the b.p. data you looked up?  If you didn't get the 
correct order what should it
         have been based on the AF?

         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).  This should be explained 
here or in the next
         paragraph.

     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?

         For instance, in exp 6 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 would use a double-walled styrofoam cup (essentially two 
cups together) with a
         special lid.  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 6 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.


Conclusion:

     This is one paragraph of about 4-6 lines.  It's a quick 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 (the average of the 
trials).  You should answer the
     purpose/objectives.

Remember, you really 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