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First, we do not do percent error calculations, but % difference
calculations. I believe Hugh's comments are more directly
applicable to percent error calculations. I might be wrong.
My students are to determine why the two values might be different.
I specifically state that we should not hold textbook values in too
high of a regard.
They must state what might cause these differences, how their
laboratory procedure might have caused these differences, and what
could be done to change the procedure to limit the error involved.
I do not give them the 'accepted' values of these substances.
Kids today will google or Wikipedia the value. If I don't ask them
to do a % diff, some (not all) will attempt to fudge data to match
the internet value. I've done labs along these lines to determine
an unknown item in the past (maybe use n or C to determine what
solution or metal sample you have been handed).
None of my labs are cookbook recipe labs. I rarely conduct
verification labs. However, students are becoming very adept at
finding some of the information that I ask them to determine. Years
ago I would ask them to use a double slit to find the wavelength of
a laser. Then kids could more easily find the wavelength. I
switched to find the slit separation. Now kids google the little
CAS image on the Cornell slides I've got and they know the openings
on the slides. I now have to find a new version of Young's Double
slit. Don't know what that will be, but it has never been a
verification lab.
I never spoke of using human error as a source of uncertainty. I
wouldn't accept it any more than you would.
I am not sure what Hugh means by an accepted value of 0.Any physical value that must be zero for certain situations or