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Chemistry 223
Designing an Analytical Method
Fall, 2009
BRING YOUR COPY OF HARRIS TO THE LAB.
All semester, indeed in most labs you've ever done, you have been told how to do experiments ("Heat to
60°C," "Weigh 0.2 g.").
The practice of quantitative analysis requires the analyst to DEVELOP methods
as well as to APPLY them.
To give you a flavor of how to develop a method, this lab will guide you to
write a procedure for the analysis of a nickel ore sample.
You will turn in a lab report after one week,
explaining how you will solve the problem of analyzing the ore sample.
You will also carry out the
procedure you devise; you will then write a report after two more weeks on the nickel determination you
have carried out.
If you devise a good method, your results will work well.
Make bad choices, and the
precision will be poor.
YOU make the decisions, YOU reap the rewards!
The TAs will grade your first
(method design) lab report for clarity, logic, and accuracy.
You will find for yourself when you're part way
through following your own instructions whether you did an adequate job.
While there will be a post-lab quiz for Week One (developing your procedure), there will NOT be post-lab
quizzes the remaining weeks of the semester.
Since no two groups will use identical procedures,
devising a fair quiz is difficult.
Furthermore, the reason we gave post-lab quizzes was so you wouldn't
quit thinking about the lab after you did it.
On this lab, your ingenuity and focus will so heavily inform the
results that additional paperwork seems superfluous.
Similarly, while there's a prelab quiz for Week One
and for Week Two, there is no pre-lab quiz for the last week of the lab.
The course "curve" (the
guarantees for minimum number of points to achieve a particular letter grade) reflect this.
The parts of the lab are:
I.
List the Universe of Possible Methods
II.
Estimate the Amount of Analyte
III.
Catalog Expected Interferences
IV.
Narrow the Possible Techniques to Those Consistent with Expected Amounts and Interferences
V.
Write Out a First Estimate of How to Carry Out Each Technique (Including Equilibrium or Kinetics of
Reactions as Appropriate).
Decide on Sample Pretreatment
VI.
Compute Masses, Volumes, and Other Signals Expected
VII. Estimate Errors
VIII. Discard Methods with Inadequate Detection Limit, Dynamic Range, or Precision
IX.
Among Remaining Methods, Choose Based on Any Additional Available Criteria
In weeks 2 and 3, you'll make use of the results of the above body of work to analyze an unknown.
Students will work in groups.
The 3 people on one side of a lab bench will form a single team.
If there
are only 2 people on a bench, they can work as a pair or absorb a single person from another bench.
If
there is only 1 person on a bench, they should preferably join a pair of people in need of a third.
If (and
only if!) the number of students in a lab section is 3N+1, N an integer (so that there's no way for everyone
to be in 3's and there are no spontaneous groups of 2), one of the 3-somes should split so that the final