Chemistry
3005
Quantitative Analysis Laboratory
GOALS
Modern academic, medical and industrial activities require the application of a variety of analytical techniques. These techniques may vary from simple procedures such as titrations to very sophisticated instrumental methods. It is important that a soundly prepared student is competent in the fundamental methods and is familiar with some of the modern methods of chemical analysis. The purpose of this laboratory course is to reach these goals by having the students participate in a series of experiments that illustrate exemplary analytical activities.
The specific goals of this course are that each student will:
These goals will be pursued by having each student perform a series of experiments which will be graded on the basis of obtaining an accurate quantitative result in a limited time period. It is the responsibility of the student to be prepared for each day's lab activity in order to make the most efficient use of the time spent in the lab. Such preparation means reading and understanding the appropriate sections of the Manual and, when necessary, asking for the instructor's assistance.
SCHEDULE
The purpose of this course is to introduce students to methods and techniques in the analytical laboratory and to require that careful and accurate measurements are made in reasonably rapid fashion. The following activities are offered for your participation:
All experiments can be carried out with your desk set and items checked out from your instructor or the stockroom. Borrowing equipment from any other source is unnecessary and prohibited. Everyone will first do the water hardness experiment. Due to limitations in specialized equipment, there will be different sequences for the remaining laboratories. Your lab instructor will assign you the schedule of experiments following the completion of the titrimetric water hardness determination. One result is due each week according to the schedule assigned to you. No result will be accepted under any circumstances after the Monday of final exam week.
GRADING
The course grade will be made up of the following: Eight experiments at 100 points each; mid-term notebook check 50 points; final notebook grade 50 points; final examination 100 points. Final examination questions will most likely be selected from those given at the end of the experiments. No repetition of experiments is permitted once a result is submitted.
UNKNOWN GRADING PROCEDURE
Unknown results will be graded on the basis of the relative error contained in the reported value. (Your answer - right answer)/right answer expressed in parts-per-thousand will be the number we look at. For many, but not all of the experiments, excellent results should be within 1 ppth (part-per-thousend) of the correct value. For each quantitative experiment, you must report the results of each individual (successful) trial, the mean, the standard deviation, and the limits of precision. Your grade will be based only on the accuracy, but all appropriate statistical quantities must also be included on the report sheet to obtain full credit ( -10 points for each missing quantity).
A good-faith effort and completion of the experiment to the point of turning in a result will obtain no lower than 50/100. Failure to complete an experiment will get you a zero.
Ten points will be deducted if you require additional sample to complete an experiment.
Ten points will be deducted for each laboratory period that a result is overdue.
If you receive a grade lower than 70 on any unknown, you will be permitted to submit a recalculation if you can convince your laboratory assistant from data in your notebook that your error was a bona fide calculation mistake. There will be a ten point deduction from the final grade on the unknown if a recalculation is required.
You may report any value you choose. It is felt that if precision were a part of the grade it would be manufactured. Thus, while the confidence you place in your result should be tempered by its precision, this will not be graded.
Your attention is called to Chapter 4 of Harris, Quantitative Chemical Analysis for a discussion of statistical treatment of data and in particular to the Q-test used to decide whether to reject a discordant result or include it in your average. You are expected to use and report on all pertinent statistical tests throughout the course.
LABORATORY NOTEBOOKS
Of all the laboratory equipment commonly used by the chemist, the most important and most frequently used and/or abused is the notebook. When properly used and witnessed, the notebook has the strength of a legal document that will withstand the test of the courts. When improperly used, it is only scrap paper.
The notebook used in this laboratory is one that is bound with string and has non-removable pages. Under no circumstances are pages to be removed from the book. These books are available in the bookstore at a modest cost. After obtaining the book, the pages should be sequentially numbered in ink if not already numbered. Number only the page on the right hand side of the book that faces the reader. At the front of the book leave several pages for a Table of Contents. This will be filled in as the experiments are performed.
All entries into the notebook are to be in ink on the front side of the right hand page only. No erasures of the entries are permitted. If any entries are to be canceled, they should be crossed out with a single line so that they are still visible. Comments explaining why the entry was canceled should be added near the cancellation.
All data taken in the lab are to be recorded directly in the notebook, never taken first on scrap paper and transcribed later.
Each experiment recorded in the notebook is broken into Background, Procedure, Data, Calculations, and Results. The Background, contains several statements regarding the theory behind the experiment and a simple statement telling what is to be done in the experiment. Chemical equations should be recorded here. The Procedure, contains the "cook book" for the experiment. Detailed step by step instructions are not necessary. Rather an outline of the procedure is given. Many scientists use this as a plan for each day's work in the lab. All data taken in the lab are recorded in the Data section. Every attempt should be made to record data in tabular form. One example of each computation should be in the Calculation section. Additional computations should be made on the left hand facing page. Results are presented in tabular form in the Results section. The lab instructor will inspect your lab book and sign and date the book at the end of each experiment.
CLOSING COMMENTS
Extra Laboratory Sessions
Students will be allowed to attend their scheduled laboratories only. On presentation of a valid excuse students may make up missed laboratories but only at regularly scheduled labs. Assistants cannot give permission for work at any other time unless they agree to be present and supervise.
Closing the Laboratory on Schedule
Students may not work beyond the stipulated closing time. Ten minutes should be allowed for cleaning up equipment and putting it away.
Grades
The components of the course grade and their relative weighing are discussed on page iv. The numerical process for grading results of individual determinations is described on page v. Results on each experiments are statistically analyzed in order to insure that no determinate error is present which would bias all results, e.g. an improperly composed reagent.
The notebook estimation grade is given by the laboratory assistant based on the following:
The total numerical grade you receive for Chemistry 361 is converted to a percent and these are analyzed for all sections of class. Letter grades are assigned from statistical analysis of the grade distribution with regard for the fact that C is defined as "average". While no guarantee is made that future grade distributions will be the same, data for several years past given the following information. The overall average achieved by 237 students was 75% with a range of averages from 72% to 78% for seven different terms offered. The standard deviation of the mean was 5% to 6% in every case. Generally, the lowest C was one standard deviation below the mean. But there is minimum cut off at 90% for A, 80% for B, 70% for C, and 50% for D. These are guaranteed grades. Statistical analysis will only `soften' the % to grade conversion by lowering the minimum % required for a grade.
These data should assist you in understanding how grades are obtained and where you stand, although no commitment is made to retain these policies in the future. Check with the instructor if you have questions about grading.
RULES OF THE QUANTITATIVE ANALYSIS LABORATORY
Safety
Good Lab Technique
Housekeeping
General Rules
SAFETY RULES
Friday, August 25, 2006